E X E R C I S E S CHAPTER 13 Our Environment SCIENCE NCERT TEXTBOOK (CBSE) CLASS 10:

 E X E R C I S E S  

CHAPTER  13  Our Environment


1. Which of the following groups contain only biodegradable items?

  • (a) Grass, flowers, and leather
  • (b) Grass, wood, and plastic
  • (c) Fruit-peels, cake, and lime-juice
  • (d) Cake, wood, and grass

Answer: (d) Cake, wood, and grass
Explanation: Biodegradable items are those that can be broken down naturally by microorganisms. Cake, wood, and grass are organic materials that will decompose over time. Leather is biodegradable, but plastic is not, so option (b) is incorrect. Fruit peels, cake, and lime-juice are also biodegradable, but option (d) fits better as all items listed are biodegradable.

2. Which of the following constitute a food-chain?

  • (a) Grass, wheat, and mango
  • (b) Grass, goat, and human
  • (c) Goat, cow, and elephant
  • (d) Grass, fish, and goat

Answer: (b) Grass, goat, and human
Explanation: A food chain is a sequence in which organisms transfer energy by eating and being eaten. In option (b), grass is eaten by the goat (primary consumer), and the goat is eaten by humans (secondary consumer). Other options do not show a correct chain of feeding relationships.

3. Which of the following are environment-friendly practices?

  • (a) Carrying cloth-bags to put purchases in while shopping
  • (b) Switching off unnecessary lights and fans
  • (c) Walking to school instead of getting your mother to drop you on her scooter
  • (d) All of the above

Answer: (d) All of the above
Explanation: All the practices mentioned here are environment-friendly:

  • Carrying cloth bags reduces the use of plastic.
  • Switching off unnecessary lights and fans conserves electricity.
  • Walking instead of using a scooter reduces carbon emissions and pollution.

4. What will happen if we kill all the organisms in one trophic level?

Answer: If we kill all the organisms in one trophic level, it will disrupt the entire food chain. The organisms in the level above will lose their food source, leading to a collapse of that level as well. This disruption can cause a cascading effect throughout the ecosystem, impacting biodiversity and ecosystem stability.

5. Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?

Answer: Yes, the impact of removing organisms from different trophic levels will vary. Producers (like plants and algae) are foundational to the food chain, and removing them would cause a collapse of the entire ecosystem. Primary consumers (herbivores) and secondary consumers (carnivores) also play critical roles, and their removal can have significant consequences on the food web. Removing an organism from any trophic level would disrupt the balance of the ecosystem, although the extent of damage may vary.

6. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?

Answer: Biological magnification (also called biomagnification) refers to the process by which the concentration of toxic substances increases as you move up the trophic levels in a food chain. For example, small organisms may accumulate pollutants like pesticides, and when they are eaten by larger predators, the toxins accumulate in greater concentrations in those predators. The magnification levels will be higher at the top of the food chain (e.g., carnivores), as they consume many organisms from lower trophic levels.

7. What are the problems caused by the non-biodegradable wastes that we generate?

Answer: Non-biodegradable wastes, such as plastics, metals, and chemicals, do not decompose naturally and accumulate in the environment. The problems they cause include:

  • Pollution of soil, water, and air.
  • Harm to wildlife that might ingest or get entangled in non-biodegradable materials.
  • Long-term environmental degradation, as these materials persist for years or even centuries.
  • Blockage of drainage systems and accumulation in landfills, contributing to waste management issues.

8. If all the waste we generate is biodegradable, will this have no impact on the environment?

Answer: Even if all waste were biodegradable, it would still have an impact on the environment. The decomposition process requires time, and large amounts of biodegradable waste can lead to:

  • Soil and water contamination due to the release of organic chemicals during decomposition.
  • Overload of organic matter, leading to the depletion of oxygen in water bodies and possibly causing dead zones.
  • Habitat destruction if large amounts of biodegradable waste are not managed properly.

So, while biodegradable waste is less harmful than non-biodegradable waste, it can still affect the environment if not managed properly.

9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?

Answer: Damage to the ozone layer is a cause for concern because the ozone layer protects life on Earth from harmful ultraviolet (UV) radiation from the sun. Increased exposure to UV radiation can lead to:

  • Skin cancer and cataracts in humans.
  • Disruption of ecosystems, particularly affecting marine life like phytoplankton, which are essential to the food chain.
  • Harm to plants and animals due to the genetic damage caused by UV radiation.

Steps being taken to limit ozone layer damage include:

  • The Montreal Protocol (1987), an international agreement to phase out the use of ozone-depleting chemicals like CFCs (chlorofluorocarbons).
  • Development and use of safer alternatives to ozone-depleting substances.
  • Monitoring of ozone layer levels through satellite technology.

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