Question 19M.1B.SL.TZ1.b
| Date | May 2019 | Marks available | [Maximum mark: 3] | Reference code | 19M.1B.SL.TZ1.b |
| Level | SL | Paper | 1B | Time zone | TZ1 |
| Command term | Describe | Question number | b | Adapted from | N/A |
Describe how the apparatus could be used to demonstrate that the transpiration rate is affected by air movement.
[3]
a. a fan is placed so that air blows on the leaves «and the experiment is repeated» ✔ Do not accept “place plant in wind”
b. a control with no air blowing «in still air/no fan» ✔
c. distance moved by the bubble in a given time is measured
OR
time is recorded for the bubble to move a given distance ✔
d. the bubble is reset to the beginning «with the tap» ✔
e. greater distance moved by bubble over time = higher transpiration rate ✔
f. repeat experiment at same temperature ✔
g. use different speeds of fan to determine effect of a range of air movement ✔
Accept different distances from fan for mpg
Few candidates defined the rate of transpiration in terms of the distance travelled by the meniscus per unit time. Common misconceptions were that the air bubble in the potometer was formed as a result of photosynthesis, or that the leaves released carbon dioxide or oxygen. Some candidates explained what the results would be, revealing a misunderstanding of a “describe” question. Weaker students did not understand that the question was asking about air movement around the plant, not the movement of the air column within the potometer.
