Our Environment Class 10 Notes Biology Chapter 15

Our Environment Class 10 Biology Ncert book Notes
Our Environment Class 10 Biology Ncert book Notes

    Our Environment

Defination: Everything that surrounds are called environment.

Biodegradable: Substances that are broken down by biological processes are said to be biodegradable.

Unbiodegradable: Substances that varnit be broken down by biological processes are said to be biodegradable.


Ecosystem: All organisms such as plants, animals, microorganisms and human beings as well as the physical surroundings interact with each other and maintain a balance in nature. All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem.

  • An ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, wind, soil and minerals.
  • For example, if you visit a garden you will find different plants, such as grasses, trees; flower bearing plants like rose, jasmine, sunflower; and animals like frogs, insects and birds. All these living organisms interact with each other and their growth, reproduction and other activities are affected by the abiotic components of ecosystem. So a garden is an ecosystem.
  • Other types of ecosystems are forests, ponds and lakes. These are natural ecosystems while gardens and crop-fields are human-made (artificial) ecosystems.
  • Organisms can be grouped as producers, consumers and decomposers according to the manner in which they obtain their sustenance from the environment.

    Food Chains and Webs

Food chain in nature (a) in forest, (b) in grassland and (c) in a pond
Food chain in nature (a) in forest, (b) in grassland and (c) in a pond

Food chain : Food chain,is the sequence of transfers of matter and energy in the form of food from organism to organism.

Food web: A food web consists of all the food chains in a single ecosystem. Each living thing in an ecosystem is part of multiple food chains.

Trophic levels : it is The number of steps an organism is from the start of the chain is a measure of its trophic level.

Trophic levels
Trophic levels

Food chains start at trophic level 1 with primary producers such as plants, move to herbivores at level 2, predators at level 3 and typically finish with carnivores or apex predators atlevel 4 or 5.


  • The food we eat acts as a fuel to provide us energy to do work. Thus the interactions among various components of the environment involves flow of energy from one component of the system to another.
  • The autotrophs capture the energy present in sunlight and convert it into chemical energy. This energy supports all the activities of the living world.
  • From autotrophs, the energy goes to the heterotrophs and decomposers.
  • When one form of energy is changed to another, some energy is lost to the environment in forms which cannot be used again.


The flow of energy between various components of the environment has been extensively studied and it has been found that:-

The green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight that falls on their leaves and convert it into food energy.

When green plants are eaten by primary consumers, a great deal of energy is lost as heat to the environment, some amount goes into digestion and in doing work and the rest goes towards growth and reproduction. An average of 10% of the food eaten is turned into its own body and made available for the next level of consumers.

Therefore, 10% can be taken as the average value for the amount of organic matter that is present at each step and reaches the next level of consumers.

Since so little energy is available for the next level of consumers, food chains generally consist of only three or four steps. The loss of energy at each step is so great that very little usable energy remains after four trophic levels.

There are generally a greater number of individuals at the lower trophic levels of an ecosystem, the greatest number is of the producers.

The length and complexity of food chains vary greatly. Each organism is generally eaten by two or more other kinds of organisms which in turn are eaten by several other organisms. So instead of a straight line food chain, the relationship can be shown as a series of branching lines called a food web.

Food web, consisting of many food chains
Food web, consisting of many food chains


  • The flow of energy is unidirectional. The energy that is captured by the autotrophs does not revert back to the solar input and the energy which passes to the herbivores does not come back to autotrophs.
  • As it moves progressively through the various trophic levels it is no longer available to the previous level.
Diagram showing flow of energy in an ecosystem
Diagram showing flow of energy in an ecosystem


  • Interesting aspect of food chain is how unknowingly some harmful chemicals enter our bodies through the food chain.

Biological magnification: the process by which the concentration of toxic substances increases in each successive link in the food chain; also called biomagnification.

In biological magnification, pesticides or heavy metals move up the food chain


1.  Ozone Layer and How it is Getting Depleted

Ozone (O3) is a molecule formed by three atoms of oxygen. While O2, which we normally refer to as oxygen, is essential for all aerobic forms of life. Ozone, is a deadly poison. However, at the higher levels of the atmosphere, ozone performs an essential function.

It shields the surface of the earth from ultraviolet (UV) radiation from the Sun. This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings.

Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen (O2) molecule. The higher energy UV radiations split apart some moleculer oxygen (O2) into free oxygen (O) atoms. These atoms then combine with the molecular oxygen to form ozone as shown—

The use of chemicals like CFCs has endangered the ozone layer. Since the ozone layer protects against the ultraviolet radiation from the Sun, this could damage the environment.

2. Managing the Garbage we Produce

  • The waste we generate may be biodegradable or non-biodegradable.
  • The disposal of the waste we generate is causing serious environmental problems.


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