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Photosynthesis Leaf Test Results
A student investigated the effect of different factors on photosynthesis. The student used three leaves growing on the same plant. Each leaf was treated in a different way. After 48 hours the student tested each leaf for starch. Table 3 shows the results.
| Leaf tested | Treatment | Result after 48 hours |
|---|---|---|
| 1 | Upper and lower surfaces covered with black paper | No starch present |
| 2 | Upper and lower surfaces covered and sealed with transparent plastic | No starch present |
| 3 | Not covered | Starch present |
Explain the results for the three leaves.
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Marking points
- 1 Explains Leaf 1 using absence of light and therefore no photosynthesis.
- 2 Explains Leaf 2 using absence of carbon dioxide and therefore no photosynthesis.
- 3 Explains Leaf 3 using the presence of light and carbon dioxide and therefore photosynthesis.
- 4 Links photosynthesis to glucose production and conversion of glucose to starch, or uses the allowed previous-starch breakdown point.
Full-mark answer
Leaf 1 received no light because of the black paper, so it could not photosynthesise. Leaf 2 received light through the transparent plastic but the seal prevented carbon dioxide entering, so it also could not photosynthesise. Leaf 3 had both light and carbon dioxide, so it photosynthesised. Photosynthesis in Leaf 3 produced glucose that could be converted to starch; Leaves 1 and 2 did not make glucose, so no starch formed.
Why this answer loses marks
The covered leaves had no starch because they were kept in the dark.
Only the opaque cover removes light; the transparent sealed cover removes carbon dioxide. Distinguish the treatments and link photosynthesis to glucose and starch.