Source of energy in an ecosystem is :

Options

A. Fermentation of sugars
B. Decomposition of plants and animals by bacteria
C. Photosynthesis by plants
D. Sunlight

Answer

### Step-by-Step Solution:

1. **Understanding Ecosystem Components**: An ecosystem consists of both biotic (living organisms) and abiotic (non-living elements) components. The interaction between these components is essential for energy flow.

2. **Identifying Producers**: In an ecosystem, the first trophic level is occupied by producers, primarily plants. These organisms are autotrophs, meaning they can produce their own food.

3. **Photosynthesis Process**: Producers prepare their food through a process called photosynthesis. During photosynthesis, plants convert sunlight into chemical energy, which is stored in the form of glucose.

4. **Energy Transfer**: The energy captured by plants through photosynthesis is then transferred to other organisms in the ecosystem. Herbivores (primary consumers) feed on these plants, and carnivores (secondary and tertiary consumers) feed on herbivores.

5. **Main Source of Energy**: The primary source of energy in an ecosystem is sunlight, which is essential for the process of photosynthesis. Without sunlight, plants would not be able to produce food, and consequently, energy would not flow through the ecosystem.

6. **Conclusion**: Therefore, the correct answer to the question is that the source of energy in an ecosystem is sunlight, which is utilized by plants during photosynthesis.