UPSC Prelims 2013 Q53: Environment & Ecology – Ecosystems & Ecology Concepts
With reference to the food chains in ecosystems, which of the following kinds of organism
is/are known as decomposer organism/organisms?
1. Virus
2. Fungi
3. Bacteria
Select the correct answer using the codes given below.
- (a) 1 only
- (b) 2 and 3 only
- (c) 1 and 3 only
- (d) 1, 2 and 3
Answer: (b) 2 and 3 only
Explanation
Decomposer organisms
Decomposers break down dead plants and animals into simple substances that return to the soil.
| Organism | Decomposer? | Reason |
|---|---|---|
| 1. Virus | No | A virus multiplies only inside living cells; it cannot digest dead matter |
| 2. Fungi | Yes | Saprophytes that release enzymes on dead matter |
| 3. Bacteria | Yes | The chief decomposers of soil and water |
Steps of decomposition:
| Step | What happens |
|---|---|
| Fragmentation | Detritivores such as earthworms break dead matter into bits |
| Leaching | Soluble nutrients wash into the soil |
| Catabolism | Bacterial and fungal enzymes break it down |
| Humification | Dark humus forms |
| Mineralisation | Humus releases inorganic nutrients |
The bank earlier stored (a) as the key; the official key is (b).
Answer: (b) 2 and 3 only.
Why each option is right or wrong
- (a) Incorrect. A virus is not a decomposer; it needs a living host.
- (b) CORRECT. Fungi and bacteria are the decomposer organisms.
- (c) Incorrect. The virus is not a decomposer, and fungi are left out.
- (d) Incorrect. The virus does not belong in the list.
Key point
Decomposers: fungi and bacteria (saprophytes). Steps: fragmentation, leaching, catabolism, humification, mineralisation. Viruses are not decomposers.
Remember
Decomposers = bacteria and fungi.
Common mistakes
- Counting viruses as decomposers because they are microbes.
- Confusing detritivores (earthworms) with decomposers.
- Forgetting the five steps of decomposition.
Exam tip
A virus is active only in a living cell. Dead matter is no use to it.
Sources
- NCERT Class XII — Biology (Ecosystem: decomposition)
- NCERT Class X — Science, Ch 13 (Our Environment)