The number of mitochondria per cell is variable depending on the _____acitivity of cell.

Answer

To answer the question "The number of mitochondria per cell is variable depending on the _____ activity of cell," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Mitochondria**: Mitochondria are known as the powerhouses of the cell because they are responsible for producing ATP (adenosine triphosphate), which is the energy currency of the cell.

2. **Cellular Activity**: Different cells have varying levels of activity based on their functions. For example, muscle cells and neurons are highly active and require more energy compared to less active cells like skin cells.

3. **Energy Demand**: The energy demand of a cell is directly related to its physiological activity. Cells that perform more work (like muscle contraction, nerve impulse transmission, etc.) need more ATP to sustain their functions.

4. **Correlation Between Activity and Mitochondria**: Therefore, the number of mitochondria in a cell is proportional to its energy requirements. More active cells will have a higher number of mitochondria to meet their energy demands.

5. **Conclusion**: Thus, the correct answer to fill in the blank is "physiological," as the number of mitochondria per cell varies depending on the physiological activity of the cell.

### Final Answer:
The number of mitochondria per cell is variable depending on the **physiological** activity of the cell.

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