All these statements about trophic levels and ecosystems are false except.
(a) Trophic level represents a functional level, not a species as such
(b) A given species never occupies more than one trophic level in the same ecosystem at the same time
(c) In most ecosystems , producers are less in number and biomass than the herbivores
(d) Pyramid of energy can never be upright .

Options

A. Trophic level represents a functional level, not a species as such
B. A given species never occupies more than one trophic level in the same ecosystem at the same time
C. In most ecosystems , producers are less in number and biomass than the herbivorous
D. Pyramid of energy can never be upright .

Answer

To solve the question about which statement regarding trophic levels and ecosystems is true, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Trophic Levels**:
- Trophic levels refer to the different levels in a food chain or food web where organisms obtain their energy. Each level represents a functional role in the ecosystem, rather than a specific species.

2. **Analyzing Option (a)**:
- **Statement**: "Trophic level represents a functional level, not a species as such."
- **Evaluation**: This statement is true. Trophic levels are defined by the role organisms play in the ecosystem (producers, consumers, decomposers), and not by specific species.

3. **Analyzing Option (b)**:
- **Statement**: "A given species never occupies more than one trophic level in the same ecosystem at the same time."
- **Evaluation**: This statement is false. A species can occupy different trophic levels depending on its role in the ecosystem (e.g., a species can be a herbivore at one time and a carnivore at another).

4. **Analyzing Option (c)**:
- **Statement**: "In most ecosystems, producers are less in number and biomass than the herbivores."
- **Evaluation**: This statement is false. In most ecosystems, producers (plants) are more numerous and have greater biomass than herbivores.

5. **Analyzing Option (d)**:
- **Statement**: "Pyramid of energy can never be upright."
- **Evaluation**: This statement is false. The pyramid of energy is always upright because energy flows in one direction from producers to consumers, and energy decreases at each trophic level.

6. **Conclusion**:
- After evaluating all options, the only true statement is option (a): "Trophic level represents a functional level, not a species as such."

### Final Answer:
The correct answer is **(a)** Trophic level represents a functional level, not a species as such.