Define transmembrane pathway.

Explanation

**Step-by-Step Solution:**

1. **Understanding Water Movement in Plants:**
- Water movement in plants occurs through different pathways after it is absorbed by root hairs. The primary pathways are the apoplast pathway and the symplast pathway.

2. **Defining the Apoplast Pathway:**
- The apoplast pathway involves the movement of water through the cell walls of adjacent cells. This pathway is continuous throughout the plant, except for the Casparian strip, which is found in the endodermis and is impermeable to water.

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