CBSE Class 10 Biology: Our Environment - Part 3: SA Questions
Top 25 SA Questions with Answers | Latest CBSE Pattern
Welcome to Part 3 of our 8-part series on the chapter Our Environment. This post contains the top 25 Short Answer (SA) Questions, perfect for 2 or 3-mark answers in your board exams.
Recommended Books for Deep Practice
Top 25 SA Questions - Our Environment
Question 1: Decomposers' Role
What are decomposers? List two important roles they play in the environment.
Answer: Decomposers are microorganisms, like bacteria and fungi, that obtain energy by breaking down the dead organic matter of producers and consumers.
Two important roles are:
Two important roles are:
- Cleaning the Environment: They break down dead and decaying organisms, preventing the accumulation of waste.
- Nutrient Recycling: They return the simple inorganic nutrients back to the soil, which are then reused by plants.
Question 2: Biomagnification
What is biomagnification? Which trophic level has the highest concentration of harmful chemicals?
Answer: Biomagnification is the process of increase in the concentration of a harmful, non-biodegradable chemical substance (like DDT) at each successive trophic level of a food chain.
The **highest trophic level** (the top consumers/carnivores) will have the maximum concentration of these harmful chemicals.
The **highest trophic level** (the top consumers/carnivores) will have the maximum concentration of these harmful chemicals.
Question 3: 10% Energy Law
Explain the 10% energy law with an example.
Answer: The 10% law, given by Lindemann, states that only 10% of the energy is transferred from one trophic level to the next. The remaining 90% is lost to the environment as heat during metabolic activities.
Example: If plants (producers) have 1000 J of energy, the deer (primary consumer) that eats them will only get 10% of 1000 J, which is 100 J. The lion (secondary consumer) that eats the deer will only get 10% of 100 J, which is 10 J.
Example: If plants (producers) have 1000 J of energy, the deer (primary consumer) that eats them will only get 10% of 1000 J, which is 100 J. The lion (secondary consumer) that eats the deer will only get 10% of 100 J, which is 10 J.
Question 4: Ozone Layer
How is the ozone layer formed in the atmosphere? Why is it important?
Answer:
- Formation: Ozone (O₃) is formed when high-energy ultraviolet (UV) radiation from the sun splits some molecular oxygen (O₂) into free oxygen (O) atoms. These free (O) atoms then combine with other oxygen (O₂) molecules to form ozone (O₃).
- Importance: The ozone layer is crucial because it absorbs the majority of the sun's harmful UV-B radiation, protecting living organisms on Earth from skin cancer, cataracts, and other health issues.
Question 5: Waste Types
Differentiate between biodegradable and non-biodegradable wastes. Give two examples of each.
Answer:
- Biodegradable Waste: Wastes that can be broken down into simple, harmless substances by the action of microorganisms (like bacteria, fungi).
Examples: Vegetable peels, paper, cotton. - Non-Biodegradable Waste: Wastes that cannot be broken down by microorganisms and persist in the environment for a long time, causing pollution.
Examples: Plastic bags, glass bottles, metal cans.
Question 6: Food Web
What is a food web? Why is it considered more stable than a food chain?
Answer: A food web is a network of multiple interconnected food chains that shows the complex feeding relationships in an ecosystem.
It is more stable than a food chain because it provides alternative food sources for organisms. If one food source (e.g., a population of rabbits) declines, the consumer (e.g., a fox) can switch to another food source (e.g., rats), ensuring its survival and the ecosystem's stability.
It is more stable than a food chain because it provides alternative food sources for organisms. If one food source (e.g., a population of rabbits) declines, the consumer (e.g., a fox) can switch to another food source (e.g., rats), ensuring its survival and the ecosystem's stability.
Question 7: Energy Flow
"The flow of energy in an ecosystem is unidirectional." Justify this statement.
Answer: This statement is true because:
- Energy enters the ecosystem from the sun and is captured by producers.
- It then flows to primary consumers, then to secondary consumers, and so on.
- At each level, a large amount of energy is lost as heat and used for metabolic activities.
- The energy that is transferred cannot flow backward (e.g., from a carnivore back to a herbivore). Therefore, the flow is only in one direction.
Question 8: Waste Disposal
List any two methods of waste disposal and explain one of them.
Answer: Two methods of waste disposal are (1) Composting and (2) Recycling.
Composting: This method is used for biodegradable waste (like kitchen scraps, leaves). The waste is placed in a pit or a bin, where microorganisms (bacteria, fungi) decompose it into nutrient-rich humus or manure. This humus can then be used to improve soil fertility.
Composting: This method is used for biodegradable waste (like kitchen scraps, leaves). The waste is placed in a pit or a bin, where microorganisms (bacteria, fungi) decompose it into nutrient-rich humus or manure. This humus can then be used to improve soil fertility.
Question 9: Trophic Levels
What are trophic levels? In the food chain: Grass -> Insect -> Frog -> Snake, which organism is at the third trophic level?
Answer: Trophic levels are the different steps in a food chain that represent the flow of energy.
In the given food chain:
In the given food chain:
- Grass = T1 (Producer)
- Insect = T2 (Primary Consumer)
- Frog = T3 (Secondary Consumer)
- Snake = T4 (Tertiary Consumer)
Question 10: Human Impact
"Humans are an integral part of the ecosystem." How do our activities negatively impact the environment?
Answer: Human activities negatively impact the environment in many ways:
- Deforestation: Cutting down trees for agriculture and urban development destroys habitats and increases CO₂.
- Pollution: The release of harmful chemicals from industries and vehicles pollutes air, water, and soil.
- Waste Generation: The use of non-biodegradable materials like plastic leads to land pollution and harms wildlife.
- Ozone Depletion: The use of chemicals like CFCs has damaged the ozone layer.
Related Posts
Question 11: Artificial Ecosystem
Why is an aquarium considered an artificial ecosystem? List its components.
Answer: It is an artificial (man-made) ecosystem because it is created and maintained by humans. It is not self-sustaining like a natural pond.
Components:
Components:
- Biotic: Fish (consumers), aquatic plants (producers), snails (scavengers).
- Abiotic: Water, light (from a lamp), oxygen (from an aerator/pump), gravel, temperature.
Question 12: Plastic Problems
The use of plastic bags is a serious environmental concern. Why? Suggest two alternatives.
Answer: Plastic is a **non-biodegradable** substance. It does not decompose and persists in the environment for centuries. It clogs drains, pollutes soil, and is often ingested by animals (like cows or marine life), leading to their death.
Two alternatives are:
Two alternatives are:
- Jute bags
- Cloth bags (or paper bags)
Question 13: Pesticides in Food Chain
Farmers spray pesticides on their crops. How do these pesticides get transferred to humans?
Answer: This happens through the food chain and biomagnification:
- Pesticides are non-biodegradable. They get absorbed from the soil by the plants (crops) or are consumed by insects.
- When herbivores (like goats or humans) eat these plants, the pesticides enter their bodies.
- When carnivores (like humans) eat the herbivores, the pesticides are transferred to them.
- At each transfer, the concentration of the pesticide increases, reaching harmful levels in top consumers like humans.
Question 14: Biotic/Abiotic
Categorise the following as biotic and abiotic components: Soil, Fungi, Sunlight, Plants, Air, Bacteria.
Answer:
- Biotic (Living): Fungi, Plants, Bacteria
- Abiotic (Non-Living): Soil, Sunlight, Air
Question 15: Nutrient Recycling
"Energy flow is unidirectional, but nutrient flow is cyclic." Explain why nutrient flow is cyclic.
Answer: Nutrient flow is cyclic because nutrients are never "used up," only recycled.
- Producers (plants) take inorganic nutrients from the soil.
- These nutrients are passed on to consumers when they eat the plants.
- When producers and consumers die, decomposers (bacteria, fungi) break down their complex organic matter.
- This process releases the simple inorganic nutrients back into the soil, where they are ready to be used by plants again, completing the cycle.
Question 16: The 3 'R's
What are the "3 Rs" to save the environment? Briefly explain the importance of "Reduce".
Answer: The 3 Rs are: Reduce, Reuse, Recycle.
Importance of "Reduce": This means using less. It is the most important 'R' because it stops the problem at the source. By reducing our consumption (e.g., using less water, electricity, or buying fewer items), we generate less waste and conserve our natural resources most effectively.
Importance of "Reduce": This means using less. It is the most important 'R' because it stops the problem at the source. By reducing our consumption (e.g., using less water, electricity, or buying fewer items), we generate less waste and conserve our natural resources most effectively.
Question 17: Food Chain Length
Why do most food chains have a limited number of trophic levels (e.g., 3 or 4)?
Answer: This is due to the 10% energy law.
- There is a progressive loss of energy (90%) at each trophic level.
- The energy that is transferred is only 10% of the previous level.
- By the time the energy reaches the 4th or 5th trophic level, the amount of available energy is so small that it cannot support a viable population of organisms.
Question 18: Protecting Crops
Suggest two methods for protecting crops from pests that are more environment-friendly than pesticides.
Answer:
- Biological Control: Introducing natural predators or parasites of the pests. For example, using ladybugs to eat aphids.
- Crop Rotation: Changing the type of crop grown in a field each season, which disrupts the life cycle of pests that are specific to one crop.
Question 19: Ozone Hole
What is meant by the "ozone hole"? What single step taken by humans has helped in its recovery?
Answer: The "ozone hole" refers to the severe thinning (depletion) of the ozone layer in the stratosphere, which was observed to be most prominent over Antarctica.
The most important step was the signing of the **Montreal Protocol** (1987), an international treaty that phased out the production and use of ozone-depleting substances, primarily CFCs.
The most important step was the signing of the **Montreal Protocol** (1987), an international treaty that phased out the production and use of ozone-depleting substances, primarily CFCs.
Question 20: Trophic Energy
CBSE PYQ 2025If 20,000 J of energy is available at the producer level (T1), calculate the energy available to the secondary consumers (T3).
Answer:
- Energy at T1 (Producers): 20,000 J
- Energy at T2 (Primary Consumers): 10% of 20,000 J = 2,000 J
- Energy at T3 (Secondary Consumers): 10% of 2,000 J = 200 J
Question 21: Kulhads vs. Plastic
Using kulhads (earthen cups) was proposed as an alternative to plastic cups. Why was this idea later discouraged?
Answer: While kulhads are biodegradable, making them requires a large amount of fertile **topsoil**. This leads to soil erosion and loss of agricultural land.
Although better than plastic, using disposable paper cups (made from recycled paper) is often considered a more sustainable alternative as it does not deplete the topsoil.
Although better than plastic, using disposable paper cups (made from recycled paper) is often considered a more sustainable alternative as it does not deplete the topsoil.
Question 22: Autotrophs vs. Heterotrophs
What is the difference between autotrophs and heterotrophs? Which one is at the base of the food chain?
Answer:
- Autotrophs (Producers): Organisms that can produce their own food from inorganic substances using light (e.g., plants) or chemical energy.
- Heterotrophs (Consumers/Decomposers): Organisms that cannot make their own food and must obtain energy by consuming other organisms (e.g., animals, fungi).
Question 23: Impact of Removing Trophic Level
What will happen if we remove all the deer from the food chain: Grass -> Deer -> Lion?
Answer:
- The population of **grass (producers) will increase** significantly, as there are no deer to eat it.
- The population of **lions (secondary consumers) will decrease** and eventually die or move away due to starvation, as their primary food source (deer) is gone.
Question 24: Garbage Segregation
Why is it necessary to segregate (separate) waste into biodegradable and non-biodegradable bins?
Answer: Segregation is necessary for proper and efficient waste disposal.
- Biodegradable waste (like kitchen scraps) can be sent for **composting** to make manure.
- Non-biodegradable waste (like plastic, glass) can be sent for **recycling** to make new products.
Question 25: Human as Consumer
Humans can be both primary and secondary consumers. Justify this statement with examples.
Answer: Humans are omnivores.
- When humans eat plants (producers), such as vegetables, fruits, or grains, they are acting as **primary consumers**.
- When humans eat animals (primary consumers), such as a goat, chicken, or fish, they are acting as **secondary consumers**.
