Which of the following is not recycled in an ecosystem:

Options

A. Water
B. Carbon
C. Energy
D. Nitrogen.

Answer

To determine which of the following is not recycled in an ecosystem, we need to analyze each option provided:

1. **Water**: Water is recycled in ecosystems through the water cycle. It evaporates, condenses, and precipitates, continuously moving through various forms and locations.

2. **Carbon**: Carbon is also recycled in ecosystems through the carbon cycle. It moves from the atmosphere into organisms and back again through processes like photosynthesis and respiration.

3. **Energy**: Energy is not recycled in ecosystems. It flows in one direction from producers to consumers and is eventually lost as heat. The 10% rule states that only about 10% of energy is transferred from one trophic level to the next, with the rest being lost.

4. **Nitrogen**: Nitrogen is recycled in ecosystems through the nitrogen cycle, where it is converted into various forms that can be used by living organisms.

After analyzing these options, we conclude that the correct answer is **Energy** (Option C), as it is not recycled in the ecosystem.

### Step-by-Step Solution:
1. **Identify the options**: Water, Carbon, Energy, Nitrogen.
2. **Analyze Water**: Water is recycled through the water cycle.
3. **Analyze Carbon**: Carbon is recycled through the carbon cycle.
4. **Analyze Energy**: Energy flows through the ecosystem and is not recycled; it is lost as heat.
5. **Analyze Nitrogen**: Nitrogen is recycled through the nitrogen cycle.
6. **Conclusion**: The only option that is not recycled in the ecosystem is Energy (Option C).