Food chain starts with -

Options

A. Respiration
B. Photosynthesis
C. N2 -fixation
D. None

Answer

### Step-by-Step Solution:

1. **Understanding the Food Chain**: The food chain is a sequence that shows how energy and nutrients flow from one organism to another in an ecosystem. It consists of different trophic levels, starting from producers to various levels of consumers.

2. **Identifying the First Component**: In a food chain, the first component is always the producers. Producers are organisms that can make their own food through processes like photosynthesis.

3. **Role of Producers**: The primary producers in most ecosystems are plants, such as grasses. They utilize sunlight, carbon dioxide, and water to produce energy-rich compounds.

4. **Nitrogen Fixation**: Before producers can effectively photosynthesize, they often require essential nutrients, particularly nitrogen. Nitrogen fixation is a process where certain bacteria convert atmospheric nitrogen into forms that plants can absorb and utilize.

5. **Photosynthesis**: After nitrogen fixation, producers like grasses perform photosynthesis, which allows them to convert light energy into chemical energy stored in glucose.

6. **Conclusion**: Therefore, the food chain starts with nitrogen fixation, which enables producers (like grasses) to grow and perform photosynthesis, ultimately leading to the establishment of the food chain.

### Final Answer:
The food chain starts with nitrogen fixation, which allows producers (like grasses) to perform photosynthesis and produce food.

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