What does apoplast refer to?

Explanation

### Step-by-Step Solution:

1. **Definition of Apoplast**: Apoplast refers to the space outside the plasma membrane of plant cells. It includes all the cell wall spaces and intercellular spaces.

2. **Location**: Apoplast is specifically found in plant cells, distinguishing it from other types of cellular spaces found in different organisms.

3. **Function of Apoplast**: The primary function of the apoplast is to allow for the diffusion of materials. It serves as a pathway for the movement of water, nutrients, and other substances throughout the plant tissue.

...