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Date	November 2018	Marks available	2	Reference code	18N.3.SL.TZ0.1
Level	Standard level	Paper	Paper 3	Time zone	TZ0 / no time zone
Command term	Discuss	Question number	1	Adapted from	N/A

Question

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]

Identify which two areas, W, X, Y or Z, in Figure 4 show that light is required for photosynthesis.

[1]

b.i.

Identify which two areas, W, X, Y or Z, in Figure 4 show that chlorophyll is required for photosynthesis.

[1]

b.ii.

Discuss briefly whether the detection of starch in this experiment was proof that photosynthesis had occurred in the leaf.

[2]

b.iii.

Using the axes, sketch the action spectrum for photosynthesis in the green area of the leaf in Figure 1.

[1]

c.i.

Predict how the action spectrum from the white areas of the leaf would differ from the green areas.

[1]

c.ii.

Suggest reasons that plants with variegated leaves are rarely found growing wild naturally.

[1]

Markscheme

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 ✔

X AND Y ✔

Both needed

b.i.

W AND X ✔

Both needed

b.ii.

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 ✔

b.iii.

sketch showing 2 peaks at either end of the spectrum ✔

c.i.

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”

c.ii.

«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