CCEA GCSE Biology, Third Edition by James Napier Denmour Boyd

Author:James Napier, Denmour Boyd [Napier, James; Boyd, Denmour]
Language: eng
Format: epub
Publisher: Hodder Education
Published: 2017-09-14T04:00:00+00:00

The potometer shown in Figure 8.9, can accurately measure the volume of water taken up by the shoot, but it cannot give an absolute value for transpiration itself. It is impossible to calculate how much of the water taken up by the plant is actually transpired through the leaf surface. Some of the water will be used in photosynthesis and in providing support through turgor, so the volume transpired will inevitably be less than the volume taken into the shoot. However, it is an excellent method for comparing rates in different conditions.

Transpiration rates can also be measured using a weighing method, by weighing how much water a plant loses over a period of time.

Test yourself

4 Define the term transpiration.

5 State three environmental factors that affect transpiration rate.

6 State four reasons why plants need water.

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