Which of the following limits the number of trophic levels in a food chain ?

Options

A. Decrease in energy at higher trophic levels
B. Defficient food supply
C. Polluted air
D. Water

Explanation

To answer the question "Which of the following limits the number of trophic levels in a food chain?", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Trophic Levels**:
- Trophic levels refer to the different levels in a food chain, where each level represents a different group of organisms that share the same function in the food web. The primary producers (like plants) are at the first trophic level, herbivores at the second, and carnivores at higher levels.

2. **Energy Transfer in Food Chains**:
- In a food chain, energy is transferred from one trophic level to the next. However, not all energy is transferred efficiently. According to the 10% law, only about 10% of the energy from one trophic level is available to the next level.

3. **Example of Energy Transfer**:
- For instance, if grass (the producer) has 10 kilojoules of energy, only 1 kilojoule (10% of 10 kJ) will be available to the deer (the primary consumer). Then, the deer will pass on only 0.1 kilojoule (10% of 1 kJ) to the lion (the secondary consumer).

4. **Energy Loss at Higher Levels**:
- As we move up the trophic levels, the energy available decreases significantly. For example, if there were a fourth trophic level, the energy available would be just 0.001 kilojoule, which is extremely low.

5. **Feasibility of Higher Trophic Levels**:
- Due to the significant loss of energy at each trophic level, it becomes less feasible for organisms at higher levels to sustain themselves. The energy they gain from food is not enough to cover the energy they expend in obtaining it.

6. **Conclusion**:
- Therefore, the limiting factor for the number of trophic levels in a food chain is the decrease in energy at each successive level. This means that as energy diminishes, fewer trophic levels can be supported.

### Final Answer:
The correct answer is that the decrease in energy at each successive higher trophic level limits the number of trophic levels in a food chain.

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