Fig. 1 shows a variegated leaf used by a teacher to investigate whether light and chlorophyll are needed before plants make starch. The plant was kept in da...
Question 1 Report
Fig. 1 shows a variegated leaf used by a teacher to investigate whether light and chlorophyll are needed before plants make starch. The plant was kept in darkness for 24 hours before the test. Opaque paper was then fixed over part of the leaf while the plant was left in bright light. The diagram shows the positions of the paper and the green and white areas before the leaf was removed.
(a) Name the carbohydrate for which the teacher will test the leaf. [1]
(b) Use Fig. 1 to describe how the leaf should be tested for this carbohydrate after it has been in light. [5]
(c) Describe the expected iodine test results for the exposed green region, the covered green region and the exposed white region. [3]
(d) Explain what these results show about the conditions needed for starch production in leaf cells. [3]
Answer Details
(a) The carbohydrate tested for is starch. [1]
(b) After exposure to light, remove the leaf from the plant [1]. Boil it in water [1], then heat it in ethanol in a water bath to remove chlorophyll [1]. Rinse or soften the leaf in water [1], then add iodine solution [1]. Ethanol is heated in a water bath rather than directly because it is flammable. [5]
(c) The exposed green region turns blue-black [1], showing starch. The covered green region remains brown or orange-brown [1], and the exposed white region also remains brown or orange-brown [1]. [3]
(d) Only the region that had both chlorophyll and light contains starch [1]. Green cells contain chlorophyll [1]. Therefore both light and chlorophyll are needed for starch to be made in leaf cells [1]. The initial 24 hours in darkness removes stored starch, so the result tests starch made during the experiment. [3]
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