Class 12 Ecosystem Mock Test (CBSE)

Topics in Ecosystem

• Ecosystem: structure and function
• Productivity
• Decomposition
• Energy flow
• Food chains and food webs
• Ecological pyramids

Ecosystem practice questions with answers

1. Q1Multiple choice·1 mark
   Which of the following components constitutes the base of a detritus food chain (DFC)?

   1. (a)Primary carnivores
   2. (b)Phytoplankton
   3. (c)Zooplankton
   4. (d)Dead organic matter
   Show answer and step marks

   1. Correct option: (d) Dead organic matter+1

   Answer: (d)
2. Q2Multiple choice·1 mark
   Which of the following statements regarding the energy flow through an ecosystem is correct?

   1. (a)Decomposers absorb 100% of the energy stored in detritus.
   2. (b)Approximately 10% of energy is transferred from one trophic level to the next.
   3. (c)The total energy increases at successive higher trophic levels.
   4. (d)Energy flow in an ecosystem is always bidirectional.
   Show answer and step marks

   1. Correct option: (b) Approximately 10% of energy is transferred from one trophic level to the next.+1

   Answer: (b)
3. Q3Short answer·3 marks
   State the two main structural components of an ecosystem. Describe briefly how the interaction between these components results in a self-sustaining functional unit.
   Show answer and step marks

   1. Biotic (living) component: producers, consumers and decomposers.+0.5
   2. Abiotic (non-living) component: inorganic nutrients, water, sunlight, temperature and other climatic factors.+0.5
   3. Producers use sunlight and inorganic nutrients from the abiotic component to make food (productivity).+0.5
   4. Energy flows from producers to consumers through food chains.+0.5
   5. Decomposers break down dead organic matter (decomposition), releasing inorganic nutrients back into the abiotic component.+0.5
   6. These nutrients are taken up again by producers (nutrient cycling), so the interacting components work as a self-sustaining functional unit.+0.5

   Answer: The two structural components are biotic (producers, consumers, decomposers) and abiotic (inorganic nutrients, water, light, temperature). Producers use light and nutrients to make food (productivity), energy flows from producers to consumers, decomposers break down dead matter and return nutrients to the abiotic component, and these nutrients are cycled back to producers, so the ecosystem sustains itself.

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