CHAPTER – 13: OUR ENVIRONMENT

CHAPTER – 13: OUR ENVIRONMENT

VOLUME – 1

SECTION-A: Multiple Choice Questions

  1. What is the ultimate source of energy which further flows through the food chain?
    (a) chemical energy
    (b) wind energy
    (c) Electric energy
    (d) solar energy
    Ans-(d) solar energy
  2. The flow of energy in an ecosystem is always:
    (a) unidirectional
    (b) bidirectional
    (c) cyclic
    (d) multidirectional
    Ans-(a) unidirectional
  3. Kitchen waste can be hygienically disposed of through
    (a) Dumping
    (b) Composting
    (c) Incineration
    (d) Recycling
    Ans-(b) Composting
  4. Which group of organisms are not constituents of same food chain?
    (a) Grass, lion, rabbit, wolf
    (b) Plankton, man, fish
    (c) Wolf, grass, snake, tiger
    (d) Frog, snake, eagle, grass, grasshopper
    Ans-(b) Plankton, man, fish
  5. The percentage of solar radiation absorbed by all the green plants for the process of photosynthesis is about:
    (a)1%
    (b)2%
    (c)3%
    (d)4%
    Ans-(a) 1%
  6. Select the mismatched pair in the following and correct it.
    (a) Bio-magnification — Accumulation of chemicals at the successive trophic levels of a food chain
    (b) Ecosystem — Biotic components of environment
    (c) Aquarium — A man-made ecosystem
    (d) Parasites — Organisms which obtain food from another living organism
    Ans- (b)Ecosystem - Biotic components of environment
  7. Which one of the following green house gases is a contributor of global warming due to the incomplete combustion of coal and petroleum?
    (a) Oxides of nitrogen
    (b) Methane
    (c) Carbon monoxide
    (d) Carbon dioxide
    Ans- Carbon monoxide
  8. Depletion of ozone is mainly due to _________.
    (a) chlorofluorocarbon compounds
    (b) carbon monoxide
    (c) methane
    (d) Sulphur dioxide
    Ans-(a)chlorofluorocarbon compound
  9. What is the role of decomposers in the ecosystem?
    (a) Photosynthesis
    (b) Consume producers
    (c) Recycle nutrients
    (d) Respiration
    Ans-(c) Recycle nutrients
  10. One major reason to avoid plastic use is:
    (a) It's expensive
    (b) It decomposes fast
    (c) It pollutes soil and water
    (d) It melts in sunlight
    Ans-(c) It pollutes soil and water

ASSERTION REASON TYPE QUESTIONS

Following questions consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:

  • (a) Both A and R are true and R is the correct explanation of A.
  • (b) Both A and R are true but R is not the correct explanation of A.
  • (c) A is true but R is false.
  • (d) A is false but R is true.
  1. Assertion: Aquarium needs regular cleaning
    Reason: There are no microbes to clean water in aquarium, therefore, it needs to be regularly cleaned.
    Ans-(a) Both A and R are true, and R is the correct explanation of A.
  2. Assertion: Food chain is responsible for the entry of harmful chemicals in our bodies.
    Reason: The length and complexity of food chains vary greatly.
    Ans(b) Both A and R are true, and R is not the correct explanation of A.

VERY SHORT QUESTIONS

  1. Define the term ‘biodegradable waste’. Select biodegradable waste(s) from the following: Insecticides, agricultural waste, plastics, sewage
    Ans- Biodegradable waste: Biodegradable waste refers to substances that can be broken down naturally by microorganisms like bacteria and fungi into simpler, harmless substances.
    Biodegradable waste(s) from the given list:
    • Agricultural waste
    • Sewage
  2. Why is energy flow in a food chain unidirectional?
    Ans: Energy flows from the sun to producers, and then to consumers in one direction. It cannot be reused by the previous level as some energy is lost as heat at each trophic level.
  3. Name two components of the biotic environment.
    Ans: Plants and animals.
  4. Name one biodegradable and one non-biodegradable waste.
    Ans: Biodegradable – fruit peel; Non-biodegradable – plastic.
  5. What do you mean by 10% law of energy transfer?
    Ans: Only 10% of energy is transferred from one trophic level to the next.

SHORT ANSWER TYPE QUESTIONS

  1. What is biological magnification? Explain with the help of an example.
    Ans: Biological magnification refers to the increase in the concentration of harmful substances like pesticides at each successive trophic level in a food chain.
    Example: DDT sprayed on crops enters the food chain and accumulates in top carnivores like birds.
  2. Why are bacteria and fungi called decomposers? List any two advantages of decomposers to the environment?
    Ans- Bacteria and fungi are called decomposers because they break down the complex organic matter of dead plants and animals into simpler substances.
    Two advantages of decomposers:
    1. They recycle nutrients back into the soil, making them available for plants.
    2. They help in cleaning the environment by decomposing dead and decaying matter.
  3. Why is excessive use of CFCs a cause of concern?
    Ans- CFCs (Chlorofluorocarbons) deplete the ozone layer in the upper atmosphere. The ozone layer protects us from harmful ultraviolet (UV) radiation. Excessive use of CFCs leads to ozone holes, which can cause skin cancer, eye damage, and harm to crops and marine life.
  4. List two advantages of using paper or cloth bags instead of plastic bags.
    Ans:
    • Paper and cloth bags are biodegradable and do not cause pollution.
    • They are recyclable and reusable, reducing environmental harm.
  5. What are the problems caused by the excessive use of non-biodegradable substances?
    Ans:
    • They pollute soil and water.
    • They may enter food chains, leading to health hazards.
    • They remain in the environment for long periods, causing land and air pollution.

LONG ANSWER TYPE QUESTIONS

  1. Explain how human activities are disturbing the balance of the environment. Suggest any three sustainable practices to reduce this impact.
    Ans-
    • Activities like deforestation, pollution, excessive plastic use, and industrial waste disturb nature.
    • These lead to global warming, loss of biodiversity, and pollution.
    Sustainable practices:
    1. Use cloth/paper bags instead of plastic
    2. Segregate waste and compost biodegradable waste
    3. Plant more trees and use clean energy (solar, wind)
  2. What is ozone? How is it formed in the atmosphere? Why is it called a protective shield? What are the effects of ozone depletion?
    Ans-
    • Ozone (\( O_3 \)) is a molecule made of three oxygen atoms.
    • It forms when UV rays split \( O_2 \) molecules; the free oxygen atom combines with another \( O_2 \) to form \( O_3 \).
    • It acts as a protective shield by absorbing harmful UV radiation.
    • Depletion effects: Skin cancer, cataracts, reduced crop yield, harm to aquatic life.
  3. "Energy flow in an ecosystem is always unidirectional." Justify this statement. Explain how pesticides enter the food chain and accumulate in our bodies.
    Ans-
    • Energy flows from \( \text{sun} \rightarrow \text{producers} \rightarrow \text{consumers} \) and is lost as heat at each level. It cannot return to the previous level—so it's unidirectional.
    • Pesticides used on crops are consumed by herbivores, then by carnivores. These non-biodegradable chemicals accumulate at higher trophic levels—a process called biological magnification.
    • Humans, being at the top, are at maximum risk.

CASE BASED QUESTIONS

  1. Food Chain in a Forest
    A forest ecosystem contains producers like grasses and trees, primary consumers like deer and insects, and secondary consumers like tigers and snakes. Decomposers such as fungi and bacteria break down dead organic matter.
    a) Which of the following correctly represents a food chain in the forest ecosystem?
    A. \( \text{Grass} \rightarrow \text{Deer} \rightarrow \text{Tiger} \)
    B. \( \text{Tiger} \rightarrow \text{Deer} \rightarrow \text{Grass} \)
    C. \( \text{Fungi} \rightarrow \text{Grass} \rightarrow \text{Deer} \)
    D. \( \text{Deer} \rightarrow \text{Grass} \rightarrow \text{Tiger} \)
    b) In the forest food chain, who are the primary consumers?
    A. Tigers
    B. Deer
    C. Fungi
    D. Trees
    c) What role do decomposers play in this ecosystem?
    OR Construct a food chain with four trophic levels.
  2. The atmosphere is a blanket of air and a precious natural resource for sustaining life on the Earth. Unfortunately, human activities based on national/personal interests are causing harm to this common resource, notably by depleting the fragile ozone layer, which acts as a protective shield for life on the Earth. Ozone molecules consist of three oxygen atoms; Ozone molecules are exceeding rare: fewer than ten in every million molecules of air. However, for nearly a billion years, their presence in the atmosphere has played a vital role in safeguarding life on Earth.
    Now answer the following questions-
    (i) Which chemicals are primarily responsible for ozone layer depletion?
    (ii) How does ozone layer depletion affect marine ecosystems?
    (iii) How can individuals contribute to protect the ozone layer?
    OR
    How ozone is formed in the atmosphere? Show with reaction.

CHAPTER-13- OUR ENVIRONMENT

WORKSHEET (VOLUME-1)

CLASS 10 NAME:
SUBJECT – SCIENCE DATE:
TIME-20 MIN MM- 21MARKS

SECTION –A (MCQ)

  1. Which of the following is a biodegradable substance?
    (a) Glass (b) DDT (c) Vegetable peels (d) Plastic
    Ans: (c) Vegetable peels
  2. Which trophic level in a food chain has the least amount of energy?
    (a) Producers (b) Primary consumers (c) Secondary consumers (d) Top carnivores
    Ans: (d) Top carnivores
  3. Which gas is mainly responsible for the depletion of the ozone layer?
    (a) \( CO_2 \) (b) \( CH_4 \) (c) CFCs (d) \( SO_2 \)
    Ans: (c) CFCs
  4. Which of the following is a correct sequence in a terrestrial food chain?
    (a) \( \text{Grass} \rightarrow \text{Cow} \rightarrow \text{Human} \rightarrow \text{Lion} \)
    (b) \( \text{Grass} \rightarrow \text{Grasshopper} \rightarrow \text{Frog} \rightarrow \text{Snake} \)
    (c) \( \text{Human} \rightarrow \text{Rice} \rightarrow \text{Cow} \rightarrow \text{Lion} \)
    (d) \( \text{Snake} \rightarrow \text{Frog} \rightarrow \text{Grasshopper} \rightarrow \text{Grass} \)
    Ans: (b) \( \text{Grass} \rightarrow \text{Grasshopper} \rightarrow \text{Frog} \rightarrow \text{Snake} \)
  5. Assertion (A): Aquarium needs regular cleaning.
    Reason (R): There are no decomposers to clean the waste in aquariums.
    Choose the correct option:
    (a) Both A and R are true, and R explains A.
    (b) Both A and R are true, but R does not explain A.
    (c) A is true, R is false.
    (d) A is false, R is true.
    Ans: (a)
  6. Assertion (A): Food chain is responsible for entry of harmful chemicals in our body.
    Reason (R): The length of food chain determines amount of energy lost.
    Ans: (b)

SECTION –B (VSA)

  1. Define biodegradable waste with an example.
    Ans: Substances that can be broken down by microorganisms (e.g., vegetable peels).
  2. What is meant by trophic level?
    Ans: Each step or level in a food chain is called a trophic level.
  3. What is biological magnification?
    Ans: Increase in the concentration of harmful chemicals at each trophic level.

SECTION –C (SA)

  1. What will happen if decomposers are removed from the ecosystem?
    Ans: Dead organisms would accumulate; nutrients won’t be recycled; ecosystem balance will be disturbed.
  2. Why should biodegradable and non-biodegradable wastes be disposed of separately?
    Ans: Biodegradable waste can decompose; non-biodegradable harms the environment and should be recycled.
  3. Why are food chains generally limited to 3–4 trophic levels only?
    Ans: Because only 10% energy passes to the next level; energy becomes insufficient for more levels.
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