A student sets up an experiment to study the photosynthesis in plants. The student de starched a potted plant by keeping it in a dark room for 3 days. Half of the portion of de starched leaf was placed in a bottle containing caustic potash (absorbs CO₂). The student then places the plant in light and tests the leaf after 5 hours for the presence of starch. The portions inside the bottle shows negative starch test by reflecting no change in colour when react with iodine, however, other upper portions of the leaf gave positive starch test showing blue-black colour with iodine. What can be evaluated from this experiment? (a)carbon dioxide is directly linked with the colour of leaf b)carbon dioxide is necessary for preparing carbohydrate (c)lack of carbon dioxide increases amount of starch in plant (d)lack of carbon dioxide slows the process of photosynthesis
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The leaf of the potted plant was covered with a piece of black cloth to destarch it. Potassium hydroxide solution is to absorb the carbon dioxide gas from the air present in the glass bottle so that no carbon dioxide is left in the air inside the glass bottle. He will find that the leaf which was inside the glass bottle having no carbon dioxide around it, does not turn blue on adding iodine solution showing that no starch is present in this leaf. From this observation, we conclude that the photosynthesis to make starch in the leaf does not take place without carbon dioxide. And by covering the flask containing leaf B with black cloth, the leaf wont get exposure of sun light and photosynthesis won't happen. From this observation, we conclude that photosynthesis (to make starch) takes place in the presence of sunlight. Hence both the leaves do not have starch.
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