A candidate studied the importance of certain factors in photosynthesis. He took a potted plant and kept it in the dark for over 24 hours. In the early hours of the next morning, he covered one of the leaves with dark paper in the centre only. Then he placed the plant in sunlight for a few hours and tested the leaf which was covered with black paper for starch.
(a) What aspect of photosynthesis was being investigated ?
(b) Is there any control in this experiment ? If so, state it.
(c) Why was the plant kept in the dark before the experiment ?
(d) Describe step by step, how the candidate proceeded to test leaf for the presence of starch.
A candidate studied the importance of certain factors in photosynthesis. He took a potted plant and kept it in the dark for over 24 hours. In the early hours of the next morning, he covered one of the leaves with dark paper in the centre only. Then he placed the plant in sunlight for a few hours and tested the leaf which was covered with black paper for starch.
(a) What aspect of photosynthesis was being investigated ?
(b) Is there any control in this experiment ? If so, state it.
(c) Why was the plant kept in the dark before the experiment ?
(d) Describe step by step, how the candidate proceeded to test leaf for the presence of starch.
a. The student wanted to show that sunlight is necessary for photosynthesis. / The role of sunlight in photosynthesis is being investigated.
b. Yes. The other uncovered leave of the potted plant act as a control.
c.To destarch the leaf. Destarching ensures that all starch present in the leaf before after the experiment are removed . this is always done before the experiiment commences. Therefore, the plant was kept in the dark before the experiment.
d.
- The student dipped the leaf in boiling water for a minute to kill the cells.
- Then he boiled the leaf in alcohol/methylated spirit over a water bath to remove chlorophyll. The leaf then becomes hard and brittle.
- He then places the leaf in hot water to soften it.
- Next the student spreads the leaf in a dish and pours iodine solution on it. The presence of starch is indicated by a blue-black colour.
- The uncovered portion (exposed to sunlight) turned blue-black colour and the covered portion showed brown colour. The difference in the colours of covered and uncovered part of leaves hilights the importance of sunlight in photosynthesis.
a. The student wanted to show that sunlight is necessary for photosynthesis. / The role of sunlight in photosynthesis is being investigated.
b. Yes. The other uncovered leave of the potted plant act as a control.
c.To destarch the leaf. Destarching ensures that all starch present in the leaf before after the experiment are removed . this is always done before the experiiment commences. Therefore, the plant was kept in the dark before the experiment.
d.
- The student dipped the leaf in boiling water for a minute to kill the cells.
- Then he boiled the leaf in alcohol/methylated spirit over a water bath to remove chlorophyll. The leaf then becomes hard and brittle.
- He then places the leaf in hot water to soften it.
- Next the student spreads the leaf in a dish and pours iodine solution on it. The presence of starch is indicated by a blue-black colour.
- The uncovered portion (exposed to sunlight) turned blue-black colour and the covered portion showed brown colour. The difference in the colours of covered and uncovered part of leaves hilights the importance of sunlight in photosynthesis.
