Our Environment

Every living organism depends on its surroundings and on other organisms. In this chapter you will study an ecosystem as a unit made of biotic components, the producers, consumers and decomposers, and abiotic components such as temperature, rainfall, soil and minerals. Ecosystems may be natural, such as forests, ponds and lakes, or artificial, such as gardens, crop fields and aquariums. You will learn how energy flows through food chains and food webs from one trophic level to the next, and why only about 10% of the energy at one level is passed to the next, so food chains rarely have more than three or four steps. You will see how non-biodegradable chemicals like pesticides accumulate at higher trophic levels by biological magnification, so that humans, at the top of many food chains, carry the highest concentrations. You will study how the ozone layer, formed by the action of ultraviolet radiation on oxygen, protects life from harmful UV rays, and how CFCs damage it. Finally, you will learn about biodegradable and non-biodegradable wastes and how garbage can be managed.

Detailed Worksheet: Our Environment Section A - Definitions (10 marks) 1. What is an ecosystem? Name its biotic and abiotic components. (2 marks) 2. Define producers, consumers and decomposers, giving one example of each. (2 marks) 3. What is a food chain? Why are food chains generally limited to three or four trophic levels? (2 marks) 4. What is biological magnification? Why is its effect greatest at the highest trophic level? (2 marks) 5. Distinguish between biodegradable and non-biodegradable substances, giving two examples of each. (2 marks) Section B - Calculations and Applications (15 marks) 6. In a grassland ecosystem, the producers fix 20,000 J of energy from sunlight. Using the 10% law, calculate the energy available to the primary consumers, secondary consumers and tertiary consumers. What percentage of the producers' energy reaches the tertiary consumers? (3 marks) 7. In a lake contaminated with DDT, the concentrations measured were: water 0.000003 ppm, zooplankton 0.04 ppm, small fish 0.5 ppm, large fish 2 ppm and fish-eating birds 25 ppm. By what factor has the concentration in the birds increased compared to water? Name this phenomenon and explain why it occurs. (3 marks) 8. A family of five produces 2.5 kg of household waste per day, of which 60% is kitchen and garden waste and the rest is plastic, glass and metal. Calculate the mass of biodegradable and non-biodegradable waste produced in a month of 30 days. Suggest one way to manage each type. (3 marks) 9. Ozone is formed in the upper atmosphere when high-energy UV radiation splits oxygen molecules. Write the two equations involved. If an agreement freezes CFC production at the 1986 level, explain how this helps the ozone layer. Name the organisation that forged this agreement in 1987. (3 marks) 10. A food chain is: grass -> grasshopper -> frog -> snake -> eagle. If the eagle receives 2 J of energy, calculate the energy present at the grass level using the 10% law. Which organism occupies the third trophic level? (3 marks) Section C - Diagrams (10 marks) 11. Draw a labelled diagram of a food web in a grassland ecosystem with at least six organisms, showing the direction of energy flow with arrows. (4 marks) 12. Draw a diagram showing the trophic levels in a food chain as a pyramid, labelling producers, herbivores, carnivores and top carnivores, and showing the energy available at each level using the 10% law, starting with 10,000 J. (3 marks) 13. Draw a flow diagram showing the flow of energy in an ecosystem from the Sun through producers, consumers and decomposers, and mark the energy lost as heat at each level. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. Why is the flow of energy in an ecosystem unidirectional? Explain what would happen if all the organisms of one trophic level, such as all the herbivores, were killed. How does a food web make an ecosystem more stable than a single food chain? (5 marks) 15. Our food grains, such as wheat and rice, and vegetables, fruits and even meat, are found to contain varying amounts of pesticide residues. State the reason, and explain why the concentration is highest in human beings. Suggest three ways to reduce pesticide residues in our food. (5 marks) 16. The use of disposable paper cups instead of plastic cups is suggested on trains. Discuss the advantages and disadvantages of this change. Explain why the introduction of kulhads (disposable clay cups) on a large scale was not a good idea, and suggest a better alternative. (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Draw all diagrams neatly in pencil with arrows showing the direction of energy flow. Use examples from Indian ecosystems wherever possible.