Answer The Following Question.
1. Why are some substances biodegradable and some non-biodegradable?
Ans: Biodegradable substances are those that can be broken down by microorganisms (decomposers). These substances are naturally decomposed into simpler, non-toxic substances.
Examples: Vegetable wastes, paper, cotton, etc.
Non-biodegradable substances are those that cannot be broken down by decomposers and persist in the environment for a long time.
Examples: Plastic, glass, polythene, etc.
2. Give any two ways in which biodegradable substances would affect the environment.
Ans: a) Breeding ground for pests: Biodegradable substances, if not properly disposed of, can serve as breeding grounds for flies and mosquitoes, which are carriers of diseases like cholera, malaria, etc.
(b) Air pollution: The decomposition of biodegradable substances can produce foul smells, leading to air pollution and an unpleasant environment.
3. Give any two ways in which non-biodegradable substances would affect the environment.
Ans: (a) Water pollution: Excess use of non-biodegradable pesticides and fertilizers can run off with rainwater into water bodies, causing water pollution.
(b) Choking of sewer systems: Non-biodegradable substances, like plastic, can clog the sewage systems of cities or towns, leading to blockages and potential overflow onto roads.
4. What are trophic levels? Give an example of a food chain and state the different trophic level in it.
Ans : Each step in a food chain constitutes a trophic level. For example,
5. What is the role of decomposers in the ecosystem?
Ans: (i) Cleansing the environment: Decomposers break down the dead bodies of plants and animals, acting as cleansing agents of the environment.
(ii) Recycling of elements: They release various elements from dead organisms back into the soil, air, and water, making them available for use by producers like crop plants.
(iii) Nutrient recycling: Decomposers play a key role in recycling nutrients, ensuring that essential elements are reused in the ecosystem.
(iv) Creating space for new life: By decomposing dead remains, they create space for new organisms to settle in the biosphere.
6. What is ozone and how does it affect any ecosystem?
Ans: Ozone (O₃) is a molecule made up of three oxygen atoms.
It is found in the upper atmosphere, forming the ozone layer.
The ozone layer absorbs and shields the Earth from harmful ultraviolet (UV) radiation from the sun.
UV radiation can cause damage like skin cancer in humans, and negatively affect plants, aquatic organisms, and other species.
By blocking UV rays, ozone helps protect ecosystems and maintains the health of living organisms.
7. How can you help in reducing the problems of waste disposal? Give any two methods.
Ans: (i) Reduce waste volume: One way to reduce waste is by burning it in an incinerator, which helps in reducing the overall volume of waste.
(ii) Recycling: Recycling materials such as paper, plastic, and glass can help reduce waste and promote the reuse of resources, minimizing the impact on the environment.
8. 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
Ans : Groups (a), (c) and (d).
9. 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.
Ans : (b) Grass, goat, human
10. Which of the following are environment-friendly practices?
(a) Carrying cloth-bag 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.
Ans : (d) All of the above.
11. What will happen if we kill all the organisms in one trophic level?
Ans: Killing all organisms in one trophic level disrupts the food chain.
The number of individuals in the next trophic level will decrease due to the lack of food.
The number of individuals in the previous trophic level will increase because there are no predators to feed on them.
This imbalance leads to disruption in the entire ecosystem.
The resulting changes can harm the environment and lead to cascading effects in the food web.
12. 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?
Ans: (Pointwise):
Different impacts on different trophic levels:
Removing producers: Herbivores would starve or migrate, leading to ecosystem collapse.
Removing herbivores: Producers would grow unchecked, and carnivores would lack food.
Removing carnivores: Herbivore populations would increase uncontrollably, potentially destroying producers.
Removing decomposers: Dead animals would accumulate, causing pollution, and nutrient recycling would stop, reducing soil fertility.
Importance of each trophic level:
All trophic levels are essential for maintaining ecosystem balance.
Removal of any trophic level would cause significant damage to the ecosystem.
13. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Ans: Definition of Biological Magnification:
It is the progressive increase in the concentration of harmful non-biodegradable chemicals (e.g., DDT) at each trophic level in the food chain.
Variation in Magnification Across Trophic Levels:
The concentration of harmful chemicals is lowest at the first trophic level (producers).
It increases as it moves up the food chain, reaching its highest concentration at the top trophic levels (carnivores).
14. What are the problems caused by non-biodegradable wastes that we generate?
Ans: Water Pollution:
Non-biodegradable pesticides and fertilizers run off into water bodies, leading to water pollution.
Biomagnification:
Non-biodegradable substances like DDT enter the food chain and accumulate, causing biomagnification in humans and other animals.
15. If all the wastes we generate is biodegradable, will this have no impact on the environment?
Ans: Short-term Impact:
Biodegradable wastes may cause some air or water pollution initially.
The action of decomposers may slow down.
Long-term Impact:
In the long run, biodegradable wastes will not have a significant impact on the environment, as decomposers will break them down and return the nutrients to the ecosystem.
16. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Ans: Cause for Concern:
Damage to the ozone layer allows harmful ultraviolet (UV) radiations from the sun to reach the Earth’s surface.
These UV rays can cause skin cancer, other health issues in humans and animals, and damage plants.
Steps to Limit Damage:
The United Nations Environment Programme (UNEP) facilitated an agreement among countries to freeze the production of CFCs (chlorofluorocarbons) at 1986 levels to protect the ozone layer.