CBSE Class 12 Biology Ecosystem Revision Notes Chapter 14

CBSE Class 12 Biology Ecosystem Revision Notes Chapter 14

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What do we mean by an Ecosystem?

We begin the topic by understanding the meaning of ecosystem.

The ecosystem comprises two words “eco” and “system”. The literal meaning of eco is environmental or which is not harmful to the environment, whereas the literal meaning of the system is an assemblage of things in regular order. Thus ecosystem means assemblage of living species and non- living elements in an orderly manner in a specific local or regional environment.

An ecosystem can be defined as a habitat (a place where an organism lives), where we find the living organisms and their relationship among themselves and their surrounding environment.

The ecosystem is the basic unit of the biosphere. Whereas, biosphere is made up of three components-

1. Atmosphere- a thin blanket of air surrounding the earth.
2. Lithosphere- total land area on the earth
3. Hydrosphere- all types of water bodies on the earth-like ponds, lakes, rivers, seas, and oceans.

The whole earth is considered as biosphere consisting of thousands of ecosystems.

Thus the ecosystem includes water, air, sunlight, soil, plants, microorganisms, insects, small animals and big animals including human beings.

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Structure of an ecosystem

The living and non- living entities of an ecosystem is classified into two components;

• Biotic components
• Abiotic components

Biotic or biological components refers to the living organisms in the ecosystem.

Abiotic or physical components comprises the non-living elements like-temperature, the wind, rain, nutrients, pollution, soil, sunlight etc…

A healthy and stable ecosystem requires both the biotic and abiotic factors/ components to be complete and self-sustaining. In an ecosystem, there is circulation, transformation, and accumulation of energy and matter through the medium of living organisms and their activities. The interaction between ever changing abiotic components of the environment as well as plants and animals existing over there, keep modifying and changing each other, hence leading to the development of that ecosystem.

The biotic components are divided into two groups, according to the role they play in the ecosystem;

• Autotrophs or producers: Green plants, trees, algae, and photosynthetic bacteria are called producers because they produce their own food material. They prepare the food using water and minerals from the soil, carbon dioxide from the air, in the presence of sunlight and chlorophyll (a green pigment present in the green leaves). This process of making food is called photosynthesis. The chemical reaction in photosynthesis is-

6H₂O +6CO₂      ͢    C₆H₁₂O₆ + 6O₂     (in the presence of sunlight and chlorophyll)

Water+ Carbon dioxide     ͢    Sugar + Oxygen (in the presence of sunlight and chlorophyll

Hence green leaves are called food factories of the plant. The plants and trees provide the food prepared by them to other organisms. These organisms are called consumers or heterotrophs.

• Heterotrophs or consumers: These organisms consume the food prepared by the plants directly or indirectly. Consumers are generally classified into four groups depending on the nature of the food they consume.

1. Herbivores: the organisms that consume the green plants directly are called herbivores, like mouse, deer, cow, goat, horse etc.
2. Carnivores: the organisms that feed upon herbivores are called carnivores, like dog, cat, tiger, lion etc.
3. Omnivores: the organisms that feed on both vegetation and other living organisms, like human beings.
4. Decomposers: the organisms that feed on dead and decaying organisms are called decomposers. They are generally microorganisms. They help in transforming the organic compounds of once live organisms back into the inorganic compounds, which are again used up in the form of minerals by the producers to prepare food.

HD Animated videos are available on Structure of an ecosystem, click at Class 12 Biology

Types of ecosystem

There are two types of ecosystems:

1. Natural Ecosystem- It operates under the natural conditions. They can be either terrestrial (occurring on land) or aquatic (present in water). Terrestrial ecosystems are forests, grasslands, deserts etc. Aquatic ecosystems are fresh water, pools, ditch, oceans etc.
2. Artificial Ecosystem- These ecosystems operate under the influence of human beings, they are called man engineered ecosystems. Like crop fields, aquariums, house gardens, etc. In artificial ecosystems, the management is done by addition of energy or planned manipulations.

Characteristics of an Ecosystem:

1. The ecosystem is the basic unit of the biosphere, where the organisms are linked to one another and to their surrounding in a given space and time.
2. It occupies certain well defined time unit and space unit on the earth.
3. It is a system which is characterized by input and output of energy and matter.
4. The structure of an ecosystem is defined by the diversity of the species.
5. The interactions between its various biotic and abiotic factors are highly complex.
6. There is a constant flow of energy among the biotic components of an ecosystem of which the solar energy is the most significant.
7. There is cycling of material within and outside the system.

Flow of energy in an Ecosystem

Sun

↓

Producers

↓

Consumers

↓

Decomposers

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