Question 18N.3.SL.TZ0.1
| Date | November 2018 | Marks available | [Maximum mark: 8] | Reference code | 18N.3.SL.TZ0.1 |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Discuss, Identify, Outline, Predict, Sketch, Suggest | Question number | 1 | Adapted from | N/A |
A variegated Pelargonium plant was grown outdoors in a plant pot. Figure 1 shows one leaf of the Pelargonium. The plant was left in the dark for 24 hours to inhibit photosynthesis. After this time, a sketch was made of the leaf to show the colours (Figure 2), then part of the leaf was covered with black card (Figure 3). Following the exposure of the plant to sunlight for six hours, the black card was removed and the leaf tested for starch (Figure 4).
Outline a reason for inhibiting photosynthesis for 24 hours.
[1]
to remove any starch already in the leaf
OR
so any starch found in the leaf was made during the experiment
OR
to prevent further production of starch ✔
Identify which two areas, W, X, Y or Z, in Figure 4 show that light is required for photosynthesis.
[1]
X AND Y ✔
Both needed
Identify which two areas, W, X, Y or Z, in Figure 4 show that chlorophyll is required for photosynthesis.
[1]
W AND X ✔
Both needed
Discuss briefly whether the detection of starch in this experiment was proof that photosynthesis had occurred in the leaf.
[2]
pro (yes it could be evidence):
a. starch is a product of photosynthesis ✔
con (not necessarily evidence):
b. starch could be made elsewhere «in the plant» and transported to/stored in leaves
OR
starch could be made by another process «other than photosynthesis»
OR
starch is being detected although glucose is the direct product ✔
OWTTE
limitations of experiment:
c. starch depletion may take more than 24 hours «of dark»
OR
starch production may take more than 6 hours «of light»
OR
starch should have been measured before and after ✔
Using the axes, sketch the action spectrum for photosynthesis in the green area of the leaf in Figure 1.
[1]
sketch showing 2 peaks at either end of the spectrum ✔
Predict how the action spectrum from the white areas of the leaf would differ from the green areas.
[1]
it would be a straight line/have no peaks
OR
no photosynthesis ✔
Accept a labelled horizontal line in the bottom third of the y-axis.
Do not accept “lower line” or “lower photosynthesis”
Suggest reasons that plants with variegated leaves are rarely found growing wild naturally.
[1]
«having the leaf partly white would be» no selective advantage/cannot compete
OR
natural selection would reduce the frequency of the mutation causing variegated leaves
OR
occur due to artificial selection ✔
Some reference to evolution or natural selection required
Do not accept reference to photosynthesis alone