WORKSHEET – CHAPTER 13: OUR ENVIRONMENT

SECTION A – MULTIPLE CHOICE QUESTIONS (20 MCQs)

  1. An ecosystem includes:
     a) Living organisms only
     b) Non-living organisms only
     c) Both living and non-living components
     d) Only plants

  2. The producers in an ecosystem are:
     a) Herbivores
     b) Carnivores
     c) Green plants
     d) Decomposers

  3. Which of the following is a decomposer?
     a) Bacteria
     b) Grasshopper
     c) Frog
     d) Goat

  4. A group of interconnected food chains is called:
     a) Food level
     b) Food cycle
     c) Food web
     d) Ecosystem

  5. At which trophic level is maximum energy available?
     a) First
     b) Second
     c) Third
     d) Fourth

  6. Energy flow in an ecosystem is:
     a) Cyclic
     b) Bidirectional
     c) Unidirectional
     d) Random

  7. 10% law was given by:
     a) Mendel
     b) Darwin
     c) Lindeman
     d) Lamarck

  8. The concentration of harmful chemicals increases at higher trophic levels. This is called:
     a) Bioaccumulation
     b) Biomagnification
     c) Eutrophication
     d) Pollution

  9. Ozone layer protects us from:
     a) IR rays
     b) Visible light
     c) UV rays
     d) X–rays

  10. Ozone layer depletion is caused by:
     a) Oxygen
     b) CFCs
     c) Nitrogen
     d) CO₂

  11. Waste that can be broken down by microorganisms is:
     a) Non-biodegradable
     b) Biodegradable
     c) Plastic
     d) Metal

  12. Which of the following is non-biodegradable?
     a) Paper
     b) Cotton
     c) Glass
     d) Food waste

  13. Biological magnification is highest in:
     a) Producers
     b) Primary consumers
     c) Top carnivores
     d) Herbivores

  14. The most stable ecosystem is:
     a) Forest
     b) Desert
     c) Grassland
     d) Pond

  15. Excessive growth of plankton due to nutrient enrichment is:
     a) Biomagnification
     b) Bioaccumulation
     c) Eutrophication
     d) Condensation

Case-Based MCQs

Read the case and answer Q16–20:

A lake receives chemical waste from a factory. Fish-eating birds show thinning of eggshells.

  1. The phenomenon occurring is:
     a) Isomerization
     b) Biomagnification
     c) Decomposition
     d) Nitrogen fixation

  2. The concentration of chemicals is highest in:
     a) Water
     b) Plankton
     c) Small fish
     d) Birds

  3. The chemicals likely responsible are:
     a) DDT
     b) Ozone
     c) CO₂
     d) Nitrogen

  4. If chemicals are fat-soluble, they will:
     a) Be excreted
     b) Accumulate in tissues
     c) Break easily
     d) Dilute

  5. To prevent this, factories should:
     a) Use filters
     b) Dump waste in water
     c) Increase pollution
     d) Kill fish

SECTION B – ASSERTION & REASON (10 Questions)

  1. A: Energy flow in ecosystem is unidirectional.
     R: Energy is lost as heat at each trophic level.

  2. A: Decomposers are essential for ecosystem.
     R: They recycle nutrients back to soil.

  3. A: Food web is more stable than food chain.
     R: Organisms have multiple food sources.

  4. A: Ozone layer protects life on Earth.
     R: It absorbs harmful UV radiation.

  5. A: Plastic is non-biodegradable.
     R: It cannot be decomposed by microbes.

  6. A: Biomagnification affects top consumers most.
     R: Harmful chemicals accumulate in the body.

  7. A: Forest is a self-sustaining ecosystem.
     R: It has rich biodiversity.

  8. A: Producers form first trophic level.
     R: They prepare food using sunlight.

  9. A: CFCs cause ozone depletion.
     R: They release chlorine in stratosphere.

  10. A: Primary consumers eat plants.
     R: They are herbivores.

SECTION C – ONE-WORD / VERY SHORT ANSWERS (10)

  1. Define ecosystem.
  2. What are producers?
  3. What is 10% law?
  4. Define non-biodegradable waste.
  5. What is trophic level?
  6. Name two decomposers.
  7. Write one use of ozone layer.
  8. What is food web?
  9. Define biomagnification.
  10. Give one example of biodegradable waste.

SECTION D – SHORT ANSWER QUESTIONS (8)

  1. Explain any three properties of food chains.
  2. Why are decomposers important in ecosystem?
  3. Explain the flow of energy through ecosystem using a diagram.
  4. What is biological magnification? Explain with an example.
  5. Why are non-biodegradable wastes harmful?
  6. Describe the structure and importance of ozone layer.
  7. Differentiate between biodegradable and non-biodegradable substances.
  8. Explain why only 3–4 trophic levels exist in a food chain.

SECTION E – LONG ANSWER QUESTIONS (5)

Q1. (Energy Flow & Trophic Levels – 5 Marks)

(a) Draw a food chain with 4 trophic levels.
 (b) Explain 10% law with calculations.
 (c) Why does energy flow become inefficient at higher levels?
 (d) Give one disadvantage of long food chains.

Q2. (Ecosystem & Food Web – 5 Marks)

(a) Define ecosystem with its biotic and abiotic components.
 (b) Draw a labelled diagram of a simple food web.
 (c) Why are food webs more stable than food chains?
 (d) Explain any two human activities that disturb ecosystems.

Q3. (Ozone Layer & Pollution – 5 Marks)

(a) Describe ozone layer formation and depletion.
 (b) How do CFCs cause ozone depletion?
 (c) Write two harmful effects of UV radiation.
 (d) Suggest three ways to protect ozone layer.

Q4. (Biomagnification – 5 Marks)

(a) Explain the process of biomagnification.
 (b) Use a diagram to show chemical concentration in food chain.
 (c) Why is biomagnification highest in top predators?
 (d) Suggest two ways to reduce it.

Q5. (Waste Management – 5 Marks)

A city produces large amounts of plastic waste daily.

(a) Why is plastic harmful?
 (b) Suggest 5 ways to manage plastic waste.
 (c) What are the long-term effects of non-biodegradable garbage?
 (d) Why is segregation of waste important?

 

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