What are porins? What role do they play in diffusion?

Explanation

### Step-by-Step Solution:

1. **Definition of Porins**:
- Porins are a type of protein that form channels or pores in the membranes of cells. These pores are relatively large compared to other types of membrane proteins.

2. **Location of Porins**:
- Porins are primarily found in the outer membranes of certain organelles, such as chloroplasts and mitochondria, as well as in the outer membranes of some bacteria.

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