Cell as a basic unit of life;

Introduction -

• Cell is the structural and functional unit of life. It is the basic unit of life.
• It is discovered by Robert Hook in 1831 in cork slice with the help of primitive microscope.
• Leeuwenhoek (1674), discovered the free living cells in pond water with the improved microscope
• Robert Brown discovered the nucleus in the cell in 1831.
• Purkinje coined the term ‘protoplasm’ for the fluid substance of the cell in 1839.

The cell theory-

• The theory that all the plants and animals are composed of cells and the cell is the basic unit of life,
was presented by two biologists, Schleiden and Schwann.

• The cell theory was further expanded by Virchow by suggesting that all cells arise from preexisting

tructure and functions of animal and plant tissues (four types in animals; meristematic and permanent tissues in plants).


→ A group of cells that are similar in structure and/or work together to achieve a particular function
forms a tissue.
→ Most of the tissues in plants are supportive, which provides them with structural strength.
→ These tissues are dead, since dead cells can provide mechanical strength as easily as live ones
and need less maintenance.
→ Plant Tissues are of two types Meristematic & Permanent tissues.

Meristematic Tissue

→ These are simple living tissues having thin walled compactly arranged immature cells which are
capable of division and formation of new cells.

Features of Meristematic tissues:

→ Thin primary cell wall (cellulosic).
→ Intercellular spaces are absent (compact tissue).
→ Generally vacuoles are absent, dense cytoplasm & prominent nuclei are present.
→ Large numbers of cell organelles are present.
→ Active metabolic state, stored food is absent.
→ Actively dividing cells are present in growing regions of plants, example: root & shoot tips.

Classification of Meristematic Tissues on the Basis of Origin

• Primary (Promeristem)

→ Derived directly from the meristems of embryo.
→ They consist of cells derived from primary meristem.
→ They add to primary growth of plants.

• Secondary Meristematic Tissues

→ Formed by permanent tissues.
→ These are having cells derived from primary permanent tissue.
→ They usually add to the diameter of plants.

Classification of Meristematic Tissues on the Basis of Location

• Apical Meristem

→ It is present at the growing tips of stems and roots.
→ Cell division in this tissue leads to the elongation of stem & root, thus it is involved in primary
growth of the plant.

• Intercalary Meristem

→ It is present behind the apex.
→ It is the part of apical meristem which is left behind during growth period.
→ These are present at the base of leaf & internode region.
→ These lead to the increase in the length of leaf (Primary), example: in grass stem, bamboo stem
mint stem etc.

• Lateral Meristem

→ It is also called as secondary meristem.
→ It occurs along the sides of longitudinal axis of the plant.
→ It gives rise to the vascular tissues.
→ Causes growth in girth of stem & root.
→ They are responsible for secondary growth.

Permanent Tissue

→ The permanent tissues are composed of those cells which have lost their capability to divide.
→ They have definite shape, size and thickness. The permanent tissue may be dead or living.
→ The division & differentiation of the cells of meristematic tissues give rise to permanent tissues.
→ In cell differentiation, developing tissue and organs change from simple to more complex form
to become specialized for specific functions.
→ The cells of permanent tissue loose the capacity to divide and attain a permanent shape, size
and function.

• Permanent tissues are classified into two types on the basis of Structure and Composition i.e.
Simple Permanent Tissues and Complex Permanent Tissues.

Simple Permanent Tissues

→ These are made up of same type of cells which are similar structurally and functionally.
→ They include two types of tissue Protective tissues and Supporting Tissues.

• Protective Tissues: These tissues are primarily protective in function.
→ They consist of Epidermis and Cork/Phellem.
(i) Epidermis
→ Epidermis forms one cell thick outermost layer of various body organs of plants such as leaves,
flowers, stems and roots.
→ Epidermis is covered outside by cuticle. Cuticle is a water-proof layer of waxy substance called
cutin which is secreted by the epidermal cells.
→ Cuticle is very thick in xerophytes.
→ Cells of epidermis of leaves are not continuous at some places due to the presence of small
pores called as stomata.
→ Each stomata is guarded by a pair of bean-shaped cells called as guard cells. These are the one
epidermal cells which possess chloroplasts, the rest being colourless.

Functions of Epidermis

→ The main function of epidermis is to protect the plant from desiccation and infection.
→ Cuticle of epidermis cuts the rate of transpiration and evaporation of water and prevents wilting.
→ Stomata in epidermis allow gaseous exchange to occur during photosynthesis respiration.
→ Stomata also helps in transpiration.

(ii) Cork or Phellem

→ In older roots and stems, tissues at the periphery become cork cells or phellem cells.
→ Cork is made up to dead cells with thick walls and do not have any intercellular spaces.
→ The cell walls in cork deposit waxy substance called as suberin.
→ The cells of cork become impermeable to water and gases due to the deposition of suberin.
→ The cork cells are without any protoplasm but are filled with resins or tannins.

Functions of Cork

→ Cork is protective in function. Cork cells prevent desiccation, infection and mechanical injury.
→ Imperviousness, lightness, toughness, compressibility and elasticity make the cork commercial
→ Cork is used for insulation, as shock absorber in linoleum.
→ Cork is used in the making of a variety of sport goods such as cricket balls, table tennis, shuttle
cocks, wooden paddles etc.

• Supporting Tissues: These are supportive in function.
→ There are three types of Supporting tissues i.e. Parenchyma, Collenchyma and Sclerenchyma.

(i) Parenchyma
→ It is the fundamental tissue.
→ Tissue first time evolved in bryophyte.
→ Thin walled cells, oval or spherical in structure.
→ Cell wall mainly composed of cellulose & pectin.
→ Large central vacuole for food & water storage.
→ Primary function is food storage.
→ Some parenchyma involved in excretory substance storage are so called as idioblast, storing
such as resin, tannin, gums & oils.
→ In typical parenchyma chlorophyll is absent.
→ Chloroplast containing parenchyma tissue are chlorenchyma which perform
photosynthesis such as mesophyll of leaves.
→ In hydrophytic plants aerenchyma (a type of parenchyma containing air spaces) provides
→ Parenchyma provides turgidity to cells.

(ii) Collenchyma

→ It is the living mechanical tissue.
→ Elongated cells with thick corners.
→ Localized cellulose & pectin thickening.
→ Provides flexibility to plant parts & easy bending of various parts of plant.
→ Present only in herbaceous dicot stem.
→ Present at thin margin of leaves.
→ Few chloroplasts may be present.
→ Gives mechanical strength & elasticity to the growing stems.

(iii) Sclerenchyma (Scleras–hard) Strengthening tissue.
→ Composed of extremely thick walled cells with little or no protoplasm.
→ Cells are dead & possess very thick lignified walls.
→ Lignin is water-proof material.
→ Intercellular spaces are absent.

• Cells of sclerenchyma are of two types Sclereids and Fibres.

• Sclereids
→ These are also called grit cells or stone cells.
→ These are small cells, where lumen is so small due to higher thickening of cell wall, as present in
drup fruit (mango, coconut, walnut) in legume seeds (Macrosclereid).

• Fibers

→ They are very long, narrow, thick, lignified cells. Lumen is large as compared to sclereids.
They are generally 1-3 mm long.
→ In the thick walls of both the fibres and sclereids are present thin areas called as pits.
→ Sclrenchyma Fibres are used in the manufacture of ropes, mats & certain textile fibres.
→ Jute and coir are obtained from the thick bundle of fibres.

Difference between Parenchyma, Collenchyma and Sclerenchyma

Difference Between Parenchyma Collenchyma and Sclerenchyma - Comparison  Summary | Study biology, Basic anatomy and physiology, Biology facts


Complex Permanent Tissues
→ It consists of more than one type of cells which work together as a unit.
→ It helps in transportation of organic materials, water & minerals.
→ It is also known as conducting or vascular tissue.
→ Xylem & phloem together form vascular bundles.


→ It is also known as wood and is a vascular and mechanical tissue.
→ Thick walled cells are found in the form of tubular passages.
→ Xylem consists of four types of cells called as elements Tracheids, Vessels, xylem parenchyma
and xylem sclerenchyma.

(i) Tracheids
→ They are elongated angular dead cells (primitive elements) mainly involved in conduction of
water and minerals in gymnosperms.
(ii) Vessles
→ They are advance element (generally found in angiosperms).
→ Vessels are cylindrical tube like structures placed one above the other end to end which form a
continuous channel for efficient conduction of water.
(iii) Xylem parenchyma
→ They are small & thick walled parenchymatous cells subjected for storage of starch (food).
(iv) Xylem sclerenchyma
→ Thy are non-living fibres with thick walls and narrow cavities provide mechanical support.
→ Except xylem parenchyma all other xylem elements are dead.
→ The annual rings present in the trunk of a tree are xylem rings.
→ By counting the number of annual rings, we can determine the age of a tree.


→ They also consist of both parenchymatous and schlerenchymatous cells.
→ Phloem consists of four types of element which are Sieve tubes, Companion cells, Phloem fibre
and Phloem parenchyma.

(i) Sieve tubes
→ Sieve tubes are slender tube like structures made up of elongated, thin walled cells placed end to
→ The end walls of sieve tube cells are perforated by numerous pores, called as sieve plates.
→ Nucleus of sieve cell degenerates at maturity. However, cytoplasm persists, because of
protoplasmic continuation of sieve tube with companion cell through plasmodesmata.
→ Sieve cells possess slime protein or protein which is concerned with growth and repair of sieve
(ii) Companion cells
→ Companion cells have dense cytoplasm and prominent nuclei.
→ Sieve cells & companion cells are so called sister cells because they originate from single mother
(iii) Phloem fibre
→ They give mechanical support to sieve tubes.
(iv) Phloem parenchyma
→They store food and help in radial conduction of food.
(v) Leptome
→ Main part of phloem involved in conduction of food, which is sieve tube.
→ In xylem, only unidirectional movement is possible while in phloem bidirectional movement can
→ In phloem, except phloem sclerenchyma all elements are living.

Difference Between Xylem and Phloem - Pediaa.Com

Diversity of plants and animals

→ All living organism are grouped on the basis of their similarities and increasing complexities into different complexities.

Chapter 13 Diversity of Life and Classification - Frank Modern Certificate  Solutions for Class 9 Biology ICSE - TopperLearning

→ Biodiversity means the variety of living organisms present on a particular region.
→ There are about 20 lac organisms known on the earth which differ from one another in externaform, internal structure, mode of nutrition, habitat, etc.
• Taxonomy:
It is a branch of biology which deals with identification, nomenclature andclassification of organisms.
Carolus Lannaeus is called the father of taxonomy.


Health and its failure.


→ ‘Health’ is a state of being well enough to function well physically, mentally and socially.

Disease: Any disturbance in the structure or function of any organ or part of body.
→ The various causes of diseases are pathogens (virus, bacteria), lack of nutritious diet/balanced
diet and lack of public health services.
→ Acute diseases occur suddenly and lasts for a short duration while chronic diseases develop
slowly and lasts for long period of time.
→ The diseases/infections can be prevented by life style (exercise, proper sleep, enough relaxatio
modification, taking balanced diet, good personal health and hygiene and also maintaining a cle
and healthy surrounding.
→ Treatment involves killing of the microbes/pathogens.


→ Health is a state of physical, mental and social well-being.

• The conditions necessary for good health are:
(i) Good physical and social environment.
(ii) Good economic conditions.
→ Good physical and social environment includes clean surroundings, good sanitation, proper
garbage disposal and clean drinking water.
→ Good economic conditions includes job opportunities for earning to have nutritious food and to
lead a healthy life.
→ Personal and Community Issues Both Matter for Health
→ All those activities which people do both individually and in groups for the development of their
society, constitute the community health.
→ Personal and community health are supplementary to each other.
→ We protect ourselves by keeping our body clean.
→ For this, we also require a good and healthy environment in our surroundings.
→ We can have this only by the means of community health and development.
→ So, both personal and community health are inter-related.
Differences between Being Healthy and Disease-free
Being Healthy Being Disease-free
It is a state of being well enough to function well
physically, mentally and socially.
It is a state of absence from diseases.
It refers to the individual, physical and social environment.
It refers only to the individual.
The individual has good health. The individual may have good health or poor health.
Disease and Its Causes

What does disease look like?
→ When a person is affected by a disease either the functioning or the appearance of one or mor
systems of the body will change for the worse.
→ These changes give rise to symptoms and signs of disease.
→ On the basis of the symptoms the physicians look for the signs of a particular disease and
conduct tests to confirm the disease.

Types of Diseases

(i) Acute Diseases: Acute diseases which last for only very short period of time and affect body
suddenly and quickly. Example: Cold, cough, typhoid etc.
(ii) Chronic Diseases: The diseases which last for a long time, even as much as a life time, are cal
chronic diseases. Example: Diabetes, tuberculosis, elephantiasis etc.
Causes of Diseases
• Diseases are caused by:
→ Pathogens like virus, bacteria, fungi, protozoans or worms.
→ Poor health and under nourishment.
→ Hereditary and genetic disorder.
→ Lack of proper treatment of immunization.
→ Environmental pollution (air, water etc.)


prokaryotic and eukaryotic cells

→ Types of organisms

• On the basis of no. of cells, organisms are of two types:
(i) Unicellular Organism
(ii) Multicellular Organism

(i) Unicellular Organism: These organisms are single celled which perform all the functions.
Example: Amoeba, paramecium, bacteria.
(ii) Multicellular Organism: Many cells grouped together to perform different function in the body
and also form various body parts. Example: fungi, plants, animals.

• The shape and size of cell are different according to the kind of function they perform. There is
division of labour in cells.
• Each cell has certain kind of cell organelles to perform different type of function like mitochondria
for respiration.

→ Types of cells
• There are two types of cells:
(i) Prokaryotes
(ii) Eukaryotes

Eukaryotic Cell — Definition & Examples - Expii

multicellular organisms

Multicellular Organism: Many cells grouped together to perform different function in the body
and also form various body parts. Example: fungi, plants, animals.

cell membrane and cell wall

Plasma membrane or Cell membrane

• This is the outermost covering of the cell that separates the contents of the cell from its external
• The plasma membrane allows or permits the entry and exit of some materials in and out of the
• It also prevents movement of some other materials. The cell membrane is called selectively
permeable membrane.
• It is made up of lipid and protein.

→ Properties of Plasma membrane

• It is flexible (made up of organic molecules called lipids and proteins).
• Its flexibility enables cell to engulf in food and other from the external environment. This process
called endocytosis. Amoeba acquire food through this process.

→ Functions of Plasma membrane

• It permits the entry and exit of some materials in and out of the cell.
• It prevents movement of some other materials not required for the cell as it acts like selectively
permeable membrane.

Cell Wall

• Cell wall is another rigid outer covering in addition to the plasma membrane found in plant cell.
The cell wall lies outside the plasma membrane.
• The plant cell wall is mainly composed of cellulose. Cellulose is a complex substance which
provides structural strength to plants.

→ Function of Cell Wall

• Cell walls permit the cells of plants, fungi and bacteria to withstand very dilute (hypotonic) external
media without bursting.
• In such media the cells tend to take up water by osmosis. The cell swells, building up pressure
against the cell wall. The wall exerts an equal pressure against the swollen cell.
• Because of cell wall, cells can withstand much greater changes in the surrounding medium than
animal cells.


• When a living plant cell loses water through osmosis there is shrinkage or contraction of the
contents of the cell away from the cell wall. This phenomenon is known as plasmolysis.

cell organelles

Difference between Animal cell and Plant cell

PMF IAS, Author at PMF IAS - Page 25 of 36Calaméo - cells

Difference Between Plant and Animal Cell Division | Characteristics,  Phases, Comparison

chloroplast, mitochondria, vacuoles, endoplasmic reticulum, Golgi apparatus


• The cytoplasm is the fluid content inside the plasma membrane.
• It also contains many specialised cell organelles. Each of these organelles performs a specific
function for the cell.

→ Function of Cytoplasm

• It helps in exchange of material between cell organelles.
• It act as store of vital chemicals such as amino acid, glucose, vitamins and iron etc.
• It is the site of certain metabolic pathways such as glycolysis.

Endoplasmic Reticulum (ER)

• The endoplasmic reticulum (ER) is a large network of membrane-bound tubes and sheets.
• It looks like long tubules or round or oblong bags (vesicles).
• The ER membrane is similar in structure to the plasma membrane. It is also made up of lipid and

→ Types of Endoplasmic Reticulum

(i) Rough endoplasmic reticulum (RER)
(ii) Smooth endoplasmic reticulum (SER)

→ Functions of Endoplasmic Reticulum

• RER looks rough under a microscope because it has particles called ribosomes attached to its
surface. The ribosomes, which are present in all active cells, are the sites of protein manufacture.
The manufactured proteins are then sent to various places in the cell depending on need, using the
• The SER helps in the manufacture of fat molecules, or lipids, important for cell function.
• Some of these proteins and lipids help in building the cell membrane. This process is known as
membrane biogenesis.
• Some other proteins and lipids function as enzymes and hormones.
• Although the ER varies greatly in appearance in different cells, it always forms a network system.
• One function of the ER is to serve as channels for the transport of materials (especially proteins)
between various regions of the cytoplasm or between the cytoplasm and the nucleus.
• The ER also functions as a cytoplasmic framework providing a surface for some of the biochemical
activities of the cell.
• In the liver cells of the group of animals called vertebrates, SER plays a crucial role in detoxifying
many poisons and drugs.

Golgi Apparatus

• The Golgi apparatus consists of a system of membrane-bound vesicles arranged approximately
parallel to each other in stacks called cisterns.
• These membranes often have connections with the membranes of ER and therefore constitute
another portion of a complex cellular membrane system.

→ Function of Golgi Body

• The material synthesised near the ER is packaged and dispatched to various targets inside and
outside the cell through the Golgi apparatus.
• Its functions include the storage, modification and packaging of products in vesicles. In some
cases, complex sugars may be made from simple sugars in the Golgi apparatus.
• The Golgi apparatus is also involved in the formation of lysosomes.


• Lysosomes are a kind of waste disposal system of the cell.
• It helps to keep the cell clean by digesting any foreign material as well as worn-out cell organelle
• Lysosomes have membrane-bounded structure whose sacs are filled with digestive enzymes.

→ Functions of Lysosomes

• Lysosomes break foreign materials entering the cell, such as bacteria or food as well as old
organelles into small pieces.
• They contain powerful digestive enzymes which are made in RER which is capable of breaking
down all organic material made in RER.
• During the disturbance in cellular metabolism such as when the cell gets damaged, lysosomes
may burst and the enzymes digest their own cell. Therefore, lysosomes are also known as the
‘suicide bags’ of a cell.


• Mitochondria are known as the powerhouses of the cell.

→ Structure of mitochondria

• Mitochondria have two membrane coverings.
• The outer membrane is very porous while the inner membrane is deeply folded.
• These folds create a large surface area for ATP-generating chemical reactions.

→ Functions of mitochondria

• The energy required for various chemical activities needed for life is released by mitochondria in
the form of ATP (Adenosine triphopshate) molecules.
• ATP is known as the energy currency of the cell. The body uses energy stored in ATP for making new
chemical compounds and for mechanical work.
• Mitochondria have their own DNA and ribosomes. Therefore, mitochondria are able to make some
of their own proteins.



• Plastids are present only in plant cells.
• There are three types of plastids:
(i) Chromoplasts (coloured plastids).
(ii) Leucoplasts (white or colourless plastids).
(iii) Chloroplasts (contains the pigment chlorophyll).

→ Structure of Plastids

• The internal organisation of the plastids consists of numerous membrane layers embedded in a
material called the stroma.
• Plastids also have their own DNA and ribosomes like mitochondria and similar to its structure.

→ Function of Plastids

• Chloroplasts are important for photosynthesis in plants.
• Chloroplasts also contain various yellow or orange pigments in addition to chlorophyll.
• Leucoplasts are primarily organelles in which materials such as starch, oils and protein granules
are stored.


• Vacuoles are storage sacs for solid or liquid contents.
• They are small sized in animal cells while plant cells have very large vacuoles.

→ Function of vacuoles

• The central vacuole of some plant cells may occupy 50-90% of the cell volume.
• In plant cells vacuoles are full of cell sap and provide turgidity and rigidity to the cell.
• Many important substance in the life of the plant cell are stored in vacuoles which include amino
acids, sugars, various organic acids and some proteins.
• In single-celled organisms like Amoeba, the food vacuole contains the food items that the Amoeba
has consumed.
• In some unicellular organisms, specialised vacuoles also play important roles in expelling excess

nucleus, chromosomes - basic structure, number


Function of Nucleus Class 9 - CBSE Class Notes Online - Classnotes123

• It is called the brain of the cell as it controls all the activities of cell.
→ Composition of Nucleus

• The nucleus has a double layered covering called nuclear membrane.
• The nuclear membrane has pores which allow the transfer of material from inside the nucleus to
the cytoplasm.
• The nucleus contains chromosomes, which are visible as rod-shaped structures only when the cell
is about to divide.
→ Functions of chromosomes

• Chromosomes contain information for inheritance of features from parents to next generation in
the form of DNA (Deoxyribo Nucleic Acid) molecules. Chromosomes are composed of DNA and
• DNA molecules contain the information necessary for constructing and organising cells.
• Functional segments of DNA are called genes.
• In non-dividing cell, this DNA is present as part of chromatin material.
• Chromatin material is visible as entangled mass of thread like structures. Whenever the cell is
about to divide, the chromatin material gets organised into chromosomes and perform cell division

→ Functions of Nucleus

• The nucleus plays a central role in cellular reproduction. It is the process by which a single cell
divides and forms two new cells.
• It also plays a crucial part, along with the environment, in determining the way the cell will develop
and what form it will exhibit at maturity, by directing the chemical activities of the cell.


• In some organisms like bacteria, the nuclear region of the cell may be poorly defined due to the
absence of a nuclear membrane.
• Such an undefined nuclear region containing only nucleic acids is called a nucleoid.

basic issues in scientific naming, basis of classification


→ The method of arranging organisms into groups or sets on the basis of similarities anddifferences is called classification.

→ It makes the study of wide variety of organisms easy and in systematic manner.
→ It helps to understand how the different organisms have evolved with
→ It helps to understand the inter-relationships among different groups of organisms.
→ It forms a base for the study of other biological sciences, like biogeography.

Basis of Classification

→ There are certain features or properties used for the classification of living organisms which areknown as characteristics.
→ Organisms with same characteristics are placed in same groups.

Classification System

• Two kingdom classification:
Carolus Linnaeus in 1758 classified the living organisms into twogroups as plants and animals.
• Five kingdom classification:
H. Whittaker in 1959 further classified the organisms into fivekingdoms as Kingdom Monera, Kingdom Protista, Kingdom Fungi, Kingdom Plantae and Kingdom Animalia.

→ Carl Woese in 1977 further divided Kingdom Monera into archaebacteria (or Archae) andEubacteria (or Bacteria).

Hierarchy of categories / groups


• Hierarchy of Classification:

Linnaeus proposed a classification system by arranging organismsinto taxonomic groups at different levels according to the characteristics they have.

Groups or Levels from top to bottom

→ The major characteristics considered for classifying all organisms into five major kingdoms.
• Type of cellular organization

(i) Prokaryotic cells: These are primitive and incomplete cells without well defined nucleus.

(ii) Eukaryotic cells: These are advanced and complete cells with well-defined nucleus.

• Body organization

(i) Unicellular organisms: These are organisms made up of single cell with all activities performed the single cell.
(ii) Multicellular organisms: These are organisms made up of large number of cells with differentfunctions performed by different cells.

• Mode of obtaining food

(i) Autotrophs: These are the organisms that make their own food by photosynthesis.
(ii) Heterotrophs: These are the organisms which depend on other organisms for food.

Five Kingdom Classification
R. H. Whittaker taxonomist was the first one to propose five kingdom classification.


(i) Type: Unicellular Prokaryotic
(ii) Mode of nutrition: Autotrophic or heterotrophic
(iii) Body: Lack well-defined nucleus and cell organelles
(iv) Examples: Bacteria, Blue-green algae


(i) Type: Unicellular Eukaryotic
(ii) Mode of nutrition: Autotrophic or Heterotrophic
(iii) Body: Some organisms use pseudopodia or cilia or flagella for movement
(iv) Examples: Amoeba, Paramecium, Euglena


(i) Type: Multicellular Non-green Eukaryotic
(ii) Mode of nutrition: Saprophytic or Parasitic Sometimes symbiotic
(iii) Body: Fungus is made up of long filaments called hyphae. The network of hyphae is mycelium.
(iv) Examples: Yeast, Rhiozpus, Mushrooms moulds


(i) Type: Multicellular Eukaryotic
(ii) Mode of nutrition: Autotrophic
(iii) Body: Exhibits high level of tissue differentiation and have specialized body organs.
(iv) Examples: Trees, Plants, Shrubs


(i) Type: Multicellular Eukaryotic
(ii) Mode of nutrition: Heterotrophic
(iii) Body: Exhibits high level of tissue differentiation and have specialized body organs. They havewell developed nervous system.
(iv) Examples: Fish, Insects, Animals, Humans, Birds

Kingdom I: Monera

(i) Prokaryotic, unicellular.
(ii) Can be autotrophs or heterotrophs.
(iii) May or may not have cell wall.
(iv) Examples: Anabaena and Bacteria (heterotrophic), Cyano-bacteria or Blue-green algae(autotrophic).

Kingdom II: Protista

(i) Eukaryotic, unicellular.
(ii) Can be autotrophic or heterotrophic.
(iii) May have cilia, flagella or pseudophodia for locomotion.
(iv) Examples: Plants like unicellular algae, diatoms; animals like protozoans (Amoeba, Paramecium,Euglena); fungi like slime molds and water molds.

Kingdom III: Fungi

(i) Eukaryotic.
(ii) Mostly multicellular but sometimes unicellular (yeast).
(iii) Source of food:
• Mostly saprophytes:
These organisms use decaying material for food.
• Some parasitic:
These organisms live inside body of other living organism to have food and canbe disease causing.

• Symbiotic relation:

These are relations between two organisms in which they live together forbenefit of one or both.
→ Lichens are a symbiotic relation between fungi and cyanobacteria.
→ Here fungi gets food from cyanobacteria and in return cyanobacteria gets water and protectiofrom sunlight through fungi.
(iv) Cell wall is made of chitin.
(v) Examples: Mushrooms (Agaricus), green mold (Penicillium), smut (Aspergilus).

Kingdom IV: Plantae

(i) Eukaryotic, multicellular.
(ii) Autotrophs.
(iii) Cell wall present.

Major groups of plants (salient features) (Bacteria, Thalophyta, Bryo phyta, Pteridophyta, gymnosperms and Angiosperms).

Basis of division in Kingdom Plantae

(i) Differentiated body parts:
Body is differentiated into leaves, stems, roots, flowers, etc.
(ii) Presence of vascular tissue:
There are two types of vascular tissues present in the plants.
• Xylem: Helps in transport of water.
• Phloem: Helps in transport of food.
(iii) Reproduction through seeds or spores:
• Phanerogamae : Plants with seeds are called phanerogamae. They contains embryo with stored food and are multicellular.
• Cryotogamae: Plants with spores are called cryptogamae. They contains only naked embryo and are generally unicellular.
(iv) Seeds are inside the fruit or naked:
• Angiospermae: These are plants with seeds inside the fruit and bears flowers.
• Gymnospermae: These are plants with naked seeds and do not bear flowers.

Division 1: Thallophyta

(i) Basic and elementary plants with undifferentiated body parts.
(ii) Generally called algae.
(iii) No vascular tissue present.
(iv) Reproduce through spores.
(v) Mainly found in water.
(vi) Example: Ulva, Spirogyra, Ulothrix, Cladophora, Chara.

Division 2: Bryophyte

(i) Body structure differentiated but not fully developed.
(ii) No vascular tissues present.
(iii) Reproduce through spores.
(iv) Found on both land and water therefore known as ‘ Amphibians of Plantae Kingdom’.
(v) Example : Liverwort (Marchantia, Riccia), Mosses (Funaria), Hornwort (Dendrocerous).

Division 3: Pteridophyta

(i) Differentiated body structure – leaves, stems, roots, etc.
(ii) Vascular tissues present.
(iii) Reproduce through spores.
(iv) Examples : Marsilea, fern, horsetails.

Division 4: Gymnosperms

(i) Differentiated body parts.
(ii) Vascular tissues.
(iii) Naked seeds without fruits or flowers.
(iv) Perennial, evergreen and woody.
(v) Examples : Pines (deodar), Cycus, Ginkgo.

Division 5: Angiosperms

(i) Also known as flower-bearing plants.
(ii) Later on flower becomes fruit.
(iii) Seeds are inside the fruit.
(iv) Embryos in seeds have structure called cotyledons. They are also called seed leaves becausemany plants they emerge and become green when they germinate.
Angiosperms are further divided on the basis of number of cotyledons into two parts i.e. Monocotsand Dicots.

Major groups of animals (salient features) (Non-chordates upto phyla and chordates upto classes).

Kingdom V: Animalia
Basis of classification of Animalia kingdom:

• Symmetry
(i) Bilateral symmetry:

It is when an organism can be divided into right and left halves, identical bumirror images, by a single vertical plane.
(ii) Radial symmetry:
It is when an organism is equally spaced around a central point, like spokes oa bicycle wheel.
• Germ layers
→ In embryonic stages there are different layers of cells called germ cells.
• The three different types of germ cells are:
(i) Ectoderm:
It is the outermost layer which forms nail, hair, epidermis, etc.
(ii) Endoderm:
It is the innermost layer which forms stomach, colon, urinary, bladder, etc.
(iii) Mesoderm:
It is the middle layer between ectoderm and endoderm which forms bones,cartilage, etc.

• According to the number of germ layers present in embryonic stage, animal could be:
(i) Diploblastic:
Organisms which are derived from two embryonic germ layers (ecto and endo).
(ii) Triploblastic:
Organisms which are derived from all the three embryonic germ layers.
• Coelom
→ Body cavity or coelom is important for proper functioning of various organs.
→ For example, heart which has to contract and expand needs some cavity or empty space, which is provided by the coelom.
• On the basis of presence or absence of coelom, organisms are divided into:
(i) Acoelomates: These are the simple organisms having no body cavity.
(ii) Coelomates:
These are complex organisms having true cavity lined by mesoderm from all side
→ These are further sub-divided into schizocoelomates or protostomes (coelom formed due to splitting or mesoderm) and enterocoelomates or dueterostomes (coelom formed from pouchespinched off from endoderm).
(iii) Pseudo coelamate:
These are organisms having false coelom. They have pouches of mesoder scattered between endoderm and ectoderm.

• Notochord

→ It is a long rod like structure, which runs along the body between nervous tissues and gut and provides place muscle to attach for ease of movement.
→ Organisms could be:
• without notochord
• with notochord
• with notochord in initial embryonic stages and vertebral column in adult phase.

Phylum 1: Porifera or Sponges

(i) Cellular level of organization
(ii) Non-motile animals
(iii) Holes on body which led to a canal system for circulation of water and food
(iv) Hard outside layer called as skeletons
(v) Examples: Sycon, spongilla, euplectelia

Phylum 2: Coelenterata

(i) Tissue level of organization
(ii) No coelom
(iii) Radial symmetry, diploblastic
(iv) Hollow gut
(v) Can move from one place to another
(vi) Examples: Hydra, sea anemone, jelly fish (solitary), corals (colonies)

Phylum 3: Platyhelminthes

(i) Also called flat worms
(ii) No coelom present
(iii) Bilateral symmetry, triploblastic
(iv) Free living or parasite
(v) Digestive cavity has one opening for both ingestion and egestion
(vi) Examples: Planaria (free living), liver fluke (parasitic)

Phylum 4: Mollusca

(i) Coelom present
(ii) Triploblastic, bilateral symmetry
(iii) Soft bodies sometimes covered with shell
(iv) Generally not segmented
(v) No appendages present
(vi) Muscular foot for movement
(vii) Shell is present
(viii) Kidney like organ for excretion
(ix) Examples: Chiton, octopus, pila, unio

Phylum 5: Annelida

(i) Second largest phylum
(ii) Coelom present
(iii) Bilateral, triploblastic
(iv) Segmented (segments specialized for different functions)
(v) Water or land
(vi) Extensive organ differentiation
(vii) Examples: Earthworm, leech, nereis

Phylum 6: Arthropoda

(i) Largest phylum (consist of 80% of species)
(ii) Generally known as insects
(iii) Coelom present
(iv) Bilateral, triploblastic
(v) Segmented, sometimes fused
(vi) Tough exo-skeleton of chitin
(vii) Joing appendages like feet, antenna
(viii) Examples : Prawn, scorpio, cockroach, housefly, butterfly, spider

Phylum 7: Echinodermata

(i) Spiny skin, marine
(ii) No notochord
(iii) Coelom present, bilateral symmetry, triploblastic
(iv) Endoskeleton of calcium carbonate
(v) Water vascular system for locomotion
(vi) Bilateral symmetry before birth and radial symmetry after birth
(vii) Examples : Antedon, sea cucumber, star fish, echinus

Phylum 8: Protochordata

(i) Marine animals.
(ii) Bilaterally symmetrical, triploblastic and have a coelom.
(iii) Gills present at some phase of life
(iv) Notochord is present which is a long rod-like support structure (chord=string) that runs along back of the animal separating the nervous tissue from the gut.
(v) Notochord provides a place for muscles to attach for ease of movement.
(vi) Examples : Balanoglossus, Herdmania and Amphioxus

Phylum 9: Nematoda

(i) Bilaterally symmetrical and triploblastic.
(ii) Body is cylindrical rather than flattened.
(iii) Tissues, but no real organs.
(iv) Sort of body cavity or a pseudocoelom, is present.
(v) Familiar as parasitic worms causing diseases.
(vi) Worms causing elephantiasis (filarial worms) or the worms in the intestines (roundworm orpinworms).
(vii) Examples: Ascaris, Wuchereria

Phylum 10: Vertebrata

(i) Notochord converted to vertebral column
(ii) 2, 3, 4 chambered heart
(iii) Organs like kidney for excretion
(iv) Pair appendages
(v) Examples: Humans (4-chambered), frog (3-chambered), fishes (2-chambered)
→ Vertebrates are divided into five classes namely Pisces, Amphibia, Reptilia, Aves and Mammalia
• Warm blooded organisms:
These are organisms which maintain same body temperatureirrespective of outside temperature.
Example: Humans. Human’s body temperature is approximately 37º.
• Cold blooded organisms:
These are organisms which change their body temperature as persurrounding temperature.
Example : Frog.

Pisces (Fishes)

→ They are fishes living in water.
→ Their skin is covered with scales or plates.
→ They respire using gills.
→ They have streamlined body and fins which help them to move in water.
→ They are cold blooded and their heart has only two chambers.
→ They lay eggs from which the young ones hatch out.
• Fishes are divided into two categories on the basis of skeleton:
(i) Fishes with cartilage skeleton called cartilaginous fishes. Example : Shark, Rays etc.
(ii) Fishes with bony skeleton called bony fishes. Example : Tuna, Rohu etc.

Amphibia (Amphibians)

→ They are found in land and water.
→ They do not have scales but have mucous glands on their skin.
→ They are cold blooded and the heart is three chambered.
→ Respiration is through gills or lungs. They lay eggs in water.
Example: Frogs, Toads, Salamanders etc.

Reptilia (Reptiles)

→ They have scales and breathe through lungs.
→ They are cold blooded.
→ Most of them have three chambered heart but crocodiles have four chambered heart.
→ They lay eggs with hard covering in water.
→ Example: Snakes, Turtles, Lizards, Crocodiles etc.

Aves (Birds)

→ They are warm blooded animals.
→ They have four chambered heart.
→ They breathe through lungs.
→ They have an outer covering of feathers.
→ Their two fore limbs are modified into wings for flying. They lay eggs.
→ Example: Crow, Sparrow, Pigeon, Duck, Stork, Ostrich etc.

Mammalia (Mammals)

→ They are warm blooded animals.
→ They have four chambered heart.
→ They have mammary glands for production of milk to nourish their young ones.
→ The skin has hairs and sweat glands. Most of them give birth to their young ones.
→ Some of them lay eggs (like Platypus and Echidna).
→ Example: Cat, Rat, Dog, Lion, Tiger, Whale, Bat, Humans etc.


→ An organism can have different names in different languages. This creates confusion in naming
→ A scientific name is needed which is same in all languages.
→ Binomial nomenclature system given by Carolus Linnaeus is used naming different organisms.

Some conventions in writing the scientific names:

(i) Genus should be written followed by the species.
(ii) First letter of the genus should be capital and that of the species should be in small letter.
(iii) When printed the name should be written in italics and when written with hands genus and
species should underlined separately.
Example : Homo sapiens for humans, Panthera tigris for tiger.

Infectious and Non-infectious diseases, their causes and manifestation

Infectious and Non-infectious Diseases

(i) Infectious Diseases: The diseases which spread due to infection by micro-organisms are called
infectious diseases.
→ It is communicated from diseased person to healthy person, caused by some biological
agents/pathogens like viruses, bacteria, fungi, protozoans, fungi worms.

(ii) Non-infectious Diseases: The disease which does not spread by contact between infected and
healthy person through air and water, is called non-infectious disease.
Example: Arthritis, heart disease.

Different Micro-organisms
SARS Viruses

→ SARS viruses are coming out of the surface of an infected cell (see the arrows for example).
→ 500 nanometer = 0.5 micrometer = 0.001 millimeter.
→ Trypanosoma is a protozoan organism.
→ It causes sleeping sickness.
→ The saucer-shaped substance lying next tothe protozoa, is a red blood cell.
Staphylococcus bacteria
→ The Staphylococcus bacteria causes acne.
→ The scale is indicated at the line at the top left of the picture. It is 5 micrometers long.
Adult roundworm
→ Adult roundworm is found in the small intestine.
→ Its technical name is Ascaris Lumbricoides.
→ The ruler next to it shows 4 centimeter to give an idea of the scale.
→ Leishmania, the protozoan organism causes kala-azar.
→ The organisms are oval-shaped, and each has one long whip-like structure.
→ The immune cell is about ten micrometres in diameter.


→ Antibiotics blocks biochemical pathways important for bacteria. Hence, they are effective against
them. Example: Penicillin, tetracycline.
→ Many bacteria make a cell wall to protect themselves, the antibiotics (Penicillin) blocks the
bacterial process that builds cell wall.
→ Antibiotics works only against the bacteria and not against the viruses.

Means of Spread of Infectious Diseases


→ Infectious diseases spread from an infected person to a healthy person through air, water, food,
vectors, physical contact and sexual contact.
• Through air: By sneezing and coughing, the microbes spread into air and enter into the body of
healthy person, like common cold, tuberculosis, pneumonia etc.
• Through water : The microbes enter into our body by drinking/eating polluted and contaminate
water/food, like cholera, amoebic dysentery etc.
• Vectors: Some organisms like female anopheles mosquito also work as a vector of disease, like
malaria, dengue, yellow fever etc.
• Through sexual contact: Syphilus, AIDS spread by sexual contact with infected person. AIDS virus
can also spread through blood transfusion and from the mother to her child during pregnancy an
through breast feeding.

Diseases caused by microbes (Virus, Bacteria and protozoans) and their prevention

Revision Notes for Science Chapter 13 - Why do we fall ill (Class 9th) |  askIITians

Principles of treatment and prevention

Principles of Treatment

→ The treatment of infectious diseases consists of two steps. They are to reduce the effects of the
disease (symptoms) and to kill the microbes which caused disease.
(i) To reduce the effects of the disease: This can be done by taking medicines to bring down the
effects of the disease like fever, pain or loose motions etc. and by taking bed rest to conserve our
(ii) To kill the microbes: This can be done by taking suitable antibiotics and drugs which kills the
microbes and the disease is cured.

Principles of Prevention

• There are two ways of prevention of infectious diseases. They are general ways and specific way
(i) General ways of prevention: Public hygiene is most important for prevention of infectious
diseases. Proper and sufficient food for everyone will make people healthy to resist the infection.
→ Air borne diseases can be prevented by living in conditions that are not crowded. Water borne
diseases can be prevented by providing safe drinking water.
→ Vector borne diseases can be prevented by providing clean environment.

(ii) Specific ways of prevention: There are disease specific measures which are used to fight them
It is done by Immunisation.
→ This is the process of introducing a weakened pathogen inside the body of the host to fool his/h
immune system to produce antibodies against that particular disease.
→ Not only does our immune system fight the disease (feeble pathogen), but also keeps a memo
of the incident by keeping those antibodies in blood.
→ Thus, next time even if the disease will strike the host’s body with full vigor, the body will be able
protect itself with the help of these antibodies.
→ This is also the basic law followed by vaccination programmes done for infants.

Classification of infectious diseases based on their causative agents.... |  Download Scientific Diagram

Pulse Polio programmes.

Pulse polio programme-

Pulse polio immunization programme forms the largest single day public health project. Pulse means a dose of a substance (here polio vaccine) especially when applied for a short period of time. It was conducted for the first time in 1995. The program uses oral polio vaccine or OPV. As per the national immunization Schedule (NIS), a dose of 3 drops is given orally to the child, i.e. one dose each at 1.5, 2.5 and 3.5 months age. Finally a booster dose si given at the age of 1.5 years. After oral administration. Virus particles in the vaccine begin to live in the intestine of the human body and multiply. It leads to production of protective molecules in the intestine and the blood.

1. About Cell and Cell Theory

The Fundamental Unit of Life

Introduction of cell

The introduction to cell began back in the year 1655 when a revolutionary observation was made by an English scientist Robert Hooke. 
In all the living beings, cells are the basic structural units. We can compare the presence of cells in our body to the bricks in a building. All the bricks are assembled to make a building. Similarly, all the cells are assembled to make the body of an organism. 
Thus, it is the basic structural and functional unit of life and all the organisms are made up of cells. The subcellular structures of the cell comprise of the plasma membrane, organelles and in some cases a nucleus as well. As for the size of the cell, it is variable and maybe anything from 1 to 100 micrometre.
Robert Hooke was examining a dried section of the cork tree using a crude light microscope. In this analysis, he observed multiple small chambers which he named the cells. 
The first theory was proposed by the German botanist Matthias Jacob Schleiden and the German physiologist Theodore Schwann in 1838. This theory was formalized in the year 1858 by the German researcher Rudolf Virchow by suggesting that all cells arise from pre-existing cells.


Cell Theory

•    The cell is the basic functional and structural unit of life. All the living organisms are composed of cells.
•    All cells are formed by the division of the already existing cells which in terms of biology means reproduction.       Every cell of our body comprises of genetic material which is passed down during the process.
•    All the basic physiological and chemical functions i.e. the growth, repair, movement, communication, immunity and digestions are performed inside the cells.
•    All the activities of the cell depend mainly on the activities of the subcellular structures that lie within the cell. These subcellular structures comprise of the plasma membrane, organelles and if present, the nucleus.

Types of Cells

Broadly, there are two key types of cells i.e., the Prokaryotic Cell and the Eukaryotic Cell. The difference between the two is defined mainly by the presence or the absence of the nuclear membrane.

  1. Prokaryotic Cell

 If a cell has a nuclear material without a nuclear membrane, then it is known as the prokaryotic cell, where ‘pro’ stands for primitive and ‘karyon’ stands for the nucleus. Some of the organisms that have prokaryotic cells include bacteria and the blue-green algae.

  1. Eukaryotic Cell

If a cell has a nuclear material with a nuclear membrane, then it is known as the Eukaryotic Cell, where ‘EU’ stands for true and ‘karyon’ stands for the nucleus. All the living organisms except bacteria and blue-green algae have Eukaryotic Cells.

1. About Cell and Cell Theory


The Fundamental Unit of Life

About Cell and Cell Theory

Introduction of cell

As you all know the body of an individual is of complex type. If we study about the detailed structure of the human body or of any lower organism, we will come across many things that makeup the body. But at the smallest level, our body is made up of tiny units called cells. Let us learn about cell in detail.

Cell is often referred as “structural and functional unit of living organisms”. The reason is that the cell is the smallest unit of body and directly or indirectly, it is responsible for functions also. If we study about the hierarchy then we will notice that the level of organization is :

That means that the smallest unit of body is cell.

Discovery of cell

The cell was discovered by Robert Hooke in a thin slice of cork in 1665. Cork is actually a dead part of tree that is bark of tree .He discovered it with the help of instrument called microscope. This microscope is an instrument that enables us to see those things that can’t be otherwise seen with the help of naked eye. It has the property to magnify the objects. He discovered with the help of instrument that is microscope which was discovered by Anton von Leeuwenhoek.

When he saw the internal structure of cork with the help of microscope it looked like compartments .So, earlier these cells were named as compartments but later on it was replaced by term cell. It was concluded that all the cells have three basic characteristics. –

  • They contain plasma membrane: – made up of lipid & proteins
  • They contain genes: – Genetic material in form of DNA or RNA containing genes is present.
  • They contain metabolic machinery: – Cytoplasm is present which contain organelles like mitochondria etc.

These all arts like plasma membrane, cytoplasm, RNA, DNA etc will be taken in to consideration step wise step. Let us first learn more about cell.

Cell theory

To know more about cell, few scientists sum up their views about cell as cell theory. It was given by volunteers: Sheldon & Schwann. According to this theory: –

  • Cell is the structural unit of life.
  • Cell is functional unit of life.
  • All cells arise from pre-existing cells. Every organism starts life as a single cell. (It was given by R. Virchow)

Types of cells – Prokaryotic and Eukaryotic cells

There are two main types of divisions of cells depending upon their basic and important difference in their structures. The types are:

  • Prokaryotic (primitive cell)
  • Eukaryotic (advanced type)

Prokaryotic and eukaryotic cell: The basic difference between the two is: In prokaryotic, the nuclear material lies naked in cytoplasm that is no special membrane is present that separates it from the cytoplasm. It is present as such in cytoplasm.

 In eukaryotic, the nuclear material is well protected and enclosed by special membrane that is nuclear membrane .We can say in it the nucleus is present. Let us some up more difference in them.

Cell shape and Cell size

Now, let’s talk about the cell shape and size. It is seen that cells can be of different shapes and sizes and even their number that make up a body can be different in different living forms as it depends upon the function the cell is going to perform. Accordingly the structures, sizes, shapes are assigned to cells . The shape of a cell may change or fixed.

Shape of cells

  • The shape can be fixed or can be variable.
  • The cells with Variable shape are WBC (white blood cell) and Amoeba.

Please do remember that “the shape of the cell depends upon the function it performs”.

Different Shapes that the cell can have: –

  • Spherical => eggs of many animals
  • Spindle shaped => smooth muscle fiber
  • Elongated => nerve cell
  • Branched => cells of skin
  • Discoid => RBC.


Size of cell

Sizes also show a lot of variations. We have cell that is too tiny like PPLO to largest cell in the form of an ostrich egg

In Human body the smallest cell is: – RBC and longest /largest is Nerve cell .Nerve cell is designed accordingly  to function it performs. As we cleared above also shapes are in accordance to function. Like, nerve cell help in transmission of impulse. So, it has to be long and branched.

Cell number

The number of cells also varies from species to species. There can be organism made up of one cell and there can also be organism like us whose body is made up of many cells. Depending upon the number of cells present, cells are of two types:

  • Unicellular
  • Multicellular

Unicellular organisms – are single celled body (example Amoeba).

Multicellular organisms – are multi-celled body that is many cells (example Man)

Structure of cell

If we look at the structure of cell we have already seen that all cells have three things in common:

  • Cell membrane
  • Nuclear material
  • Metabolic machinery.

 Let us study about cell membrane first:

2. Cell Membrane and Cell Wall

Cell Size

The cell size is variable. In the living organisms, the cell size may be as small as a millionth of a metre or may be as large as a few centimetres. Usually, all the cells are microscopic in size and aren’t visible to the naked eye. Thus, they need to be enlarged by a microscope for seeing.

Cell Shape

  • Usually, the cells are round, elongated or spherical.
  • There are also some cells which are long and pointed on both the ends. Such cells exhibit spindle shape.
  • In some cases, the cells are very long.
  • Some may be branched like the neuron or the nerve cell. The nerve cell transfers and receives messages.

It, therefore, helps in coordinating and controlling the working of the different parts of the body. The components of the cell are enclosed in a membrane. This membrane provides shape to the cells of animals and plants. There is a cell wall surrounding them. The cell wall is an additional covering over the cell membrane in the plant cells. It offers rigidity and shape to the cells.

Depending on the purpose, the cell takes on a number of forms. Cells come in a variety of forms, including:

Skin cells

  1. These skin cells have a flat surface.
  2. They are a protective body cover with a flat form that allows them to cover a large area.

Muscle cells

            i. Muscle cells are long, thin, and elongated.
            ii. Muscle cells expand and contract, and their long and thin structure aids in this process.

Nerve cells

            i. These nerve cells have a lengthy fibrous structure.
            ii. Long, thin extensions (axons and dendrites) connect these nerve cells to other nerve cells.
            iii. The extensions aid the neuron in swiftly transmitting chemical and electrical information throughout                    the body.
            iv. Nerve cells can contain fibres that are over a metre long.
             v. Messages are transmitted down these fibres from one nerve cell to the next.

 Blood cells

            i. White blood cells are disc-shaped but have the ability to alter form.
            ii. WBC in the blood alters their form to kill bacteria or any pathogens that are disease-causing                                organisms.                                                                                                                                                           
iii. The structure of red blood cells (erythrocytes) allows them to pass through capillaries with ease.

Plant cells

            i. Depending on their purpose, plant cells might be rectangular, circular, oval, or elongated. Plant cells                   on the outside of the stem give the plant its strength.
            ii. For support, these cells have strong cell walls. Food is stored in specific cells in plants, and these                       cells are bigger than other cells.

Cell Wall

           The cell wall is the outer covering of a cell, present adjacent to the cell membrane, which is also called the plasma membrane. The cell wall is normally present in all plant cells, fungi, bacteria, algae, and some archaea. Animal cells are not regular in their shape and this is mainly due to the lack of cell walls in their cells. Cell wall composition usually varies along with organisms.

The Function of the Cell Wall

There are various functions of cell wall like:

•    The cell wall of the plants provides definite shape, strength, and rigidity.
•    The cell wall also protects against mechanical stress and physical shocks.
•    Cell wall helps to control cell expansion due to the intake of water.
•    The cell wall also helps in preventing water loss from the cell.
•    The cell wall is responsible for transporting substances between and across the cell.
•    The cell wall acts as a barrier between the interior cellular components and the external environment.

Cell Membrane

•    The cell membrane is also called the plasma membrane. 
•    Cell membrane is found in all cells and separates the interior of the cell from the outside environment.
•     The cell membrane also consists of a lipid bilayer that is semipermeable. 
•    The cell membrane is also responsible for the transportation of materials entering and exiting the cell.
•     The thin membrane surrounds every living cell, fixing the cell from the environment around it. 
•    The cell membranes are the cell’s constituents, often large, water-soluble, highly charged molecules such as proteins, nucleic acid, carbohydrates, and substances involved in cellular metabolism. 
•    The surrounding of the cell membrane is a water-based environment, containing ions, acids, and alkalis that are toxic to the cell, as well as nutrients that the cell must absorb to live and grow. 

Functions of the Cell Membrane

•    There are various functions of cell membrane-like:
•    The cell membrane protects the integrity of the interior cell.
•    The cell membrane provides support and maintains the shape of the cell.
•    The cell membrane helps in regulating cell growth through the balance of endocytosis and exocytosis.
•    It also plays an important role in cell signalling and communication.
•    The cell membrane acts as a selectively permeable membrane by allowing the entry of only selected substances into the cell.




2. Cell Membrane and Cell Wall

Cell Membrane and Cell Wall

Cell membrane and cell wall

This gives a covering to all cells and the characteristics that it possess are listed below :

  • It is present in both plant & animal cell
  • It is an outer covering of cell
  • It is living, thin and delicate membrane.
  • It is semi-permeable – “allows selective particle to pass through.”
  • It is made up of lipids & proteins.

It allows only selected substances to move through it .The movement of substances takes place by activities like: –

  • Diffusion – “movement of molecules from higher concentration to lower concentration”.  It is mostly seen in case of Gases.   For example: Cell respire i.e. intake of O2 & giving out CO2 take place through diffusion.
  • Osmosis: “movement of solvent molecules from higher cone. to lower conc. across the semi-permeable membrane.

Functions of plasma membrane are as follows

a) It provides support to cell

b) It allow exchange of materials.

c) It provides shape to the cell.

In plant cells outer to cell membrane another layer or covering is present called as cell wall. It is present in all plant cells .It is somehow different from cell membrane in many aspects as it is listed below .

Cell wall

  • It is outer to cell membrane
  • It is dead
  • It is present only in plant cell
  • It is made up of cellulose (in fungus it is made of chitin)
  • It is freely permeable

Functions of cell wall are as follows –

  • It   provides mechanical support to cell.
  • It allows materials to exchange.
  • It maintains the shape of cells.

Now, if we go into detail, we can say that cell consist of cell membrane and it encloses called a living material protoplasm. Protoplasm is defined as living material of cell. The term protoplasm was coined by: J.E Purkinjee. It is further divided into two parts:

  • Nucleus (discovered by Robert Brown)
  • Cytoplasm


Like we have brain, the cell has a nucleus. All the activities are controlled by nucleus. It is located in the centre of the cell. It consists of different components:

1. Nuclear membrane

2. Nucleoplasm

3. Nuclear material

4. Nucleolus

1. Nuclear membrane: -It is the membrane that separates the nucleus from the cytoplasm. The membrane has pores in it which allow only selected exchange of materials. It is therefore called semi permeable in nature.

2. Nucleoplasm: It is the liquid in the nucleus that is cytoplasm of nucleus. It is similar to cytoplasm outer to nucleus except that it lacks organelles.

3. Nucleolus: It is a small oval body rich in proteins and RNA, RNA is ribonucleic acid and it is the genetic material. It is site for ribosome formation. That is why it is often termed as factory for ribosome.

4. Nuclear material: It contains thread like structures which further condense at the time of cell division to ribbon like structures called chromosomes. These chromosomes are made up of DNA and proteins. There are segments of DNA that are responsible for characters in a body or transfer of characters from parents to offspring and are called genes. They act as hereditary vehicles.

Functions of nucleus are as follows

  • It regulates the cell cycle.
  • It controls metabolic activities of cell.
  • It contains genes that help in transmission of characters from parents to offspring .


It is the liquid material of cell. Its soluble part is called cytosol. It contains organelles. These organelles perform necessary functions for the cell like some organelles help in cleaning the cell, some help in synthesizing certain substances for the cell, some perform catabolic function like breakdown of food, etc. Let us study them in detail:

1. Introduction-Biodiversity

Diversity in Living Organisms



  • We all know that there are abundant of living organisms present on the earth. Many organisms are not identical to each other.
  • This variety of living beings present on the earth is called as a Biodiversity.
  • Here is a separate branch of Biology called Taxonomy which identifies, names and classifies different organisms present on the earth.
  • Carolus Linnaeus is known as the Father of the Modern Taxonomy.
  • Binomial nomenclature is the naming of organisms with two names- genus and species.
  • It was first established by Carl Linnaeus and later adopted by all scientists for the universal naming of organisms.
  • The Law of priority is established if the same name is shared by two different species or two different taxa.
  •  Taxonomy deals with the identification, nomenclature, and classification of organisms. 


2. Classification System

                                              Classification of Living Things                                                             

•    Classification presented by Aristotle – He classified animals on the basis of their habitats – land, water and air.
•    But it can be easily observed that the animals that live at a particular habitat say land are still so different from each other.
•    Therefore, it was decided to classify the living organisms on the basis of a hierarchy.
•    This hierarchical classification was based on the similarities and dissimilarities in the characteristics of the living organisms.
•    Organisms having similar characteristics were placed in a similar category.

  Why do we need to classify organisms?
1. If we classify organisms into several categories, it will be easier for us to study them.
2. It will help us in understanding how did these organisms evolve.
3. We can also understand how different organisms are related to each other.
4. We can learn why different organisms are found at distinct geographical conditions.

Hierarchy Classification - Formation of Kingdoms
Biologists categorized different organisms into several kingdoms.


Proposed by

Type of organisms


Two kingdom classification

Carolus Linnaeus in 1758

1. Plants 


2. Animals


Five Kingdom classification

Robert Whittaker in 1959

1. Monera


2. Protista 


3. Fungi


4. Plantae


5. Animalia


Carl Woese in 1977 

1. Monera


(i) Archaea


(ii) Eubacteria


2. Protista 


3. Fungi


4. Plantae


5. Animalia






 The order of Classification

1. Kingdom
2. Phylum / Division
3. Class
4. Order
5. Family
6. Genus
7. Species
Species is called as the Basic Unit of Classification. Species is a group of organism which can interbreed with each other. The picture below explains how humans are classified in a hierarchical order.

Hierarchical Order of Classifying Humans

Five Kingdom Classifications


                                                                                      Five Kingdom Classification

  • The organization inside the cells
    • Prokaryotic Cells – Cells with no definite nucleus
    • Eukaryotic Cells – Cells with a definite nucleus
  • The organization of cells in the body


    • Unicellular – Single-celled organisms
    • Multicellular – Multi-cell organisms
  • organisms obtain their food


    • Autotrophs – Produce their food on their own 
    • Heterotrophs – Depend on other organisms for their food


                                                          Classification of Organisms       

Classification of Organisms







Organization inside the cells

Consists of Prokaryotes.

Eukaryotes – some of them use appendages to move around such as flagella (whip-like structure) and Cilia (hair-like structure)




Organization of cells in the body



Initially unicellular. Can become multicellular in later stages of life 



Organisms obtain their food 

Some of them are autotrophs like blue green algae while others are heterotrophs

Both autotrophs and heterotrophs 

Heterotrophs. Most of them are decomposers or may be parasitic.



Presence of cell wall

Some lack a cell wall while others have a cell wall 

Only some have cell wall 

Have cell walls. They are made up of complex sugar called chitin.

Have cell walls made of cellulose.

No cell walls


Blue-green algae, Bacteria, Mycoplasma

Protozoan, Diatoms and Golden algae

Yeast and Mushroom ( Agaricus), Rhizopus ( Bread mould), Pencillium

Flowering plants, moss 

Insects, reptiles 

Archea Kingdom

    The monera kingdom is further classified as Archaea.
    These are microbes (bacteria) that can live in harsh conditions. Since they can live in extreme temperatures, they are also called Extremophiles
    These organisms lack a cell wall. 
    Their cell membrane is made up of lipids.
They are further classified into three categories, based on their habitat:




These are salt loving bacteria. They live in extremely salty water.

They live in boiling water such as hot springs and volcanoes.

They are found in the guts of animals like cow and sheep. They produce methane gas from their dung. 


Who are Saprophytes?
Fungi also called as Saprophytes because they grow over the organic material and survive on them.
What are Symbiotic relationships?
Some species of fungi live in permanent mutually dependent relations with blue-green algae. They are said to have a symbiotic relationship. For Example, Lichens are often found on the bark of the trees.

3. Plant Kingdom

Kingdom Plantae

Plant Kingdom

•    Components of Plants – whether they are distinct or not
•    Presence of Special Tissues in plants for the transportation of food and water
•    Presence of Seeds – whether the seeds are present inside the fruits or not.
Classification of plants on the ability to produce seeds -
•    Cryptogams – These plants do not have well developed reproductive organs. The organs cannot be seen clearly as well and appear as if they are hidden. Example are Thallophyte, Bryophyta and Pteridophyte.
•    Phanerogams – These plants have well developed reproductive organs hence they can produce seeds. They are further classified as the ones which have seeds hidden inside fruits or not - Gymnosperms and Angiosperms






Components of plants

No distinct components. Undifferentiated Body 

Little differentiated body. Distinct components are present as leaves and stem 

Distinct components are present as roots, leaves and stem

Presence of special tissues- Vascular tissue




Presence of seeds




Found in  

Aquatic environment, snow

First terrestrial plants but but need water for sexual reproduction. So called as Amphibian of plant kingdom.

Terrestrial or dry areas 


Spirogyra, Ulothrix, Volvox

Moss and liverworts






The ability to produce seeds

Naked seeds

Seeds develop in an organ which then turns into the fruit


Exist for long time periods, Evergreen 

Grow for varied time periods 


Woody, No flowers

Flowering plants


Gymno – naked 

Angio – Covered 

Sperm – seeds 

Sperma – seeds 


Pines, Deodar

Mustard, Maize


What are Cotyledons?

The seed leaves in Angiosperms are called Cotyledons. They turn green on the germination of the seeds. Angiosperms can be divided into two types on the basis of the presence of cotyledons in them-

  • Monocotyledons or monocots
  • Dicotyledons or Dicots


Monocotyledons or Monocots

Dicotyledons or Dicots

Cotyledons (Seed Leaves)

Single Cotyledon

Two Cotyledons


Long leaves, with parallel veins

Broad leaves with network of veins



Long taproot

Floral Parts

Multiples of three

Multiples of four or five


Corn, Wheat, Grass

Rose, Sunflower, Lily

4. Animal Kingdom

Kingdom Animalia

Basic Characteristics of the Animalia Kingdom

1. Animals are eukaryotic, multicellular organisms that lack a cell wall.
2. They are heterotrophs therefore they rely on others for food.
3. They have a growth pattern. The adult animals have a specific shape and size.
4. Most of the organisms have well-defined organ systems such as Respiratory System, Digestion System and so on.
5. Most of the animals can move. They aren’t stationary as Plants.
6. Animals have a nervous system which is why they are able to respond to an external stimulus.

Animals are classified on the basis of differences in their body type and design. The body cavity or coelom in animals contains the organs. Based on the presence of body cavity animals can be categorized as:

1. Coelomate – They have true body cavity called Coelom
2. Pseudocoelomate – It means false cavity. They have a body cavity which is filled with fluid
3. Acoelomate – They have no body cavity at all.

1. Phylum - Porifera

Phylum- Porifera

•    Level of Organization – Cells are present
•    Symmetry – Asymmetrical
•    Segmentation – No segments
•    Body Cavity/ Coelom – No
•    Presence of Organs – No
•    Examples – Sycon, Spongilla, Euspongia
•    Other Characteristics-
o    They cannot move and are attached to a support.
o    They have pores in their body
o    These pores form a Canal system through which water and food circulate in the body and waste is removed.

o    They have a skeleton made of spongin protein and calcium carbonate – hard covering on them

2.Phylum - Coelentrata

                                                                          Phylum- Coelenterata 

•    Level of Organization – Tissues, Cells have two layers – so called as Diploblastic Organism
•    Symmetry – Radial
•    Segmentation – No segments
•    Body Cavity/ Coelom – No
•    Presence of Organs – No
•    Examples – Aurelia (Jelly fish) and Adamsia (Sea Anemone)
•    Other Characteristics –
o    Some of them live in colonies - They are physically attached to each other such as Corals
o    Some of them live solitary such as Hydra

3.Phylum - Platyhelminthes

                                                                         Phylum Platyhelminthes

•    Level of Organization – Organs, The cells have three layers – so are called Triploblastic
•    Symmetry – Bilaterally Symmetrical - Left half of the body is identical to the right half
•    Segmentation – No segments
•    Body Cavity/ Coelom – No so called as Acoelomates
•    Presence of Organs – Yes
•    Examples – Taenia solium (Tapeworm), Fasciola hepatica (Liver Fluke)
•    Other Characteristics -
o    They have a flat body and thus are called Flatworms
o    They can be Free-living like Planaria or parasitic.

4. Phylum- Nematode

                                                                               Phylum Nematoda

•    Level of Organization – Tissues so are called Triploblastic
•    Symmetry – Bilaterally Symmetrical - Left half of the body is identical to the right half
•    Segmentation – No segments
•    Body Cavity/ Coelom - False body cavity so called as Pseudocoelomates
•    Presence of Organs – Organ System Level Organisation
•    Examples – Parasitic worms and worms in the intestine
•    Other Characteristics–
o    They are called as Round Worms.
o    Sexual dimorphism visible - Female and male worms are distinct.

  • 5. Phylum Annelida

                                                                           Phylum Annelida

•    Level of Organization – Organ system level, the cells have three layers so called Triploblastic
•    Symmetry – Bilaterally Symmetrical
•    True Segmentation – Present  (organs can be identified separately)
•    Body Cavity/ Coelom – True body cavity so called as Coelomates
•    Presence of Organs – Definite organs 
•    Examples – Leech, Earthworms
•    Other Characteristics –
o    They are found in freshwater and marine water.
o    They have closed Circulatory system.

6. Phylum Arthropoda

                                                                           Phylum Arthropoda

•    Level of Organization – Organ systems
•    Symmetry – Bilaterally symmetrical
•    Segmentation – Present (organs can be identified separately)
•    Body Cavity/ Coelom – True body cavity
•    Presence of Organs – Definite organs 
•    Examples – Prawns and butterflies
•    Other Characteristics
o    They have jointed legs
o    They have an open circulatory system – There are no well-defined blood vessels
o    They have chitinous exoskeleton


7. Phylum - Mollusca



Phylum Mollusca

•    Level of Organization – Organ systems, the cells have three layers– called Triploblastic
•    Symmetry – Bilaterally symmetrical
•    Segmentation – Little segmentation 
•    Body Cavity/ Coelom – Reduced
•    Presence of Organs – Definite organs 
•    Examples – Snails
•    Other Characteristics
o    Body is divided into head, Visceral Mass and Muscular Foot.
o    Some of the molluscs have hard external shell like that of Snails and some have internal reduced shell like that in Octopus.
o    They have an open circulatory system
o    There is a kidney-like organ for excretion


1. Introduction

Why do we fall ill


Health is a state of complete physical, mental and social well-being.

Basic conditions for good health:

•    Proper balanced and nutritious diet.
•    Personal hygiene.
•    Clean environment and surroundings.
•    Healthy air, no pollution in the surrounding.
•    Regular exercise.
•    Proper rest.
•    Good standard of living and economic status.

Disease: when the body is not at ease i.e., comfortable then it is said to have a disease.
When there is a disease, the functioning or appearance of one or more systems of the body changes.

Disease is classified as Acute and Chronic.

Acute disease: Diseases that last for only short period of time, e.g., headache, common cold etc.
Chronic disease: Diseases that last for long time,’ are called chronic diseases, e.g., elephantiasis, tuberculosis, etc.

Causes of diseases: Immediate cause and contributory cause.

Immediate cause: The organisms that enter our body and causes disease is called immediate cause. For example, virus, bacteria, protozoa etc.

Contributory cause: The secondary factors which led these organisms enter our body are called as contributory cause. For example, dirty water, unclear
surroundings, contaminated food, improper nourishment, poverty, poor standard of living etc.
Diseases may be due to infectious and non-infectious causes.

(a) Infectious causes: Diseases where microbes are the immediate causes are called infectious diseases. The infection spreads from one person to another.

(b) Non-infectious causes: Some diseases that do not spread in the community, but remains internal are called non-infectious diseases. Example, cancer, genetic abnormalities, high blood pressure etc.

2. Types of Diseases

Infectious diseases (Communicable diseases): When a disease-causing organism enters our body it causes infection, it multiplies and grows in the body called host and micro-organisms multiplies in the host body.
Non-Infectious diseases (Non communicable diseases): Diseases that are not contagious are called non-infectious or non-communicable diseases because they can't be spread from one person to another. So, there's no vector for them to move from one host to another, no virus, no bacteria, no pathogen.
Instead, these diseases are caused by other factors, such as genetics, environment, and lifestyle behaviours.

3. Mode of Transmission of Diseases

Infectious diseases spread through:

•    Air: Causes air-borne diseases due to bacteria, virus e.g., common cold, influenza, measles, tuberculosis.
Food and water: Is caused due to contaminated food and water that contains bacteria, virus, worm etc. Example, cholera, typhoid and hepatitis.
Contact: Many diseases spread by contact of infected person with the healthy person. Examples, fungal infection, scabies etc.
AIDS and syphilis spread due to sexual contact.
Body fluids: Body fluids like blood, semen, mother milk when infected can also cause disease. Example, AIDS.


1. Introduction and Plant Tissues



•    Living organisms in this world comprise of cells.
•    There are unicellular as well as multicellular organisms present in this world.
•    In unicellular organisms, the only single cell is capable of performing several functions such as Respiration, Digestion and Clearing of the cell.
•    In multicellular organisms, there is a division of labour. There are different types as well as groups of cells that perform different functions in a multicellular organism.
•    Cells form groups cells that need to perform a single task often group together.
•    This grouping of cells together to perform a function efficiently is called a Tissue. For Example, Muscles and Blood.
•    The tissue cells have the same structure and they perform the same function.

Plant Tissues

                                                      Types of Plant Tissues

Meristematic Tissue

•    Only certain parts of a plant tend to grow. The tissues located in such parts are called meristematic tissues.
•    They have the capability to divide themselves and form new tissues. They have thin cell wall made of cellulose. Also have dense nucleus and cytoplasm but lack vacuoles.
•    They can further we classify differently based on the areas of the plants where they are located -
o    Apical
o    Lateral
o    Intercalary


                                                                                Location of meristematic tissue

Apical Meristem 

Lateral Meristem

Intercalary Meristem

  • They are responsible for the growth of stems and roots in the plants
  • They are found on the tips of the roots and stems. 
  • They are responsible for increasing the circumference of the middle part of the stem and hence are found there.
  • These tissues are present at internodes or stem regions between the places at which leaves attach.

                        Why there are no vacuoles in the intercalary meristem?

  • Vacuoles are responsible for storage of food in water. The intercalary tissues do not store them. They are rather responsible for manufacturing them.
  • Moreover, vacuoles contain sap which provides rigidity to a cell. This property of vacuoles may not allow the intercalary tissues to divide and manufacture new cells. Hence vacuoles are not present in them.

1. Introduction and Plant Tissues



Introduction and Plant Tissues


As you all know that we have a complex body organization starting from cellular level to a well-developed individual. If we look at the hierarchy of organization we see that:

Cells → Tissue→ organ→ organ system→ organism

As far as cells are concerned, we have studied that cells are structural and functional units of life. The cells, when formed, undergo the process of differentiation according to the functions that they will perform. The cells that have the same structure, features and perform the same functions form a particular type of tissue. Let us start with the chapter where we will learn all about it.

The cells which are specialized in a function are grouped together and form a particular type of tissue. We have different tissues in our body that performs different functions like:

1. They play the role of protection.

2. They help in control and coordination.

3. They help in transportation.

4. They act as insulators.

5. Many more functions are performed.

Let us learn about Plant tissue

Types of plant tissues

They are classified into mainly two types as given below

  • Meristematic tissue
  • Permanent tissue

Meristematic tissue and its types

You all have seen that plants have a tendency to grow and keep growing throughout their life. This is because of certain cells in it that keep on dividing and they are called meristematic cells. Let us learn about them. They are formed of cells that have the ability to divide continuously throughout their life and help in increasing the length and girth of the plant.

Characteristics of meristematic cells

  • They have thin cellulose cell walls.
  • The meristematic cells may be spherical, oval, polygonal or rectangular in shape. The meristermatic cells are compactly arranged.
  • Each meristematic cell contains dense or abundant cytoplasm and a single large nucleus.
  • The meristematic cells contain few vacuoles or no vacuoles at all.


According to their position in the plant, meristems are of three types:

  • Apical meristem
  • Lateral meristem
  • Intercalary meristem

Apical meristems

  • It is present at the growing tip of stems and roots. It is at shoot apex and root apex.
  • Its function is to increase the height of the plant.

Lateral meristems

  • These are found beneath the bark (called cork cambium).
  • The function is to help increase in diameter.

Intercalary meristems

  • It is located at the base of leaves or at internodes.
  • Its function is to increase the number of branches.

2. Permanent Tissues

Permanent Tissue

The cells that are formed by the meristematic tissues often have to take a certain role in the plant and thus, they lose their ability to divide and form more cells. They then become the permanent tissues of the plants.

  • Differentiation - The process by which cells of the meristematic tissues convert themselves into a permanent tissue by taking a fixed shape, size and function is called differentiation.
  • Types of Permanent Tissues:
    • Simple Permanent Tissues
    • Complex Permanent Tissues
    • Parenchyma
    • Chlorenchyma
    • Aerenchyma
    • Collenchyma
    • Sclerenchyma






These tissues are responsible for photosynthesis, storage of food, gaseous exchange and floating of plants. 

These tissues are responsible for providing flexibility to the plants so that they can bend easily. 

These tissues are responsible for making plants hard and rigid. 

They are a group of living cells with cell wall made of cellulose.

They are a group of living cells with cell wall made of cellulose and pectin.

They are made up of dead cells having cell wall made of lignin. 

The parenchyma cells have large intercellular spaces between them.

They have a little intercellular space in between them.

The cells do not have any intercellular spaces.

There are thin walls that surround each cell.

The cells present in these tissues are broad and irregularly thick at corners. 

The cells have a long structure with thick walls.

They are found in leaves and newly formed branches.

They are present in leaves and stems of a plant.

They are found in stems, veins of the leaves and coverings of nuts and seeds.



  • These tissues are similar to that of parenchyma but they also contain chlorophyll in them.
  • Due to the presence of chlorophyll, they are capable of performing the process of photosynthesis in plants.


  • They are found in aquatic plants.
  • They are also similar in structure to that of the parenchyma but they have large air cavities in them.
  • These cavities allow the aquatic plants to float in water.

What is Lignin?

The cell walls of dead cells have a substance called lignin in them which provides rigidity to the cells. Lignin acts as the cement for the cells.


  • The outermost layer of the cell is known as the Epidermis.
  • It covers the entire plant.
  • It is a thin layer of single cells but in places with less water, the epidermis of the plants can become thick in order to avoid frequent water loss.
  • The cells are flat and they have no intercellular spaces between them.
  • The outer walls of the epidermal cells are thick and the inner walls are thin.
  • The epidermal cells often have long hair-like structures in roots which facilitate the absorption of water.
  • The main function of the epidermis is to protect the plants from fungi, water loss and any injuries by secrets a wax-like water-resistant substance called as Cuticle on the surface of the plants which protects the plants.


  • Stomata are pore-like structures that are present in the epidermis of the leaves.
  • These pores are enclosed by two cells that have a similar shape as a kidney. These are called Guard Cells of Stomata. Guard cells are modified epidermal cells.
  • Guard cells are responsible for the exchange of gases and transpiration.

Why do plants in desert areas have a waxy coating of cutin over them? 

The epidermis cells of plants that are found in deserts have a waxy coating of cutin over them because it prevents water loss from the plants surface since water is already scarce in such areas.


Why do branches of old trees are different than the stems of a new plant?

  • As a plant grows older the meristematic cells start covering the upper layer of the plants instead of the epidermis.
  • These are the dead cells that have no special function in the plants but to provide them rigidity. They make the branches of the plants thick.
  • This is often called the Bark or the thick cork of the tree.
  • The bark of the trees contains a substance called Suberin which makes it waterproof and does not allow gaseous exchanges. 


Complex Permanent Tissues


Complex Permanent Tissues comprise of different kinds of cells. These different types of cells coordinate with each other and perform a common function in these tissues. Two Complex Permanent Tissues are

Xylem and Phloem.


                                                                                         Xylem and Phloem

Similarities between Xylem & Phloem

  • Their main function is to carry food and water in the plant.
  • Both have a vascular bundle which is a conductive tissue in plants that helps them survive in different environmental conditions.


Xylem is made up of dead cells having a thick cell lining. It consists of following elements-

  • Tracheids and Vessels – They have broad tubular structure so that we can allow transportation of food and water in the plants vertically.
  • Xylem Parenchyma – It stores food and helps in transportation of water horizontally in the plants.
  • Xylem Fibers – They support transportation


Phloem is made up of living cells and it allows the movement of food from leaves to other parts of the plant. It has the following elements –

Sieve Tubes – Broad shaped cells with porous walls

  • Companion Cells – They facilitate the functions of the sieve tubes
  • Phloem Fibers – Provide flexibility to the phloem
  • Phloem Parenchyma – Stores starch and proteins





Made of

Dead Cells

Living Cells

Cell wall thickness



Cell wall material

Lignin (rigid)







Cytoplasm lining


Water & minerals


Carried to….


Growing parts & storage organs

Direction of flow


Up & down

Tissue alos has …


Companion cells


2. Permanent Tissues

Permanent Tissues

Permanent Tissues

There are certain meristematic cells that can not divide throughout their life. They actually lose their tendency to form new cells. As a result, they form another tissue that is Permanent. They have particular functions except forming new cells. These tissues are derived from the meristematic tissue but their cells have lost the power of division. They are of two types:

  • Simple permanent tissue
  • Complex permanent tissue

Simple permanent tissues

These tissues are composed of cells which are structurally and functionally similar. Thus, these tissues are all made of one type of cells. Depending upon the composition and function they are further classified into three types:

  • Parenchyma
  • Collenchyma
  • Sclerenchyma

Let us learn about the difference between the three:


This tissue is widely distributed in plant body such as stem, roots, leaves, flowers and fruits. It performs various functions and also has distinct features in xerophytes and hydrophytes. Let us see the features it possesses.


  • Parenchyma cells are living and possess the power of division.
  • The cells are rounded or isodiametric that isequally expanded in all sides.
  • The parenchymatous cells are oval, round, polygonal or elongated in shape.
  • The cell wall is thin and enclosed but dense cytoplasm which contains a small nucleus.
  • Intercellular spaces are present


1. Parenchyma serves as a packing tissue.

2. Parenchyma acts as the main support to the stem.

3. Parenchyma serves as food storage tissue.

4. It helps in transporting materials.

5. It allows gaseous exchange.

6. It stores waste products of plants.

7. If chloroplast is present, the parenchyma tissue is called chlorenchyma and it helps in performing photosynthesis.

8. In hydrophytes large air cavities present called arenchyma that provide buoyancy to plants.


You must have seen that some plant parts can bend without breaking. This feature is due to the presence of a mechanical tissue called collenchymas. They are generally found below epidermis of dicot stem and petiole. They also occur in midribs of dicot leaves but are absent in monocots.


  • They are living cells.
  • They are characterized by the deposition of extra cellulose at the corners of the cells.
  • The intercellular spaces are generally absent.


  • It is a mechanical tissue so, it provides mechanical support to plant and its parts.
  • It also provides strength and flexibility.


You all have used and seen coconut for various purposes like performing some rituals, for eating, drinking coconut water, etc. The husk that is found outside the coconut looks like thin fibres and is hard too. This is made up of cells that is Sclerenchyma. Let us study about it.


  • They are actually dead cells.
  • The walls of these cells are thickened with deposition of lignin.
  • There are no intercellular spaces.

Cells of sclerenchyma are basically of two types:

  • Fibres
  • Sclereids

Fibres: They consist of very long, narrow, thick and lignified cells. They are usually pointed at both ends.

Sclereids: They are irregular in shape. They are also dead and are found under different parts like cortex, pith, phloem, etc.

Both fibres and sclereids have thin areas on them that are called pits.


  • They provide mechanical support andare protective in nature.

Protective tissue

Plants and plant parts also need protection from external factors. So, there are certain tissues that perform this action. Let us learn about them. It includes epidermis and cork (or phellem).


Epidermis is one cell thick layer and is covered with cuticle. It is a waterproof layer as it has a waxy substance called cutin. The cells of the epidermis are elongated and flattened and do not contain any intracellular space. Function of the epidermis is to protect the plant from desiccation and infection.


As plants grow older, epidermis undergoes certain changes and transforms into phellogen or cork. The cambium cells of cork are rectangular and are dead. The walls of cork cells are heavily thickened by the deposition of suberin which makes these cells impermeable to water and gases. Cork cells prevent desiccation, infection and mechanical injury.


Epidermis of a leaf has small pores, called stomata. Each stoma is bounded by specialized epidermal cells called guard cells. These Guard cells are the epidermal cells only and contain chloroplasts. The stoma allows gaseous exchange to occur during photosynthesis and respiration.

Complex permanent tissues

You all know that green plants can carry out photosynthesis and also absorb water through roots. But it may make you curious to know that how these substances are transported to whole plant. As we know, they don’t have blood, lymph or so. It is due to this complex tissue that water is transported and food is translocated. Let us learn about it. They consist of more than one type of cells. They are of the following two types:

  • Xylem
  • Phloem

Xylem and phloem are popularly known as vascular tissues


Xylem is composed of cells with four different parts:

  • Tracheids
  • Vessels
  • Xylem parenchyma
  • Xylem sclerenchyma.

Except xylem parenchyma, all other xylem elements are dead and bounded by thick lignified walls. Vessels are shorter and wider than tracheid. Vessels are very long tube-like structures. Tracheids are elongated cells with tapering ends. They also conduct water. Since, tracheids do not have open ends like vessel, so the water has to pass from cell to cell via the pits.


  • The main function of xylem is to carry water and mineral salts upward from the root to different parts of shoots.
  • Since walls of tracheids vessels and sclerenchyma of xylem are lignified they give mechanical strength to the plant body.


It consists of four components:

  • Sieve tubes
  • Companion cells
  • Phloem parenchyma
  • Phloem fibres.

Sieve tubes

Sieve tubes are slenderical tube –like structures composed of elongated thin-walled cells, placed end to end. Their end walls are perforated by numerous pores and are called sieve plates.

Companion Cells

They are small thin-walled cells containing dense and very active cytoplasm and large elongated nucleus.


  • Photo-synthetically prepared food materials are transported from the leaves to the storage organs.

3. Animal Tissues

Animal Tissues

Types of Animal Tissues


                                                                                     Types of Animal Tissues

    1. Epithelial Tissue
  • They are the protective tissues of the human body. They cover many organs and cavities that are present inside the body.
  • Where are the epithelial tissues found in the human body?
    1. The lining of the blood vessels
    2. The lining of the mouth
    3. Kidney tubules
    4. Skin
    5. Lung alveoli

 Structure and functions of the epithelial tissues -


    1. The main function of the epithelial tissues is to act as a barrier and separate different organs and systems from each other.
    2. There is no space between the cells of epithelial tissues
    3. The cells are permeable. This makes it possible for them to exchange materials between different parts of the body and also between the body and the external environment.
    4. The epithelial tissues remain separated from the tissues beneath them because of a thin membrane over them.

                                                                 Types of Epithelium

Different types of epithelium tissues

Simple Squamous 

Stratified Squamous


Ciliated Columnar




They have delicate cell lining and possess a flat thin structure

The epithelium Squamous cells are arranged in several layers

They are the column-like shape tissues

Columnar epithelial tissues which have Cilia present on them

They are cube-shaped cells which are involved in absorption and secretion.

These are special gland cells that can secrete substances

Found in

Alveoli and bowman’s capsule- nephron in kidney 



Respiratory system 

Kidney tubules

Sweat glands in the skin


Connective Tissue

Structure and function of connective tissues

    • They are loosely bound cells present in an intercellular Matrix.
    • This matrix can be of different types – Dense, Rigid, Fluid or Jelly-like.
    • Depending upon the functionality of the connective tissue, the nature of the matrix varies in them.



  • The main function of blood is to transport gases, food, waste materials and hormones in the body.
  • Therefore, blood has a fluid Matrix present in it which is called Plasma.
  • The plasma contains the red blood cells, the white blood cells and blood platelets.
  • The RBC have hemoglobin pigment which carries oxygen to tissues.
  • White blood cells fight diseases and platelets are involved in clotting of blood when injured.
  • The plasma also contains proteins and hormones in it.


  • Bones form a framework of the body over which the muscles are wrapped together.
  • The bone tissue is strong and inflexible in nature.
  • Therefore, the bone cells are present in a rigid matrix which is formed from calcium and phosphorus.


  • Cartilage is present over the joints of the bones and provides them with a smooth structure.
  • For Example, in the nose tip and ear pinna, trachea, larynx.
  • They contain solid matrix made of protein and sugar. They have homogenous matrix.
  • It provides support and flexibility to various parts of our body.



  • A ligament connects two bones together.
  • It has an elasticity which facilitates the connection.
  • The cells of ligaments have a little matrix.


  • The tendons tissues are responsible for connecting bones and muscles together.
  • They have limited flexibility but very great strength.


  • This tissue acts as a filter in between the spaces present inside the organs of the body.
  • It helps in repairing other tissues as well.
  • It is found in the skin and bone marrow.


  • Fats are stored in our body in the adipose tissues.
  • They are found below the skin and between the organs of the body.
  • Provides cushioning to the organs.

Muscular Tissue

  • It is made up of muscle fibers which are long cells.
  • It allows movements in our body.
  • How muscles can cause movement?

They contain special proteins called Contractile Proteins. These proteins cause contraction and relaxation of the muscles.

  • There are two kinds of muscles found in our body - Voluntary Muscles and Involuntary Muscles.

Striated/ Skeletal/ Voluntary muscles

Smooth/ Unstriated/Involuntary muscles

We can move them according to our own will

We cannot start or stop the movement of involuntary muscles. 

They are also called Skeletal Muscles as they are attached to the bones. 

They also called Smooth Muscles

They are also called Striated Muscles because of the presence of dark and light bands over them

They are also called Unstriated Muscles because they do not have any light or dark bands on them. 

The cells of voluntary muscles have more than one nucleus, they do not have any branches, and have a long cylindrical structure. 

The cells of the involuntary muscles are long and have pointed ends. 

For Example, Muscles of our hands and legs.

For Example, The muscles in the alimentary canal and the Iris of our eyes.


Cardiac Muscles

  • These are special kinds of involuntary muscles.
  • The muscles of the heart are called Cardiac Muscles they perform rhythmic contraction and relaxation throughout our life.
  • They are cylindrical in shape; they have branches and there is a single nucleus.
  • Cardiac muscle consists of individual heart muscle cells connected by intercalated discs to work as a single functional organ

3. Animal Tissues

Animal Tissues

Animal Tissue

Man is multicellular, containing many organs and many systems operating in the body which help to carry out different activities like Breathing, Transportation of substances, Movement and many more. All these systems need different types of tissues that help perform these functions.

Epithelial tissue

This tissue forms the outer layer of all body parts. It is protective in nature as it acts a barrier to keep different organs separate. It is present almost everywhere like in skin, lining of buccal cavity, blood vessels, etc. The cells of this tissue are tightly packed and form a continuous sheet. Cells of epithelium contain very little or no intercellular matrix. Epithelial cells lie on a delicate non-cellular basement membrane which contains a special form of matrix that contains a protein called collagen.


  • These cells protect the underlying cells.
  • Epithelial cells form the lining of the mouth and alimentary canal and protect these organs.
  • It helps in absorption of water and nutrients.
  • It helps in the elimination of waste products.
  • It also acts as a secretor.

Types of epithelial tissue

  • Squamous epithelium
  • Cuboidal epithelium
  • Columnar epithelium
  • Ciliated epithelium

Squamous Epithelium

You all are familiar with cavities of our body parts like mouth, esophagus, nose pericardium, alveoli, etc. and blood vessels. This tissue forms the lining of cavities of all these parts and also the covering of the tongue and skin. It is made up of thin, flat, irregular shaped cells which fit together like floor tiles to form a compact tissue.


  • It protects the underlying parts of body from mechanical injury, entry of germs, chemicals and drying.

Cuboidal Epithelium

We all know that we have kidneys for purifying blood and also, vessels that run into or through it. This tissue forms those tubules and also the glands in our body that perform functions of secretion. It consists of cube-like (cubical) cells.


  • It helps in absorption, excretion and secretion.

Columnar Epithelium

We all know that we have a slimy substance called mucus in our body that performs function in respiration activities and also in digestion activities. The mucus membrane is formed by it. It also forms lining of gall bladder and oviducts. It consists of cells which are taller in comparison to being broad. Their nuclei is towards the base and the free ends of cells contain thread – like structures called microvilli.

Ciliated Epithelium

In our body, substances are made to move like the ovum, air, etc. So, in our body, parts where propelling of substances takes place, there we have thread – like structures that act as propellers. They are villi. The villi are formed of these cells. They also line the trachea (wind-pipe), bronchi (lungs), kidney tubules and oviducts (Fallopian tubes). They are certain cubical or columnar cells that have a free border which bears thread-like cytoplasmic outgrowths called cilia. Such cells form the ciliated epithelium.


  • The rhythmic beating of the cilia moves solid particles in one direction through the ducts.

Muscle Tissue

We have 600 muscles in our body and they are contractile in nature. They help in bringing about movements in body parts. Like it helps us to move, it helps our heart to beat, it helps in bringing about all movements through our limbs. On the basis of their location, structure and functions there are following three types of muscle fibres:

  • Striated muscles
  • Smooth muscles
  • Cardiac muscles

Striated Muscles

(Also called as Striped, skeletal or voluntary muscles) It is seen in muscles of limbs, body wall, neck, etc. Striated muscles are present in tongue, pharynx, diaphragm and upper part of the esophagus. They are called visceral striated muscles. It is cylindrical un-branched. These cells have a number of nuclei and each muscle cell is multinucleated. Each muscle cell is enclosed in a thin but distinct plasma membrane called sarcolemma and contain a fluid called sarcoplasm.

  • The entire muscle fibres show alternate dark and light stripes. They are called striped muscles.
  • They are attached to bones and are responsible for body movements they are called skeletal muscles.
  • These muscles work according to our will. They are also called voluntary muscles.
  • They are long or elongated with non-tapering ends.


  • Striated muscles are powerful and undergo rapid contraction. These muscles can be tired and need rest.
  • Striated muscles provide the force for locomotion and all other voluntary movements of the body.

Smooth Muscles

They are seen in the walls of the hollow (tubular) visceral organs except that of the heart that is why they are called visceral muscles.

  • There is a single centrally located cigar-shaped nucleus in the centre of cytoplasm or sarcoplasm.
  • These fibrils do not bear any bands , stripes or striations across the muscle hence, called smooth or unstrained muscles.


  • Smooth muscles do not work and contract according to our will. So they are also called involuntary muscles. The movement of food in the alimentary canal, opening and closing of tubes are involuntary movements.
  • Smooth muscles contract slowly but can remain contracted for a long period of time.

Cardiac Muscles

As you all know that we have an important organ that is heart and it keeps on pumping blood to all body parts without getting tired. It is because of a special muscle in it that is cardiac muscle. These muscles show the characteristics of both smooth and striated muscles. Cardiac muscles are composed of branched fibres, the branches join to form a network. Each fibre or cell is surrounded by sarcolemma and has cytoplasm (sarcoplasm) with longitudinal myofibrils and a centrally located nucleus. Cardiac muscles have stripes or light and dark bands. They show densely stained cross-bands called Intercalated discs.


  • Cardiac muscles contract and relax rapidly.
  • The contraction and relaxation of the heart muscles help to pump and distribute blood to various parts of the body.

Connective Tissue

The connective tissue is specialized to connect and anchor various body organs. It binds the tissue and gives support to various parts of the body by forming packing around organs so that they do not get displaced by body movements. They act as binding, supporting and packing tissue.

Its cells are living and separated from each other and are few in number. They have homogeneous gel-like intercellular substance called medium or matrix which forms the main bulk of the connective tissue. Thus, the space between cells is filled with the non-living matrix which may be solid like in bones and cartilages and fluids as in the blood. Matrix is fibrous in nature and binds other tissues in fact the nature of matrix decides the function of connective tissue.

Types of connective tissue In animals there are of following five types as given below:

  • Areolar (loose) connective tissue
  • Dense regular connective tissue
  • Adipose tissue
  • Skeletal tissue
  • Fluid connective tissue

­­Areolar loose connective tissue

The tissue that joins skin to muscles and fills space inside organs is none other than the areolar connective tissue. It is a loose and cellular connective tissue. It has a matrix that consists of two kinds of fibres that is white collagen fibres and yellow elastic fibres or elastin.


  • It acts as a supporting and packing tissue between organs lying in the body cavity. Matrix of this tissue is important in diffusion of oxygen and nutrients from small blood vessels.
  • It helps in repair of tissues after an injury.
  • It also helps in combating foreign toxins.
  • It fixes skin to underlying muscles.

Dense Regular Connective Tissue

It is a fibrous connective tissue. It is characterized by ordered and densely packed matrix composed of fibres and cells. It is of two types:

  • Tendons
  • Ligaments

 Tendons are cord-like, strong inelastic structures that join skeletal muscles to bones. They have great strength but their flexibility is limited. The cells of tendons are called tendinocytes.

Ligaments are elastic structures which connect bones to bones and have great strength but contain very little matrix. Sprain is caused by excessive pulling (stretching) of ligaments.

Adipose Tissue

This adipose tissue is abundant below the skin. It is the tissue that gives shape to our body and is a fat reservoir. Adipose tissue is basically an aggregation of fat cells or adipocytes. Each fat cell is rounded or oval and contains a large droplet of fat that almost fills it. It has collagen and elastin fibres. The partitions carry blood vessels.


  • It serves as a fat reservoir.
  • It provides shape to the limbs and the body.
  • It keeps visceral organs in position.
  • It acts as an insulator.

Skeletal Tissue

The skeletal or supporting tissue includes cartilage and bone which forms the endoskeleton of vertebrate body. It mainly consists of:

  • Bone
  • Cartilage


It is very strong and non-flexible tissue. Its matrix is made up of protein that is heavily coated with salts of calcium and magnesium that are responsible for the hardness of the bone. Bone cells called osteoblasts or osteocytes, are present lamellae with fluid-filled spaces is called lacunae.


Bones form endoskeleton of human beings and other vertebrates except the sharks. It serves the following functions.

  • It provides shape to the body.
  • It provides skeletal support to body,
  • It protects vital body organs such as brain, lungs, etc.
  • It serves as a storage site of calcium and phosphate.
  • It anchors the muscles.


It has less vascular matrix which is composed of calcium salts. Its cells are called chondrocytes. The matrix of cartilage consists of collagen fibres. Chondrocytes are present in fluid-filled space known as lacunae, blood vessels are absent in matrix. It forms the ear pinna , nose tip, epiglottis, etc.


  • It provides support and flexibility to the body parts.

Fluid connective tissue

This tissue helps in creating link between different parts of the body and maintains a continuity of life. They are of two types: Blood and Lymph

Blood It is formed of two components:

  • Plasma
  • Blood cells


It is a yellow colored fluid which is 90% water and 10% organic and inorganic substances. Due to the presence of these substances, it acts as a nutrient medium for blood cells.

The blood cells present are:

  • Red blood cells
  • White blood cells
  • Platelets

Red blood cells

  • These are incomplete cells with no nucleus, mitochondria and endoplasmic reticulum
  • These cells are the smallest cells of our body.
  • They are cells that have disc – like shape.
  • These cells have red colour as they contain a pigment made up of iron called haemoglobin.
  • The function of this hemoglobin is to transport gases by forming complexes i.e oxyHb and carbinoHb.
  • These cells are synthesized in bone marrow of adults and in infants in spleen from stem cells.
  • The life span of these cells is 120 days.
  • These cells are also called erythrocytes.

White blood cells

  • These cells are irregular in shape and are complete cells enclosing all organelles.
  • These cells do not have any pigment in them that is the reason that they have no colour.
  • These cells have a life span of 2 to 4 weeks.
  • They are also called leucocytes.
  • They are also called soldiers of our body as they protect our body from infection causing agents – either they engulf infection causing agent or they secrete certain proteins that make infection causing agent harmless.


  • Platelets are tiny fragments that may or may not have a nucleus.
  • Their function is to secrete certain proteins that help in blood clotting.
  • Their life span is 60 to 120 days.
  • They are also called thrombocytes.


It is a colorless fluid that gets filtered out of the blood capillaries.


  • Lymph transports the nutrients (oxygen, glucose) that may have filtered out of the blood capillaries back into the heart to be re-circulated in the body.
  • It brings CO2 and nitrogenous wastes from tissue fluid to blood.
  • Being loaded with WBCs such as lymphocytes, the lymph protects the body against infection.
  • It forms the defense or immune system of the body.

3. Cell Organelles and their Functions


Cytoplasm Structure

  • Cytoplasm is a jelly-like substance found between cell membrane and nucleus.
  •  All the cell organelles are embedded in the cytoplasm. It is composed of water, organic and inorganic compounds. 
  • Cytoplasm is one of the essential components of the cell that is present in both plant and animal cells. 
  • Cytoplasm functions by controlling all the metabolic activities taking place within the cell and most of the chemical reactions are carried within it.


Endoplasmic reticulum

Endoplasmic reticulum is a network of tiny tubular structures scattered in the cytoplasm. It divides the intracellular space into two distinct compartments, one is luminal (inside ER) and another is extra luminal (outside ER). They function as the transport system of a cell, involved in transporting materials throughout the cell.

Endoplasmic reticulum is divided into two types based on presence and absence of ribosomes.

  • Rough endoplasmic reticulum: The endoplasmic reticulum bearing ribosomes on their surface is called rough endoplasmic reticulum (RER). It is involved in the protein synthesis and secretion. They are extensive and continuous with the outer membrane of the nucleus.
  • Smooth endoplasmic reticulum: The endoplasmic reticulum with the absence of ribosomes on its surface is called smooth endoplasmic reticulum (SER). They are responsible for lipid syntheses. In animal cells, lipid like steroid hormones is synthesized in SER. They are also responsible for detoxifying the cell.



  • Mitochondrion is a double membrane bound cell organelle that are not normally visible under the microscope.
  • This cylindrical or sausage shaped structure is also called the power house of the cell as they are the sites for aerobic respiration of the cell and produce cellular energy in the form of ATP. 
  • The outer membrane and the inner membrane divide its lumen into two compartments i.e., inner compartment called matrix possessing single circular DNA molecule and a few RNA molecules. forming a number of infoldings called cristae and the outer membrane forming the continuous limiting boundary of the organelle.
  • Depending on the shape, size and physiological activity of the cell, the number of mitochondria per cell are variable. 
  • The structure has a diameter of 0.2 to 1µm (average 0.5 µm) and length 1.0 to 4.1 µm.


Plastids are large and membrane bound organelles that are found in all plants and in euglenoids. They contain some specific pigments that are responsible for imparting specific colours to the plants. On the basis of the type of pigment, plastids can be classified into three types.

  • Chloroplasts: Chloroplasts are double membrane bound cell organelles that contain chlorophyll and carotenoid pigments that are responsible for trapping light energy and this energy is used for the purpose of photosynthesis.


The inner membrane surrounds a space called stroma. Chlorophyll containing structures called thylakoids are arranged as piles of coins and each pile is called a granum. Thylakoids are connected by flat membranous tubules known as stromal lamella.

  • Chromoplasts: These include carotenoid, fat soluble pigments like carotene, xanthophyll etc. providing characteristic colours like yellow, orange, red, etc. to the plants.
  • Leucoplasts: These types of plastids store nutrients and are colourless. They include amyloplasts storing carbohydrates, leucoplasts storing proteins, and leucoplasts storing oils and fats.

The Golgi Apparatus

  • It is responsible for sorting, modifying, and shipping off the cellular products that come from the rough endoplasmic reticulum (ER), just like a post office.
  • The Golgi apparatus is similar to stacked flattened discs, almost like stacks of oddly shaped pancakes.
  • The Golgi apparatus has two distinct sides with each having a different role. 


  • An organelle that contains enzymes that break down and digest inessential cellular components, such as a damaged organelle is called the lysosome.
  • Protein products packaged by the Golgi such as digestive enzymes are meant to stay inside the cell in order to break down certain materials.
  • The enzyme-containing vesicles are released by the Golgi, and they may form new lysosomes or fuse with existing lysosomes.


  • Vacuoles are generally characterized as storage bubbles of unpredictable shapes which are found in cells.
  • They are liquid-filled organelles enclosed by a film.
  • The vacuole stores the food or a spread of nutrients that a cell might need to survive.
  • In addition, it also stores waste products.
  • The by products are at last tossed out by vacuoles. Thus, the remainder of the cell is shielded from contamination.
  • The animal and plant cells have different sizes and numbers of vacuoles. Compared to animals, plant cells have larger vacuoles.

3. Cell Organelles and their Functions

Cell Organelles and their Functions

Cell organelles and their functions

There are many types of organelles that help the cell in performing different functions. The different organelles are :

  • Endoplasmic reticulum
  • Ribosome
  • Golgi bodies
  • Lysosomes
  • Mitochondria
  • Plastids
  • Vacuole
  • Centrosome

Let us study them in detail:

1. Endoplasmic reticulum

It is an irregular network of membranes enclosing fluid in its cavity .they are of two types that is:

  • Rough endoplasmic reticulum(RER)
  • Smooth endoplasmic reticulum(SER)

The basic difference between the two is that:

  • RER – It has ribosomes attached to it.
  • SER : – No ribosome  are attached

Functions of endoplasmic reticulum are as follows –

  • SER helps in synthesizing fats etc.
  • Endoplasmic reticulum forms skeleton framework of cell.
  • Rough endoplasmic reticulum helps in transportation of proteins.
  • Smooth endoplasmic reticulum helps in detoxification.
  • Oxidative enzymes of lysosomes are produced by Rough endoplasmic reticulum.
  • Endoplasmic reticulum helps in formation of membrane of cell .That is :

RER – SER – Golgi body – sec. vesicles – p membrane

2. Ribosomes

They are present in plant as well as in animal cell. They are spherical particles found free or attached to Rough Endoplasmic Reticulum. They contain their own genetic material that is RNA & proteins .Their function is protein synthesis. Due to the reason they are called as factory of proteins.

3. Golgi bodies

This organelle is present in plant and animal cells both. They  are membrane bound fluid filled vesicles and flattened membranes stacked over one another called  cisternae. In plant cells  it is called by a special name that is  Dictyosome. Function: They secrete, packages and dispatch the cellular secretions and also helps in the formation of cell membrane.

4. Lysosomes

They are present in plant as well as in animal cell. They are membrane bound vesicle containing powerful digestive enzymes. These enzymes can carry out the catabolic function

Function: Its functions are:

  • They can destroy foreign material.
  • They can remove worn out parts of the cell.

It acts as suicidal bags as they can even eat up their own cells if in case it gets damaged.

5. Mitochondria

They are rod shaped structures having a double membrane.

  • Its outer membrane is – porous
  • Its inner membrane is folded to form cristae & contain small bodies called oxysomes.
  • It has a cavity that is filled with matrix (fluid) containing DNA and ribosomes.
  • Its function is to produce energy in the form of ATP (Adenosine triphosphate) and is also designated as called as Power House of cell (due to production of energy).

6. Plastids

These are only found in plant cells. They are of three types: –

  • Leucoplast – It is colorless plastid.
  • Chromoplast – It is colored plastid.
  • Chloroplast –It is green colored plastid.

As you all know that plants have the ability to synthesize their own food. They do so with the   help of pigment chlorophyll. This chlorophyll is present in organelle chloroplast.

Chloroplasts are double membrane organelles containing liquid stoma and stacked structures called lamellae. When lamellae are stacked over one another they give rise to grana. Grana contain green pigment chlorophyll. This chlorophyll actually helps in capturing solar energy and converting it to chemical energy of food.

Functions of plastids are as follows –

  • Chloroplast helps in photosynthesis
  • Leucoplast – stores food, fats etc.
  • Chromoplast impart colour to flowers.

7. Vacuole

They are fluid filled membrane bound spaces. They are prominent and large in plants but in animal cell they are either absent or if present they are small and temporary. In animal cell it helps in  storing substances. In plant cell vacuole are large & permanent. Outer membrane is called as tonoplast and is filled with fluid called cell sap Functions of vacuole are as follows

  • It provides turgidity & rigidity to cell.
  • It stores substances.
  • It maintains the osmotic pressure of cell.

8. Centrosome

It is found only in animal cell. It consists of two granules called centrioles. The function of centrioles is to help in spindle formation during cell division.

Transportation of substances

As we have seen that substances move in and out from the cell. These exchange mainly occur by two processes:

  • Diffusion
  • Osmosis

4. Diffusion and Osmosis


Diffusion is the net movement of molecules of a substance from a region of their higher concentration to a region of their lower concentration. Net movement means there are more molecules moving in one direction than in the opposite direction.

Example: Opening a bottle of perfume in a room will result in the gradual diffusion of the perfume from the region of higher concentration (the bottle) out into the room. Diffusion will continue until the perfume has a more or less uniform concentration throughout the bottle and room.


It can be defined as the movement of water molecules from a higher water concentration area to the area of less water concentration through a semipermeable membrane. For example, water in the roots of plants is transported through osmosis.

Difference between diffusion and osmosis:



It happens only in the liquid state.

It occurs in all states of matter i.e., solids, liquids or gases.

It should be movement of only water or solvent through semipermeable membrane from lower concentration to higher concentration.

Any type of substance that moves from higher concentration area to lower concentration area.

It is applied only for the solvent part of the solution.

Diffusion is applied to all states of matter.


It requires semipermeable membrane.

This phenomenon does not require semipermeable membrane.

Osmotic Solutions

There are three different types of solutions:

Isotonic Solution
Hypertonic Solution
Hypotonic Solution

An isotonic solution is one that has the same concentration of solutes both inside and outside the cell.

A hypertonic solution is one that has a higher solute concentration outside the cell than inside.

A hypotonic solution is one that has a higher solute concentration inside the cell than outside.


Types of Osmosis

Osmosis is of two types:

Endosmosis– When a substance is placed in a hypotonic solution, the solvent molecules move inside the cell and the cell becomes turgid or undergoes de plasmolysis. This is known as endosmosis.
Exosmosis– When a substance is placed in a hypertonic solution, the solvent molecules move outside the cell and the cell becomes flaccid or undergoes plasmolysis. This is known as exosmosis.






4. Diffusion and Osmosis

Diffusion and Osmosis

Diffusion and Osmosis

Diffusion: It is the movement of any substance from higher concentration to lower concentration. Have you noticed the fragrance of your favorite food at your home when it surprisingly cooked for you by your mom. This is due to the process diffusion. When it is being cooked in kitchen its fragrant  molecules from kitchen start moving out into the kitchen’s surroundings and with time get dispersed in the air. The diffusion is seen in solids, liquids and gases but the rate of diffusion is faster in gases. This is because gas particles are energetic as they possess high kinetic energy. The movement of gases in and out from the cell occurs by diffusion

Osmosis: It is the movement of pure liquid from  higher concentration to lower concentration across the semipermeable membrane . For example: if you take two flasks and fill one with low sugar so lution and other flask with highly concentrated sugar solution. Both the beakers are separated by a semipermeable membrane. Then we will notice that the water will move from the beaker where it is more to the side where it is less. The membrane allows only water to pass through it not sugar as it is semi-permeable that is selectively permeable.

Types of solutions

We can make three different types of solutions that is :

1. Hypotonic solution – The solution that has higher water concentration.

2. Hypertonic solution- The solution that has less water concentration.

3. Isotonic solution-The solution that has the same concentration of water as in cell.

Now let’s do an activity in which we will be placing a cell say red blood cell in three different solutions. Let’s see what happens:

Cells placed in different types of solutions

This is because when it is placed in a hypotonic solution, the water from solution moves into cell (endo-osmosis) due to  which cell starts swelling up .The fully swollen cell in which the protoplasm almost touches the cell membrane is called Turgid cell.

Have you seen the red blood cell kept in hypertonic solution looks flaccid This is because when it is placed in a hypertonic solution, the water from cell moves into solution (exo-osmosis) occurs due to which cell starts shrinking up .The cell whose protoplasm almost gets shrunk is called flaccid cell.

Have you seen the cell in isotonic solution It remains as such. Nothing happens. The reason being the concentration of cell and a solution is the same.

Q. Have you noticed that sometimes when you forget to water plants especially in summers they droop, dry and ultimately they are about to die .

A. This is because the water from the plant is moving out due to transpiration. So, when there is no water left in them they start to droop. This basically occurs due to exo-osmosis. But when it is watered again, the endo osmosis occurs and it again become turgid .this is called plasmolysis (shrinkage) and deplasmolysis (again becoming healthier).

4. Nervous Tissue

                     The Nervous Tissue

  • How do we react to stimuli?

            This is becaus e of the nervous tissues present in our body.                                                                            They are capable of transmitting information quickly from the brain to different parts of the body                 and vice-versa.

  • Therefore, nervous tissues are found in nerves, brain, and spinal cord.
  • The Nervous tissue is made up of cells called the Nerve Cells or Neurons.
  • These neurons connect together to form the nerves of our body.

Structure of a Neuron

    • It is an elongated cell with a Cell Body that consists of some branch-like structure called Dendrites.
    • There is a Nucleus present in the centre of the cell body.
    • The Nerve Endings of the cell are connected with the cell body via Axon.
    • A nerve cell can be up to 1 m long.


                                                                                             Structure of Neuron


  • They are tree-like extensions (highly-branched) at the beginning of a neuron.
  • They increase the surface area of the neuron.
  • They receive chemical signals from different neurons of the body.
  • They then convert these chemical signals into electrical signals and pass them to the neuron cell body.
  • A neuron can have a single dendrite or multiple dendrites

2. Cell Body

  • Also called Soma.
  • The main function of the cell body and nucleus of the neuron is to maintain the functionality of the cell.
  • It does not play an active role in the transmission of the signal.
  • It produces proteins that are required by different parts of the neuron to work properly.
  • It contains different cell organelles such as mitochondria, Golgi apparatus etc that perform various functions of the cell.

3. Axon

  • Neurons have one axon in general.
  • It is a long structure that connects the cell body to the terminals and it also connects with other neurons, cells and organs of the body through nerve terminals.
  • It allows in fast transmission of signals. The larger the diameter of the axon the faster it will transmit signals.
  • It is covered with a special insulating substance called myelin. It helps in rapid transmission of signals.

4. Nervous Tissue

Nervous Tissue

Nervous tissue

This tissue helps us in thinking, listening, conveying messages, etc. On the whole, we can say that it helps in control and coordination in the body. It is a specialized tissue that helps in transmitting messages within our body. It contains highly specialized cells called neurons. The neurons have the ability to receive stimuli from within or outside the body and to conduct impulses to different parts. Each neuron consists of:

  • Cyton
  • Dendrite
  • Axon

The irregular structure called cell body encloses a nucleus in neuroplasm. From cell body, small branches arise on upper side called dendrite. On the lower side, it gives out only one branch that is elongated called axon. The whole neuron is made up of neurolemma. It has a fatty layer on it as a modulated sheath that creates nodes of ranvier that help in saltatory conduction. Axon ends into nerve endings.

Function of neuron

  • It is to form nerves that further helps in control and coordination of body.

4. Symptons and Signs, Prevention of Diseases

Antibiotics: These are the chemicals (medicine, drugs) that block biochemical pathways important for bacteria. They are used for diseases caused by bacteria.

Inflammation: When an active immune system releases many cells to the affected tissue to heat-off the disease-causing microbes it is called inflammation. Local effects caused on body due to inflammation are—swelling, pain, fever and redness.

Principles of treatment

•    To reduce the effects of the diseases.
•    To kill the cause of the disease i.e., to kill the microbes like bacteria fungi, protozoa.

Principles of Prevention

•    General method
•    Specific method

General ways of preventing infections relate to preventing exposure.

Prevention of exposure can be done by following ways:

•    For air borne infections—valid -visiting public place, cover your nose and mouth while coughing.
•    For water borne infections- Drink, clean and boiled drinking water.
•    For vector borne infections Keep the surroundings clean, do not keep any puddle of water open in the surrounding as it allows the breeding of mosquitoes.
•    Self-immune system that can (fight off and kill microbes when it enters our body.
•    Availability of proper and sufficient -food for everyone.

Vaccination & Immunization

•    Vaccination: The use of vaccines to stimulate your immune system to protect you against infection or disease
•    Immunization: The process of making you immune or resistant to an infectious disease, typically via vaccination

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