Unit I: Diversity of Living Organism

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WHAT IS LIVING?

 Life is a unique, complex organisation of molecules expressing itself through chemical reactions (metabolism) which lead to growth, development, responsiveness, adaptation and reproduction. Hence, "the object by itself exhibiting the growth, development, death, consciousness, reproduction etc. is designated as living being."

A. Characteristics of Living Beings

All the living beings share certain unique and basic characteristics which set them apart from non-living objects. These characteristics are listed below :         

1. Growth                   

2. Reproduction         

3. Metabolism           

4. Cellular structure  

5. Consciousness

1. Growth:

Increase in mass and increase in number of cells are twin characters of growth. Growth refers to irreversible increase in mass or overall size of a tissue, an organism or its parts.

Growth is the result of difference between anabolism (building up reactions) and catabolism (breakdown reactions).

Growth occurs when anabolism or synthetic processes exceeds catabolism.

Degrowth or negative growth will occur when catabolism exceeds anabolism. It will decrease the mass of body.

Unicellular organisms also grow by cell division. In majority of higher animals and plants, growth and reproduction are mutually exclusive events, but in unicelled organisms like Amoeba, reproduction is synonymous with growth, i.e., increase in number of cells.

Non-living objects also grow if we take increase in body mass as a criterion of growth. But in these objects extrinsic growth is present i.e. increase in the mass of body from outside e.g., mountains, boulders and sand mounds. Growth, therefore, cannot be taken as a defining property of living organisms.

2. Reproduction:

Reproduction is the formation of new individuals of similar kind. It is, however, required for survival of the population as it compensates for the loss of life due to death.

Reproduction is of two types, asexual and sexual. Asexual reproduction is uniparental multiplication that occurs through binary fission, multiple fission, spore formation, fragmentation and vegetative multiplication.

Fungi multiply by asexual spores, yeast and Hydra show budding, Planaria exhibits true regeneration. Fungi, filamentous algae, protonema of mosses easily multiplies by fragmentation. But, when we notice single-celled organisms like bacteria, unicellular alga and Amoeba, we are not clear about the usage of these two terms -growth and reproduction, i.e., increase in number of cells.

Hence, reproduction also cannot be an all inclusive property of living organisms. Still, no non-living object is capable of reproducing or replicating by itself. Further, there are some organisms which do not reproduce at all, e.g., worker bees, mules etc.

3. Metabolism:

Life is a never ending flow of energy and materials.

The energy are required by all living cells for building and functioning of their living matter.

Metabolism is the sum total of all chemical reactions occurring in an organism due to specific interactions amongst different types of molecules within the interior of cells.

Metabolism involves exchange of matter and energy between an organism and its environment and transformation of matter and energy within an organism.

Despite vast differences occurring in structure and functioning of cells in different organisms, metabolic reactions are unusually similar.

Metabolic reactions can be demonstrated outside the body in cell free systems.

An isolated metabolic reaction(s) in a test-tube is neither living nor non-living. Hence, while metabolism is a defining feature of all living organisms without exception , isolated metabolic reactions in-vitro are not living things but surely living reactions.

An isolated metabolic reaction(s) in a test-tube is neither living nor non-living. Hence, while metabolism is a defining feature of all living organisms without exception , isolated metabolic reactions in-vitro are not living things but surely living reactions.

4. Cellular structure:

Body of all living organisms consists of cells and their products. Hence, cellular organisation of the body is the defining feature of life forms.

5. Consciousness:

All living beings, plants and animals, are aware of their environment. All organisms sense their surroundings and respond to sudden or smooth changes in it.

All organisms from prokaryota to eukaryota can sense and respond.

Humans also have "self-consciousness" hence, this becomes the defining property of living beings.

It is most obvious and technically complicated feature of all living organisms.

The foregoing discussion, nevertheless concludes that living beings are organized, self-replicating, evolving and self-regulating interactive systems, with consciousness at the head of all.

A question may arise whether a man lying in coma on the life support systems is living or non-living? The answer lies in the quantitative presence of consciousness in the living being in that particular state. Infact, the person in coma has lost the requisite quantity of consciousness to exhibit the features of living being, but still exhibits life. If the requisite consciousness is restored, the person may again start to be as living being or die otherwise.

Other characteristics of living beings are adaptation, life span, homeostasis, healing and repair, movement and variation.

Biodiversity

From a current estimation, approximately 1.7 million species have been scientifically named and classified. These include nearly 1.2 million animals and over 0.5 million species of plants.

Amongst animals, insects form the largest group, i.e., over 10,25,000 species. It is estimated that majority of species diversity is confined to tropical rain forests and huge diversity exist in under water reef formations in tropical oceans.

Existing living species are the outcome of about 3.5 billion years of evolutionary process on this earth. Nearly 15,000 new organisms are discovered every year.

A clearer understanding of this huge variety of organisms can be studied by dividing these into smaller groups or sub-groups (categories) and each group or sub-group comprising of organisms with more or less similar characters.

Method of placing organisms into groups or sub-groups depending upon extent of similarities and differences is called classification.

The division of organisms into different groups follows certain rules, that is why the term called taxonomy is used for classification of organisms following certain rules or principles.

 Need for classification

There are millions of plants and animals varying greatly in their form, structure and complexity.

It is impossible to study all of them individually. To make the study of organisms possible and easier, scientists have divided organisms into different ranks or categories on the basis of similarities and differences.

Classification is just like systematically arranged library where we can easily find out the required book, in the same way, if the organisms are arranged according to a system, it makes their study easy.

Some important needs are

It is essential to understand the inter-relationship among different groups of organisms.

It serves as a base for the development of other biological sciences like biogeography.

Various applied biology fields also depend upon exact identification and classification.

Taxonomy and Systematics

Taxonomy: The branch of science dealing with the study of principles and procedures of classification is called taxonomy. The term taxonomy was coined by A.P. de Candolle. Linnaeus is considered as Father of Taxonomy. Santapau is considered as Father of Indian Taxonomy. The fundamental elements of taxonomy are as follows :

• Characterisation and identification : It is the determination of the similarities of an organism with an already known organism, based upon specific characters.
• Nomenclature: It is the determination of correct name of an organism according to established universal rules.
• Classification: It is grouping of organisms into convenient categories on the basis of easily observable characters.

• The classical taxonomy is based on observable morphological characters, however the modern taxonomy deals with several characters for the classification of organisms like

 (a)     External and internal structure alongwith the structure of cell.

 (b)    Development process.

 (c)    Ecological information of organisms

Systematics : The word "systematics" is derived from Latin word systema which means systematic arrangement of organisms. It was first used by Carolus Linnaeus. According to him, "systematics is the discipline of biology which deals with the kind and diversity of all organisms and the existing relationships amongst them."

Generally, the terms such as classification, systematics and taxonomy are used interchangeably but some taxonomists like Simpson (1961) relate them with a separate field. He defined systematics as

"The study of diversity of organisms and all their comparative and evolutionary relationships based on comparative anatomy, comparative ecology, comparative physiology and comparative biochemistry."

The main uses of systematics are as given below :

(i)      It helps in providing knowledge of great diversity of animals and plants. It provides information regarding evolution which took place among plants and animals by knowing the distinction, relationship, habitat and habits. It thus, gives a vivid picture of entire organic diversity.

(ii)    It helps in the identification of fossils which gives useful information about the phylogeny of organisms.

(iii)   Newly discovered organisms can be identified through systematics. well as the specimens

Concept Builder

1. The reasons for large scale biodiversity amongst living beings are :

1. 1. Adaptations in organisms to diverse habitat in order to reduce competition.
   2. Change in genetic constitution.
   3. Isolation

2. Ontogeny is the life history of organisms. Phylogeny is the evolutionary history of organisms.

3. Systematics is taxonomy alongwith phylogeny.

4. Classical or old or descriptive systematics is based upon morphological characters. According to it basic unit of classification is species. Pioneer workers are Aristotle and linnaeus.

5. New systematics / Biosystematics / Neosystematics is based upon all characters" i.e., morphological, cytological, ecological, biochemical, genetical etc. The term was coined by Julian Huxley. Basic unit of classification is population or sub-species for the new systematics.

6. Founder of taxonomy / Father of biology / Zoology–Aristotle, Father of Botany –Theophrastus, Father of Indian Botany/Indian herbaria -William Rouxburgh.

7. About 5-30 million species of living organisms exist today. Taxonomically or scientifically known number of species is 1.7 million or 13 percent.

Representing global biodiversity: proportionate number of species of major taxa of plants, invertebrates and vertebrates

The dog I can hear barking is alive, and so is the tree outside my window. However, snow falling from the clouds is not alive. The computer you’re using to read this article is not alive, and neither is a chair or table.

What is living?

Anything which shows characteristics of life is called living. The fundamental characteristics of life are- growth, reproduction, metabolism, cellular organization and consciousness. Living things are highly organized, meaning they contain specialized, coordinated parts.

Growth

Living things tend to grow in size. The increase in the number and mass of individuals are two unique characteristics of growth. Multicellular organisms exhibit growth by cell division. Growth varies in plants and animals. If we consider unicellular organisms, they tend to grow in size by cell division. Moreover, this can be easily detected by counting the cells during in vitro cultures under a microscope.

Reproduction

Reproduction is the process by which organisms replicate themselves.

Reproduction can primarily be of two types- sexual reproduction and asexual reproduction.   

Reproduction generally refers to sexual reproduction. Asexual reproduction is used by the lower organisms like Bacteria that divide asexually via Binary fission, Virusestake control of host cells to produce more viruses; Hydras (invertebrates of the order Hydroidea) and Yeast are able to reproduce by Budding.

Sexual reproduction is a biological process that creates a new organism by combining the genetic material of two organisms in a process that starts with, meiosis a specialized type of Cell division

 

Metabolism

Metabolism is the sum of the chemical reaction that takes place within each cell of a living organism and that provides energy for vital processes and for synthesizing new organic material.

All living organisms are made up of chemicals. These chemicals, small and big belonging to various classes, size and function, etc are constantly being made and changed into other biomolecules.

There are thousands of metabolic reactions occurring simultaneously inside all living organisms, be they unicellular or multicellular.

Cellular organization

Cellular organization – All living organisms are made up of cells that perform all functions inside the body. The cellular organization is the components that make up the cell and how they are arranged inside it. Each component called an organelle, performs a specific function vital for the cell.

Consciousness

All living organisms have an inherent ability to sense their surroundings or environment and respond to their environmental stimuli which could be physical, chemical, or biological. Plants and animals both respond to external stimuli. Human beings are the only organisms who are aware of themselves, i.e., have self-consciousness.

Chapter 1

The living world

What is living?

Biology is the study of biological organisms and processes. There is an incredible diversity of living organisms around the globe. Any system capable of executing processes including feeding, metabolizing, excreting, breathing, moving, growing, reproducing, and responding to external stimuli is characterized as living. Living refers to anything that exhibits the attributes of life. Growth, reproduction, metabolism, cellular organization, and consciousness are the basic features of life. On the other hand, self-consciousness is seen as the defining quality of living organisms. Let us take a detailed look at all the unique features of living organisms.

(A) Growth:

Growing is a process that occurs in all living creatures. The twin features of growth are an increase in bulk and an increase in the number of individuals. Cell division is a process that enables a multicellular organism to grow. Plants grow by the division of cells constantly throughout their lives. This growth is only visible in animals up to a particular age. Cell division, on the other hand, happens in some tissues to replace lost cells. Cell division is responsible for the growth of unicellular creatures.  Growth and reproduction are mutually exclusive phenomena in the majority of higher animals and plants. It's important to note that growth is defined as a rise in bodily mass.

If we use body mass as a criterion for growth, non-living objects grow as well. Mountains, boulders, and sand mounds are all formed through erosion. Non-living objects, on the other hand, demonstrate this type of growth by accumulating material on the surface. Growth occurs from the inside out in living organisms. As a result, growth cannot be considered the only distinguishing characteristic of living beings. It must be described under what conditions it can be observed in all live species before we can grasp that it is a property of living systems. A dead creature can’t grow.

(B) Reproduction:

In multicellular organisms, reproduction refers to the generation of offspring with characteristics that are comparable to those of their parents. It refers to sexual reproduction invariably and implicitly. Asexual reproduction is also used by living species. Fungi, for example, can quickly proliferate and spread because they produce millions of asexual spores. We see budding in smaller species like yeast and hydra. True regeneration is observed in Planaria (flatworms), in which a fractured organism regenerates the missing section of its body and transforms into a new creature. Filamentous algae and moss protonema may all easily reproduce through fragmentation. In unicellular organisms such as bacteria, unicellular algae, and Amoeba, reproduction takes place through cell division (fission) which is synonymous with growth, or an increase in the number of cells.

Growth has already been characterized as a rise in cell number or mass. As a result, we find that the definitions of these two terms – growth and reproduction – are not always apparent in single-celled organisms. Furthermore, a large number of species do not reproduce (mules, sterile worker bees, infertile human couples, etc). As a result, reproduction alone cannot be considered a universal distinguishing trait of living entities. Of course, no non-living object can reproduce or replicate on its own.

(C) Metabolism:

Chemicals are found in all living things. Small and large compounds of diverse classes, sizes, functionalities, and other characteristics are constantly created and transformed into new biomolecules. Chemical or metabolic reactions are involved in these transformations. All living creatures, whether unicellular or multicellular, have millions of metabolic events going on at the same time. Metabolism is found in all plants, animals, fungi, and microorganisms. Metabolism is the sum of all chemical events that take place in our bodies. Metabolism does not exist in non-living objects.In cell-free systems, metabolic events can be demonstrated outside of the body. An isolated metabolic reaction(s) performed in a test tube outside the body of an organism is neither life nor non-living. While metabolism is a defining property of all living organisms, isolated metabolic reactions, referred to as in vitro, are not live objects but living reactions. As a result, the body's cellular organization is a fundamental defining property of all life forms.

(D) Self-consciousness:

The ability of all living organisms to detect their surroundings or environment and respond to these environmental stimuli, which can be physical, chemical, or biological, is perhaps the most evident and technically complex attribute. Our sense organs allow us to perceive our surroundings. External elements such as light, water, temperature, other species, contaminants, and so on affect plants. Environmental signals can be sensed and responded to by all species, from prokaryotes to the most complex eukaryotes. Seasonal breeders, both plants and animals, are affected by photoperiod. Chemicals that enter an organism's body are dealt with in the same way by all species. As a result, all organisms are 'conscious' of their surroundings. Humans are the only organisms that are aware of themselves or have self-consciousness.As a result, consciousness becomes the defining characteristic of living beings.

Underlying interactions are responsible for all life phenomena. Tissue properties are not found in the constituent cells but emerge as a result of interactions between them. Similarly, features of cellular organelles are not contained in the organelle's molecular elements but occur as a result of interactions among the organelle's molecular components. Emergent features emerge at a higher level of organization as a result of these interactions. This phenomenon occurs at all levels of the organizational complexity hierarchy. 

As a result, living creatures can be described as self-replicating, evolving, and self-regulating interacting systems that can respond to external inputs. The narrative of life on Earth is told via biology. Biology is the study of how living species have evolved on our planet. All living species, present, past, and future, are related to one another to differing degrees via the sharing of similar genetic material.

 Need for classification

• There are millions of plants and animals varying greatly in their form, structure and complexity.
• It is impossible to study all of them individually. To make the study of organisms possible and easier, scientists have divided organisms into different ranks or categories on the basis of similarities and differences.
• Classification is just like systematically arranged library where we can easily find out the required book, in the same way, if the organisms are arranged according to a system, it makes their study easy.

Some important needs are

• It is essential to understand the inter-relationship among different groups of organisms.
• It serves as a base for the development of other biological sciences like biogeography.
• Various applied biology fields also depend upon exact identification and classification.

Diversity in the living world

The biological variety and variability of life on Earth are referred to as biodiversity. Looking around, one will see a wide range of living organisms, including potted plants, insects, birds, pets, and other animals and plants. Other species are invisible to the naked sight but are all around us. A species is represented by each different type of plant, animal, or organism you see. Between 1.7 and 1.8 million species have been identified and described. This refers to the diversity of species on the planet or the quantity and varieties of creatures that exist.

There are millions of plants and animals throughout the world that are known by their regional names. These regional names might differ from one location to the next, even within a country. When referring to organisms, such names can cause confusion. As confuse necessary to standardize the naming of living entities so that they are known by the same name all over the world. This is referred to as nomenclature.

This naming or nomenclature is only achievable if the organism is correctly characterized and we know to which organism the term refers. This is calledidentification.

Scientists have developed processes to assign a scientific name to each known organism in ordering the process. Scientific names for plants are determined by agreed-upon principles and criteria outlined in the International Code for Botanical Nomenclature (ICBN). Taxonomists have developed the International Code of Zoological Nomenclature (ICZN) for animals.  Each creature has just one name thanks to the scientific names. Any organism's description should allow anyone (from all over the world) to come up with the same name. They also check to see if the name has been used for any other organism.

To give known creatures scientific names, biologists use broadly accepted rules. Each name is made up of two parts: a generic name and a specific epithet. Binomial nomenclature is a system for naming organismsconsisting of two parts. Carolus Linnaeus devised a naming system that is used by biologists all around the world. He is also known as the Father of Taxomy. This two-name approach was proven to be convenient.Mangiferaindica is the scientific name for the mango where, Mangifera denotes the genus, while indica denotes a specific species or epithet. The following are the universal rules of nomenclature:

1. Biological names are usually written in italics and written in Latin. Regardless of their origin, they are Latinized or derived from Latin.

2. In a biological name, the first component identifies the genus, whereas the second component denotes the specific epithet.

3. In handwriting, both words in a biological name are underlined or typed in italics to reflect their Latin origin.

4. The genus name begins with a capital letter, but the particular epithet begins with a tiny letter. 

The author's name occurs after the specific epithet, i.e., the after the zoological name, and is shortened, e.g., Mangiferaindica Linn. It denotes that Linnaeus was the first to describe this species.

Classification is the procedure of grouping things into useful categories based on plainly observable characteristics. Plants and animals, as well as dogs, cats, and insects, are easily identifiable. These phrases link certain characteristics to the organisms in that group. When we talk about mammals,' we're talking about animals with external ears and body hair. As a result, terminology like "Dogs," "Cats," "Mammals," "Wheat," "Rice," "Plants," and "Animals," among others, are useful categories for studying creatures. Taxa is the scientific word for these classifications. A taxon can denote a variety of categories at various levels. Plants are classified as a taxon. 'Wheat' is a taxon as well. 'Animals,' 'Mammals,' and 'Dogs,' for example, are all taxa. As a result, the terms 'animals,"mammals,' and 'dogs' all refer to taxa at various levels.

As a result, all living species can be divided into different taxa based on their properties. Taxonomy is the term for this classifying procedure. The external and internal structure of organisms, as well as cell structure, development process, and ecological information, are essential and form the basis of modern taxonomic investigations.  As a result, the fundamental stages of taxonomy are characterization, identification, categorization, and nomenclature. Humans, fora long, have been learning more about different types of organisms, particularly concerning their own Hence, the early classifications were based on the diverse utilities of organisms.

Humans have long been fascinated not only by diverse types of species and their diversity but also by the links that exist between them. The term "systematics" was coined to describe this field of study. The name "systematics" comes from the Latin word "systema," which means "an orderly arrangement of organisms." The title of Linnaeus' publication was SystemaNaturae. Identification, naming, and classification was later added to the scope of systematics. Systematics is the study of organisms' evolutionary relationships.

Biodiversity

• From a current estimation, approximately 1.7 million species have been scientifically named and classified. These include nearly 1.2 million animals and over 0.5 million species of plants.
• Amongst animals, insects form the largest group, i.e., over 10,25,000 species. It is estimated that majority of species diversity is confined to tropical rain forests and huge diversity exist in under water reef formations in tropical oceans.
• Existing living species are the outcome of about 3.5 billion years of evolutionary process on this earth. Nearly 15,000 new organisms are discovered every year.
• A clearer understanding of this huge variety of organisms can be studied by dividing these into smaller groups or sub-groups (categories) and each group or sub-group comprising of organisms with more or less similar characters.
• Method of placing organisms into groups or sub-groups depending upon extent of similarities and differences is called classification.
• The division of organisms into different groups follows certain rules, that is why the term called taxonomy is used for classification of organisms following certain rules or principles.

Taxonomic Categories

Classification is not a one-step procedure, but rather a series of stages, each representing a rank or category. The category is called a taxonomic category because it is a part of the larger taxonomic arrangement, and all categories combined make up the taxonomic hierarchy. Each category, also known as a classification unit, indicates a rank and is frequently referred to as a taxon (plural taxa). A taxonomic category is a category that is part of a taxonomic arrangement, and all categories combined make up the taxonomic hierarchy. Thus, organisms are divided into kingdoms, phyla or divisions, classes, orders, families, genera, and species.

Insects are a group of organisms with three pairs of jointed legs and other characteristics in common. It indicates that insects are recognizable concrete objects that can be categorized and so have a rank or category assigned to them. The categories are represented by groups of people. Rank is also indicated by category. Each rank, or taxon, is a classification unit. These taxonomic groups/categories are biological entities in their own right, not just morphological aggregations.

The establishment of common categories such as kingdom, phylum or division (for plants), class, order, family, genus, and species have resulted from taxonomic investigations of all known organisms. Species is the lowest level of classification for all organisms, including those in the plant and animal kingdoms. The knowledge of characteristics of an individual or group of organisms is required to categorize an organism into distinct categories. This aids in the identification of similarities and differences between individuals of the same species as well as individuals of different species.

Let us take a detailed look at different taxonomic categories:

(A)Species: A species is a group of individual beings that share fundamental characteristics. Based on morphological features, one species is separated from other closely related species. Mangiferaindica, Solanum tuberosum (potato), and Pantheraleo are just a few examples (lion). The first three words, Mangifera, Solanum, and Panthera, are genera and denote a higher level of taxon or category, while the first three words, indica, tuberosum, and leo, are specific epithets. Each genus may have one or more specific epithets that refer to various creatures that share morphological characteristics. Panthera, for example, has the specific epithet tigris, and Solanum comprises species such as nigrum and melongena. Humans are members of the species sapiens, which is part of the genus Homo.As a result, the scientific designation for a human being is Homo sapiens. Species is regarded as the least inclusive and highly specific category of the taxonomic hierarchy.

(B) Genus: A genus is a collection of related species that share more characteristics than those from other genera. Genera can be defined as groups of closely related species. Potato and brinjal, for example, are two separate species that both belong to the Solanum genus. Panthera species include the lion (Pantheraleo), leopard (Pantherapardus), and tiger (Pantheratigris), all of which share several characteristics. This genus is distinct from the Felis genus, which includes cats.

(C) Family:In comparison to genus and species, a family consists of a set of related genera with fewer similarities. In plants, vegetative and reproductive characteristics are used to classify them into families. Solanum, Petunia, and Datura are three separate genera of plants that belong to the Solanaceae family. The genus Panthera, which includes the lion, tiger, and leopard, is placed in the family Felidae with the genus Felis (cats). Similarly, if you compare and contrast the characteristics of a cat and a dog, you would notice some parallels and variances. Felidae and Canidae are the two different families that they belong to.

(D) Order:Species, genus, and family are all based on a set of comparable characteristics. The aggregates of characters are used to identify the order and other higher taxonomic groups. The group of families that have a few similar characteristics is called order, which is a higher category. When compared to the different genera in a family, there are fewer comparable characters. Plant groups such as Convolvulaceae and Solanaceae are classified as Polymoniales based on their floral characteristics. Carnivora is an animal order that includes families like Felidae and Canidae.

(E) Class: A class is a taxonomic rank (a taxon) that contains species with similar characteristics; it is further divided into one or more orders. A class is a major taxonomic rank below the phylum (or division) and above the order in the biological categorization of life. This category includes orders that are related. Order Primata, which includes monkeys, gorillas, and gibbons, is placed in class Mammalia alongside order Carnivora, which includes tigers, cats, and dogs. Other orders also exist in the Mammalia class.

(F) Phylum/Division:A phylum is a classification or taxonomic rank that falls between kingdom and class. The Phylum is the next higher classification, which includes animals such as fish, amphibians, reptiles, birds, and mammals. All of these are classified as members of the phylum Chordata because they share characteristics such as the presence of a notochord and a dorsal hollow neural system. Classes with a few comparable features in plants are given to a higher category called Division.

In biological classification, the division is a taxonomic rank that is employed differently in zoology and botany. The division is a level similar to a phylum in botany and mycology. The term division is used in zoology to refer to an optional rank that is subordinate to the infraclass and superordinate to the cohort.

(G) Kingdom:In the classification system of animals, all animals belonging to distinct phyla are placed in the top category, Kingdom Animalia. The Kingdom Plantae, on the other hand, is unique in that it includes all plants of diverse divisions. These two groups are today referred to as the animal and plant kingdoms.

(H) Domain:A domain is the largest of all groupings in the classification of life in biology. At this level, the Archaea domain, Bacteria domain, and Eukarya domain are the three agreed-upon categories. The domain is considered to be the most inclusive category of the hierarchy.

The amount of shared features decreases as we progress from species to kingdom. The lower the taxon, the more features the members of the taxon share. The more difficult it is to determine a taxon's relationship to other taxa at the same level, the higher the category. As a result, the classification problem gets more complicated. Therefore, the taxonomists have also created sub-categories in the hierarchy to make the placement of distinct taxa more sound and scientific.

 

Taxonomy and Systematics

Taxonomy: The branch of science dealing with the study of principles and procedures of classification is called taxonomy. The term taxonomy was coined by A.P. de Candolle. Linnaeus is considered as Father of Taxonomy. Santapau is considered as Father of Indian Taxonomy. The fundamental elements of taxonomy are as follows :

• Characterisation and identification : It is the determination of the similarities of an organism with an already known organism, based upon specific characters.
• Nomenclature: It is the determination of correct name of an organism according to established universal rules.
• Classification: It is grouping of organisms into convenient categories on the basis of easily observable characters.

• The classical taxonomy is based on observable morphological characters, however the modern taxonomy deals with several characters for the classification of organisms like

 (a)     External and internal structure alongwith the structure of cell.

 (b)    Development process.

 (c)    Ecological information of organisms

Systematics : The word "systematics" is derived from Latin word systema which means systematic arrangement of organisms. It was first used by Carolus Linnaeus. According to him, "systematics is the discipline of biology which deals with the kind and diversity of all organisms and the existing relationships amongst them."

    Generally, the terms such as classification, systematics and taxonomy are used interchangeably but some taxonomists like Simpson (1961) relate them with a separate field. He defined systematics as

   "The study of diversity of organisms and all their comparative and evolutionary relationships based on comparative anatomy, comparative ecology, comparative physiology and comparative biochemistry."

The main uses of systematics are as given below :

  (i)      It helps in providing knowledge of great diversity of animals and plants. It provides information regarding evolution which took place among plants and animals by knowing the distinction, relationship, habitat and habits. It thus, gives a vivid picture of entire organic diversity.

  (ii)    It helps in the identification of fossils which gives useful information about the phylogeny of organisms.

(iii)   Newly discovered organisms can be identified through systematics.

TAXONOMIC CATEGORIES

•  Classification is not a single step process. It involves hierarchy of steps in which each step represents a rank or category.  
•  The category is a part of overall taxonomic arrangement. All categories together make taxonomic hierarchy.  
• Each category is also termed as a unit of classification. It represents a rank and is commonly called as taxon.  
• The taxon must be recognisable and order should belong to a category.  
• Taxonomic hierarchy is a series of different ranks placed in ascending or descending order.
• It was Linnaeus who for the first time introduced five categories in the taxonomic hierarchy, viz., class, order, genus, species and variety.
• Later on three more categories, viz., kingdom, division or phylum and family were added.
• Variety was Species discarded to make a hierarchy of seven obligate categories.     
• Taxonomic categories kingdom -division (in plants) or phylum (in animals) -class -order -family -genus -species. (descending order)
• Higher the category, higher is the number of organisms in it. Higher the category, fewer will be the number of common characters and greater is the difficulty of determining the relationship to other taxa at the same level. Hence, the problem of classification becomes more complex.
• Taxonomic categories and hierarchy can be illustrated by an example. Insects represent a group of organisms sharing common features like three pairs of jointed legs.
• It means insects are recognisable concrete objects which can be classified, and thus were given a rank or category.
• Similarly, mammals represent animals with external ears, body hairs, mammary glands etc. Dog, mammals, animals are all taxa but of different categories.
• Taxon dog, mammals and animals represent categories like species, class and kingdom respectively.  

 Species:

• Term given by John Ray. It is lowest category of classification. It is a group of closely related individuals with similar morphological, anatomical, biochemical and cytological characters.
• It is a group of naturally interbreeding population with the ability to produce fertile offsprings.
• Individuals of a species share common gene pool.
• It is reproductively isolated, thus genetically closed system.

      e.g,  Pisum sativum                    – Pea

Mangifera indica                 – Mango

Solanum tuberosum            – Potato

Panthera leo                         – Lion

 Homo sapiens                      – Human being

 In these, sativum, indica, tuberosum, leo, sapiens represent the specific epithet, while Pisum, Mangifera, Solanum, Panthera and Homo represent genus.

Genus:

• Genus is a group of related species. Species has more characters in common in comparison to species of other genera. 
•  e.g., Potato, (Solanum tuberosum), makoi (S. nigrum) and brinjal (S. melongena) are three different species belonging to same genus Solanum.  
•  Lion, leopard and tiger with several common features belong to the same genus Panthera.

Family:

It is a group of related genera with still less number of similarities as compared to genus and species. Families are characterised on the basis of both vegetative and reproductive features of plants.

• For example, four related genera Solanum, Petunia, Datura and Atropa belong to the family Solanaceae. Genus Panthera and Felis (cat) are put together in family Felidae.

Order:

•  It is a group of related families which exhibit a few similar characters. The similar characters are less in number as compared to different genera included in a family. 
•   For example, plant families like Convolvulaceae and Solanaceae are included in order Polymoniales mainly based on floral characters.
•    In animals, order carnivora includes families like Felidae (cat) and Canidae (dog).

Class:

•   It is a group of related orders. 
•  For example , plants order like Sapindales (mango) and Polymoniales are included in   Class -Dicotyledonae, Order -Volvocales (Volvox) and Conjugales (Spirogyra) are included in Class -Chlorophyceae (green algae).In animals, order Primata (man, monkey) and Carnivora (cat, dog) are included in class -Mammalia.

Phylum/Division :

• It is a group of related classes.
•  The phylum Chordata of animals contains not only the class mammalia but also aves (birds), reptilia (reptiles) amphibia (amphibians) and osteichthyes (fishes).
• In case of plants, classes with few similar characters like dicots and monocots constitute division -Angiospermae.
• The category phylum is used in animalia while division is used in plantae.

Kingdom:

•  It is highest category in hierarchy with related phylums or divisions.

           Kingdom animalia includes all animals belonging to different phyla. Kingdom Plantae includes all plants of various divisions.

 

Concept of Species :

            Biological concept of species (was given by Ernst Mayr) : Species is the fundamental unit of classification. A species is a group of organisms (i) which are closely related (structurally and functionally) sharing a common gene pool (ii) which can interbreed freely in nature and produce fertile offspring in a natural environment. This concept of species is based upon reproductive isolation and called biological concept.

           Some important interspecific hybrids (exception of biological concept of species)

  (i)      Sterile Hybrid (under natural conditions)
Mule = Between male donkey and female horse (Mare)
Hinny = Between male horse (Stal'lion) and female donkey

  (ii)     Fertile Hybrid (under captive conditions)
Tigon = Between male tiger and female lion
Liger = Between male lion and female tiger

Types of Species :

TAXONOMICAL AIDS

• The laboratory and field studies are required for identification of various species and their placement in taxonomical hierarchy.
• The information thus gathered about the species, needs to be stored for future use.
• The taxonomical aids developed by biologists have established certain procedures and techniques to store and preserve the information as well as the specimens

NOMENCLATURE

There is a need to standardize the naming of living organisms, such that a particular organism is known by same name all over the world. A variety of nomenclatural methods are described below :

  1.Vernacular name: Names in local or common language are called vernacular names. So, many vernacular names exist for an organism in different languages. These may vary from place to place.

  2.Scientific names: These names were based on definite rules and criteria. These are of following types :

(i) Polynomial nomenclature

(ii) Trinomial nomenclature [both given in concept builder]

(iii) Binomial system of nomenclature:

a.Swedish naturalist Carolus Linnaeus established binomial nomenclature though, it was first proposed by Casper Bauhin in his book PINAX.

b. In binomial nomenclature, the first word is a generic name and second word is a specific epithet like Mangifera indica Linn.

c. After end of biological name, the name of author is written in abbreviated form who gave the name of the organism.

d.Scientific names are in Latin, because Latin was the language of scholars at the time of Linnaeus, and no change is possible in the language because this language has no synonyms.

e.Linnaeus gave some principles of the binomial nomenclature in Philosophia Botanica.

f. The nomenclature was used first in Species Plantarum (1753), where names and description of 5900 species of plants were given.

g.He published Systema Naturae (1758), where 4326 species of animals were described.           

A. International Code of Nomenclature

Scientific names have been standardised through some international agencies, viz., International Code of Botanical Nomenclature (ICBN, 1961) and International Code of Zoological Nomenclature (ICZN, 1964), International Code for Nomenclature of Bacteria (ICNB), International Code of Nomenclature for Cultivated Plants (ICNCP) and currently being developed is International Committee for the Taxonomy of Viruses (ICTV).

B. Rules for Binomial Nomenclature

ICBN and ICZN formulated certain rules and regulations for giving scientific names to all organisms. These rules are as follows :

• The valid name of an organism has two components, i.e., a generic name and a specific epithet. The generic name should begin with a capital letter and species name should begin with a small letter.
• Both the words in a biological name when handwritten are separately underlined or printed in italics to indicate their Latin origin.
• The name of the author should be written after the scientific name in Roman type with capital letter without any comma in between and is written in an abbreviated form, e.g., Homo sapiens Linn. is the complete scientific name for modern man. This shows that Linnaeus was the first scientist who named man as Homo sapiens.
• Scientific names should not contain less than three and more than twelve letters.
• Principle of priority: It is the most important of all the rules of ICBN. If first name given to the organism is valid (in terms of rules), that will be considered at the first preference. Any other valid name given after that will be considered as synonym. No names are recognised prior to those used by Linnaeus in 1758 in the 10th edition of Systema Naturae for animals and 1753 for plants.
• All the three words (generic name, species epithet and author citation) collectively form Binomial epithet.
• If a species name has two or more words in its name, a hyphen is put between these. Such names are compound specific names (e.g., Hibiscus rosa-sinensis).

 Zoological Parks

• Zoos or zoological gardens (parks) are protected areas or enclosed space where live wild animals are kept, under human care. This enables us to learn their food habits and behaviour.
• Objectives are public exhibition to understand wild life, recreation, education, ex situ conservation and breeding of rare fauna.
• Largest zoo of the world is situated in Kruger (S. Africa).
• National Zoological Park (Delhi) is one of the finest zoo of Asia.

  

    Herbarium (Dry Garden)

• It is defined as "a store house of collected plant specimens that are dried, pressed and preserved on sheets."
• These sheets are arranged in the sequence of an accepted classification system.
• These specimens, along with their description on herbarium sheets, become a store house or repository for future use. The herbarium sheet contains a label on the right-hand side at lower corner.
• Label provides information about date and place of collection, English, local and botanical names, family, collector's name etc.
• Herbaria also serve as quick referral systems in taxonomical studies.

Herbarium Sheet

Functions of a Herbarium

The two primary functions of herbarium are accurate identification and alpha taxonomic research (based on gross morphology).

The secondary functions include closer interaction between the student of general systematics and the herbarium.

Other important functions of a herbarium are –

  1.To preserve plant wealth including type material and palaeobotanical collections.

  2.To carry out exchange and loan of preserved plant material for research, exhibitions etc.

A list of important herbaria of the world is given below along with their standard abbreviations and the approximate number of specimens they hold

TYPE SPECIMEN (HERBARIUM SHEET)

Type specimen (Herbarium Sheet) of newly discovered plant should be place in herbarium (Dry garden). Standered size of herbarium sheet is 11.5 × 16.5 inches.

Holotype - Herbarium sheet on which the first description of plant is based.

Isotype - Duplicate of holotype - In presence of holotype a second herbarium sheet prepared from the original plant is called isotype.

Paratype - Additional herbarium sheet used in the first description of plant is called paratype. It is prepared from some other plant of same species having some variations.

Lectotype - In case of holotype is lost, second herbarium sheet prepared from the original plant is called lectotype.

Neotype - In case of holotype and original plant is lost, then herbarium sheet prepared from some other plant of same species is called neotype.

Syntype - In case of holotype and original plant is lost then many herbarium sheet prepared from many plants of same species is called syntype.

Note : Nomenclature is invalid in absence of Herbarium sheet.

Botanical Gardens

• From the time of Theophrastus, gardens have contributed to the science of botany. But, there was an impetus to the botanical explorations only in the Post-Linnean period.
• In ancient Indian culture, cultivation of food and medicinal plants is known since 4000 to 2000 B.C. The 'Hanging Gardens of Babylon' are amongst the wonders of the ancient world.
• During the Middle Ages, from A.D. 600-1600, there was a lapse in learning and introduction of plants.
• In the seventeenth century, there was a revival in the interest and by eighteenth century, most of the famous Botanical Gardens known today had already been established.

  The functions of a botanical garden are:

1. Provide records of local flora for monographic work.
2. Provide facilities for collections and identification of living plant material for biosystematic studies / references.
3. Supply seeds and material for botanical investigations.
4. Botanical gardens have an aesthetic appeal and attract a large number of visitors for observing general plant diversity.
5. Provides means of ex-situ conservation strategies.

• There are about 525 botanical gardens in various countries, but only about 125 have documented collections of authenticated taxa.

       6.The International Association of Botanical Gardens was established in 1962. This association has published the International Directory of Botanical Gardens (1983).

BOTANICAL GARDENS OF INDIA

• The Indian Botanical Garden, Kolkata, India: It was founded in 1787, by Lt.Col. Robert Kyd. It covers an area of 273 acres and contains collections of world's tropical plants.
• It is one of the greatest botanical gardens of the world and one of the first to be established in tropics.
• William Roxburgh, 'Father of Indian Botany' was its director from 1793 to 1813.
• It has the largest herbarium of east and is famous for the Great Banyan tree, Ficus benghalensis, which is two centuries old, the palm houses, nurseries and the Amazon lily, Victoria amazonica (Nymphaeaceae), the plant with the largest leaves.

It is now under control of BSI (Botanical Survey of India).

Other botanical gardens of India are -   

Lloyd Botanical Garden                    – Darjeeling
National Botanical Garden               – Lucknow
Lalbag Gardens                                – Bangalore
Saharanpur Botanical Garden          – Saharanpur

Diversity in the Living World

From a current estimation, approximately 1.7 million species have been scientifically named and classified. These include nearly 1.2 million animals and over 0.5 million species of plants.

Amongst animals, insects form the largest group, i.e., over 10,25,000 species. It is estimated that majority of species diversity is confined to tropical rain forests and huge diversity exist in under water reef formations in tropical oceans.

Existing living species are the outcome of about 3.5 billion years of evolutionary process on this earth. Nearly 15,000 new organisms are discovered every year.

A clearer understanding of this huge variety of organisms can be studied by dividing these into smaller groups or sub-groups (categories) and each group or sub-group comprising of organisms with more or less similar characters.

Method of placing organisms into groups or sub-groups depending upon extent of similarities and differences is called classification.

The division of organisms into different groups follows certain rules, that is why the term called taxonomy is used for classification of organisms following certain rules or principles.

Diversity in the Living World 

Diversity in the world can be experienced everywhere on the earth. Each different kind of plant, animal, or organism that you see represents a species. The number of species that are known and described ranges from 1.71.7 to 1.81.8 million, which is referred to as biodiversity. Every individual is unique with respect to structure, body functions, genetic make-up, etc

Living organisms inhabiting different habitats have different structural organs or functions developed according to the conditions of the habitat. The warm and humid regions of the earth have diverse organisms and thus are known as the region of mega biodiversity.

Terminology utilized as a part of classification includes Nomenclature, Classification, Taxonomy and Systematics.

The process of naming an organism is known as nomenclature. A principle and criterion were given for naming the organisms, by scientists known as International Code for Botanical nomenclature (ICBN). For animals, International Code of Zoological Nomenclature. This helps scientists from all over the world to interact with each other using the same name.

Each name consists of two parts the first part is the generic name and the second part is the name of the species. This is known as Binomial Nomenclature. This was given by a scientist known as Carolus Linnaeus. 

Examples: Mangifera Indica (Mango); Homo sapiens (Man)

In this case, Mangifera and Homo are the generic names; indica and sapiens are specific epithets.

Rules of Nomenclature:

• Each biological name has two words-The principal word speaks about the genus and the second speaks to the specific epithet.
• The expressions of the name ought to be independently underlined when manually written and ought to be in italics when printed.
• The generic name ought to begin with a capital letter and the specific epithet ought to begin with a little letter.
• The names ought to be either Latin or Latinized.

Classification: It is the process of assigning creatures to particular groups or classes taking into account some defined characters. These classes are called Taxa (sing. taxon)

Taxonomy: It is the investigation of identification, nomenclature and arrangement of life forms taking into account outer and inside the structure with cell structure, advancement process and biological data.

 systematics: It is the investigation of life forms with reference to identification, nomenclature, arrangement and evolutionary correspondence.

Diversity in the living world

The biological variety and variability of life on Earth are referred to as biodiversity. Looking around, one will see a wide range of living organisms, including potted plants, insects, birds, pets, and other animals and plants. Other species are invisible to the naked sight but are all around us. A species is represented by each different type of plant, animal, or organism you see. Between 1.7 and 1.8 million species have been identified and described. This refers to the diversity of species on the planet or the quantity and varieties of creatures that exist.

There are millions of plants and animals throughout the world that are known by their regional names. These regional names might differ from one location to the next, even within a country. When referring to organisms, such names can cause confusion. As confuse necessary to standardize the naming of living entities so that they are known by the same name all over the world. This is referred to as nomenclature.

This naming or nomenclature is only achievable if the organism is correctly characterized and we know to which organism the term refers. This is calledidentification.

Scientists have developed processes to assign a scientific name to each known organism in ordering the process. Scientific names for plants are determined by agreed-upon principles and criteria outlined in the International Code for Botanical Nomenclature (ICBN). Taxonomists have developed the International Code of Zoological Nomenclature (ICZN) for animals.  Each creature has just one name thanks to the scientific names. Any organism's description should allow anyone (from all over the world) to come up with the same name. They also check to see if the name has been used for any other organism.

To give known creatures scientific names, biologists use broadly accepted rules. Each name is made up of two parts: a generic name and a specific epithet. Binomial nomenclature is a system for naming organismsconsisting of two parts. Carolus Linnaeus devised a naming system that is used by biologists all around the world. He is also known as the Father of Taxomy. This two-name approach was proven to be convenient.Mangiferaindica is the scientific name for the mango where, Mangifera denotes the genus, while indica denotes a specific species or epithet. The following are the universal rules of nomenclature:

1. Biological names are usually written in italics and written in Latin. Regardless of their origin, they are Latinized or derived from Latin.

2. In a biological name, the first component identifies the genus, whereas the second component denotes the specific epithet.

3. In handwriting, both words in a biological name are underlined or typed in italics to reflect their Latin origin.

4. The genus name begins with a capital letter, but the particular epithet begins with a tiny letter. 

The author's name occurs after the specific epithet, i.e., the after the zoological name, and is shortened, e.g., Mangiferaindica Linn. It denotes that Linnaeus was the first to describe this species.

Classification is the procedure of grouping things into useful categories based on plainly observable characteristics. Plants and animals, as well as dogs, cats, and insects, are easily identifiable. These phrases link certain characteristics to the organisms in that group. When we talk about mammals,' we're talking about animals with external ears and body hair. As a result, terminology like "Dogs," "Cats," "Mammals," "Wheat," "Rice," "Plants," and "Animals," among others, are useful categories for studying creatures. Taxa is the scientific word for these classifications. A taxon can denote a variety of categories at various levels. Plants are classified as a taxon. 'Wheat' is a taxon as well. 'Animals,' 'Mammals,' and 'Dogs,' for example, are all taxa. As a result, the terms 'animals,"mammals,' and 'dogs' all refer to taxa at various levels.

As a result, all living species can be divided into different taxa based on their properties. Taxonomy is the term for this classifying procedure. The external and internal structure of organisms, as well as cell structure, development process, and ecological information, are essential and form the basis of modern taxonomic investigations.  As a result, the fundamental stages of taxonomy are characterization, identification, categorization, and nomenclature. Humans, fora long, have been learning more about different types of organisms, particularly concerning their own Hence, the early classifications were based on the diverse utilities of organisms.

Humans have long been fascinated not only by diverse types of species and their diversity but also by the links that exist between them. The term "systematics" was coined to describe this field of study. The name "systematics" comes from the Latin word "systema," which means "an orderly arrangement of organisms." The title of Linnaeus' publication was SystemaNaturae. Identification, naming, and classification was later added to the scope of systematics. Systematics is the study of organisms' evolutionary relationships.

 TAXONOMIC CATEGORIES

Classification is not a single step process. It involves hierarchy of steps in which each step represents a rank or category.  

The category is a part of overall taxonomic arrangement. All categories together make taxonomic hierarchy.  

Each category is also termed as a unit of classification. It represents a rank and is commonly called as taxon.  

The taxon must be recognisable and order should belong to a category.  

Taxonomic hierarchy is a series of different ranks placed in ascending or descending order.

It was Linnaeus who for the first time introduced five categories in the taxonomic hierarchy, viz., class, order, genus, species and variety.

Later on three more categories, viz., kingdom, division or phylum and family were added.

Variety was Species discarded to make a hierarchy of seven obligate categories.     

Taxonomic categories kingdom -division (in plants) or phylum (in animals) -class -order -family -genus -species. (descending order)

Higher the category, higher is the number of organisms in it. Higher the category, fewer will be the number of common characters and greater is the difficulty of determining the relationship to other taxa at the same level. Hence, the problem of classification becomes more complex.

Taxonomic categories and hierarchy can be illustrated by an example. Insects represent a group of organisms sharing common features like three pairs of jointed legs.

It means insects are recognisable concrete objects which can be classified, and thus were given a rank or category.

Similarly, mammals represent animals with external ears, body hairs, mammary glands etc. Dog, mammals, animals are all taxa but of different categories.

Taxon dog, mammals and animals represent categories like species, class and kingdom respectively.  

 Species:

Term given by John Ray. It is lowest category of classification. It is a group of closely related individuals with similar morphological, anatomical, biochemical and cytological characters.

It is a group of naturally interbreeding population with the ability to produce fertile offsprings.

Individuals of a species share common gene pool.

It is reproductively isolated, thus genetically closed system.

e.g,  Pisum sativum                    – Pea

Mangifera indica                 – Mango

Solanum tuberosum            – Potato

Panthera leo                         – Lion

 Homo sapiens                      – Human being

 In these, sativum, indica, tuberosum, leo, sapiens represent the specific epithet, while Pisum, Mangifera, Solanum, Panthera and Homo represent genus.

Genus:

Genus is a group of related species. Species has more characters in common in comparison to species of other genera. 

 e.g., Potato, (Solanum tuberosum), makoi (S. nigrum) and brinjal (S. melongena) are three different species belonging to same genus Solanum.  

 Lion, leopard and tiger with several common features belong to the same genus Panthera.

Family:

It is a group of related genera with still less number of similarities as compared to genus and species. Families are characterised on the basis of both vegetative and reproductive features of plants.

For example, four related genera Solanum, Petunia, Datura and Atropa belong to the family Solanaceae. Genus Panthera and Felis (cat) are put together in family Felidae.

Order:

 It is a group of related families which exhibit a few similar characters. The similar characters are less in number as compared to different genera included in a family. 

  For example, plant families like Convolvulaceae and Solanaceae are included in order Polymoniales mainly based on floral characters.

   In animals, order carnivora includes families like Felidae (cat) and Canidae (dog).

Class:

It is a group of related orders. 

 For example , plants order like Sapindales (mango) and Polymoniales are included in   Class -Dicotyledonae, Order -Volvocales (Volvox) and Conjugales (Spirogyra) are included in Class -Chlorophyceae (green algae).In animals, order Primata (man, monkey) and Carnivora (cat, dog) are included in class -Mammalia.

Phylum/Division :

It is a group of related classes.

The phylum Chordata of animals contains not only the class mammalia but also aves (birds), reptilia (reptiles) amphibia (amphibians) and osteichthyes (fishes).

In case of plants, classes with few similar characters like dicots and monocots constitute division -Angiospermae.

The category phylum is used in animalia while division is used in plantae.

Kingdom:

 It is highest category in hierarchy with related phylums or divisions.

Kingdom animalia includes all animals belonging to different phyla. Kingdom Plantae includes all plants of various divisions.

Concept of Species :

Biological concept of species (was given by Ernst Mayr) : Species is the fundamental unit of classification. A species is a group of organisms (i) which are closely related (structurally and functionally) sharing a common gene pool (ii) which can interbreed freely in nature and produce fertile offspring in a natural environment. This concept of species is based upon reproductive isolation and called biological concept.

Some important interspecific hybrids (exception of biological concept of species)

  (i)      Sterile Hybrid (under natural conditions)
Mule = Between male donkey and female horse (Mare)
Hinny = Between male horse (Stal'lion) and female donkey

  (ii)     Fertile Hybrid (under captive conditions)
Tigon = Between male tiger and female lion
Liger = Between male lion and female tiger

Types of Species :

Concept Builder

In accordance with International Code of Botanical Nomenclature, the names of different categories must end in the standard endings (suffixes) given below :

Tournefort gave the term genus and John Ray gave the term species 
    (b)     Names of some families are changed according to ICBN rules for suffixes. 

Old Name          New Name

Palmae               Arecaceae

Graminae            Poaceae

Leguminosae      Fabaceae

Compositae         Asteraceae

Cruciferae           Brassicaceae

Umbelliferae        Apiaceae

Labiatae               Lamiaceae

Guttiferae            Clusiaceae

(c)     Tribe is an intermediate category between sub-family and genus. 
(d)     In asexually reproducing organisms, physical resemblances and differences are used for delimiting species. 
(e)     Basic function of biological classification : 

• (a) Recognition and description of species. 
• (b) Grouping the species on the basis of similarities and relationship. 
• (c) To establish evolutionary relationship amongst different organisms. 

(f)    The genera which have more than one specific epithets, are known as polytypic. 

Lion    – Panthera leo 
Leopard    – Panthera pardus 
Tiger    – Panthera tigris 

(g)    There are 7 obligate categories and about 21 intermediate categories. Prefixes: sub-and super-used for intermediate categories. 
(h)    Species name is given on the basis of some characters or habit, colour and distribution, e.g., niger (black), alba (white), tuberosum (tuber). 
(i)    Taxon is a group of real organisms which is assigned for any category. It is the unit of classification for any rank. Term taxon was introduced by ICBN in 1956 and defined by Mayr (1964). 
(j)    Category is an abstract term and represents only rank or level in a hierarchy and does not represent the living organisms. Example: Reptile is taxon but reptilia is category.

(k)    Typological concept of Species

It was proposed by “Aristotle” and “Plato”. According to this concept, “There is a definite type or pattern of characters are present in the each species and all the members of species shows maximum resemblance with this pattern”. The species in which one fixed pattern of characters is present are called as monotypic species. e.g., Bacteria, Blue green algae if more than one type of pattern of characters are present. These are called “Polytypic species” or “Macrospecies”. e.g., Brassica oleracea  Cauliflower, Cabbage, Knol-Knol.

Type of Polytypic Species :

Biotype : Members of same species inhabiting similar environment and having some genetic variations are known as biotypes. Variations found in these members are permanent. These members can not interbreed among themselves. e.g. Cauliflower, Cabbage, Knol-Khol are three biotypes of one species
Ecotypes : Members of same species inhabiting different environment and having some genetic variations are known as ecotypes. Variations are permanent. These members can interbreed among themselves but due to geographical barrier they can not interbreed.
e.g., Crow (Corvus splendense) found in different regions are ecotype of one species
Corvus splendense splendense - Indian crow
Corvus splendense insolense - Myanmar crow
Corvus splendense protegatus - Srilankan crow
Ecospecies : It contains one or more ecotype which although interfertile (capable of interbreeding), but do not produce viable offsprings due to some natural interruption (mountain, ocean etc).
Ecads or Ecophenes : Members of same species having some non genetic variation due to environment. These variations are temporary. 
e.g.,    

Taxonomic Categories

Classification is not a one-step procedure, but rather a series of stages, each representing a rank or category. The category is called a taxonomic category because it is a part of the larger taxonomic arrangement, and all categories combined make up the taxonomic hierarchy. Each category, also known as a classification unit, indicates a rank and is frequently referred to as a taxon (plural taxa). A taxonomic category is a category that is part of a taxonomic arrangement, and all categories combined make up the taxonomic hierarchy. Thus, organisms are divided into kingdoms, phyla or divisions, classes, orders, families, genera, and species.

Insects are a group of organisms with three pairs of jointed legs and other characteristics in common. It indicates that insects are recognizable concrete objects that can be categorized and so have a rank or category assigned to them. The categories are represented by groups of people. Rank is also indicated by category. Each rank, or taxon, is a classification unit. These taxonomic groups/categories are biological entities in their own right, not just morphological aggregations.

The establishment of common categories such as kingdom, phylum or division (for plants), class, order, family, genus, and species have resulted from taxonomic investigations of all known organisms. Species is the lowest level of classification for all organisms, including those in the plant and animal kingdoms. The knowledge of characteristics of an individual or group of organisms is required to categorize an organism into distinct categories. This aids in the identification of similarities and differences between individuals of the same species as well as individuals of different species.

Let us take a detailed look at different taxonomic categories:

(A)Species: A species is a group of individual beings that share fundamental characteristics. Based on morphological features, one species is separated from other closely related species. Mangiferaindica, Solanum tuberosum (potato), and Pantheraleo are just a few examples (lion). The first three words, Mangifera, Solanum, and Panthera, are genera and denote a higher level of taxon or category, while the first three words, indica, tuberosum, and leo, are specific epithets. Each genus may have one or more specific epithets that refer to various creatures that share morphological characteristics. Panthera, for example, has the specific epithet tigris, and Solanum comprises species such as nigrum and melongena. Humans are members of the species sapiens, which is part of the genus Homo.As a result, the scientific designation for a human being is Homo sapiens. Species is regarded as the least inclusive and highly specific category of the taxonomic hierarchy.

(B) Genus: A genus is a collection of related species that share more characteristics than those from other genera. Genera can be defined as groups of closely related species. Potato and brinjal, for example, are two separate species that both belong to the Solanum genus. Panthera species include the lion (Pantheraleo), leopard (Pantherapardus), and tiger (Pantheratigris), all of which share several characteristics. This genus is distinct from the Felis genus, which includes cats.

(C) Family:In comparison to genus and species, a family consists of a set of related genera with fewer similarities. In plants, vegetative and reproductive characteristics are used to classify them into families. Solanum, Petunia, and Datura are three separate genera of plants that belong to the Solanaceae family. The genus Panthera, which includes the lion, tiger, and leopard, is placed in the family Felidae with the genus Felis (cats). Similarly, if you compare and contrast the characteristics of a cat and a dog, you would notice some parallels and variances. Felidae and Canidae are the two different families that they belong to.

(D) Order:Species, genus, and family are all based on a set of comparable characteristics. The aggregates of characters are used to identify the order and other higher taxonomic groups. The group of families that have a few similar characteristics is called order, which is a higher category. When compared to the different genera in a family, there are fewer comparable characters. Plant groups such as Convolvulaceae and Solanaceae are classified as Polymoniales based on their floral characteristics. Carnivora is an animal order that includes families like Felidae and Canidae.

(E) Class: A class is a taxonomic rank (a taxon) that contains species with similar characteristics; it is further divided into one or more orders. A class is a major taxonomic rank below the phylum (or division) and above the order in the biological categorization of life. This category includes orders that are related. Order Primata, which includes monkeys, gorillas, and gibbons, is placed in class Mammalia alongside order Carnivora, which includes tigers, cats, and dogs. Other orders also exist in the Mammalia class.

(F) Phylum/Division:A phylum is a classification or taxonomic rank that falls between kingdom and class. The Phylum is the next higher classification, which includes animals such as fish, amphibians, reptiles, birds, and mammals. All of these are classified as members of the phylum Chordata because they share characteristics such as the presence of a notochord and a dorsal hollow neural system. Classes with a few comparable features in plants are given to a higher category called Division.

In biological classification, the division is a taxonomic rank that is employed differently in zoology and botany. The division is a level similar to a phylum in botany and mycology. The term division is used in zoology to refer to an optional rank that is subordinate to the infraclass and superordinate to the cohort.

(G) Kingdom:In the classification system of animals, all animals belonging to distinct phyla are placed in the top category, Kingdom Animalia. The Kingdom Plantae, on the other hand, is unique in that it includes all plants of diverse divisions. These two groups are today referred to as the animal and plant kingdoms.

(H) Domain:A domain is the largest of all groupings in the classification of life in biology. At this level, the Archaea domain, Bacteria domain, and Eukarya domain are the three agreed-upon categories. The domain is considered to be the most inclusive category of the hierarchy.

The amount of shared features decreases as we progress from species to kingdom. The lower the taxon, the more features the members of the taxon share. The more difficult it is to determine a taxon's relationship to other taxa at the same level, the higher the category. As a result, the classification problem gets more complicated. Therefore, the taxonomists have also created sub-categories in the hierarchy to make the placement of distinct taxa more sound and scientific.

 

Taxonomy

Taxonomy Definition

Taxonomy is the branch of biology that classifies all living things. It was developed by the Swedish botanist Carolus Linnaeus, who lived during the 18^th Century, and his system of classification is still used today. Linnaeus invented binomial nomenclature, the system of giving each type of organism a genus and species name. The Father of taxonomy was Carolus Linnaeus. He also developed a classification system called the taxonomic hierarchy, which today has eight ranks from general to specific: domain, kingdom, phylum, class, order, family, genus, and species.

The Taxonomic Hierarchy

A taxon (plural: taxa) is a group of organisms that are classified as a unit. This can be specific or general. The hierarchy has two categories i.e., obligate and intermediate. Obligate is the one that is followed strictly and ranges from kingdom to species. Intermediate is not observed strictly and they. Also, they are added to the obligate lists like subdivision, superfamily, superclass, suborder, subspecies etc.

The following is a brief description of the taxonomic ranks of the taxonomic hierarchy.

Domain

A domain is the highest (most general) rank of organisms. Linnaeus did invent some of the taxonomic ranks, but he did not invent the domain rank, which is relatively new. The term domain wasn’t used until 1990, over 250 years after Linnaeus developed his classification system in 1735.

The three-domain system of Carl Woese, introduced in 1990, with top-level groupings of Archaea, Bacteria, and Eukaryota domains.

Kingdom

Before domains were introduced, the kingdom was the highest taxonomic rank. In the past, the different kingdoms were Animalia, Plantae, Fungi, Protista, Archaea, and Bacteria (Archaea and Bacteria were sometimes grouped into one kingdom, Monera)

Phylum

Phylum (plural: phyla) is the next rank after kingdom; it is more specific than kingdom but less specific than class. There are 35 phyla in the kingdom Animalia, including Chordata (all organisms with a dorsal nerve cord), Porifera (sponges), and Arthropoda (arthropods).

Class

Class was the most general rank proposed by Linnaeus; phyla were not introduced until the 19th Century. There are 108 different classes in the kingdom Animalia, including Mammalia (mammals), Aves (birds), and Reptilia (reptiles), among many others.

Order

Order is more specific than class. Some of Linnaeus’ orders are still used today, such as Lepidoptera (the order of butterflies and moths). There are between 19-26 orders of Mammalia, depending on how organisms are classified—sources differ. 

Genus

Genus (plural: genera) is even more specific than family. It is the first part of an organism’s scientific name using binomial nomenclature; the second part is the species name. An organism’s scientific name is always italicized, and the genus name is capitalized while the species name is not. Genus and species are the only taxonomic ranks that are italicized. The scientific name for humans is Homo sapiens. Homo is the genus name, while sapiens is the species name. 

Species

Species are the most specific major taxonomic rank; species are sometimes divided into subspecies, but not all species have multiple forms that are different enough to be called subspecies. There are an estimated 8.7 million different species of organisms on Earth, While each genus name is unique, the same species names can be used for different organisms. For example, Ursus americanus is the American black bear, while Bufo americanus is the American toad.

TAXONOMICAL AIDS 

The laboratory and field studies are required for identification of various species and their placement in taxonomical hierarchy. 

The information thus gathered about the species, needs to be stored for future use. 

The taxonomical aids developed by biologists have established certain procedures and techniques to store and preserve the information as well as the specimens. 

1. Botanical Gardens 

From the time of Theophrastus, gardens have contributed to the science of botany. But, there was an impetus to the botanical explorations only in the Post-Linnean period. 

In ancient Indian culture, cultivation of food and medicinal plants is known since 4000 to 2000 B.C. The 'Hanging Gardens of Babylon' are amongst the wonders of the ancient world. 

During the Middle Ages, from A.D. 600-1600, there was a lapse in learning and introduction of plants. 

In the seventeenth century, there was a revival in the interest and by eighteenth century, most of the famous Botanical Gardens known today had already been established. 

    The functions of a botanical garden are: 

1.    Provide records of local flora for monographic work. 

2.    Provide facilities for collections and identification of living plant material for biosystematic studies / references. 

3.    Supply seeds and material for botanical investigations. 

4.    Botanical gardens have an aesthetic appeal and attract a large number of visitors for observing general plant diversity. 

5.    Provides means of ex-situ conservation strategies. 
        There are about 525 botanical gardens in various countries, but only about 125 have documented collections of authenticated taxa. 
6.    The International Association of Botanical Gardens was established in 1962. This association has published the International Directory of Botanical Gardens (1983). 

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Some of the important Botanical Gardens are listed below :

1. Royal Botanical Garden, Kew, England : It was founded in 1759 by William Alton, but was officially opened in 1841 and was called the Botanical Capital of the World. Sir J.D. Hooker was one of its directors. It is famous for its Alpine house, Rose Garden, Green house, Temperature house, Bamboo garden and Lily pond. It is associated with Jodrell laboratory of experimental taxonomy. It is spread in 200 acres. It is famous for collection of Acacias, Acer, Rhus, Citrus, Rosa, Prunus, Magnolia. It has Chelsa Physic Garden for horticulturists. Kew

2. Orto Botanico (Padua Gardens), Italy: It is said to be the first botanical garden. It is famous for collections of grasses, Alliums, Irids, Paeonias, succulents and hydrophytes.

3. Pisa, Italy: Almost as old as Padua Gardens, it was the first to introduce palaeontological practises; for the study of plants fossils. It is known for trees like Magnolia grandiflora, Liriodendron tulipifera etc. Caesalpino and John Ray have been associated with this garden.

4. Villa Taranto, Italy: It is the most beautiful garden of Italy and important from the horticultural study point of view.

5. Main Botanical Garden, Moscow: Largest Botanical Garden, spread over an area of 900 acres.

BOTANICAL GARDENS OF INDIA

The Indian Botanical Garden, Kolkata, India: It was founded in 1787, by Lt.Col. Robert Kyd. It covers an area of 273 acres and contains collections of world's tropical plants.

It is one of the greatest botanical gardens of the world and one of the first to be established in tropics.

William Roxburgh, 'Father of Indian Botany' was its director from 1793 to 1813.

It has the largest herbarium of east and is famous for the Great Banyan tree, Ficus benghalensis, which is two centuries old, the palm houses, nurseries and the Amazon lily, Victoria amazonica (Nymphaeaceae), the plant with the largest leaves.

It is now under control of BSI (Botanical Survey of India).

Other botanical gardens of India are -

Lloyd Botanical Garden                – Darjeeling
National Botanical Garden           – Lucknow
Lalbag Gardens                           – Bangalore
Saharanpur Botanical Gardens   – Saharanpur

Herbarium (Dry Garden)

It is defined as "a store house of collected plant specimens that are dried, pressed and preserved on sheets."

These sheets are arranged in the sequence of an accepted classification system.

These specimens, along with their description on herbarium sheets, become a store house or repository for future use. The herbarium sheet contains a label on the right-hand side at lower corner.

Label provides information about date and place of collection, English, local and botanical names, family, collector's name etc.

Herbaria also serve as quick referral systems in taxonomical studies.

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Herbarium Technique 
The herbarium technique involves the following steps: 

• (a) Collection    
• (b) Drying    
• (c) Poisoning    
• (d) Mounting      
• (e) Stitching     
• (f) Labelling    
• (g) Deposition 

(a)    Collection: Collection of plant material is done with an aesthetic sense and scientific mind. 
The material should be perfect and complete for determination, i.e., must have fully grown 
leaves, complete inflorescence etc. 
Woody elements are well represented by flowering twigs with 30-40 cm in lengths, while 
herbaceous plants are collected alongwith underground parts. 
Diseased plants, infected twigs should be avoided. 
The collections are kept inside metallic vasculum or polythene bags. 

(b)     Drying: The plant collections are pressed in ordinary newspaper folders, avoiding overlapping. The folders, in turn, are pressed in a field press. The moistened folders are changed frequently to avoid blackening and decay of plant material. 

(c)     Poisoning: The specimens are poisoned to keep away the microbes. When the specimens are partially dehydrated, they are poisoned by using chemicals like 0.1% of corrosive, sublimate (HgCl2).

(d-f)     Mounting, Stitching and Labelling : Dried specimens are glued and stitched on herbarium sheets made up of thick card sheets cut to the required size. The international size of the herbarium sheet is 41× 29 cm (16  ×11  inches) . The field data is entered on label on the right hand side lower corner of the herbarium sheet. Size of label is commonly 7 × 12cm. The small paper envelopes called fragment packets are often attached to the herbarium sheet to hold seeds, extra flowers or loose plant parts. 

(g)    Deposition: Arrangement of specimen, according to accepted classification, is called deposition. In India, herbaria are arranged according to Bentham and Hooker system of classification. 
The specimens so preserved are sprayed with repellents or disinfectants such as DDT powder, copper sulphate solution at intervals of 4 to 6 months to keep off small insect pests such as silver fish. 

Functions of a Herbarium 

The two primary functions of herbarium are accurate identification and alpha taxonomic research (based on gross morphology). 

The secondary functions include closer interaction between the student of general systematics and the herbarium. 

Other important functions of a herbarium are 

1.  To preserve plant wealth including type material and palaeobotanical collections. 

2.  To carry out exchange and loan of preserved plant material for research, exhibitions etc. 
A list of important herbaria of the world is given below along with their standard abbreviations and the approximate number of specimens they hold 
1.Royal Botanical Gardens, Kew (K)         over 6,000,000
4. Central National Herbarium, Calcutta (CAL)       2,000,000 

TYPE SPECIMEN (HERBARIUM SHEET)

Type specimen (Herbarium Sheet) of newly discovered plant should be place in herbarium (Dry garden). Standered size of herbarium sheet is 11.5 × 16.5 inches.

Holotype - Herbarium sheet on which the first description of plant is based.

Isotype - Duplicate of holotype - In presence of holotype a second herbarium sheet prepared from the original plant is called isotype.

Paratype - Additional herbarium sheet used in the first description of plant is called paratype. It is prepared from some other plant of same species having some variations.

Lectotype - In case of holotype is lost, second herbarium sheet prepared from the original plant is called lectotype.

Neotype - In case of holotype and original plant is lost, then herbarium sheet prepared from some other plant of same species is called neotype.

Syntype - In case of holotype and original plant is lost then many herbarium sheet prepared from many plants of same species is called syntype.

Note : Nomenclature is invalid in absence of Herbarium sheet.

3. Keys [Given by John Ray] 

The scheme for identification of plants and animals based upon similarities and dissimilarities is known as a key. It is based on the set of contrasting characters known as couplet, each character of couplet is called as lead. Separate taxonomic keys are required for each taxonomic category. Keys are generally analytical in nature and are of two types (1) Indented key (2) Bracketed key –
1. Indented Key: It has a sequence of choice between two or more statements of characters of species. These require great taxonomic skills to prepare, so are generally less followed. 
2 Bracketed Key: In the Bracketed key the pairs of contrasting statements are used for identification. The bracketed number on the right side indicates the next choice of paired contrasting statements. These are most popular keys. 

4. Zoological Parks

Zoos or zoological gardens (parks) are protected areas or enclosed space where live wild animals are kept, under human care. This enables us to learn their food habits and behaviour.

Objectives are public exhibition to understand wild life, recreation, education, ex situ conservation and breeding of rare fauna.

Largest zoo of the world is situated in Kruger (S. Africa).

National Zoological Park (Delhi) is one of the finest zoo of Asia.

5. Museums

These have collections of preserved plants and animals for study and reference.

Specimens are preserved in jars or containers in preservative solution.

Plant and animal specimens may also be preserved as dry specimens.

Insects are preserved in insect boxes after collecting, killing and pinning.

Larger animals are usually stuffed and preserved.

These often have collections of skeletons of animals too.

Museums are prepared to preserve algae, fungi, mosses, ferns and organs of gymnosperms since they cannot be kept in herbaria. These differs from parks because no living object is displayed in museums.

Some important Museums: 

(i) Natural History Museum, London (England) 

(ii) United States National Museum, Washington 

(iii) National Museum of Natural History (NMNH), Delhi 

(iv) Prince of Wales Museum, Mumbai etc.
Comperative Study of Botanical Garden, Herbarium and Museum : 

6.Flora, Manuals, Monographs and Catalogues 

Flora: Contains the actual account of habitat and distribution of plants of a given area. These provide the index to the plant species found in a particular area. 
Some important flora are given below: 

(i) Flora of British India by J.D. Hooker. 

(ii) Flora of Delhi by J.K. Maheshwari. 

(iii) Flora Indica by William Roxburgh. 

(iv) Flora Simlensis by H. Collet 

Manuals: The complete listing and description of the plants growing in a particular area. 
e.g., Manual of Cultivated Plants by L.H. Bailey 

 Monographs: Contain information on anyone taxon. 
e.g., The Genus Pinus by N.T. Mirov 

Catalogues: This includes the alphabetical arrangements of species describing their features.

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1.    Ex-situ / Off-site conservation strategies for organisms includes Botanical gardens and Zoological parks. 

2.    Succulent plants or those plants which are unsuitable for pressing and drying techniques, are fixed in suitable liquid preservative like 2.5% solution of formaldehyde, glacial acetic acid and ethyl alcohol [FAA]. 

3.    Herbarium technique was first introduced by Caesalpino et. al. 

4.    Botanical gardens of world have 15% or 35,000 plants species of the world flora.
Tapiary -Beautifying areas 
Bonsai trees -Dwarf trees are grown,in pots 

5.    According to WZCS (World Zoo Conservation Strategies), zoological parks are meant to conserve the species that are particularly endangered in their natural environment. India has about 200 zoological parks. 

 

SUMMARY
1.    The living world is rich in variety. Millions of plants and animals have been identified and described but a large number still remains unknown. 

2.    The very range of organisms in terms of size, colour, habitat, physiological and morphological features make us seek the defining characteristics of living organisms. 

3.    In order to facilitate the study of kinds and diversity of organisms, biologists have evolved certain rules and principles for identification, nomenclature and classification of organisms. 

4.    The branch of science dealing with these aspects is referred to as taxonomy. 

5.    The taxonomic studies of various species of plants and animals are useful in agriculture, forestry, industry and in general for knowing our bio-resources and their diversity. 

6.    The basics of taxonomy like identification, naming and classification of organisms are universally evolved under international codes. 

7.    Based on the resemblances and distinct differences, each organism is identified and assigned a correct scientific/biological name comprising two words as per the binomial system of nomenclature. 

8.    An organism represents/occupies a place or position in the system of classification. There are . many categories/ranks and are generally referred to as taxonomic categories or taxa. All the categories constitute a taxonomic hierarchy. 

9.     The basis of modern taxonomic studies is : External and internal structure, along with the structure of cell, development process and ecological information of organisms 

10.     Taxonomists have developed a variety of taxonomic aids to facilitate identification, naming and classification of organisms. These studies are carried out from the actual specimens which are collected from the field and preserved as referrals in the form of herbaria, museums and in botanical gardens and zoological parks. It requires special techniques for collection and preservation of specimens in herbaria and museums. 

11.     Live specimens, on the other hand, of plants and animals, are found in botanical gardens or in zoological parks. 

12.     Taxonomists also prepare and disseminate information through manuals and monographs for further taxonomic studies. 

13.     Taxonomic keys are tools that help in identification based on characteristics. 

Taxonomic Aids

Taxonomic studies of various plant, animal, and other organism species are useful in agriculture, forestry, and industry, and they aid in our understanding of biodiversity. These studies necessitate accurate organism taxonomy and identification. Identifying organisms necessitates extensive laboratory and field research. Taxonomic aids are collections of samples or preserved species that aid in the extended investigation for taxonomic hierarchy identification. The primary source of taxonomic studies is the collection of genuine specimens of plant and animal species. These are also necessary for systematics training and are crucial to studies. It's used to classify organisms, and the data acquired is saved alongside the specimens. In some situations, the specimen is saved for further research. Some popular taxonomic aids are discussed below

(I) Herbarium: A herbarium is a reference collection of properly selected and dried plants that are connected to standard-sized paper sheets and filed systematically so that they can be quickly found for study. It's a repository for plant specimens that have been collected, dried, pressed, and preserved on sheets. These sheets are organized according to a widely accepted classification scheme. These specimens, coupled with their descriptions on herbarium sheets, form a repository or storehouse for future use. A label on the herbarium sheets provides information such as the date and location of collection, English, local, and botanical names, family, and collector's name, among other things. In taxonomic investigations, herbaria also function as rapid referral systems.

The Museum of Natural History in Paris, The Royal Botanic Gardens in Kew, England, The New York Botanical Garden, and The Komarov Botanical Institute in St. Petersburg, Russia, have some of the world's largest herbaria, each having 7 to 9.5 million specimens.

Figure 3: Different stages of herbarium preparation.

(II) Botanical Gardens:

For reference, these specialty gardens have collections of living plants. Plant species are planted in these gardens for identification, and each plant is labeled with its botanical/scientific name as well as its family. Botanical gardens commit their resources to plant research and conservation, as well as public awareness of the world's plant diversity. Royal Botanical Garden, Kew (England), Indian Botanical Garden, Howrah (India), and National Botanical Research Institute, Lucknow are all well-known botanical gardens.

(III) Museum:

A museum is a building where historical, artistic, or scientific objects are displayed, maintained, or researched. Modern museums are designed to collect, preserve, interpret, and show objects of aesthetic, cultural, or scientific significance for public study and education. Biological museums are most commonly found at educational institutions like schools and colleges. For study and reference, museums have collections of preserved plant and animal specimens. Preservative solutions are used to preserve specimens in containers or jars. Dry specimens of plants and animals can also be preserved. After capturing, killing, and pinning insects, they are kept in insect boxes. Stuffed and preserved larger creatures, such as birds and mammals, are common. Animal skeletons are frequently shown in museums.With 19 museums and galleries, the National Zoological Park, and many examination stations, the Smithsonian is the world's largest exploration and museum complex. The company's headquarters are in Washington, D.C.

(IV) Zoological Parks:

Zoological parks are protected areas where animals are kept under human supervision and cared for. In zoological parks, many endangered species that are on the verge of extinction are rescued. These are facilities where wild animals are housed in safe conditions under human supervision so that we can learn about their eating habits, behavior, etc. Animals at zoos are kept in settings that are as close to their natural habitats as possible. These parks also contribute to the preservation of the natural balance by increasing the percentage of rainfall. They play a critical role in the conservation of animals. There are a total of 164 zoological parks in India. The Arignar Anna Zoological Park in Chennai is India's largest zoological park covering about 1300 acres with rare species of flora and fauna.

(V) Key:

Keys are used foridentifying and classifying various plants and animals based on their similarities and variances in characteristics. As a result, only one is accepted while the other is rejected. A lead is a name given to each assertion in the key. For identification purposes, separate taxonomic keys are necessary for each taxonomic group such as family, genus, and species. The majority of keys are analytical these are used to distinguish between classes, orders, families, genera, and species. It is split into pairs of characters that are either present or absent.

Other methods of recording descriptions include flora, manuals, monographs, and catalogs. They also assist with proper identification. Flora includes a detailed description of a certain area's habitat and plant distribution. These provide an index to the plant species that can be found in a certain area. A Catalogue is a comprehensive list, pamphlet, or register that contains a collection of traits and their variants found in diverse taxa.Manuals are important for identifying the names of species that can be found in a given area. Monographs are documents that focus on a single taxon.

Taxonomic Aids: Taxonomic studies of animals, plants, microorganisms and other species are highly useful in the field of forestry, industry, agriculture and the study of biodiversity. Hence, the organism should be identified, and classified and information about the organism should be stored for future studies and references. This storehouse of information and specimens that helps in taxonomic studies are called Taxonomic Aids.

Herbarium: A herbarium is the storehouse of plant specimens.
It is a collection of dried, pressed, plant specimens that are arranged systematically according to a universally accepted system of classification. The Bentham and Hooker system is followed in most of Herbaria. The sheets on which the specimens are mounted are called Herbarium sheets 

The total number of plant specimens are about 6.56.5 million.
 Another Botanical Herbarium called Central National Herbarium is at Indian Botanical Garden, Howrah, Kolkata.

Some of the other examples are as follows:
a. National Botanical Garden, Lucknow
b. Lalbagh Botanical Garden, Bangalore, Karnataka
c. Government Botanical Garden, Ooty
d. Tropical Botanical Garden and Research Institute, Trivandrum, Kerala.

Botanical Garden: Botanical gardens are the place where varieties of plants collected from different places of the world are grown together in a protected environment. It may consist, of many rare, elite, exotic species. It shows rich biodiversity and plays an important role in germplasm conservation. In the Botanical Garden, all plants carry identification plates, having a common name, botanical name and the name of the family that belongs

Museum: It is the collection of preserved plants and animal specimens for study and reference. Specimens are preserved in jars using preservative solutions of alcohol and formalin. Only those plants that cannot be kept in the herbarium are preserved. Some of the specimens include algae, fungi, mosses, ferns, succulents, fruits, etc. Even fishes, reptiles, amphibians, etc., are stored. Large animals are preserved in skeleton forms. Insects are dried out and mounted over pins inside the insect boxes. Others are preserved as dry specimens in the Biological Museum.

Zoological Park: Zoological Park is an enclosed area where wild animals are kept in an open, natural, but protected environment under human care. Zoological parks are the best places to study the behavior and food habitats of wild animals. Zoological parks help in conserving endangered animals and their multiplication through captive breeding. In India, there are around 200200 Zoological parks.
Zoological Parks are also important spots for children, students and the public to see wild animals

Keys: Key is another taxonomical aid used for the identification of plants and animals based on similarities and dissimilarities.Keys are of two types, i.e., dichotomous keys (bracketed key and indented key) and poly clave keys. Dichotomous Keys is the one in which the choices allow only two alternative couplets. There are two types of dichotomous keys – Indented Keys, also called yoked and Bracketed Keys. Poly clave key is relatively a new alternative to dichotomous keys and becoming increasingly popular, especially because of the ease of computerizing them and is also termed multiple access or synoptic key. This key is based on the identification of species by the process of elimination.

KINGDOM SYSTEMS OF CLASSIFICATION

(1) Two Kingdom Classification: It was given by Linnaeus. Traditionally all the organisms of the world were divided into two kingdoms -the animal kingdom (Animalia) and the plant kingdom (Plantae). The major criterion of classification was the presence or absence of cell wall. Other criterias were locomotion, mode of nutrition, response to external stimuli etc

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 Shortcomings of two-kingdom system of classification:

This system did not distinguish between the eukaryotes and prokaryotes, unicelled and multicelled organisms, photosynthetic and non-photosynthetic organisms.

There are few organisms like Chlamydomonas, Euglena and the slime moulds which have been claimed by both zoologists and botanists (organisms which share characteristics of both animals and plants).

Since there are certain organisms that do not fall naturally into either plant or animal kingdom, it was proposed that a new kingdom is to be established to accommodate such organisms.

(2) Three Kingdom Classification:

Haeckel, a German zoologist (1866), suggested that a third kingdom Protista, be created to include all unicellular microorganisms.

This includes a wide variety of unicellular, mostly aquatic eukaryotes like -Fungi, Protozoa, Algae, Bacteria and Slime moulds.

Thus, he proposed three kingdoms, namely -Plantae, Protista and Animalia.

 (3)  Four Kingdom Classification:

Copeland (1956) gave four kingdom of classification and included Monera as fourth kingdom.

Copeland originally called it as kingdom 'Mychota'.

It was called 'Monera' by Daugherty and Allen.

Kingdom Monera includes all the prokaryotic organisms i.e., eubacteria (including cyanobacteria, formerly known as blue-green algae) and archaebacteria.

The actinomycetes (filamentous bacteria) are also included in this kingdom.

(4) Five Kingdom Classification:

According to five-kingdom concept proposed by R.H. Whittaker.

Whittaker (1969), the organisms are divided into five kingdoms namely Monera, Protista, Fungi, Plantae, Animalia, on the basis of the following criteria 

(a)    Complexity of cell structure: prokaryotic vs eukaryotic organisation of cells.
(b)    Complexity of body organisation: unicellularity vs multicellularity; simple multicellular forms to complex multicellular forms.
(c)    Mode of nutrition: Autotrophic vs heterotrophic (parasitic or saprobic or ingestive organisms). It was the major criteria of this classification system.
(d)    Reproduction.
(e)    Phylogenetic or evolutionary interrelations

Table 1 : Comparative account of different characteristics of the Five Kingdoms

 (5)  Six Kingdom Classification :

Carl Woese proposed six kingdom classification.

These six kingdoms are Archaebacteria, Eubacteria, Protista, Fungi, Plantae and Animalia.

He separated the archaebacteria from eubacteria on the basis of some major differences such as the absence of peptidoglycan in the cell walls of the former and the occurrence of branched chain lipids (a monolayer instead of a phospholipid bilayer) in the membrane.

Based on the sequence of 16S ribosomal RNA genes, Woese found that the six kingdoms naturally cluster into three main categories.

He called these categories as domains of life.

These domains are Bacteria, Archae and Eukarya and are believed to have originated from common ancestor called progenote.

Three Domains of life

Based on the sequence of 16 S ribosomal RNA genes, woese found that the six kingdoms naturally cluster into three domains.

These domains are Archae, Bacteria and Eukarya, and are believed to be originated from common ancestor called Progenate. Domain is a category higher than kingdom.

 

Chapter 2

Biological Classification

Biological classification is the practice of categorizing living and extinct organisms into groups based on shared traits. Classifying organisms is necessary because it allows us to better understand biodiversity. It aids in the identification of living entities as well as the comprehension of their diversity. Classification aids in our understanding of different types of plants and animals and their characteristics, similarities, and differences. It allows us to see how complex organisms develop from simpler organisms. Different categories are used to understand and research the characteristics, similarities, and differences among various living species. Classification is the tool that allows us to manage a wide range of living organisms. Understanding the inter-relationships between different groups of organisms is critical. Other biological sciences are built on the foundation of classification.

Kingdom Systems of Classification:

Aristotle was the first to attempt to classify things on a more scientific basis. He classified plants into trees, shrubs, and herbs based on simple physical characteristics. He also separated the animals into two groups: those with red blood and those without. A Two Kingdom system of classification was devised during Linnaeus's time, with Plantae and Animalia kingdoms encompassing all plants and animals, respectively. Eukaryotes and prokaryotes, unicellular and multicellular organisms, photosynthetic (green algae), and non-photosynthetic (fungi) species were all lumped together in this system. Plant and animal classifications were simple to implement and understand, but a huge number of creatures did not fit into either group. As a result, the long-used two-kingdom classification was determined to be inadequate. Aside from gross appearance, there was a need to include other characteristics such as cell structure, wall nature, manner of nourishment, habitat, reproduction strategies, evolutionary linkages, and so on. As a result, classification systems for living organisms have experienced several alterations over time. Though the plant and animal kingdoms have remained consistent throughout all systems, the understanding of which groups/organisms should be included inside these kingdoms has evolved; the number and character of additional kingdoms have also been interpreted differently over time by different scientists.

A Five Kingdom Classification was proposed by R.H. Whittaker in 1969. Monera, Protista, Fungi, Plantae, and Animalia were the kingdoms he defined. Cell structure, body arrangement, manner of nourishment, reproduction, and phylogenetic links are among his key classification criteria. A three-domain approach has also been proposed, which divides Kingdom Monera into two domains and leaves the remaining eukaryotic kingdoms in the third domain, resulting in a six-kingdom categorization.

Let's take a look at this five-kingdom classification to see what concerns and considerations affected the system. Plants included bacteria, blue-green algae, fungi, mosses, ferns, gymnosperms, and angiosperms in previous classification systems. The fact that all of the species in this kingdom had a cell wall in their cells served as a unifying characteristic. This grouped people who had a lot of things in common but also had a lot of things in common. It brought together prokaryotic bacteria and blue-green algae (cyanobacteria), as well as other eukaryotic species. It also combined unicellular and multicellular species together, such as Chlamydomonas and Spirogyra being categorized together under algae.The classification did not distinguish between the heterotrophic fungus and the autotrophic green plants, albeit they did have a distinct difference in the composition of their cell walls, with the fungi having chitin and the green plants having a cellulose cell wall. When these qualities were taken into account, the fungi were given their own kingdom: Kingdom Fungi. Kingdom Monera was created to unite all prokaryotic species together, while Kingdom Protista was created to group all unicellular eukaryotic organisms together. Chlamydomonasand Chlorella (both of which have cell walls and were previously put in Algae within Plants) have been combined with Paramoecium and Amoeba in the kingdom Protista (which were earlier placed in the animal kingdom which lack cell walls). It has brought together organisms that were previously classified into various kingdoms.

KINGDOM: MONERA

The Kingdom Monera includes all prokaryotes.

Monerans are the most primitive forms of life, originating from more ancient living stock termed progenote.

The kingdom Monera includes eubacteria and archaebacteria.

Eubacteria includes Cyanobacteria, Actinomycetes, Mycoplasma, Rickettsiae, Chlamydiae and Spirochaetes etc.

Classification of Monera

(1)  In 4 kingdom system, a new kingdom was created to accommodate all prokaryotic organisms i.e, eubacteria and archaebacteria. Copeland called it kingdom Mychota. It was called 'Monera' by Daugherty and Allen.
(2)  Actually, archaebacteria differ from eubacteria in many respects and resemble eukaryotes in some ways.
(3) (i) Carl Woese separated the archaebacteria from eubacteria on the basis of some major differences such as the absence of peptidoglycan in the cell walls of the former and the occurrence of branched chain lipids (a monolayer instead of a phospholipid bilayer) in the membrane.

(ii)  Therefore, 6 kingdoms given by Carl Woese are
Kingdom-1 -Archaebacteria    Kingdom-2 -Eubacteria
Kingdom-3 -Protista        Kingdom-4 -Fungi
 Kingdom-5 -Plantae        Kingdom-6 -Animalia

Salient Features of Monera

1. These are unicellular, colonial, multicellular prokaryotic organisms without nuclear membrane, nucleolus, chromatin and histone proteins.

2. Cell wall is made up of peptidoglycan (exceptions are Archaebacteria and Mycoplasma).

3. Membrane bound organelles are absent.

4. Cyclosis is absent and ribosomes are of 70 S type .

5. Respiratory enzymes are found associated with plasma membrane.

6. Nucleoid or genophore or incipient nucleus or prochromosome is composed of naked DNA, RNA and nonhistone proteins.

7. Reproduction by asexual method.

8. Cell division is amitotic type and lacks spindle formation.

Let us discuss various monerans in detail :

 1. EUBACTERIA

Bacteria are cosmopolitan and occur in every habitat wherever living or dead organic matter is present.

Anton Von Leeuwenhoek discovered bacteria in rain water which had been allowed to stand for many days and tartar scrapped from teeth.

In 1695, he published his work "The Secrets of Nature".

A.V. Leeuwenhoek termed these microorganisms as dierkens which was later translated as animalcules by the Royal society.

Term microbe for animalcules was coined by Se' dillot, but the term microorganism was proposed by Pasteur.

 Concept Builder

Ehrenberg first of all coined the word 'bacteria'

Louis Pasteur is considered father of modern microbiology. He introduced the term aerobic and anaerobic for the life in the presence or absence of oxygen respectively.

Robert Koch, a German doctor, demonstrated that the anthrax disease of sheep was caused by bacteria. Koch had followed four experimental steps (Koch's postulates) which help to establish a relationship between a microorganism and a disease.

Smallest bacterium : Dialister pneumosintes

Largest filamentous bacterium : Beggiatoa mirabilis

 Shapes of Bacteria

Bacteria occur in four basic forms or shapes.

These are spherical (Cocci), rod shaped (Bacilli), Vibrio and Spiral.

Though most bacterial species have cells that are of a fairly constant and characteristic shape, some species are pleomorphic (i.e., these can exhibit a variety of shapes), e.g., Rhizobium leguminosarum.

 (a) Coccus : Spherical or nearly spherical, aflagellate, sub-divided into six groups on the basis of cell arrangement:

Monococcus -Only single cell represents the bacterium, e.g., Micrococcus luteus, M. roseus.

Diplococcus -Cocci divide in one plane and remain attached in pairs, e.g., Meningococcus, Gonococcus, Diplococcus pneumoniae.

Streptococcus -Cocci remain attached to form chains of different lengths, e.g., Streptococcus lactis.

Tetracoccus -Cocci divide in two planes at right angles to one another and form groups of four, e.g., Tetracoccus, Neisseria.

Staphylococcus -Cocci divide in several planes resulting in formation of irregular bunches of cells, sometimes resembling a cluster of grapes, e.g., Staphylococcus aureus.

Sarcinae -Cocci divide in 3 planes at right angles to one another and resemble cubical packets of 8 or more cells forming three dimensional geometrical figures, e.g., Sarcina lutea.

(b)    Bacillus : Rod-like forms, either singly or may be arranged differently. They are generally flagellate. It is the most common of all the shapes. They are of following types :

(i)  Monobacillus -The bacteria occur singly, e.g., Bacillus anthracis, Lactobacillus.

(ii) Diplobacillus -Bacteria are arranged in pairs. e.g., Bacillus subtilis

(iii) Streptobacillus -Bacteria form a chain of rods, e.g., Streptobacillus.

(iv) Palisade-like -If the cells are lined side by side like match sticks and at angles to one another.

e.g., Corynebacterium diphtheriae.

 (c) Spiral bacteria : Coiled forms of bacteria exhibiting twists with one or more turns are called spirilla, e.g., Spirillum volutans.

 (d) Vibrio : Bacteria with less than one complete twist or turn are called vibrio. These resemble a comma (,) in appearance, e.g., Vibrio cholerae.

 (e) Stalked bacteria : The body of bacterium possesses a stalk, e.g., Caulobacter.

 (f)  Budding bacteria : The body is swollen at places, e.g., Rhodomicrobium

Bacterial Cell Structure

Bacterial cell structure is very simple although they are very complex in behaviour. They show the most extensive metabolic diversity. Electron microscope can only reveal the detailed structure of bacterial cell. It consists of following structures:

 1.    Glycocalyx: 
(i)  It is outermost part of cell envelope (Glycocalyx, cell wall, plasma membrane)

(ii)  Represented by either slime layer or capsule

(a) Slime layer is composed of dextran, dextrin and lavan sugars and protect the cell against desiccation and loss of nutrients.

(b) Capsule is made up of polysaccharides and D-glutamic acid. It provides gummy or sticky character and virulent property to the cell.

 2. Cell wall :

It is present outside the cell membrane and is a rigid structure.

Due to its rigidity, it protects the internal structures of the cell and provides shape to the cell.

However, its main function is to prevent the cell from expanding and bursting because most bacteria live in hypotonic environments, and are likely to take in much water and eventually burst.

The cell walls of almost all the eubacteria (true bacteria) are made up of peptidoglycan, also called murein or mucopeptide.

It is found only in prokaryotes.

As the name suggests, the peptidoglycan consists of two components-a peptide portion which is composed of amino acids connected by peptide linkages, and a glycan or sugar portion.

The glycan portion, which forms the backbone of peptidoglycan, is composed of alternating units of amino sugars N-acetyl-glucosamine (NAG) and N-acetylmuramic acid (NAM) joined together by b-1, 4 linkages.

The peptidoglycan chains are laterally linked by short chains of four amino acids which are attached to N-acetylmuramic acid residues.

The four amino acids of this tetrapeptide are D-alanine, L-alanine, D-glutamic acid and L-Iysine (in Gram +ve bacteria) or diaminopimelic acid (in Gram -ve bacteria).

The tetrapeptide chains are also interlinked by a peptide bridge between the carboxyl group of an amino acid in one tetrapeptide chain and amino group of an amino acid in another tetrapeptide chain.

The cross linkages can occur between tetrapeptides in different chains, as well as between adjacent tetrapeptide chains. As a result, peptidoglycan forms a rigid, multilayered sheet.

Another component, teichoic acid, an acidic polymer consisting of a carbohydrate (e.g., glucose), phosphate and an alcohol is found in cell walls of Gram +ve bacteria.

Teichoic acid has several functions such as binding metals, acting as receptor sites for some viruses and maintaining cells at low pH to prevent degradation of cell walls by self-produced enzymes.

The walls of Gram positive bacteria contain very little amount of lipids.

The cell walls of Gram negative bacteria are much more complex.

The peptidoglycan layer is very thin making up only 10% or less of the cell wall.

However, the most interesting feature is the presence of an outer membrane that covers a thin underlying layer of peptidoglycan.

The outer membrane is a bilayered structure consisting chiefly of phospholipids, proteins and lipopolysaccharides (LPS).

The outer membrane serves as a barrier to prevent the escape of important enzymes from the space (periplasmic space) between the cytoplasmic membrane and the outer membrane.

It also prevents the entry of various chemicals that could damage the cell.

It acts as main surface antigen in cell wall.

However, permeability of outer membrane to nutrients is provided by proteins called porins which form channels in the membrane through which substances of hydrophilic nature and low molecular weight can diffuse.

Christian Gram (1884) developed a staining method for bacteria, using Gram stain (crystal violet).

On the basis of stainability with Gram Stain, bacteria are classified into two groups; Gram positive and Gram negative.

Flow chart representing Gram staining technique

 3. Surface Appendages : These include flagella and fimbriae (or pili).
(a) Flagella are long, fine, wavy, filamentous appendages that protrude through the cell wall, responsible for the motility of bacteria. These are much thinner than the flagella or cilia of eukaryotes.

Structure of Flagella: The entire flagellar apparatus is made up of three distinct regions: basal body, hook and filament.

Basal body: It is most complex portion of flagellum and has four rings (L, P, S and M), only two rings S and M are present in gram +ve bacteria. L and P rings in cell wall constitute distal set, while S and M rings are present in plasma membrane, forming proximal set.

Hook: Made up of different protein units.

Filament: Bacterial flagella are made up of identical spherical subunits of a protein called flagellin. Longitudinal chains of flagellin molecules run longitudinally around each other to form a wavy helical or rope-like structure. Therefore, a cross section of the flagellum reveals a number of flagellin molecules around a central space.

 Concept Builder

Depending upon the presence or absence, number and position, following types of flagellar arrangements are observed among bacteria :

Atrichous: Flagella absent, e.g., Pasteurella, Lactobacillus.

Monotrichous: Only one flagellum attached at one pole of the organism, e.g.,Thiobacillus, Vibrio.

Amphitrichous: One flagellum at both ends, e.g., Nitrosomonas.

Cephalotrichous: Two or more flagella attached at one end, e.g., Pseudomonas fluorescence.

Lophotrichous: Two or more flagella attached at both ends, e.g., Spirillum volutans.

Peritrichous: Flagella distributed all over the surface of the cell, e.g., Escherichia coli, Clostridium tetani.

(b) Pili and fimbriae are hollow, non helical, filamentous appendages projecting from the walls of Gram-negative bacteria. These are thinner and shorter and more in number than the flagella. These are made up of specific proteins called pilin.
There are different types of pili which serve different functions. One type, known as type I pili, (somatic pili) play a major role in infection by facilitating the attachment of bacterial cell to the host cell. Another type, termed sex pili, serve as portals of genetic material from donor to recipient cell during conjugation.

Differences between Gram positive and Gram negative bacteria

4. Protoplast: Cell wall encloses the protoplast, the living matter. It includes (i) Cell membrane (ii) Cytoplasm, (iii) Nucleoid and may have plasmid and episome.
(i) Cell membrane: 

It lies inner to the cell wall, actually representing the outermost layer of the protoplast.

It is living and semipermeable, controlling the movements of various dissolved substances in and out of the cells.

Functionally, the cell membrane of bacteria resembles mitochondria of eukaryotic cells as respiratory ETS enzymes and succinate dehydrogenase (Kreb's Cycle) are associated with the membrane.

The cell membrane gets invaginated and folded to form a structure called mesosome (chondroid) in some bacteria, particularly the Gram positive bacteria.

These may be central or peripheral in position and they are supposed to play a role in replication of DNA during cell division, as these are often attached to the nuclear body.

Besides, these increase the surface area of absorption and help in septa formation during binary fission.

(ii)    Cytoplasm:

It is homogenous colloidal mass of carbohydrates, fats, proteins, lipids, nucleic acids, minerals and water.

It does not show streaming movements.

It lacks sap vacuoles and gas vacuoles (may be present in some bacteria which live in aquatic condition).

Typical membrane bound organelles of eukaryotic cells like endoplasmic reticulum, mitochondria, golgi complex and plastids are absent.

The cytoplasm appears granular due to the presence of ribosomes.

However, these are 70S type in bacteria as compared to 80S type in eukaryotes.

Ribosomes lie scattered freely in the cytoplasm, but sometimes may form a small chain of 4-6 ribosomes attached to mRNA constituting polyribosome or polysome.

Various non living inclusions like glycogen particles, fat bodies, volutin granules (polymetaphosphate -source of energy) and lipid molecules acting as food reserve lie dispersed in the cytoplasm.

The cytoplasm is usually colourless, lacking pigments.

However, in photosynthetic bacteria, the cytoplasm contains pigments like bacteriochlorophyll and bacterioviridin.

The pigments either lie dispersed in the cytoplasm or present in membrane bound spherical vesicles called chromatophores.

These pigments are capable of entrapping solar energy for photosynthesis

(iii)  Nucleoid (Prochromosome, Genophore, Incipient nucleus) –

Bacterial cell lacks a well organized nucleus.

It consists of a long double stranded DNA molecule repeatedly folded with the help of RNA to form a circular ring.

DNA has no free ends and not associated with histone proteins (polyamines present). Circular DNA ring, without histones is often termed bacterial chromosome.

Plasmid (Minichromosome) :

Term plasmid was given by Lederberg and Hays.

These are small, extrachromosomal, non-essential, circular, double stranded, free naked DNA molecules.

The genes present on them have no vital role in survival and growth of bacteria.

These perform autonomous replication.

If plasmids temporarily integrate with bacterial chromosome, then they are called episomes.

Concept Builder

Types of plasmids :

(a)  F-Plasmid: It forms sex pilus and is responsible for process of conjugation or fertility factor transfer.

(b)  R-Plasmid: These plasmids have resistance gene (Resistance Transfer Factor, RTF) for antibiotics like penicillin, tetracycline.

(c)  Col-Plasmid: Genes of this plasmid are responsible for production of colicins (bacteriocin) for killing other bacteria.

(d)  Ti Plasmid: From Agrobacterium tumefaciens, used in genetic engineering

(e)  Degradative plasmid of Pseudomonas putida (superbug) helps to decompose hydrocarbons of petroleum in oil spills

5.  Bacterial Life Processes

Discussion of bacterial life processes revolves around the study of the prominent metabolic activities like respiration and nutrition.

(A) Respiration: On the basis of mode of respiration, the bacteria are divided into two main groups: i.e., aerobes and anaerobes. Each group is further of two types i.e. strict or obligate and facultative.

(a) Obligate or strict aerobes : These bacteria can live only in presence of oxygen they possess the enzyme system for aerobic respiration only. In the absence of oxygen, they cannot respire and thus, die, e.g., Bacillus subtilis.

(b) Facultative anaerobes : They normally respire aerobically. However, they are capable of switching over to anaerobic mode to get energy for their survival, if sufficient oxygen to sustain aerobic respiration is not available in the environment, e.g., Pseudomonas.

(c) Obligate or strict anaerobes: These bacteria respire anaerobically only. The growth of such bacteria will certainly be slower as anaerobic respiration liberates much less amount of energy as compared to aerobic respiration. They lack enzymes necessary for carrying out aerobic respiration e.g., Clostridium botulinum.

(d) Facultative aerobes: They normally respire anaerobically, but are capable of respiring aerobically as well, if oxygen is available. Most of the photosynthetic bacteria are facultative aerobes e.g., photosynthetic bacteria Chlorobium.

Concept Builder

(i)  Aerotolerant anaerobes: Bacteria that continue to perform anaerobic respiration even in the presence of oxygen, e.g., Lactic acid bacteria.

(ii)  Anaerotolerant aerobes: Aerobic bacteria continue to perform aerobic respiration even in absence of free oxygen by using oxygen of oxidised salts, e.g., Denitrifying bacteria

(B) Nutrition :

Nutrition in bacteria is of two types i.e. autotrophic and heterotrophic.

Bacteria having autotrophic mode of nutrition may be photoautotrophs and chemoautotrophs, carrying out photosynthesis and chemosynthesis, respectively.

(I)    Autotrophic Nutrition
(i)    Photoautotrophic bacteria: 

These bacteria are capable of entrapping solar energy and utilizing it for the synthesis of complex food materials due to the presence of pigments like bacteriochlorophyll (bacteriopurpurin) and bacterioviridin.

Purple sulpher bacteria (e.g., Thiospirillum) and green sulpher bacteria (Chlorobium limicola) are the most familiar examples containing pigment bacteriochlorophyll, bacteriopurpurin and bacterioviridin respectively.

Concept Builder

Bacterial photosynthesis, however, differs from photosynthesis of higher plants in not liberating oxygen.

This type of photosynthesis, characteristic of bacteria, is termed as anoxygenic.

Normal photosynthesis, occurring in higher plants, is termed as oxygenic.

In bacterial photosynthesis water is not the source of electron that acts as reducing power to convert CO₂ into glucose.

The bacteria obtain reducing power from various compounds such as hydrogen sulphide, thiosulphate or even some organic compounds.

No oxygen is evolved as it does not involve splitting of water.

Hydrogen released by various compounds mentioned above is picked up by NAD⁺ which gets reduced to NADH₂ acting as reducing power.

NADH₂ alongwith ATP, produced generally by entrapping solar energy are used to reduce CO₂ to glucose.

Simple equation for anoxygenic photosynthesis may be written as follows :

Most of the photosynthetic bacteria are anaerobes (facultative aerobe

(ii) Chemoautotrophic Bacteria:

Bacteria belonging to this category obtain energy for the synthesis of food by oxidising certain inorganic substances like ammonia, nitrates, nitrites, ferrous ions etc.

Thus, they do not utilise light as energy source.

The chemical energy thus obtained, is trapped in ATP molecules.

This energy is then used in carbon assimilation with the help of hydrogen from some source other than water, e.g., hydrogen bacteria, nitrifying bacteria, sulphur bacteria, etc.

They play a great role in recycling nutrients like nitrogen, phosphorous, iron, sulphur.

 (a) Hydrogen bacteria. These bacteria oxidise hydrogen in the presence of oxygen, e.g., Hydrogenomonas.

(b) Nitrifying bacteria obtain energy by oxidizing ammonia into nitrate, oxidation of ammonia occurs in two steps. Each step is carried out by a specialised group of bacteria.

In the first step, ammonia is oxidised into nitrites by the species of the genus Nitrosomonas and Nitrococcus.

In the second step, the nitrite is converted into nitrate. This is brought about by species of the genus Nitrobacter and Nitrocystis which use this energy for chemosynthesis.

(c)  Sulpher bacteria. These bacteria obtain energy either by the oxidation of elemental sulphur or oxidation of H2S.

Oxidation of elemental sulpher. Sulpher bacteria (Thiobacillus thioxidans) oxidise elemental sulpher to sulphuric acid and utilise energy produced in this process. These bacteria can survive even in extreme acidic environment.

Oxidation of H2S to S. Some bacteria like Beggiatoa use the energy from oxidation of H2S and store the sulphur so produced in the form of granules.

(d)  Iron bacteria. These bacteria (e.g., Ferrobacillus, Leptothrix) inhabit water which contain iron compounds. These bacteria convert ferrous ions to ferric form. The ferric ion is deposited as insoluble ferric hydroxide. The energy so released, is utilised in the assimilation of CO2.
    (e)    Methane bacteria. Methanomonas, is one example which oxidises methane to carbon dioxide.
 
    (II)    Heterotrophic bacteria : 

These bacteria are most abundant in nature and are incapable of synthesizing their own food from simple raw materials.

They obtain nourishment either from dead and decaying organic matter or directly from a living host.

All heterotrophic bacteria are segregated into three main categories, i.e., saprophytic, symbiotic and parasitic forms.

(i)   Saprophytic bacteria :

They are free living bacteria, obtaining nourishment from organic remains such as dead animals, animal excreta, fallen leaves, decaying vegetables, fruits, bread and other products of animal and plant origin.

These bacteria secrete digestive enzymes into the substrate and the complex insoluble Substances are converted into simple soluble compounds like water, hydrogen sulphide, ammonia, CO₂ etc.

Some of the simpler substances are absorbed and assimilated by the bacteria, whereas the others are added to the soil and atmosphere to complete the nature's material cycle.

Anaerobic breakdown of carbohydrates and proteins is termed fermentation and putrefaction respectively.

Aerobic breakdown of organic compounds is called decay.

(ii)    Symbiotic bacteria :

They are mainly Gram negative type.

A familiar example of symbiotic bacteria is Rhizobium leguminosarum, associated with roots of leguminous plants.

They are capable of fixing atmospheric nitrogen as ammonia, inside the nodule only and not in free state.

However, some bacteria like Azotobacter, Beijerinckia, Klebsiella are free living, aerobic and capable of nitrogen fixation in free state, enriching the soil.

Clostridium pasteurianum is anaerobic N₂ fixing bacteria.

(iii)   Parasitic bacteria

These bacteria draw nourishment and obtain special organic compounds required for growth from living organisms, either plants or animals, called hosts.

The disease causing bacteria are termed pathogenic and the ones not causing any disease are termed as non-pathogenic.

6.. Reproduction

Bacteria reproduce mainly by asexual method and also show sexual recombination (True sexual reproduction is absent).

A.  Asexual Reproduction :

Bacteria produce several types of asexual spores like, sporangiospores, oidia, conidia and endospores. However, the most common mode of asexual reproduction is binary fission.

Under favourable conditions of nutrient availability, moisture and temperature, daughter cells may repeat binary fission many times and may forms a large population.

Fortunately, such a rapid rate is seldom achieved.

The process gradually slows down and ultimately stops because of:

(i)    Shortage of space.

(ii)    Lack of nutrient availability.

(iii)    Accumulation of waste products (making environmental conditions unfavourable for growth).

(iv)    Development of bacteriophages, destroying bacteria.

(a)  Binary Fission :

It is the most common method under favourable conditions of temperature, moisture and availability of nutrients.

Mature bacterial cell divides into two daughter cells.

In this process the cell division is amitotic type i.e., not involving the spindle formation

(b)   Endospores :

Cells of certain bacteria, e.g., Bacillus, Clostridium etc. form thick-walled, highly resistant bodies within the cell, called endospores.

One bacterial cell normally produces only a single endospore.

The endospores may be spherical or oval in shape and are terminal or central in position.

Anticoagulant nature of endospore is due to the presence of Ca-dipicolinic acid in cortex layer of wall.

 Concept Builder

            Structure of Endospore :

The endospore consists of a central core made up of nuclear material and spore cytoplasm.

The cytoplasm includes DNA, RNA and proteins, lipid, Ca, Mn.

The central core is surrounded by a delicate membrane called core wall.

Around the wall is another layer, which is much thicker and is of relatively low density.

This layer, called cortex, mainly consists of peptidoglycan and calcium dipicolinic acid (CaDPA).

It is an anticoagulant which provides resistance to heat.

This complex may also be present in spore cytoplasm.

Endospore is highly resistant to desiccation, chemicals and radiations.

The cortex, in tum, is enclosed in spore coat which may be smooth, grooved, or raised into ridges. The whole structure may be wrapped in an exosporium.

The endospores are formed probably upon induction by the exhaustion of nutrients (unfavourable conditions).

During endospore formation, a part of the protoplast containing nuclear body undergoes dehydration, stores food material and gets separated from rest of the protoplast to form endospore.

It gets surrounded by different layers.

These can withstand temperature as high as 1000e or as low as -100°C, so these can remain unharmed during pasteurisation.

The remarkable resistance shown by endospores is due to :

(i) Thick and impermeable spore coat

(ii) Low water content

(iii) Low metabolic activity

(iv) Ca-DPA Complex

Under favourable conditions, endospore absorbs water, becomes metabolically active, ruptures thick spore coat and the bacterium surrounded by thin cell wall emerges out.

Endospores are actually the means of perennation and not reproduction as only one endospore is formed per cell and subsequently each endospore grows into single bacterium cell after the commencement of favourable conditions.

 B.  Sexual Recombination (Genetic Recombination) :

The bacteria exhibit a primitive form of sexual reproduction which differs from eukaryotic sexual reproduction because there is no gamete formation and fusion.

However, the essential feature of sexual reproduction, i.e., exchange of genetic material does take place and is called genetic recombination.

Three methods are known by which genetic recombination is achieved by bacteria.

In the order of their discovery, these are transformation, conjugation and transduction.

 (a)  Transformation :

Griffith (1928) worked on the effect of Diplococcus or Streptococcus pneumoniae bacteria on mice and discovered the process of transformation.

In transformation, the donor and recipient do not come in contact.

The donor cell releases a piece of DNA which is actively taken up by the recipient cell from the solution.

This ability to pick up DNA from the solution is called competence.

Two strains of D. pneumoniae are :

• Capsulated or S-III (Virulent strain) and Non-capsulated or R-II (non-virulent strain).
• Four steps were performed in experiment:

 

(But R-II is not virulent and S-III lost its virulent capacity upon heating).

Griffith concluded that 'something' passed from heat killed S-III to R-II bacteria, so that non virulent strain changed or transformed into virulent bacterial strain.

Avery, Macleod and McCarty (1948) repeated this experiment using various enzymes and proved that the transformation principle is DNA of heat killed S-III strain.

They proved that DNA is a genetic material.

(b)  Conjugation:

Lederberg and Tatum (1946) demonstrated in E. coli that during conjugation, one cell containing F-plasmid acts as donor (F⁺ or male) cell and the other lacking F-plasmid as recipient (F^– or female) cell.

The plasmid contains fertility factor or F gene which produces protrusions termed sex pili.

These help the donor F⁺ cell in attaching to the recipient cell.

The plasmid replicates and a replica is transferred to recipient cell, changing it into F⁺.

Often the plasmid integrates with bacterial chromosome, converting it into Hfr (High frequency of recombination) cell or super male and a part or whole of bacterial chromosome is transferred to recipient cell through-conjugation tube.

Such association of episome with the endogenote increases the efficiency of genetic transfer.

The number of genes transferred depends upon the time for which the two cells remain joined together.

When F^-conjugates with super male, the frequency of recombination increases by 1000 times, that is why it is called as Hfr (super male).

(c)       Transduction :

During transduction, a small double stranded piece of DNA is transferred from donor to recipient by a bacteriophage.

This mode of genetic recombination in bacteria was first demonstrated by Zinder and Lederberg (1952) while working with Salmonella typhimurlum.

Some viruses have the ability to integrate their DNA with bacterial DNA, which is replicated at the same time as the host DNA and is passed from one bacterial generation to the next.

Such bacteria carrying phage (viral) DNA with their own DNA are called lysogenic bacteria.

Occasionally, the phage DNA becomes active and codes for the production of new virus particles.

A number of phage particles are synthesised followed by the destruction of the host cell and release of phage particles.

Upon release, the phage particles attack sensitive bacterial cells, multiply and release more phage particles.

However, sometimes faulty deatchment of phage DNA from bacterial DNA results in the incorporation of a small amount of bacterial DNA into the phage DNA.

Subsequent infection of another bacterium with this aberrant phage called transducing phage, introduces the piece of foreign bacterial DNA into the recipient's chromosomes, producing a genetic change.

Types of transduction:

The ability of the bacteriophage to carry the genetic material from any region of bacterial DNA is called generalised transduction, e.g., T₄-phage.

On the other hand, there are bacteriophages such as lambda phage (l) of E coli which can carry only a specific region of the bacterial DNA to a recipient.

This is called specialised transduction (or restricted transduction).

Sometimes, the DNA brought by the phage does not integrate with the genome of the recipient bacterium and is lost after one or two generations.

Such a transduction is called abortive transduction

7. Economic Importance of Bacteria

Bacteria play significant role in day to day activities of human beings.

A.    Beneficial activities

(a)    Role in agriculture

(i)    Decay and decomposition of organic matter : 

They bring about decay and decomposition of dead remains of plants and animals.

These are the most important for mineral cycling to occur.

(ii) Sewage disposal :

The bacteria decompose the organic matter present in the sewage, converting into simpler inorganic substances.

The inorganic substances thus formed, being soluble, pass out through filter alongwith water which is highly useful for irrigation purposes, e.g., Clostridium, E. coli.

 (iii)  Nitrogen cycle :

The proteins present in dead remains of living organisms are converted into amino acids by different types of saprophytic bacteria.

Amino acids are converted into ammonia by ammonifying bacteria (Bacillus vulgaris, B. ramosus).

Nitrifying bacteria convert ammonium salts first into nitrites (Nitrosomonas, Nitrococcus) which are subsequently converted into nitrates (Nitrobacter).

In presence of denitrifying bacteria (Pseudomonas denitrificans), nitrates and nitrites of soil are converted to gaseous nitrogen.

 (iv)  Nitrogen fixation :

It is the biological process in which atmospheric nitrogen is converted into nitrogenous compounds by nitrogen fixing bacteria.

These bacteria are of 2 types :

(a) Free living 

(b) Symbiotic

(a) Free living bacteria are Azotobacter and Beijerinckia (aerobic) & Clostridium (anaerobic).

(b) Common symbiotic bacteria are Rhizobium leguminosarum and Xanthomonas. These convert nitrogen into ammonia which is directly converted into amino acids by plants.

(v)    Manure preparation :

Saprotrophic bacteria help in preparation of farmyard manure by converting farm refuse, dung and other organic wastes into humus.

(b)    Role in Industry :

Man has utilized the metabolic activities of bacteria in preparation of a number of industrial products as listed below :

(i)   Butter milk and sour cream

(ii)  Yoghurt

(iii)  Cheese

(iv)  Vinegar

(v)   Retting of fibres : Retting is a controlled microbial decomposition for separation of fibres. The tissues are immersed in water tanks where anaerobic butyric acid bacteria dissolve the pectin of middle lamella of cells, thus, separating the fibres. Clostridium perfringens and Pseudomonas fluorescence are useful in this process.

(vi)  Curing of leaves: To improve the flavour and taste in tea, using Micrococcus candidans and in tobacco leaves by Bacillus megatherium.

(vii)  Single cell proteins (SCP) : Like -Methylophilus methylotropus and Rhodopseudomonas capsulata.

(c)  Role in Medicine :

Bacteria have been used extensively in preparation of antibiotics, vaccines, serums and vitamins.

(i)     Antibiotics :

The term antibiotic was given by Waksman, who discovered streptomycin.

These are the organic substances produced by microorganisms which inhibit the growth of other organisms (mostly pathogens) but do not affect the growth of organisms secreting these.

The first commercial antibiotic penicillin was discovered by Flemming (1959) from a fungus called Penicillium.

Some antibiotics of eubacterial origin:
(a)    Bacitracin ........................... Bacillus licheniformis
(b)    Polymixin ........................... Bacillus polymyxa
(c)    Gramicidin ........................... B. brevis
(d)    Subtilin ........................... B. subtilis

(ii)    Vaccine production

Vaccines and serums against typhoid, cholera, TB, pertussis, tetanus and diphtheria are made with the help of bacteria or their toxins e.g., DPT (against diphtheria, pertussis and tetanus), TI(against tetanus), BCG (Bacille of Calmette-Guerin against TB), DT (against diphtheria and tetanus).

(iii)   Vitamins :

Escherichia coli present in human intestine produces large quantities of B-complex vitamins and vitamin K. Bacteria are utilized in industrial production of a number of vitamins like riboflavin from Clostridium butylicum, Cobalamine (B12) from Bacillus megatherium and Pseudomonas denitrificans.

(iv)   Pollution control :

Pseudomonas putida degrades petroleum wastes.

Flavobacterium can decompose 2, 4-D. DDT can be decomposed by Acetobacter aerogens.

Ganga's water contains Bdellovibrio bacteriovorus that maintains purity of its water.

(v)    Poly--hydroxybutyrate is used to produce biodegradable plastic.

B.    Harmful activities

(i) Spoilage of food : Saprophytic bacteria cause decay of vegetables, fruit, meat, bread and other foods, making these unfit for human consumption. Some bacteria even produce strong toxins in the infected food stuffs which cause food poisoning when consumed.

(ii)  Deterioration of Domestic Articles : Some saprophytic bacteria like Cellulomonas, Spirochaete cytophaga cause deterioration of domestic articles of daily use such as leather, woolen, canvas articles etc.

(iii) Denitrification of Soils : Denitrifying bacteria like Thiobacillus denitrificans, Micrococcus denitrificans and Pseudomonas convert nitrates and nitrites present in the soil into gaseous nitrogen, thus depleting the soil nitrogen, thereby decreasing soil fertility.

(iv) Desulphurification : Desulphovibrio desulphuricans.

(v)  Diseases : Common disease of humans, animals and plants are listed below respectively –

Table: 2

Table : 3

II. CYANOBACTERIA

Cyanobacteria are Gram negative photosynthetic prokaryotes, being the most primitive organisms to have oxygenic photosynthesis.

They added oxygen to the atmosphere, which is indispensible for the existence of aerobic forms of living organisms.

They are also known as BGA (Blue green algae) and are classified variously under cyanophyceae or myxophyceae.

Occurrence

They are mainly fresh water forms, though few are marine.

Red sea is named so because of abundant occurrence of a cyanobacterium Trichodesmium erythraeum, which imparts red colouration to water.

They occur in symbiotic association with almost every group of eukaryotes i.e. green algae, fungi, bryophytes like mosses and Anthoceros, ferns, gymnosperms, angiosperms, sponge, shrimps, mammals etc.

Anabaena azollae is associated with Azolla, an aquatic fern.

Anabaena cycadeae is associated with coralloid roots of Cycas.

In many lichens (symbiotic association of algae and fungi), the algal partner may be a cyanobacterium.

When they live endozoically in protozoans they are called cyanelle.

Structural Organization

These may be unicelled or multicelled. The latter may be filamentous or colonial.

Filamentous form consists of one or more cellular strands, called trichomes, surrounded by mucilagenous sheath.

Cyanobacteria are characterised by the absence of flagellum throughout life cycle.

Cell Structure

• The cell structure in cyanobacteria is typically prokaryotic.
• The cell lacks a well defined nucleus and the chromatin material is centrally located, resembling the bacterial chromosome.
• The cell wall is 4 layered and is invariably covered by mucilagenous sheath, composed largely of mucopeptides.
• Protoplasm in cyanobacterial cell can be distinctly divided into two parts the centroplasm and chromoplasm.
• The central colourless centroplasm contains the chromatin material.
• The peripheral protoplasm is coloured or pigmented because of the presence of thylakoids, called as chromoplasm.
• The protoplast lacks membrane-bound organelles like endoplasmic reticulum, golgi bodies, mitochondria, lysosomes, plastids and contains 70S ribosomes.
• Similar to the mesosome of bacteria, a group of coiled membrane called lamellasome is found which connects nucleoid to the cell membrane.
• It helps in respiration and replication of DNA.
• The cell membrane lack sterols. The sap vacuoles are absent.
• Instead, the cell may contain gas filled vacuoles which help to regulate the buoyancy of the organism in water.
• The characteristic feature of cyanobacterium cell is the presence of a system of photosynthetic lamellae called thylakoids.
• The characteristic photosynthetic pigments present in the thylakoids are chlorophyll a and phycobilins i.e., phycocyanin (blue coloured), phycoerythrin (red coloured) and allophycocyanin (light blue coloured).

The cyanobacterial cell contains reserve food material in the following forms
(i)    Cyanophycean granules (Protein)

(ii)   

(iii)    Cyano-or myxophycean starch or -granule (Similar to glycogen but negative to iodine test)

(iv)    Volutin body (Reserve phosphate)

(v)    Polyhedral body (Rubisco rich)

Concept Builder

Gaidukov's phenomenon or complementary chromatic adaptation -Cyanobacteria or blue green algae can adaptively change their body colour according to different wavelengths of available light, e.g., Trichodesmium erythraeum. It is also known as "red sea" causing alga.

Metabolism

They are the most self-dependent organisms, because most of these are capable of converting atmospheric nitrogen into ammonium compounds besides utilizing atmospheric CO₂ for synthesis of organic food during photosynthesis.

Biological nitrogen fixation is an anaerobic process as nitrogenase enzyme required for the process acts efficiently in the absence of oxygen.

Nitrogen fixation under anaerobic conditions occurs mainly in large, specialized cells called heterocysts as in Nostoc.

Heterocyst has terminal pores which at maturity develops a polar granule.

Thickened cell wall of these cells is impermeable to oxygen so this creates anaerobic environment in the cell even under aerobic conditions.

Besides this, heterocysts also lack PS II activities and CO₂ fixation is done only by vegetative cells.

Oxygen is not evolved due to absence of PSII.

However, PSI remains active in heterocyst which generates ATP required to fix nitrogen.

Besides N₂ fixation heterocyst promotes fragmentation.

This property of nitrogen fixation, most of the BGA enrich the soil by releasing nitrogenous compounds in the surroundings.

Reproduction

Cyanobacteria reproduce asexually. Typical sexual reproduction is absent.

Asexual reproduction occurs by following methods :

(i) Binary fission: It occurs in unicellular forms. The daughter cells formed by amitotic division separate immediately after the division.
(ii)  Fragmentation: It occurs in filamentous forms. The filament breaks up into short pieces or fragments which grow to form new filaments.
(iii)  Heterocysts : Under special conditions, the heterocysts germinate to form new filaments.
(iv)  Hormogonia: Due to the formation of biconcave, mucilage filled dead cells called necridia, in between living cells of trichome, the filament breaks into hormogonia.
(v)  Akinetes: Vegetative cells are transformed into thick walled akinetes due to the deposition of food material followed by the thickening of wall. On the arrival of favourable conditions, they germinate to form new filaments.

Importance of Cyanobacteria

(i)    They are the most ancient organisms having oxygenic photosynthesis and thus, played a significant role in the evolution of aerobic forms of life.
(ii)    They convert atmospheric nitrogen into ammonium compounds and excess of these compounds is excreted out, enriching the soil. The death and decay of these also increase the soil fertility, particularly the nitrogen content of the soil. Tolypothrix and Aulosira fix N2 non-symbiotically in rice fields .
Cyanobacteria like Nostoc and Anabaena have been used for reclaiming usar soils. As they can live in damp or aquatic habitat, they enrich the root environment in any wetland condition as in rice fields.
(iii)    Cyanobacteria are associated in symbiotic relationship with almost every group of plants. They benefit the partner by providing nitrogenous compounds because of their capability of nitrogen fixation.
(iv)    Some cyanobacteria serve as food to several aquatic animals. Spirulina is edible, non-toxic, fast growing cyanobacterium. It is cultivated in tanks as source of protein rich animal food (SCP).
(v)    Extract of Lyngbya is used for the manufacture of antibiotic.
(vi)    Some cyanobacteria like Microcystis aeruginosa, Anabaena flos-aquae, Aphanizomenon flos-aquae are known to cause algal blooms in water bodies. These also secrete toxins into the surroundings, which are harmful to aquatic animals and even to human beings. Water from such sources is harmful and may even prove fatal for organisms drinking it. They also deplete the oxygen from the water reservoir and thereby, cause large scale death of the fishes and other aquatic animals.

III. MYCOPLASMA

E. Nocard and E.R. Roux (1898)-two French Scientists, discovered these organisms from pleural fluid of cattles suffering from pleuropneumonia.

These are pleomorphic and were called PPLO (Pleuropneumonia Like Organisms) or Jokers of plant kingdom.

This organism was later on given the name Asterococcus mycoides by Borrel et al. (1910).

Nowak (1929) placed Asterococcus mycoides under the genus Mycoplasma.

All such organisms are now called Mycoplasma, or MLO's (Mollicutes like organisms).

These are sometimes placed in a separate class called Mollicuta.

Mycoplasma infects animals (e.g., dog, sheep, mice and man) and plants (e.g., potato, corn, brinjal etc.).

• They are generally found in soil, sewage water, plants and animals.

Structure:

These are unicellular, simplest free living prokaryotes.

They do not have cell wall so they are highly pleomorphic and can assume various shapes like spherical, granular, filamentous, coccoid etc.

Cell membrane is the outermost limiting layer.

It is trilamellar unit membrane structure.

In culture, colonies of mycoplasma show a characteristic fried egg appearance with an opaque central area and translucent peripheral zone.

The cells are generally non motile, but a few are gliding type.

The protoplasmic matrix contains ribosomes (70S type), fatty acid substances and proteins.

Organized nucleus, endoplasmic reticulum, plastids, mitochondria, golgi bodies, Iysosomes, centrioles, flagella, etc. are absent.

Mycoplasma has both RNA and DNA.

RNA is single stranded, present in both ribosomes and cytoplasm and DNA is double stranded, long coiled thread extending almost throughout the cell.

Enzymes are present freely in the cytoplasm as well as associated with the plasma membrane.

Replicating disc assist in replication and separation of the genetic material.

Nature of Mycoplasma:

Mycoplasma can pass through bacteriological filters and lack cell wall.

This shows that they are not bacteria.

Since they can multiply in abiotic medium having sterols, so they are not considered as virus.

Due to many similarities with bacteria they are said to be "Bacteria with their coats off".

Mode of nutrition is heterotrophic.

Some are saprophytic, but mostly they are parasitic.

They are parasitic, because they are unable to synthesize required growth factors, e.g., M. gallisepticum (0.3 to 0.5 µm, smallest prokaryote).

They can survive without oxygen.

 Sensitivity to Antibiotics:

Mycoplasma are Gram negative, insensitive to penicillin but sensitive to streptomycin, erythromycin, chloramphenicol (metabolic inhibitors) etc.,

They are insensitive to penicillin because they are wall less and penicillin interferes in the synthesis of peptidoglycan, a component of cell wall of bacteria.

Reproduction - Much is not known about reproduction of Mycoplasma but they mainly reproduce by means of elementary bodies.

 Concept Builder

Mycoplasmas cause various diseases in plants, animals and human beings.

Some are given below :

1. Plant diseases: The Mycoplasma diseases are generally transmitted through insects such as leaf hopper, mites and flies.

(i) Witches' broom        (ii) Aster yellow
(iii) Brinjal little leaf        (iv) Bunchy top of Papaya
(v) Sesame phyllody        (vi) Sandal spike

2. Diseases in animals
(i)    Pleuropneumonia in cattle
(ii)    Inflammation of genitals

3. Diseases in human beings
(i)    Infertility in man
(ii)    Primary atypical pneumonia

IV. ARCHAEBACTERIA

They are believed to have evolved immediately after the origin of life on earth, as even now these are living under extremely adverse conditions such as extreme salty areas (halophiles), hot springs (thermoacidophiles) and marshy areas (methanogens).

Very few other organisms can survive under such environmental conditions. So these are termed as "living fossils".

These possess introns in DNA, their ribosomal proteins are highly acidic, these prokaryotes possess histone proteins different from that of eukaryotes.

These being the most primitive and ancient most bacteria.

Archaebacteria differ from other bacteria in having a different cell wall structure and this feature is responsible for their survival in extreme conditions.

The cell wall in archaebacteria contains proteins and non-cellulosic polysaccharides.

It lacks peptidoglycan, the characteristic cell wall material in bacteria and cyanobacteria.

It consists of glycoprotein, pseudomurein and non cellulosic polysaccharide.

Pseudomurein is like bacterial peptidoglycan, but contain N-acetyltalosaminuronic acid instead of NAM and lacks D-Amino acid.

The cell membrane contains branched chain lipids (phytanyl side chains) which decreases membrane fluidity.

This chemical composition of the cell membrane enables these organisms to withstand extremes of temperature and pH.

Archaebacteria are divided into three groups· methanogens, halophiles and thermoacidophiles

(a) Methanogens:

They are obligate anaerobes occurring in marshy habitats.

They are capable of converting CO₂, methanol and formic acid (HCOOH) into methane and hence the name methanogens.

This property is exploited commercially in the production of fuel gas and methane in gobar gas plants (biogas fermenters).

Some of the methanogens live in rumen of herbivorous animals like buffalo, cow etc. (ruminants).

These microorganisms assist in fermentation of cellulose in such animals, e.g., Methanococcus, Methanobacterium, Methanosarcina, Methanospirillum.

(b) Halophiles:

They are aerobic chemoheterotrophic coccoid forms and are Gram negative. They occur in high salt concentration medium like sea, salt lake, brines, marshes, salted field etc.

In high light intensity a reddish pigment bacteriorhodopsin develops in their membrane to trap sun light to produce ATP, but they cannot use this ATP in food synthesis.

Sap vacuoles are absent in halophiles, hence, they cannot get plasmolysed in high salt concentration.

They maintain a high osmotic concentration of KCl in their cells.

These bacteria get lysed if NaCl level falls below 10%, e.g., Halococcus, Halobacterium.

These can grow well in a medium containing 25-30% of NaCl.

(c) Thermoacidophiles:

They are capable of tolerating high temperature as well as high acidity and hence, the name thermoacidophiles.

They often live in hot-water springs where the temperature is as high as 80°C and the pH as low as 2.

They oxidise sulphur to sulphuric acid under aerobic conditions and the energy obtained in this reaction is utilized for the synthesis of organic food.

The medium becomes highly acidic due to the production of sulphuric acid. Under anaerobic conditions sulphur is reduced to H₂S, e.g., Thermoplasma, Thermoproteus, Thermococcus. Hence, these are chemosynthetic in nature.

 Concept Builder

Thermoacidophiles are capable of withstanding extremely low pH and high temperature due to:

(a) The cell membrane containing branched chain lipids

(b) The presence of resistant enzymes which can operate under acidic conditions.
It seems probable that archaebacteria, living in extreme environmental conditions got separated from the main line of bacterial evolution quite early. They survived through long period of geological changes successfully, existing at present and are perhaps the oldest "living fossil".

V. ACTINOMYCETES (Ray Fungi)

(1)    These are branched, filamentous bacteria and are considered as intermediate form between bacteria and fungi, e.g., Nocardia, Mycobacterium, Corynebacterium, Frankia, Streptomyces.

(2)    These filaments form radiating colonies in cultures so are also called mycelial bacteria.

(3)    Cell wall contains peptidoglycan and is Gram positive in nature. It contains mycolic acid.

(4)    They are facultative anaerobic, saprophytic, non-motile and are important decomposers of dead organic matter. 

(5)    They reproduce commonly by conidia, sporangiospore, oidia and fragmentation. 

(6)    They are acid fast in nature.

Concept Builder

Economic Importance of Actinomycetes : They are the source of more than 100 antibiotics. Most common antibiotics used in medicine are produced by filamentous bacteria and are listed below :

Frankia can fix N₂ symbiotically by root nodule formation in non legumes like -Alnus, Myrica and Casuarina.

Earthy or musty smell of freshly ploughed soil or soil after first shower of rain, is due to oily secretion geosmin by some members like Nocardia, Micromonospora and Streptomyces

Concept Builder

1. In 1798, Edward Jenner used cowpox virus for immunising people against small pox.

2. Pasteurization simply kills bacteria but does not sterilize milk. It frees the latter of all vegetative cells of pathogens, but not the endospores.

3. Mycobacterium and Xanthomonas form nodules in leaves of Ardisia, Pavetta.

4. Bacterial cell membrane contains pentacyclic sterol like molecule termed as hopanoids as membrane stabiliser.

5. Kleinberger discovered tuberculosis and anthrax bacteria & developed "L-form" bacteria.

6. H. T. Ricketts described some new types of organisms (now considered a type of bacteria) in the blood of victims of Rocky Mountain spotted fever and similar organisms were called Rickettsiae, in honour of Ricketts. They occur as obligate intracellular parasites. The Q fever is caused by Coxiella burnetti. Rocky mountain fever is caused by Rickettsia rickettsii.

7. Chlamydiae: They are obligate intracellular parasite of vertebrates. They reproduce by elementary bodies. They do not have their own ATP generating system and obtain this energy from host. So that they are called energy parasite.

1. Diseases

• Trachoma (eye disease)                     – C. trachomatis
• Conjuctivitis                                       – C. trachomatis
• Psittacosis (influenza like)                – C. psittaci

8. Joseph Lister developed the technique of aseptic cultures.

9. Nostoc develops symbiotic associations with Gunnera stem and Trifolium roots.

Kingdom Monera

Monera is a biological kingdom that is solely made up of prokaryotes.  Their DNA is not enclosed within the nucleus as these single-celled organisms lack a true nucleus. The Monerans also do not possess any membrane-bound organelles.

The Kingdom Monera is made up entirely of bacteria. They are the most common microorganisms on the planet. Bacteria can be found practically anywhere. A handful of soil contains hundreds of bacteria. They also exist in harsh environments like hot springs, deserts, snow, and deep oceans, where only a few other species can survive. As parasites, many of them live in or on other organisms.

The spherical Coccus (pl.: cocci), the rod-shaped Bacillus (pl.: bacilli), the comma-shaped Vibrium (pl.: vibrio), and the spiral Spirillum are the four types of bacteria classified by their shape.

Although bacteria have a simple structure, their activity is extremely sophisticated. Bacteria, in comparison to many other creatures, have the greatest metabolic diversity.Some bacteria are autotrophic, meaning they produce their own nourishment from inorganic sources. They can be either photosynthetic or chemosynthetic autotrophs. The great majority of bacteria are heterotrophs, meaning they feed on dead organic matter or other species. Archaebacteria, Eubacteria, and Cyanobacteria are the three sub-kingdoms of the kingdom Monera.

A. Archaebacteria:

These bacteria are unique in that they survive in extremely salty environments (halophiles), hot springs (thermoacidophiles), and marshy environments (methanogens). Archaebacteria vary from other bacteria in that they have a unique cell wall construction that allows them to survive in harsh environments. Methanogens are bacteria that live in the guts of ruminant animals like cows and buffaloes and are responsible for the creation of methane (biogas) from their feces.

B. Eubacteria:

"True bacteria" is another name for Eubacteria. The existence of a hard cell wall and, if motile, a flagellum distinguishes them. A few bacteria have pili, which are small appendages on the cell surface that aid the bacterium in sexual reproduction. Pili also aids in the attachment of pathogens to their hosts. Depending on the type of the cell wall and the stain they take, they are classified as gram-positive or gram-negative.

C. Cyanobacteria:

Cyanobacteria are photosynthetic autotrophs with chlorophyll similar to green plants. They are unicellular, colonial, or filamentous algae that can be found in freshwater, marine, or terrestrial environments. Gelatinous sheath surrounds the colonies in general. Blooms are common in contaminated water bodies. Some of these species, such as Nostoc and Anabaena, can fix atmospheric nitrogen in specialized cells called heterocysts. Chemosynthetic autotrophic bacteria utilize the energy released by oxidizing inorganic compounds like nitrates, nitrites, and ammonia to produce ATP. They are vital in the recycling of nutrients such as nitrogen, phosphorus, iron, and sulfur.

 In nature, heterotrophic bacteria are the most common. The majority of them are significant decomposers. Many of them have a major influence on human affairs.They aid in the creation of curd from milk, the manufacture of antibiotics, and the fixation of nitrogen in legume roots, among other things. Some of these are infections that harm humans, crops, farm animals, and pets. Bacterial infections such as cholera, typhoid, tetanus, and citrus canker are well-known. Bacteria mostly reproduce through fission. They may generate spores in unfavorable conditions. They also reproduce by adopting a rudimentary method of DNA transfer from one bacteria to the next, which is similar to sexual reproduction.

Mycoplasma are creatures that lack a cell wall entirely. They are the world's tiniest living cells, capable of surviving without oxygen. In animals and plants, many mycoplasmas are pathogenic. 

KINGDOM : PROTISTA

All unicellular eukaryotes, irrespective of their mode of nutrition, are included in the kingdom Protista in Whittaker's system. The term protista was coined by Ernst Haeckel. This kingdom forms a link between kingdom Monera on one hand and other three kingdoms i.e. , Plantae, Fungi and Animalia on the other hand. Protistans are ancestors of all multicellular eukaryotes (plants, fungi and animals).

Kingdom Protista includes

General Characteristics of Protista

1. Unicellular, eukaryotic organisms. Some are colonial without much cellular differentiation. Organisation at tissue level is absent.

2. Mostly aquatic organisms.

3. Cell structure is eukaryotic type having all kinds of membrane bound organelles and 80 S cytoplasmic ribosomes and cells may possess cellulosic cell wall.

4. Flagella and cilia have (9+2) pattern of microtubule organization consisting of tubulin protein.

5. Movement by pseudopodia, flagella or cilia where ciliary mode is fastest.

6. Mode of nutrition may be photosynthetic (holophytic), holozoic (ingestive), saprobic or parasitic (absorptive). Some have mixotrophic nutrition (photosynthetic and saprobic) as in Euglena.

7. Reproduction occurs by asexual and sexual means.

8. Life cycle is of 2 types-(i) Showing zygotic meiosis (ii) Showing gametic meiosis.

9. These are decomposers, photosynthetic or parasites. Parasitic protists may cause diseases like dysentery, malaria, sleeping sickness etc.

 Photosynthetic protists and Slime moulds are described below:

(1) Photosynthetic Protists 

These are popularly called protistan algae. Protistan algae constitute the major portion of the phytoplanktons. 

A. Diatoms

Diatoms are golden brown photosynthetic protists and are called Chrysophytes (including both diatoms and desmids). They are both aquatic and terrestrial. Some are marine. They support much of marine life. Their important characters are

These are microscopic organisms possessing varying colours.

They are basically unicellular, but may form pseudofilament and colonies, lacking flagella except in the reproductive stage. They may be free floating (phytoplanktonic) due to presence of light weight lipids.

The cellulosic cell wall is impregnated with silica to form transparent siliceous shell, known as frustule. Depending upon the symmetry, diatoms may be pennate type, having bilateral symmetry (e.g., Navicula) and centric type, having radial symmetry (e.g., Melosira).

The cell wall is characteristic, made up of two halves; one half covering the other (epitheca over  hypotheca) resembling a soap box.

The cell wall encloses the peripheral layer of cytoplasm (primordial utricle) surrounding a large central vacuole.

Nucleus lies in the central vacuole, suspended with the help of cytoplasmic strands.

Mode of nutrition is holophytic (photoautotrophic), photosynthetic pigments are chlorophyll a, chlorophyll c, b-carotene and special carotenoids containing fucoxanthin; xanthophylls like diatoxanthin, diadinoxanthin.

The reserve food is oil and a polysaccharide called leucosin (chrysolaminarin), volutin granules are also present.

They are responsible for almost 50% of the total organic matter synthesized in the biosphere.

Movement occurs by mucilage propulsion.

They mainly undergo asexual reproduction. The common mode of asexual reproduction is binary fission.

During binary fission, one half of the cell wall is retained by each of the daughter cells formed. The other half of the cell wall is secreted afresh.

Resting spores are called statospores (centric diatoms).

They reproduce sexually as well. Sexual reproduction varies from isogamy to oogamy. It involves gametic meiosis as diatoms are generally diploid (diplontic life cycle).

  Concept Builder

1. Silica shells of dead diatoms are nearly indestructible and thus, get accumulated at the sea bed. Such huge rock-like deposits of hard shells of diatoms constitute diatomaceous earth, which is mined to obtain a whitish powder called diatomite or kieselguhr or diatomaceous earth. Diatomite is rough and gritty. Because of these features, it is used in filters in brewing industry, sugarcane refineries, in polishes for metals, tooth pastes, for making insulating bricks, in insulation of refrigerators, houses and for making the latter sound proof, in the manufacture of dynamite, water glass or sodium silicate and strong acids. This is added to paint to increase their night visibility.

2. They are very good indicators of water pollution. Common examples of diatoms are Triceratium, Melosira, Navicula, Cymbella.

   B. Dinoflagellates

Dinoflagellates are golden brown photosynthetic protists, belonging to class Dinophyceae (Pyrrophyta). They are mainly marine, though few are fresh water forms.

They may appear red, yellow, green, brown or blue depending upon the main pigment present in cell.

     General characters : 

Unicellular, motile, biflagellate, golden brown photosynthetic protists (some are non-motile, amoeboid, palmelloid or filamentous).

They are mostly marine, some are found in fresh water.

The body is enclosed by a rigid coat called theca or lorica consisting of 2 to many articulated or sculptured plates of cellulose and pectin , hence are also called armoured dinoflagellates.

Theca has generally two grooves i.e., longitudinal called sulcus and transverse called cingulum or annulus or girdle.

Flagella are heterokont (different). One is longitudinal and other is transverse. The flagella pass out through the pores in the lorica and lie in the grooves. The transverse flagellum lies in the circular groove and the longitudinal flagellum in the longitudinal groove. The longitudinal flagellum is narrow, smooth directed posteriorly and the transverse flagellum is ribbon like

Both are oriented at right angle to each other producing spinning movements. Therefore, these protists are also called 'whirling whips'.

Most of the species have brown, green or yellow chromatophores with chlorophyll a, c,        a-carotene, xanthophyll (e.g., Peridinin). Plastids are generally surrounded by 3-membrane envelope and contain 3-thylakoid lamellae. They are autotrophic or photosynthetic (Ceratium), a few are saprobic or parasitic.

Reserve food is carbohydrate and oils.

Nucleus is relatively larger in size, has condensed chromosomes even in interphase, chromosomes do not have histone. Nuclear envelope and nucleolus remain present even during cell division. This organisation is called Mesokaryon (Dodge, 1966).

A non-contractile vacuole called pusule is present near the flagellar base. It may have one or more vesicle and takes part in floatation and osmoregulation.

Some dinoflagellates possess trichocysts and cnidoblasts like those of coelentrates.

Reproduction is commonly asexual and occurs through cell division.

Isogamous and anisogamous sexual reproduction is reported from some dinoflagellates                                               

e.g., Ceratium.

Life cycle involves zygotic meiosis (Ceratium, Gymnodinium). Gametic meiosis occurs in Noctiluca.

Concept Builder

1. Some marine dinoflagellates show bioluminescence, i.e., emit light, e.g., Noctiluca, Pyrodinium, Pyrocystis. Due to phosphorescence the sea glows at night.

2. Some dinoflagellates like Gonyaulax catenella produce a toxin called saxitoxin into the sea water which is highly poisonous to vertebrates, e.g., fishes and other aquatic animals. Marine shell fish consume dinoflagellates and accumulate the poison which is not harmful to the shell fish (mussel) but upon being consumed causes severe illness in man called paralytic shell fish poisoning (PSP) and even prove fatal.

3. Some dinoflagellates proliferate in large number and cause red tide of the sea, e.g., Gonyaulax, Gymnodinium.

C. Euglenoid (Euglena-like)

   It is a group of chlorophyllous and non chlorophyllous flagellate protists. Largest genera being Euglena amongst them.

Euglenoids are unicellular, flagellate protists found in water or damp soil. Majority of them are fresh water organisms found in stagnant water.

Body is spindle shaped with blunt anterior end and pointed posterior end.

Cell wall is absent but a covering periplast or pellicle is present which is proteinaceous (elastic) in structure.

Locomotory organs are flagella.

The cell bears a single long tinsel type flagellum (stichonematic) arising at the anterior end. Actually, there are two flagella but one of these is reduced. The longer flagellum has two branches at the base each having its own basal granule. In the area of union of two flagella is present a photosensitive paraflagellar body.

Myonemes are oblique but parallely arranged strips in pellicle. Euglenoids perform creeping movement of contraction and expansion with the help of myonemes which is called metaboly or euglenoid movement.

The apical end of the cell bears an invagination with three distinct parts, i.e., mouth (cytostome), canal (gullet or cytopharynx) and reservoir. It helps in the ingestion of solid food particles.

Stigma or an eye spot is attached to the membrane of the reservoir at the level of paraflagellar body and along with it seems to be involved in perception of light stimulus. It contains photosensitive red-orange pigment called astaxanthin.

A contractile vacuole occurs in the anterior end of the cell just below the reservoir, meant for osmoregulation and excretion.

Single large nucleus lies near the centre of the protoplast.

Nutrition in Euglena viridis is photoautotrophic. However, it is capable of getting nourishment from dead and decaying organic matter in the substrate by secreting digestive enzymes (saprophytic nutrition) in the absence of light. This dual mode of nutrition is termed as mixotrophic. Holozoic nutrition is absent in Euglena. Some forms are holozoic (Paranema) or saprobic (Rhabdomonas).

Photosynthetic pigments are chlorophyll a, chlorophyll b, xanthophyll and b-carotene.

Reserve food material is paramylon, stored in cytoplasm in the form of paramylum granules. They are chemically b 1,3-glucans.

Under favourable conditions, they mainly reproduce by longitudinal binary fission. During unfavourable conditions, palmella stage and cysts are formed for perennation. Sexual reproduction is not known to occur in euglenoids, e.g., Euglena and Paranema.

 Concept Builder

1. Euglena is producer-decomposer protist.

2. It is studied as plant as well as animal and is called as plant animal.

3. Plant characters of Euglena:

1.  

• Presence of chloroplast with photosynthetic pigments.
• Holophytic nutrition

4. Animal characters of Euglena:

1.  

• Absence of cell wall and presence of proteinaceous pellicle.
• Presence of stigma and paraflagellar body.
• Presence of contractile vacuole.
• Presence of longitudinal binary fission.

  (2) Slime moulds or consumer-decomposer protists 

They were included in class myxomycetes of fungi in two-kingdom classification. They were called mycetozoa by DeBary as they are closely related to animals. Mycologists include them in gymnomycota. Because of their nature they are called protistan fungi. 

    General characteristics of the slime moulds are :

They are usually free-living, creeping over debris like fallen leaves and rotting logs of wood.

They have naked protoplast, not covered by any cell wall in vegetative stage.

They lack chlorophyll and have saprobic or phagotrophic mode of nutrition.

During life cycle they are amoeboid and non-cellulosic, but spores have cellulosic wall so that their vegetative phase resembles with animals while reproductive phase resembles with plants.

Amoeboid plasmodial stage resembles protozoa and spore forming nature is like fungi.

Spores are extremely resistant and survive for many years, even under adverse conditions. The spores are dispersed by air currents.

Reproduction is both asexual and sexual. This group is represented by two separate types of organisms i.e. acellular and cellular.

    A.    Acellular or Plasmodial slime moulds 
        General characters: 

Slimy masses found on decaying leaves and lumber.

Somatic body is free living, multinucleate, naked, diploid mass called Plasmodium. Movement occurs by means of pseudopodia.

During unfavourable conditions, entire plasmodium forms many fructifications/fruting bodies (polycentric). The fruiting body is called sporocarp which contains a stalk having a sporangium at its tip. The wall of sporangium is called peridium.

Sporangium has an intricate network of cytoplasmic threads called capillitium.

DiploId protoplast forms haploid spores by meiosis.

Spore wall is double, outer wall is spiny and sculptured.

On germination, spores produce biflagellate swarm cells or non-motile myxamoebae which act as gametes.

Sexual reproduction is isogamous.

Diploid zygote directly forms the plasmodium which becomes multinucleate by repeated mitotic divisions of the diploid nucleus.

Chief mode of nutrition is saprotrophic.

Vegetative reproduction is by fission .

e.g., Physarum, Physarella, Fuligo, Dictydium, Lycogala

B.    Cellular slime moulds or communal slime moulds 
General characters : 

Wall less, uninucleate myxamoebae present. Complete absence of flagellated cells during life cycle.

Formation of pseudoplasmodium stage as a result of chemotactic movement of myxamoebae due to release of cAMP and acrasin.

Sporangia are naked.

Spores have cellulosic wall.

Sexual reproduction is anisogamous.

Common cellular slime mould, Dictyostelium, is a colonial form in which hundreds of uninucleate, haploid amoeboid cells are aggregated without any fusion to form a colony.

The colony gives the appearance of single multinucleate mass of protoplasm and thus, called pseudoplasmodium.

Under exhausted food supply and stimulation by cAMP and chemical acrasin, many cells come close together by chemotactic movement during the formation of pseudoplasmodium.

Pseudoplasmodium exhibits primitive form of multicellularity and division of labour.

So these are also called as communal slime moulds.

On these basis cellular slime moulds are regarded as advanced protists and primitive fungi.

During unfavourable conditions, the myxamoebae may form a cyst called microcyst for perennation and dispersal.

Under dry conditions, the pseudoplasmodium produces stalked sporocarp, which may be branched or unbranched, each branch bearing single sporangium terminally (monocentric).

Sporangium is wall less. Within the sporangium, amoeboid cells become rounded to secrete a spore wall around.

On the approach of favourable conditions, spores are liberated.

Each spore germinates by rupturing cellulosic wall to form myxamoeba and the myxamoebae may live independently, multiply by repeated mitotic divisions or get aggregated to form pseudoplasmodium.

Sexual reproduction is anisogamous type. During sexual reproduction, a number of myxamoebae form a clump.

One of the myxamoeba becomes larger and engulfs the surrounding smaller myxamoebae.

The plasmogamy occurs and the fused protoplast secretes a thick wall around to form macrocyst.

In the macrocyst, karyogamy occurs and it thus, becomes zygote.

It is followed by meiosis and several mitotic divisions to form a large number of haploid myxamoebae, which are released by rupture of macrocyst wall.

• e.g., Dictyostelium, Polysphondylium.