__________ is the main characteristic phenomenon taking place in living cells which is responsible for growth of an individual.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the main characteristic phenomenon that occurs in living cells, which is responsible for the growth of an individual.

2. **Identifying Life Processes**: In living organisms, several life processes are essential for maintaining life, including nutrition, respiration, circulation, and excretion.

3. **Focusing on Growth**: Among these processes, we need to identify which one is directly responsible for growth. Growth in living organisms involves an increase in size and number of cells.

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