Q. What plant is used in an experiment commonly performed in laboratory to demonstrate evolution of oxygen in photosynthesis?
Solution:
To show that oxygen is evolved in the process of photosynthesis by the green plants, the water-weeds like Hydrilla or Ceratophyllum are preferred. Hydrilla is an aquatic angiospermic plant and it performs photosynthesis inside the water, as it is a hydrophyte. Hydrilla is also comparatively smaller in size so it is easy to handle the plant during the experiment.
Experiment: Take some water-weeds and cut the bases of the plant and tie them with a thread. Put them in a beaker containing water and invert a funnel over them as shown in the figure. Fill a test tube with water and invert it over the nozzle of the funnel so that no air-bubble gets in. Expose the whole apparatus to light.
It is seen that some bubbles come out continuously and are collected at the top of the test tube by displacing the water.
On testing the gas it is found to be oxygen. This evolved oxygen is produced by the green aquatic plant in the process of photosynthesis.
Experiment: Take some water-weeds and cut the bases of the plant and tie them with a thread. Put them in a beaker containing water and invert a funnel over them as shown in the figure. Fill a test tube with water and invert it over the nozzle of the funnel so that no air-bubble gets in. Expose the whole apparatus to light.
It is seen that some bubbles come out continuously and are collected at the top of the test tube by displacing the water.
On testing the gas it is found to be oxygen. This evolved oxygen is produced by the green aquatic plant in the process of photosynthesis.