The movement of energy from lower to higher trophic level is

Options

A. always unidirectional
B. sometimes unidirectional
C. always bidirectional
D. undeterminable.

Explanation

**Step-by-Step Solution:**

1. **Understanding Trophic Levels**: Trophic levels refer to the different positions that organisms occupy in a food chain. The primary levels include producers (plants), primary consumers (herbivores), secondary consumers (carnivores), and tertiary consumers (top carnivores).

2. **Energy Movement in Ecosystems**: In an ecosystem, energy flows from one trophic level to the next. This flow of energy is crucial for the survival of organisms at different levels.

3. **Direction of Energy Flow**: The movement of energy in an ecosystem is always in one direction, from lower trophic levels (like producers) to higher trophic levels (like consumers). This means that energy is transferred from plants to herbivores and then to carnivores.

4. **Unidirectional Flow**: The energy flow is described as unidirectional because once energy is transferred to a higher trophic level, it does not flow back to the lower levels. For example, herbivores cannot return energy back to plants.

5. **Conclusion**: Therefore, the correct answer to the question is that the movement of energy from lower to higher trophic levels is always unidirectional.

**Final Answer**: The movement of energy from lower to higher trophic levels is always unidirectional.

---