Experiments on Photosynthesis for High School - Class 11 PDF Download

1. Experiment to demonstrate Moll’s half-leaf experiment for showing that CO2, light, chlorophyll and water are necessary requirements for photosynthesis:

Requirements:

A potted plant, caustic potash, wide- mouthed bottle, iodine, split cork, water.

Method:

1. De-starch a potted plant by putting it in complete darkness for two days.

2. Fill partly a wide-mouthed bottle with strong solution of caustic potash and fit a split cork on its mouth.

3. Insert about half of the portion of a leaf of the de-starched plant into the bottle through the split cork (Fig. 36).

4. Place the whole apparatus in light after applying grease on the upper portion of split cork, and test the leaf for stach after about 10 hours.

Observations:

Portions of the leaf inside the bottle as well as in between the split cork show negative test for starch indicating the absence of photosynthesis while the portions outside the split cork show positive test for starch indicating the presence of process of photosynthesis in this region.

Results:

Negative starch test by the leaf portion present inside the bottle indicates that process of photosynthesis is absent in this region. This portion of leaf is getting all the essential requirements, i.e., light, chlorophyll and water except the CO2 because the latter is absorbed by the caustic potash. Thus, it can be concluded that CO2 is necessary for this process.

Negative test of starch, which is also shown by the portion of the leaf present in between the split of the split cork, can be explained that it is due to the lack of CO2 and light, thus indicating that both of them are essential requirements.

Positive test of starch shown by the portions of the leaf present outside the bottle indicates that photosynthesis process is continuously going on there because all the essential requirements, i.e., light, chlorophyll, water and CO2 are readily available to this portion.

That the chlorophyll is also an essential requirement for photosynthesis can be shown by testing starch in a variegated leaf. Only green portions of the leaf show positive starch test.

2. Experiment to demonstrate that oxygen is evolved during the process of photosynthesis:

Requirements:

Beaker, water, test tube, funnel, Hydrilla plant.

Method:

1. Fill the beaker with the water and take an aquatic plant, such as Hydrilla, in the beaker.

2. Cut the bases of the plants, tie them with a thread and cover them with an inverted funnel in such a fashion that the cut ends of plants are towards the neck of the funnel (Fig. 37).

3. Fill a test tube with the water and invert it on the upper end of the funnel.

4. Keep the whole apparatus in sunlight and observe for some time.

Observations:

From the cut ends of the plant some bubbles are coming out continuously and they are collected at the top of the test tube by displacing the water. On testing this gas it is found that it is oxygen.

Results:

The liberated gas is oxygen and it is evolved due to the photolysis of water under the process of photosynthesis. The liberated gas comes in the intercellular spaces and ultimately evolves out through the stomata.