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Question 18M.3.HL.TZ1.b

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Date May 2018 Marks available [Maximum mark: 3] Reference code 18M.3.HL.TZ1.b
Level HL Paper 3 Time zone TZ1
Command term Evaluate Question number b Adapted from N/A
b.
[Maximum mark: 3]
18M.3.HL.TZ1.b

Transpiration in plants can be measured using a bubble potometer or a mass potometer.

Evaluate the limitations of using a potometer in the investigation you suggested in (a).

[3]

Markscheme

a. not all of the water taken up by the plant is used for transpiration 

b. some water taken up might be used for photosynthesis/ cell turgidity 

c. (bubble) potometer measures rate of water uptake (not transpiration directly)
OR
bubble in potometer may expand due to changes in temperature/pressure

d. (cut) plant/twig gets damaged/may not survive 

e. conditions in a lab are not equivalent to those in nature/ difficult to change only one abiotic factor 

f. difficult to extrapolate values from a twig to whole plant

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