Two forces control passive transport of ions across membranes: ……… and ………….

Explanation

To answer the question regarding the two forces that control passive transport of ions across membranes, we can break down the solution into clear steps:

### Step-by-Step Solution:

1. **Understand Passive Transport**:
- Passive transport refers to the movement of ions or molecules across a membrane without the need for energy input. This process occurs naturally along the concentration gradient.

2. **Identify the Concentration Gradient**:
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