DP Biology (first assessment 2025)

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Question 22M.2.SL.TZ1.6b

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Date May 2022 Marks available [Maximum mark: 5] Reference code 22M.2.SL.TZ1.6b
Level SL Paper 2 Time zone TZ1
Command term Describe Question number b Adapted from N/A
b.
[Maximum mark: 5]
22M.2.SL.TZ1.6b
(b)

Describe how changes in weather conditions affect the transport and loss of water in plants.

[5]

Markscheme
  1. water (vapor) lost by transpiration/through stomata;
  2. transpiration/loss of water from leaves causes transport of water (in xylem);
    Temperature:
  3. faster/more water loss/transpiration/transport in hotter weather;
  4. more heat for evaporation;
    Humidity:
  5. slower/less water loss/transpiration/transport in more humid weather;
  6. faster diffusion of water (vapor) out of the leaf/through the stomata with low humidity outside;
    OR
    no evaporation if air is saturated with water vapor/with 100 % humidity;
    Wind:
  7. faster/more water loss/transpiration/transport in windy/windier weather;
  8. wind/air movement carries away water vapor from around the leaf/stomata;
  9. high winds can cause stomatal closure and so reduce transpiration;
    Drought:
  10. drought causes stomata to close so reduces loss/transport;
Examiners report

More marks were scored here, but again there was widespread misunderstanding of the forces that cause water to evaporate and diffuse out of leaves, and of how conditions such as humidity, temperature and wind can influence the process. Few candidates mentioned concentration gradients between air spaces in the leaf and the atmosphere outside the leaf. There was a tendency to get trends the wrong way round, for example by suggesting that transpiration increases during rainfall because plants have plenty of water and therefore choose to open their stomata more widely.

Syllabus sections