Water uptake and movement through the plant

Overview

Recall questions on root hair cells and water entry by osmosis, the apoplast, symplast and vacuolar pathways, the Casparian strip, root pressure, cohesion, adhesion and transpiration pull, the water potential gradient through the plant, and the evidence for the cohesion-tension theory.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   State three adaptations of a root hair cell for absorbing water and minerals.

   Model answer

   Its long narrow extension gives a large surface area, its wall is thin so the diffusion path is short, and it contains many mitochondria to supply ATP for the active uptake of mineral ions.

2. 2

   Explain how water enters a root hair cell.

   Model answer

   It enters by osmosis, because the soil solution has a higher water potential than the cytoplasm of the root hair cell.

3. 3

   What are the three pathways by which water crosses the root cortex?

   Model answer

   The apoplast pathway, the symplast pathway and the vacuolar pathway.

4. 4

   Describe the apoplast pathway.

   Model answer

   Water moves through the cellulose cell walls and the spaces between them, without crossing any plasma membrane.

5. 5

   Why is the apoplast the main route for water across the root cortex?

   Model answer

   Cell walls are freely permeable and offer far less resistance than crossing a series of membranes, so most of the water travels this way.

6. 6

   Describe the symplast pathway.

   Model answer

   Water passes through the cytoplasm of the cortex cells, moving from one cell to the next through the plasmodesmata.

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