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1. What are trophic levels? Give an example of food chain and state the different trophic levels in it.
Answer:
Trophic levels refer to the various steps in a food chain where the transfer of food (or energy) takes place. E.g.,
Grass → Grasshopper → Frog → Eagle
In this:
- Grass: First trophic level (producer).
- Grasshopper: Second trophic level (primary consumer).
- Frog: Third trophic level (secondary consumer).
- Eagle: Fourth trophic level (tertiary consumer).
2. What is the role of decomposers in the ecosystem?
Answer:
- Decomposers break down the dead bodies of plants and animals, acting as natural cleansing agents for the environment.
- They return essential elements from dead organisms back to the soil, air, and water, making them available for reuse by producers such as crop plants.
- They play a vital role in the recycling of nutrients.
- By decomposing dead remains, they free up space and resources for new life in the biosphere.
Page 262
1. Why are some substances biodegradable and some non-biodegradable?
Answer:
Decomposer organisms like bacteria and fungi are specific in their action. They can break down substances made from natural materials (e.g., paper), but not synthetic materials like plastics. This selective action makes some substances biodegradable and others non-biodegradable.
2. Give any two ways in which biodegradable substances would affect the environment.
Answer:
- Biodegradable substances are broken down by microorganisms, and the resulting materials are recycled through natural cycles.
- Their decomposition helps keep the environment clean and free from waste buildup.
3. Give any two ways in which non-biodegradable substances would affect the environment.
Answer:
- They contribute to air, water, and soil pollution.
- They can lead to bio-magnification, where harmful substances accumulate through the food chain and ultimately affect humans.
Page 264
1. What is ozone and how does it affect any ecosystem?
Answer:
Ozone (O3) is a molecule made up of three atoms of oxygen and is considered an isotope of oxygen.
In the upper atmosphere, ozone plays a crucial role by absorbing harmful ultraviolet (UV) rays from the sun, thereby protecting living organisms on Earth. Without this layer, UV radiation could cause severe damage, including skin cancer.
2. How can you help in reducing the problem of waste disposal? Give any two methods.
Answer:
- Recycling: Solid wastes such as paper, plastics, and metals can be collected and processed for reuse.
- Composting: Biodegradable kitchen waste like food scraps, vegetable peels, and plant leaves can be buried in pits to create compost, which enriches the soil.