A: Detrivores and decomposers hold up a part of nutrients contained in detritus.
R: Immobilised after the death of saprotrophs.

Options

A. If both Assertion &Reason are true and the reason is the corect explanation of the assertion , then mark (1)
B. If both Assertion & Reason are true but the reason, is not the correct explanation of the assertion , then mark (2)
C. If Assertion is true statement but Reason is false , them mark (3).
D. If both Asseration and Reason are false statements , then mark (4).

Answer

To analyze the given statements regarding detritivores and decomposers, we will break down the assertion (A) and the reason (R) step by step.

### Step 1: Understanding the Assertion (A)
- **Assertion (A)**: "Detrivores and decomposers hold up a part of nutrients contained in detritus."
- **Explanation**: Detrivores (organisms that feed on dead organic matter) and decomposers (microorganisms that break down dead material) play a crucial role in nutrient cycling. They break down detritus, which is composed of dead plant and animal matter, and in doing so, they absorb some of the nutrients. This process helps in recycling nutrients back into the ecosystem.

### Step 2: Understanding the Reason (R)
- **Reason (R)**: "Immobilised after the death of saprotrophs."
- **Explanation**: The term "immobilized" refers to nutrients that are tied up in the biomass of organisms (like microbes) and become unavailable for other organisms. However, the statement suggests that these nutrients are immobilized after the death of saprotrophs (which are a type of decomposer). This is misleading because while saprotrophs do immobilize nutrients during their life, they do not cause nutrients to become immobilized after their death. Instead, when they die, their nutrients can be released back into the ecosystem.

### Step 3: Conclusion
- **Assertion (A)** is true because detritivores and decomposers do hold up some nutrients from detritus.
- **Reason (R)** is false because nutrients are not immobilized after the death of saprotrophs; rather, they can be released back into the ecosystem.

### Final Answer
- The assertion is true, but the reason is false.

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