1What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
Answer & Reference:
Trophic levels are the various steps in a food chain where transfer of food (energy) takes place. Each step represents a trophic level.
Example of a food chain: Grass → Grasshopper → Frog → Snake
- Grass (Producer) - First trophic level
- Grasshopper (Primary consumer) - Second trophic level
- Frog (Secondary consumer) - Third trophic level
- Snake (Tertiary consumer) - Fourth trophic level
(Reference: Page 210, Section 13.1.1)
2What is the role of decomposers in the ecosystem?
Answer & Reference:
Decomposers (bacteria and fungi) break down dead remains and waste products of organisms into simple inorganic substances that go into the soil and are used up once more by plants. They play a crucial role in:
1. Recycling nutrients in the ecosystem
2. Cleaning the environment by decomposing dead organic matter
3. Maintaining soil fertility by releasing nutrients
Without decomposers, dead organisms and waste would accumulate, and nutrients would not be recycled back to producers.
(Reference: Page 209, Activity 13.2 explanation)
3Why are some substances biodegradable and some non-biodegradable?
Answer & Reference:
Biodegradable substances can be broken down by biological processes (microorganisms like bacteria and fungi) because they contain organic matter that these organisms can digest. Examples include vegetable peels, paper, and cotton.
Non-biodegradable substances cannot be broken down by biological processes because they are either inert or made of complex synthetic materials that microorganisms cannot digest. Examples include plastics, glass, and metals.
(Reference: Page 214, Section 13.2.2)
4Give any two ways in which biodegradable substances would affect the environment.
Answer & Reference:
1. Positive effect: When properly managed (e.g., composting), biodegradable waste enriches soil fertility and supports plant growth.
2. Negative effect: If not managed properly, large quantities of biodegradable waste can produce foul smell, attract pests, and become breeding grounds for disease-causing organisms.
(Reference: Page 214-215, Activity 13.7)
5Give any two ways in which non-biodegradable substances would affect the environment.
Answer & Reference:
1. Non-biodegradable substances persist in the environment for a long time, causing land and water pollution.
2. They can enter food chains and cause biological magnification, leading to harmful effects on organisms at higher trophic levels, including humans.
(Reference: Page 214, Section 13.2.2 and Page 211-212, Activity 13.3)
6What is ozone and how does it affect any ecosystem?
Answer & Reference:
Ozone (O₃) is a molecule formed by three atoms of oxygen. In the upper atmosphere (stratosphere), it forms a protective layer that shields the Earth's surface from harmful ultraviolet (UV) radiation from the Sun.
Effects on ecosystem:
- Protects living organisms from UV radiation which can cause skin cancer, cataracts, and damage to immune systems in humans
- Prevents damage to plants (reduced photosynthesis) and phytoplankton (base of aquatic food chains)
- Maintains ecological balance by protecting DNA from UV damage
(Reference: Page 212-213, Section 13.2.1)
7How can you help in reducing the problem of waste disposal? Give any two methods.
Answer & Reference:
1. Segregation at source: Separate biodegradable and non-biodegradable waste at home to facilitate proper disposal and recycling.
2. Reduce and reuse: Minimize waste generation by using reusable items (cloth bags instead of plastic bags) and avoiding disposable products.
Additional methods:
- Composting biodegradable kitchen waste
- Participating in community recycling programs
(Reference: Page 215-216, Activity 13.7 and Think it over section)
8Which 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 & Reference:
Options (a), (c), and (d) contain only biodegradable items.
- (a) Grass, flowers and leather: All are natural organic materials
- (c) Fruit-peels, cake and lime-juice: All are food-based organic materials
- (d) Cake, wood and grass: All are natural organic materials
Option (b) contains plastic which is non-biodegradable.
(Reference: Page 216, Exercise Question 1)
9Which 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 & Reference:
Option (b) Grass → Goat → Human constitutes a valid food chain.
- Grass (Producer)
- Goat (Primary consumer/herbivore)
- Human (Secondary consumer/omnivore)
Other options are invalid:
- (a) All are producers
- (c) All are consumers with no producer
- (d) Fish typically don't eat grass, and goat doesn't eat fish
(Reference: Page 216, Exercise Question 2)
10Which 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 & Reference:
(d) All of the above are environment-friendly practices.
- (a) Reduces plastic waste
- (b) Conserves energy
- (c) Reduces air pollution and fossil fuel consumption
(Reference: Page 216, Exercise Question 3)
11What will happen if we kill all the organisms in one trophic level?
Answer & Reference:
If all organisms in one trophic level are killed:
1. The trophic level above it will not get food and may die or migrate
2. The trophic level below it will increase in number due to lack of predators
3. This will disrupt the entire food chain and ecosystem balance
Example: If all herbivores (deer, rabbits) are killed:
- Carnivores (lions, tigers) will starve
- Plants will overgrow, potentially leading to other ecological imbalances
(Reference: Page 216, Exercise Question 4)
12Will 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 & Reference:
Yes, the impact will be different depending on which trophic level is removed:
- Removing producers (first trophic level) would collapse the entire ecosystem as all other levels depend on them
- Removing top carnivores might cause overpopulation of herbivores, leading to overgrazing and habitat destruction
No trophic level can be completely removed without causing damage to the ecosystem. Each level plays a crucial role in maintaining ecological balance through energy flow and nutrient cycling.
(Reference: Page 216, Exercise Question 5)
13What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer & Reference:
Biological magnification is the process where the concentration of harmful chemicals (like pesticides) increases at each successive trophic level in a food chain.
Yes, the levels of magnification are different at different trophic levels:
- Producers (plants) have the lowest concentration
- Primary consumers have higher concentration
- Secondary consumers have even higher concentration
- Tertiary consumers (top carnivores including humans) have the highest concentration
This happens because these chemicals are non-biodegradable and accumulate in the bodies of organisms. When a consumer eats many organisms from the lower level, it accumulates all the chemicals stored in them.
(Reference: Page 211-212, Activity 13.3)
14What are the problems caused by the non-biodegradable wastes that we generate?
Answer & Reference:
Problems caused by non-biodegradable wastes:
1. Persistence in environment: They remain in the environment for hundreds of years, occupying space and causing visual pollution
2. Soil pollution: They reduce soil fertility and prevent water percolation
3. Water pollution: They block drains and waterways, and release toxic chemicals into water bodies
4. Biological magnification: Toxic chemicals from non-biodegradable waste enter food chains and accumulate in higher trophic levels
5. Harm to wildlife: Animals may ingest plastics or get entangled in waste materials, leading to injury or death
15If all the waste we generate is biodegradable, will this have no impact on the environment?
Answer & Reference:
Even if all waste is biodegradable, it can still impact the environment if generated in excessive quantities:
1. Decomposition of large amounts of biodegradable waste produces foul-smelling gases (like methane and hydrogen sulfide)
2. It can become a breeding ground for disease-causing organisms (flies, mosquitoes, bacteria)
3. If dumped in water bodies, decomposition consumes oxygen, leading to death of aquatic organisms (eutrophication)
However, biodegradable waste is less harmful than non-biodegradable waste and can be managed through composting and proper disposal methods.
(Reference: Page 217, Exercise Question 8)
16Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Answer & Reference:
Damage to the ozone layer is concerning because:
1. It allows more harmful UV radiation to reach Earth's surface
2. UV radiation causes skin cancer, cataracts, and immune system damage in humans
3. It harms phytoplankton (base of aquatic food chains) and reduces crop yields
Steps taken to limit damage:
1. Montreal Protocol (1987): International agreement to phase out ozone-depleting substances like CFCs
2. Ban on CFC production: Manufacturing companies now produce CFC-free refrigerators
3. Development of alternatives: Using substitutes like HFCs (hydrofluorocarbons) that don't deplete ozone
17Explain the flow of energy in an ecosystem with a diagram.
Answer & Reference:
Energy flow in an ecosystem follows these principles:
1. Energy enters the ecosystem through producers (green plants) via photosynthesis
2. Only about 1% of solar energy is captured by producers
3. Energy transfer between trophic levels follows the 10% law - only about 10% of energy is transferred to the next level
4. Energy flow is unidirectional - it doesn't cycle back to previous levels
5. Energy is lost as heat at each trophic level
Figure: Energy flow in an ecosystem showing 10% energy transfer between trophic levels
(Reference: Page 210-211, Figure 13.4 and Section 13.1.1)
18Provide examples of food chains in different ecosystems as shown in Figure 13.1.
Answer & Reference:
Examples of food chains in different ecosystems: