Simple diffusion mainly based on ___________.

Answer

**Step-by-Step Solution:**

1. **Understanding Simple Diffusion**: Simple diffusion is a passive process where molecules move from an area of higher concentration to an area of lower concentration without the need for energy.

2. **Identifying Key Factors**: The process of simple diffusion is primarily based on:
- Concentration Gradient: The difference in concentration of a substance across a space.
- Pressure Gradient: The difference in pressure that can influence the movement of gases.

3. **Considering Solubility**: The solubility of the gases involved also plays a significant role. Gases that are more soluble will diffuse more readily compared to less soluble gases.

4. **Membrane Thickness**: The thickness of the membrane through which diffusion occurs affects the rate of diffusion. A thinner membrane allows for a higher rate of diffusion, while a thicker membrane slows it down.

5. **Conclusion**: Therefore, simple diffusion mainly depends on the concentration gradient, pressure gradient, solubility of the gases, and the thickness of the membrane.

**Final Answer**: Simple diffusion mainly based on **concentration gradient**.

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