Chapter 15

Our Environment

 

Introduction

Things around us is known as Environment. It consists of living component also known as biotic component and non-living component also known as Abiotic Components.

Ecosystem

  • The interaction between abiotic and biotic components is defined as ecosystem. 
  • It is a self-sustaining and functional unit of biosphere.
  • The term ecosystem was coined by Sir Arthur Tansley.

Types of Ecosystem

There are two types of ecosystem-natural ecosystem and artificial ecosystem.

  • The ecosystem present naturally is known as Natural Ecosystem. Example of Natural Ecosystem are forests, grasslands, deserts, ponds, lakes, rivers, estuaries, sea.
  • The ecosystem which is man-made is known as Artificial Ecosystem. For Example Gardens, Aquariums and Agro ecosystem which is the largest man made ecosystem.

 Components of ecosystem
Abiotic Factors Include 
- Climatic factors such as rain, temperature, wind etc. Another abiotic factor is edaphic factors such as soil, pH, minerals etc.
Biotic Factors include:
Producers
 which can make their own food, such as plants, blue-green algae etc.
Consumers feed on producers. Such as herbivores. In consumers there are-primary consumers, secondary consumers, tertiary consumers etc.
Carnivores are flesh eating animals.
Omnivores consume both plants and animals.
Parasites live inside and depend upon living host.
Saprophytes feed on dead remains of plants and animals.

Food Chain is defined as series of organisms in order in which organisms feeds on another organism. There are various steps in food chain in which energy is transferred, each level is known as trophic level. Energy is always transferred uni directionally.

Characteristics of Food Chain

  • There is a unidirectional flow of energy from producers to consumers.
  • There are generally 3 to 4 trophic levels.
  • It is always straight
  • Organism can occupy different trophic levels in different food chain.

A 10 percent law is followed in energy transfer which was given by Raymond Lindeman. This law states that “only 10 percent of energy is transferred from one trophic level to another trophic level”. The remaining 90 percent will be used by the present trophic level in different processes. Therefore there are usually 3-4 trophic levels in a food chain.

 Energy transfer in trophic level

Food Web
Interconnection of food chain is known as Food Web. It shows how food chain are interdependent.

Characteristic of food web

  • Food webs are never straight as they are formed by interlinking of food chains.
  • Food web provides alternative pathways of food availability. If a particular species is destroyed, the predator can feed on an alternative species.
  • Food webs increase ecosystem stability.
Food web

Ecological Pyramid

  • Ecological Pyramid is a graphical representation to show biomass or bio productivity.
  • There are different ecological pyramids such as pyramid of biomass, pyramid of number and pyramid of energy.
  •  Pyramid of number indicates number of individuals at different trophic levels.
  • Pyramid of biomass indicates biomass of the members of the food chain present at different trophic levels.

 Pyramid of energy indicates energy at different trophic levels.

Upright Pyramids

  • Pyramid of number and pyramid of biomass can be inverted alsoIn aquatic ecosystem pyramid of biomass is inverted.

 

Inverted pyramid