Photosynthesis: Experimental Studies


Experiment: 1 Starch Test

Plucked a plant leaf in the evening and boiled it in water and alcohol one by one. The green colour of the leaf is removed. Now, the leaf is spread carefully in a Petri plate and some iodine is dropped over it. The leaf becomes blue in colour. It shows that the leaf contains chloroplast.

Experiment: 2To prove that sunlight is essential for Photosynthesis

A potted plant is placed in the dark for 24 hours so that its starch is consumed by the plant. Now covered some part of one of its leaves and the plant is placed in sunlight for 6hours. Now the leaf is subjected to the starch test. The covered part of leaf does not turn blue on dropping iodine on it. Rest of its part turns blue. It shows that sunlight is necessary for Photosynthesis.

Experiment 3: To certify the release of oxygen in photosynthesis

Some twigs of an aquatic plant (say Hydrila) are plucked and put into a beaker filled with water. It is now covered with an inverted funnel. A test tube is filled with water and put on the tube of the funnel in inverted position. The whole apparatus is placed into the sun for some hours.

After some time, it is observed that bubbles of air start coming up from leaves and the level of water starts coming down. Gradually, both the levels of water – in the test tube and in the beaker become equal. The empty portion of the test tube is now filled with air that was released from the leaves of Hydrila plant. On testing the gas; it was found that the test tube contained oxygen. It certifies that oxygen is released during photosynthesis.

Experiment 4: To certify the necessity of chlorophyll for photosynthesis

A croton leaf with variegated areas is plucked in the evening. Black spots on the surface of the leaf show absence of chlorophyll within its surface area. The leaf is boiled in water and then in alcohol so as to remove chlorophyll content of the leaf. After washing the leaf in water, it is spread in a Petri dish and some drops of iodine solution are dropped on it. The area except black spots becomes blue. It shows that areas under black spots do not contain starch as they do not have any chlorophyll. Thus it is certified that chlorophyll is necessary for photosynthesis.

Experiment 5: To certify the necessity of carbon dioxide for photosynthesis

A potted plant is taken with the plant having long and narrow leaves. Inserted one leaf into the broad mouth of a bottle with the help of two half pieces of cork. Put some grease on the cut portions to make the apparatus air-tight. Some KOH was taken in a small tube and the tube was placed inside the bottle carefully much before inserting the leaf into it. KOH absorbs carbon dioxide of the bottle. Now, the whole arrangement was placed into sunlight. After 6 hours the leaf is carefully separated from the bottle and from the plant for the starch test. The result shows that part of the leaf inside the bottle did not contain starch as photosynthesis did not occur in that area of the leaf.

Experiment 6: To test the effect of saliva on starch

Prepared 1% solution of 1 ml starch and put it into test tubes A and B. Put about 1ml saliva in the test tube A and put both the test tubes A and B undisturbed for half an hour. Now, poured small quantities of iodine solution in both the test tubes. It is observed that the colour of the solution in the test tube A did not change because its starch was converted to maltose due to reaction of saliva. In the test tube B, the colour turned to blue because the starch was not digested.

Photosynthesis, starch, oxygen, chlorophyll

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