Question 23M.3.HL.TZ1.3
| Date | May 2023 | Marks available | [Maximum mark: 6] | Reference code | 23M.3.HL.TZ1.3 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Describe, Explain, Suggest | Question number | 3 | Adapted from | N/A |
Researchers set up apparatus that continuously monitored the rates of water uptake and loss from cut flowers. A rose shoot was inserted into a flask of water placed on a balance. The flask was kept full by a water supply from a reservoir. The graph shows the results over five days.
[Source: Lü, P., Huang, X., Li, H., Liu, J., He, S., Joyce, D. C. and Zhang, Z., 2011.
Continuous Automatic Measurement of Water Uptake and Water Loss of Cut Flower Stems,
HortScience horts, [e-journal] 46(3), pp. 509–512. https://doi.org/10.21273/HORTSCI.46.3.509.]
Suggest a reason for including a lid with vents above the water reservoir.
[1]
- lowers evaporation of water;
- vents allow air to enter as water leaves the reservoir;
- allows for pressure changes in the reservoir as water flows to the flask;
There were many incorrect reasons for a lid with air vents given but perhaps a quarter were able to give a correct reason.
Explain the differences in the water loss rate in dark and light conditions.
[2]
- more water is lost during the day than at night;
- temperature is higher so more loss of water by evaporation;
- stomata are open for gas exchange/ photosynthesis (so more water can evaporate/transpire);
Many received one mark for noting that water loss was higher during the day than night but then struggled to correctly explain why this was so.
Describe how the rose shoot could be treated to show what part of the plant loses water.
[1]
parts of the shoot/leaves are removed/covered in petroleum jelly/Vaseline;
Accept part wrapped in plastic
Very few received a mark here. Many incorrectly indicated they would add a dye, which they may have done in class to show water transport in xylem, but which is not relevant here.
A standard potometer only measures water uptake. Explain how this apparatus measures the amount of water lost by the shoot as well as uptake.
[2]
- water uptake by shoot causes a decrease in reading for balance 2;
- water lost by the shoot would be total loss from the system;
OWTTE
Very few received the marks available here. They did not know the difference between water uptake and water loss and could not determine which was being measured by the balances shown.