UPSC Prelims 2014 Q80: Environment & Ecology – Ecosystems & Ecology Concepts
Which one of the following is the correct sequence of a food chain?
- (a) Diatoms - Crustaceans - Herrings
- (b) Crustaceans - Diatoms - Herrings
- (c) Diatoms - Herrings - Crustaceans
- (d) Crustaceans - Herrings - Diatoms
Answer: (a) Diatoms - Crustaceans - Herrings
Explanation
Correct sequence of a food chain
A food chain always starts with a producer.
| Level | Organism | Role |
|---|---|---|
| First | Diatoms | Producers: microscopic algae (phytoplankton) that make food by photosynthesis |
| Second | Crustaceans | Primary consumers: small animals such as copepods and krill (zooplankton) that eat diatoms |
| Third | Herrings | Secondary consumers: fish that eat the crustaceans |
Rules of a food chain:
| Rule | Detail |
|---|---|
| Starts with | A producer (plant or alga) |
| Energy passed on | Only about 10 percent to the next level |
| Length | Usually three to five levels |
So the sequence is Diatoms - Crustaceans - Herrings.
Answer: (a) Diatoms - Crustaceans - Herrings.
Why each option is right or wrong
- (a) CORRECT. Diatoms (producers), then crustaceans, then herrings.
- (b) Incorrect. A food chain cannot start with crustaceans; they are consumers.
- (c) Incorrect. Herrings do not eat diatoms directly and are not eaten by crustaceans.
- (d) Incorrect. Diatoms are producers and must come first, not last.
Key point
Marine food chain: diatoms (phytoplankton, producers), crustaceans (zooplankton), herrings (fish); about 10 percent of energy passes to each next level.
Remember
Diatoms first: they are the producers.
Common mistakes
- Not knowing that diatoms are algae, not animals.
- Starting the chain with a consumer.
- Forgetting the 10 percent law of energy transfer.
Exam tip
Find the producer first. It always begins the chain.
Sources
- NCERT Class XII — Biology (Ecosystem: food chains and energy flow)
- NCERT Class X — Science, Ch 13 (Our Environment)