CBSE Class 10 Science Our Environment Important Questions Set 01

Answer: (c) both living organisms and non-living objects. An ecosystem consists of the biotic components (organisms) and the abiotic components (air, water, soil, sunlight) of an area.

Teacher's Note:
1. Both biotic and abiotic components interact in an ecosystem.
2. Plants, animals and the physical environment together form it.

Answer: (d) 5000 kJ. Only 10% of the energy passes to the next level, so the producer level has 10 × 10 × 10 times that of the 4th level (snake): 5 × 1000 = 5000 kJ.

Teacher's Note:
1. Grass is the first trophic level and the snake is the fourth.
2. Three transfers each reduce the energy to one tenth.

Answer: (c) chemical energy. The energy stored in the food of an organism is chemical energy, and it is this that is passed to the next trophic level.

Teacher's Note:
1. Most of the energy is lost as heat in respiration.
2. The part that is passed on is stored in the body as food.

Answer: (a) unidirectional. Energy flows from the Sun to producers and then to consumers, and it cannot return to the previous level.

Teacher's Note:
1. Energy captured by plants does not go back to the Sun.
2. This is also why energy is always lost along a food chain.

Answer: (a) Decrease in energy at higher trophic levels. Only about 10% of the energy is passed on at each step, so very little remains after 4 or 5 levels.

Teacher's Note:
1. Energy lost at each step cannot be reused.
2. Consider how much energy would be left at the fifth level.

Answer: Ozone in the upper atmosphere absorbs the harmful ultraviolet (UV) radiation of the Sun and protects living things on the Earth's surface.

Teacher's Note:
1. UV rays can cause skin cancer and damage crops.
2. Ozone (O₃) is formed from oxygen by the action of UV light.

Answer: Only green plants (producers) can capture the energy of sunlight and convert it into chemical energy by photosynthesis. All other organisms depend directly or indirectly on this food.

Teacher's Note:
1. Producers make their own food.
2. All consumers get their energy from the producers.

Answer: A forest develops and sustains itself without human help. Its living and non-living components interact on their own, so it is a natural ecosystem.

Teacher's Note:
1. Natural ecosystems are not made or managed by humans.
2. Ponds, lakes and grasslands are also natural ecosystems.

Answer: Waste that is thrown away carelessly pollutes air, soil and water. It spreads diseases and harms living organisms, and non-biodegradable waste remains in the environment for a very long time.

Teacher's Note:
1. Waste must be segregated and treated properly.
2. Pollution of one part of the environment affects other parts as well.

Answer: Crop fields are created and managed by humans, who control the crops grown, the water supplied and the use of fertilisers and pesticides. Because some biotic and abiotic components are manipulated by humans, they are artificial ecosystems.

Teacher's Note:
1. An artificial ecosystem depends on human management.
2. Gardens and aquariums are also artificial ecosystems.

Answer: Only about 10% of the energy at one trophic level passes to the next, and the rest is lost as heat or used in life processes. After 3 or 4 steps too little usable energy remains to support another level.

Teacher's Note:
1. Energy decreases at each successive level.
2. This is the ten per cent law of energy transfer.

Answer: 1. Polythene is non-biodegradable and stays in the soil for years, reducing soil fertility and blocking water seepage.
2. Animals die when they swallow polythene bags.
3. Discarded bags choke drains and sewers, which causes water logging and floods.
Alternatives: cloth bags, jute bags and paper bags.

Teacher's Note:
1. Polythene cannot be broken down by decomposers.
2. Reusable cloth or jute bags are a better choice.

Answer: Energy captured by producers moves to consumers at higher trophic levels and is not available again to the earlier level, so the flow is one-way.
Pesticides washed from the fields go into the soil and water. They are absorbed by plants and enter the food chain; being non-biodegradable, they accumulate at each level (biological magnification) and reach us through the food we eat, with the highest concentration in the top consumer.

Teacher's Note:
1. Energy moves forward and is lost as heat at each level.
2. Harmful chemicals become more concentrated as they move up the food chain.

Answer: 1. Biodegradable waste can be put in a biogas plant or compost pit to make biogas and manure.
2. Solid waste can be buried in landfills.
3. Waste such as paper, plastic and metals can be recycled.

Teacher's Note:
1. Waste is first segregated into biodegradable and non-biodegradable.
2. Recycling saves resources and reduces the amount of waste.

Answer: 1. Separate biodegradable and non-biodegradable waste.
2. Use cloth, jute or paper bags in place of plastic bags.
3. Use compost or vermicompost instead of chemical fertilisers.
4. Harvest rainwater and save water.
5. Switch off lights and appliances when not in use, and plant trees.

Teacher's Note:
1. Eco-friendly habits reduce waste and pollution.
2. Any five such activities will be accepted.

Answer: Daily household wastes are kitchen waste, vegetable and fruit peels, paper waste and plastic bags.
Measures: 1. Segregate the waste into dry and wet. 2. Compost kitchen waste and peels in a compost pit. 3. Send paper and plastic for recycling. 4. Dispose of plastic bags safely and avoid using them.

Teacher's Note:
1. Wet waste is mostly biodegradable.
2. Segregation at home makes disposal easier.

Answer: 1. Excess use of fertilisers changes the soil chemistry and kills useful soil microbes.
2. Non-biodegradable pesticides pollute soil and water and cause biomagnification.
3. Growing crops again and again without rest reduces soil fertility.
4. Excessive use of groundwater for irrigation lowers the water table.

Teacher's Note:
1. Modern farming uses large amounts of chemicals.
2. Sustainable methods include organic manure and crop rotation.

Answer: Ozone depletion is caused by chemicals called chlorofluorocarbons (CFCs), used in refrigerators, air conditioners and aerosol sprays. In the stratosphere, UV rays break them down and the released chlorine atoms destroy ozone molecules. In 1987 the UNEP agreed to freeze the production of CFCs.

Teacher's Note:
1. CFCs are very stable and rise to the upper atmosphere.
2. Less ozone lets more UV radiation reach the Earth.

Answer: Biodegradable substances are broken down by the action of decomposers such as bacteria and fungi; examples are vegetable peels and paper. Non-biodegradable substances cannot be broken down in this way and remain in the environment; examples are plastics and DDT.

Teacher's Note:
1. Biodegradable waste is decomposed naturally.
2. Non-biodegradable waste pollutes for a long time.

Answer: Each transfer passes only 10% of the energy, so the energy at the previous level is 10 times greater. Energy in deer = 20 × 10 = 200 J, and in grass = 200 × 10 = 2000 J.

Teacher's Note:
1. Work backwards from the top consumer.
2. Multiply by 10 for every step down the chain.