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A piece of black paper was placed over the leaf of a plant - OCR Gateway - GCSE Biology - Question 9 - 2021 - Paper 1
Question 9
A piece of black paper was placed over the leaf of a plant. The plant was kept in the light for 2 days. Four discs were cut from the leaf. Disc A Disc B Disc C ... show full transcript
Worked Solution & Example Answer:A piece of black paper was placed over the leaf of a plant - OCR Gateway - GCSE Biology - Question 9 - 2021 - Paper 1
Step 1
Which disc A, B, C or D, would test positive for starch?
Answer
To determine which disc tests positive for starch, we must understand that starch is produced through photosynthesis in the presence of light.
In this scenario, the black paper prevents light from reaching the leaf areas beneath it. The discs that were cut from the green parts of the leaf (those exposed to light) will contain starch, while those covered by the black paper will not.
Since disc B is the only one that is not covered by the black paper and remains green, it will test positive for starch when treated with iodine solution, which turns blue-black in the presence of starch.