Root hair cells, xylem and phloem

Overview

How root hair cells absorb water by osmosis and mineral ions by active transport, why salty water makes a plant wilt, how dead, lignified xylem vessels carry water, and how phloem sieve tubes and companion cells use energy to move sucrose up and down the plant.

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 the function of a root hair cell.

   Model answer

   It absorbs water and dissolved mineral ions from the soil into the root.

2. 2

   Explain how the long, narrow extension of a root hair cell helps it carry out its function.

   Model answer

   It gives a large surface area in contact with the soil water, so more water and mineral ions can be absorbed.

3. 3

   By which process does water enter a root hair cell, and why?

   Model answer

   By osmosis, because the soil solution is more dilute than the cell contents, so water moves in across the partially permeable membrane.

4. 4

   Explain why mineral ions usually enter a root hair cell by active transport rather than by diffusion.

   Model answer

   Mineral ions are more concentrated inside the cell than in the soil, so they must be moved against the concentration gradient using energy.

5. 5

   Explain why root hair cells contain large numbers of mitochondria.

   Model answer

   Mitochondria release energy in respiration, and this energy is needed for the active transport of mineral ions into the cell.

6. 6

   Explain how having a thin surface layer helps a root hair cell absorb substances.

   Model answer

   The short distance to cross means water and mineral ions enter the cell quickly.

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