Photosynthesis Experiments - Class IX

Jan Ingenhousz (1730-1799), in his experiment with an aquatic plant, showed that in bright sunlight, small bubbles were formed around the green parts while in the dark, no such bubbles formed. He found out these bubbles to be of oxygen. He thus, confirmed that purification of air or formation of dephlogiston is carried out by green plants only in presence of sunlight. 

Boiling a leaf in alcohol is a standard procedure in photosynthesis experiments to extract chlorophyll, which allows for the subsequent detection of starch using iodine solution.

Potassium bicarbonate (KHCO3) is commonly used in photosynthesis experiments to provide a controlled source of carbon dioxide for aquatic plants. When the plant performs photosynthesis, the oxygen evolved can be collected and observed.

To test that oxygen is evolved during photosynthesis few fresh Hydrilla plants in a glass beaker filled with water. A pinch of KHCO$ _{3}$ is added to it. It is kept in sunlight. After some time some bubbles (oxygen) escapes from the plant. This proves that oxygen is produced during the photosynthesis. It is evolved during the light reaction of the photosynthesis.

The plant kept in continuous light will live longer, because it will be able to produce oxygen required for its respiration by the process of photosynthesis.

The starch in the leaves is eliminated by keeping the plant in a dark place for 3 days. A leaf is selected and covered with a black strip on both sides. The plant is kept in sunlight for 4 hours. The experimental leaf is plucked and the strip is removed from it to perform the starch test. It is found that he leaf covered with black paper will turn brown and the part of the exposed leaf will turn blue-black. This result proves that starch is formed in the leaf where sunlight is available and is not formed in absence sunlight. Thus the correct answer is option  C.

Jan Ingenhousz (1730-1799), in his experiment with an aquatic plant, showed that in bright sunlight, small bubbles were formed around the green parts while in the dark, no such bubbles formed. He found out these bubbles to be of oxygen. He thus, confirmed that purification of air or formation of dephlogiston is carried out by green plants only in presence of sunlight. 

• Warburg discovered that a decrease in photosynthesis by increasing the oxygen concentration. Oxygen is the competitive inhibitor of the carbon dioxide fixation by RuBisCo, which initiates photosynthesis. Furthermore, oxygen stimulates photorespiration which reduces photosynthetic output. These two mechanisms working together are responsible for the Warburg effect. So, this option is incorrect.
• Arnon discovered the photosynthetic phosphorylation. So, this option is incorrect.
• Samuel Ruben discovered that oxygen, which is released during photosynthesis came from a water molecule. So, this option is incorrect.
• Emerson observed that when Chlorella cells are exposed to continuous light, the rate of photosynthesis was less as compared to those exposed to the intermittent light. 

If boiled water is used in the test tube, there will be no air bubbles. This is hydrilla cannot survive the high temperature of boiled water. 

Sunlight is essential for photosynthesis as the plant is kept in dark room for a week there is a lack of sunlight hence photosynthesis has not taken place.