Transpiration and translocation

Overview

Transpiration and the path of water from soil to air, how evaporation pulls water up the xylem, stomata and how guard cells open and close them, wilting, and the translocation of sucrose in the phloem from the leaves to growing regions and storage organs using energy from respiration.

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

   What is transpiration?

   Model answer

   Transpiration is the loss of water vapour from a plant, mainly by evaporation from the leaf cells and diffusion out through the stomata.

2. 2

   Describe the path taken by water from the soil to the air outside a leaf.

   Model answer

   Water enters the root hair cells, travels up the xylem to the leaf, evaporates from the mesophyll cells and diffuses out through the stomata.

3. 3

   Explain how water is pulled up a tall plant even though the plant has no pump.

   Model answer

   Evaporation from the leaves creates a pull that draws the continuous column of water up the xylem from the roots.

4. 4

   Describe the structure and function of a stoma.

   Model answer

   A stoma is a small pore in the leaf surface, mostly on the underside, that lets carbon dioxide diffuse in and oxygen and water vapour diffuse out.

5. 5

   Explain how guard cells open a stoma.

   Model answer

   The guard cells take in water by osmosis and become turgid, and their change of shape pulls the pore between them open.

6. 6

   Explain why the stomata of most plants close at night and during a drought.

   Model answer

   The guard cells lose water and become flaccid, closing the pore, which conserves water at times when little or no photosynthesis is possible.

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