These notes are based on the chapter Our Environment from class 10 science NCERT book and CBSE syllabus.
Our surrounding is called environment. The clasroom, playground and garden in your school make the environment of your school. Even your teachers and fellow students are part of that environment. Similarly, the houses in your neighbourhood, neighbours, stray animals, trees, park, etc. make the environment of your neighbourhood.
- Components of ecosystem
- Food chain and food web
- Ozone layer and its depletion
- Problem of waste disposal
This is a system of interdependencies among various living beings and non-living things in a given habitat. Every component of an ecosystem is dependent on each other.
To understand this, you can take the example of a garden. The plants in the garden depend on soil, air and water. Soil, in turn, depends on decomposition of plants to get back nutrients. Many creatures depend on plants for food and shelter. Many of these creatures help plants in pollination and dispersal of seeds.
Components of Ecosystem
An ecosystem has two types of components, viz. biotic component and abiotic component.
All the non-living things make the abiotic component of an ecosystem. Air, water and soil are abiotic components.
- Air provides oxygen (for respiration), carbon dioxide (for photosynthesis) and other gases for various needs of living beings.
- Water is essential for all living beings because all the metabolic activities happen in the presence of water.
- Soil is the reservoir of various nutrients which are utilised by plants. Through plants, these nutrients reach other living beings.
All living beings make the biotic component of an ecosystem. Different types of biotic components are as follows:
Producer: Green plants play the role of producers because they prepare their own food.
Consumer: Animals and other living beings play the role of consumers because they take food (directly or indirectly) from plants.
Decomposer: Bacteria and fungi play the role of decomposers, as they decompose dead remains of plants and animals so that raw materials of organisms can be channelized back to the environment.
A food chain is a simple representation of transfer of energy from the sun to different biotic components of an ecosystem. Sun is the ultimate source of energy, because most of the sources of energy on earth have got energy from sun. Green plants convert solar energy into chemical energy during photosynthesis. When an animal takes food, this energy is supplied to the animal and the process goes on. A simple food chain can be shown as follows:
Producer → Primary Consumer → Secondary Consumer
Real life cannot be as simple as a food chain shown above. For a given prey, there can be many predators. For example, grass is eaten by many animals. A goat is eaten by many carnivores. In any ecosystem, there can be many food chains which are interlinked at various levels. Thus, many food chains form a network which is called food web.
Transfer of Energy through a food chain
Different levels in the food chain are called trophic level. Out of the energy consumed by an organism at a particular trophic level, 90% is utilised for its own need and rest 10% is left for the organism of the next trophic level. So, very little energy is left for the organism which is at the tertiary level.
Let us assume that a green plant makes 100% energy in the form of chemical energy. 90% of this energy would be utilised for its own purpose. This would leave just 10% energy for the primary consumer.
Now, primary consumer shall also utilize 90% of energy which was consumed by it. This would leave just 1% energy for (10% of 10 = 1) for the secondary consumer.
By this logic, the tertiary consumer would get just 0.1% of energy which was originally made by the green plant. This is the reason, there can be just one or two organisms at the top of the food pyramid.
This explains why the population of producers is always the largest in an ecosystem, followed by the population of herbivores and then that of carnivores. Moreover, an herbivore needs to eat many plants in its lifetime to fulfill its energy need. Similarly, a carnivore needs to eat many herbivores in its lifetime.
Balance in the Ecosystem
There is a delicate balance in an ecosystem, as far as number of organisms at a particular trophic level is concerned. An increase or decrease in population of any organism can disturb this balance.
What will happen if all the deer are killed in a jungle?
Let us take a hypothetical example to understand this. If all the deer are killed in a jungle, the lions would be left with no food. This would endanger the existence of lions. Once the lions and deer would be finished, it would result in population explosion of green plants.
What will happen if all the lions are killed in a jungle?
If all the lions die in a jungle, it would create another problem. Since no lion would be left to kill the deer, the population of deer would increase substantially. This will finish off all the green plants and finally even the deer would be left with no food for them.
Biodegradable Substance: Substances which can be decomposed by microorganisms are called biodegradable substances. All the organic substances are biodegradable.
Non-biodegradable: Substances which cannot be decomposed by microorganisms are non-biodegradable. All inorganic substances are non-biodegradable. Many synthetic substances are also non-biodegradable.
Ozone Layer Depletion
The stratosphere is composed of ozone and is also called ozone layer. It prevents ultraviolet radiations from entering the earth's surface.
Fully or partly halogenated form of hydrocarbons is called chlorofluorocarbon. They contain only carbon, hydrogen, chlorine and fluorine. They are used in refrigerants and aerosols. They damage the ozone layer.
Ozone layer is also known as stratosphere. When ultraviolet radiations act on oxygen, the oxygen gets converted into ozone.
Ozone layer works like a protective shield for living beings. The ozone layers wards off harmful ultraviolet radiations from the sun.
Effect of CFCs
Use of CFCs (Chlorofluorocarbon) has damaged the ozone layer. As a result, the ozone layer has become thinner at certain parts.
Tackling ozone layer depletion
In 1987, the UNEP (United Nations Environment Programme) succeeded in forging an agreement among different nations to freeze the CFC production at 1986 level. Later, an agreement was signed among different nations to phase out CFCs. It is important to note that CFC is used in refrigerators and aerosol spray. India is also a signatory of that agreement and thanks to the efforts by the United Nations and different environmentalists, the CFC emission has been put under some control.
Problems of Waste Disposal
During our day to day activities, we produce lot of waste. While some of the waste is biodegradable, a large chunk is composed of non-biodegradable substances. Plastic waste is a serious concern because plastic is non-biodegradable. We need to respect our environment and find out ways to reduce the burden on our environment.