Class 10 Our Environment Mock Test (CBSE)

Topics in Our Environment

• Ecosystem and its components
• Food chains and webs
• Trophic levels
• Biological magnification
• Ozone layer and its depletion
• Managing the garbage we produce

Our Environment practice questions with answers

1. Q1Assertion and reason·1 mark
   Assertion (A): A food web is more stable than a single food chain. Reason (R): A food web contains many interconnected food chains, so organisms have alternative food sources.

   1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
   2. (b)Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A).
   3. (c)Assertion (A) is true but Reason (R) is false.
   4. (d)Assertion (A) is false but Reason (R) is true.
   Show answer and step marks

   1. Correct option: (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).+1

   Answer: (a)
2. Q2Multiple choice·1 mark
   In a pond, the food chain is phytoplankton → zooplankton → small fish → big fish. If all the small fish are removed from the pond, which population is most likely to decrease immediately?

   1. (a)Phytoplankton
   2. (b)Zooplankton
   3. (c)Big fish
   4. (d)Algae
   Show answer and step marks

   1. Correct option: (c) Big fish, because small fish are its only food source in this chain and its food supply is cut off.+1

   Answer: (c)
3. Q3Multiple choice·1 mark
   Which of the following groups contains only non-biodegradable waste materials?

   1. (a)Polythene, plastic and glass
   2. (b)Wood, paper and grass
   3. (c)Fruit peels, cake and lime juice
   4. (d)Grass, flower and leather
   Show answer and step marks

   1. Correct option: (a) Polythene, plastic and glass. Evaluate each group for items that cannot be broken down by biological processes (microorganisms); polythene, plastic and glass are non-biodegradable.+1

   Answer: (a)
4. Q4Assertion and reason·1 mark
   Assertion (A): Energy flow in an ecosystem is cyclic, in the same way as the flow of nutrients. Reason (R): Energy is lost as heat at each trophic level and cannot be recycled back to the producers.

   1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
   2. (b)Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A).
   3. (c)Assertion (A) is true but Reason (R) is false.
   4. (d)Assertion (A) is false but Reason (R) is true.
   Show answer and step marks

   1. Correct option: (d) Assertion (A) is false but Reason (R) is true, because energy flow is one-directional and is lost as heat at each trophic level.+1

   Answer: (d)
5. Q5Assertion and reason·1 mark
   Assertion (A): The concentration of DDT is higher in an eagle, which feeds on small fish, than in the small fish themselves. Reason (R): DDT is non-biodegradable and is stored in the fatty tissues of organisms, so its amount builds up at each successive trophic level.

   1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
   2. (b)Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A).
   3. (c)Assertion (A) is true but Reason (R) is false.
   4. (d)Assertion (A) is false but Reason (R) is true.
   Show answer and step marks

   1. Correct option: (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).+1

   Answer: (a)
6. Q6Short answer·3 marks
   Define a trophic level. In a terrestrial food chain consisting of grass, grasshopper, frog, and snake, identify the organism that occupies the third trophic level. Explain why the flow of energy in an ecosystem is always unidirectional.
   Show answer and step marks

   1. Definition: Each specific feeding stage in a food chain at which energy transfer takes place is called a trophic level.+1
   2. Identification: Frog occupies the third trophic level (primary carnivore / secondary consumer).+1
   3. Reason for unidirectional flow: Energy captured by autotrophs does not revert back to the Sun, and the energy moving to the next trophic level is unavailable to the previous level, being progressively lost as heat at each transfer.+1

   Answer: A trophic level is each step (feeding stage) of a food chain at which transfer of energy takes place. The frog occupies the third trophic level (secondary consumer). Energy flow is unidirectional because energy captured by autotrophs does not revert to the Sun and energy passed to the next trophic level is not available to the previous one; much of it is lost as heat at each level.

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