Chapter 13: Our Environment
Ecosystem and food chains
An ecosystem has biotic and abiotic components. Producers (green plants), consumers (herbivores, carnivores, omnivores) and decomposers (bacteria, fungi). A food chain example: grass → deer → lion. Many connected food chains form a food web.
Flow of energy and the 10 per cent law
Only about 10 per cent of the energy passes from each trophic level to the next. That is why food chains usually have only 3 or 4 steps. Producers receive the most energy.
Effect of our activities on the environment
Biological magnification: non-biodegradable chemicals like pesticides keep increasing higher up the food chain, so humans receive the most. Ozone layer: O3 in the stratosphere protects us from ultraviolet rays. It is being depleted by CFCs. The 1987 Montreal Protocol was made to reduce CFCs.
Waste disposal
Biodegradable: vegetable peels, paper. Non-biodegradable: plastic, glass, DDT. To reduce waste follow the three Rs: Reduce, Reuse, Recycle.
Important questions
Q1. What is an ecosystem?
A system in which all the living (biotic) and non-living (abiotic) components of an area, such as water, air and soil, interact with each other.
Q2. Differentiate between producers, consumers and decomposers.
Producers (green plants) make food by photosynthesis. Consumers (animals) eat others. Decomposers (bacteria, fungi) break down dead organisms and waste.
Q3. What is a food chain? Give an example.
A series of organisms in which one eats the other, such as grass → grasshopper → frog → snake → eagle.
Q4. What is a trophic level?
Each step of a food chain. Producers are at the first trophic level.
Q5. What is a food web?
A network of many interconnected food chains in an ecosystem.
Q6. How much energy passes from one trophic level to the next?
About 10 per cent, and the rest is used up in life processes or lost as heat. This is called the 10 per cent law.
Q7. Why do food chains usually have only 3 or 4 steps?
Energy decreases at each step, so after 4 or 5 steps very little energy is left for the next one.
Q8. Why are green plants called producers?
Because they make their own food by photosynthesis using sunlight and supply energy to others.
Q9. What is the role of decomposers?
They break dead organisms and waste into simple substances, return nutrients to the soil and keep the environment clean.
Q10. What are biodegradable and non-biodegradable substances?
Biodegradable substances are broken down by microbes, such as vegetable peels and paper. Non-biodegradable ones are not, such as plastic, glass and DDT.
Q11. Why is plastic harmful for the environment?
It is non-biodegradable, stays for hundreds of years, chokes drains and is dangerous for animals.
Q12. What is biological magnification?
The increase in the concentration of harmful non-biodegradable chemicals at each higher trophic level of a food chain.
Q13. Why is the concentration of harmful chemicals highest in humans?
Because humans are at the top of the food chain. Chemicals accumulate through grains, vegetables, milk and meat and reach humans in the highest amount.
Q14. What is the ozone layer and where is it?
A layer of ozone (O3) in the stratosphere that protects us from the Sun’s harmful ultraviolet rays.
Q15. How is ozone formed?
Ultraviolet rays split oxygen (O2) into atoms, and an oxygen atom combines with an O2 molecule to form O3.
Q16. What is the main cause of the depletion of the ozone layer?
Chlorofluorocarbons (CFCs), which were used in refrigerators, aerosol sprays and fire extinguishers.
Q17. What is the Montreal Protocol?
A 1987 agreement under the United Nations Environment Programme (UNEP) that limited and reduced the production of CFCs.
Q18. State the harmful effects of ozone depletion.
Skin cancer, cataract and damage to ecosystems, because more ultraviolet rays reach the Earth.
Q19. What are the three Rs for reducing waste?
Reduce, Reuse and Recycle.
Q20. What can we do to reduce waste at home?
Use cloth bags, make compost from kitchen waste, separate the waste and avoid single-use plastic.
Quiz
1. Who are the producers in an ecosystem?
Green plants make food by photosynthesis.
2. Who break down dead organisms?
Bacteria and fungi are decomposers.
3. How much energy passes from one trophic level to the next?
About 10%, by the 10 per cent law.
4. What is the main cause of ozone depletion?
CFCs destroy the ozone layer.
5. Which of these is non-biodegradable?
Plastic does not decay.