Chapter Questions
1. What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
Trophic levels are the different steps or levels in a food chain at which transfer of food (or energy) takes place. Each trophic level represents a feeding level in an ecosystem.
Example of a food chain: Grass → Grasshopper → Frog → Snake
Trophic levels:
- First trophic level: Grass (Producer)
- Second trophic level: Grasshopper (Primary consumer/Herbivore)
- Third trophic level: Frog (Secondary consumer/Carnivore)
- Fourth trophic level: Snake (Tertiary consumer/Top carnivore)
2. What is the role of decomposers in the ecosystem?
Decomposers play a crucial role in the ecosystem by:
- Breaking down dead organic matter and waste products into simpler inorganic substances
- Recycling nutrients back into the soil for reuse by plants
- Cleaning the environment by decomposing dead bodies and organic wastes
- Maintaining the nutrient cycle in the ecosystem
- Preventing accumulation of dead matter in the environment
Without decomposers, dead organisms and waste would accumulate, nutrients would not be recycled, and the ecosystem would eventually collapse.
3. Why are some substances biodegradable and some non-biodegradable?
Substances are classified as biodegradable or non-biodegradable based on their ability to be broken down by biological processes:
- Biodegradable substances: Can be broken down by microorganisms (bacteria, fungi) into simpler substances. Examples include food waste, paper, cotton, wood, etc.
- Non-biodegradable substances: Cannot be broken down by biological processes. Examples include plastics, glass, metals, synthetic fibers, etc.
The difference arises because microorganisms produce specific enzymes that can break down natural organic materials but not synthetic or man-made materials like plastics.
4. Give any two ways in which biodegradable substances would affect the environment.
Biodegradable substances affect the environment in both positive and negative ways:
Positive effects:
- They get decomposed and enrich the soil with nutrients
- They are part of natural nutrient cycles and don't accumulate in the environment
Negative effects (when in excess):
- Can cause foul smell and spread diseases if not properly managed
- Can pollute water bodies if dumped in large quantities
5. Give any two ways in which non-biodegradable substances would affect the environment.
Non-biodegradable substances negatively affect the environment in several ways:
- They persist in the environment for long periods and accumulate, causing pollution
- They can enter food chains and cause biological magnification of harmful substances
- They can clog drains and waterways, causing floods
- They can be ingested by animals, causing health problems or death
6. What is ozone and how does it affect any ecosystem?
Ozone (O₃) is a molecule formed by three atoms of oxygen. It exists in two layers of the atmosphere:
- Ground level ozone: Harmful pollutant that can damage plants and cause respiratory problems
- Stratospheric ozone: Forms the ozone layer that protects the Earth from harmful ultraviolet (UV) radiation
The ozone layer affects ecosystems by:
- Shielding all living organisms from harmful UV radiation
- Preventing damage to plant tissues and phytoplankton (base of aquatic food chains)
- Reducing the risk of skin cancer and other health issues in animals and humans
- Maintaining the balance of ecosystems by protecting producers (plants) from UV damage
7. How can you help in reducing the problem of waste disposal? Give any two methods.
We can help reduce the problem of waste disposal through:
- Reduce, Reuse, Recycle: Minimize waste generation, reuse items whenever possible, and recycle materials like paper, plastic, glass and metals
- Segregation of waste: Separate biodegradable and non-biodegradable waste at source for proper treatment and disposal
- Composting: Convert kitchen and garden waste into compost for plants
- Avoiding single-use plastics: Use cloth bags, metal containers, and other sustainable alternatives
- Proper disposal: Ensure hazardous waste like batteries, medicines, and e-waste are disposed of through proper channels
Exercise Questions
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: (a) Grass, flowers and leather; (c) Fruit-peels, cake and lime-juice; (d) Cake, wood and grass
Explanation: All these items are natural organic materials that can be broken down by microorganisms. Option (b) contains plastic which is non-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: This represents a proper food chain where grass (producer) is eaten by goat (primary consumer) which is then eaten by human (secondary consumer). The other options don't represent proper 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 these practices help in conserving resources, reducing pollution and protecting the environment.
4. What will happen if we kill all the organisms in one trophic level?
If we kill all organisms in one trophic level, it would disrupt the entire ecosystem:
- The trophic level below would increase in number due to lack of predators
- The trophic level above would starve due to lack of food
- The food chain would break down
- Ecological balance would be disturbed
- Nutrient cycling would be affected
For example, if all herbivores are killed, plants would overgrow while carnivores would die of starvation.
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?
Yes, the impact would be different for different trophic levels:
- Removing producers would collapse the entire ecosystem as no food would be produced
- Removing herbivores would cause overgrowth of plants and starvation of carnivores
- Removing carnivores would cause herbivore population explosion leading to overgrazing
- Removing decomposers would halt nutrient recycling and cause waste accumulation
No trophic level can be removed without damaging the ecosystem as all are interconnected and play vital roles in maintaining ecological balance.
6. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Biological magnification is the process where certain non-biodegradable substances (like pesticides, heavy metals) become increasingly concentrated in the tissues of organisms at higher trophic levels of a food chain.
Yes, the levels of magnification are different at different trophic levels:
- Producers have the lowest concentration
- Primary consumers have higher concentration
- Secondary consumers have even higher concentration
- Tertiary consumers (top carnivores) have the highest concentration
This happens because these substances are not metabolized or excreted, so they accumulate in bodies and get passed on and concentrated at each trophic level.
7. What are the problems caused by the non-biodegradable wastes that we generate?
Non-biodegradable wastes cause several environmental problems:
- Pollution: They persist in the environment and cause land, water and air pollution
- Health hazards: Can cause diseases and health problems in humans and animals
- Clogging of drains: Leading to water logging and floods
- Soil degradation: Reduce soil fertility and affect plant growth
- Biological magnification: Enter food chains and become concentrated in top consumers
- Visual pollution: Spoil the beauty of landscapes
- Threat to wildlife: Animals may ingest plastic or get entangled in it
8. If all the waste we generate is biodegradable, will this have no impact on the environment?
No, even if all waste is biodegradable, it can still impact the environment negatively if not managed properly:
- Large quantities can produce foul smell and attract pests
- Can spread diseases if not treated properly
- Can cause water pollution if dumped in water bodies
- Decomposition produces methane gas which contributes to global warming
- Can deplete oxygen in water bodies during decomposition, killing aquatic life
However, when managed properly through composting and other methods, biodegradable waste can be beneficial as it enriches the soil.
9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Damage to the ozone layer is a cause for concern because:
- It allows harmful UV radiation to reach the Earth's surface
- Increases risk of skin cancer and cataracts in humans
- Damages plant tissues and reduces crop yields
- Harms phytoplankton, the base of marine food chains
- Weakens immune systems in animals
Steps taken to limit this damage:
- Montreal Protocol (1987) to phase out ozone-depleting substances like CFCs
- Development of CFC-free refrigerators and air conditioners
- Ban on production and use of ozone-depleting chemicals
- Promotion of alternative technologies that don't harm the ozone layer
- International cooperation and monitoring of ozone layer recovery