Main source of ATP in a cell is …………………. .

Explanation

**Step-by-Step Solution:**

1. **Understanding ATP Production**: ATP (adenosine triphosphate) is the primary energy currency of the cell. It is produced during cellular respiration, which is a series of metabolic processes that convert food into energy.

2. **Identifying the Process of Respiration**: The main process responsible for ATP production in cells is respiration. This involves the breakdown of glucose and other substrates to release energy.

3. **Glycolysis**: The first step in cellular respiration is glycolysis, where glucose is broken down into pyruvic acid. This process occurs in the cytoplasm and produces a small amount of ATP (2 molecules).

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