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Chapter: Biology: Physiological Activities in Plants Nutrition

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Some Experiments on Photosynthesis

1. Experiment to demonstrate that Oxygen is evolved during Photosynthesis 2. Experiment to show that photosynthesis do not occur without chlorophyll 3. Experiment to show that light is essential for Photosynthesis: Requirements 4. Experiment to show that photosynthesis cannot occur without CO2 : Requirements 5. Evolution of O2 during photosynthesis

Some Experiments on Photosynthesis:

 

1. Experiment to demonstrate that Oxygen is evolved during Photosynthesis:

 

Requirements: A large Beaker, SomeHydrillaPlant, One Funnel, One Testtube, water and a glowing splinter of wood.

 

Procedure: The Hydrilla plant should be kept in the beaker and coveredwith the funnel. Hydrilla plant be placed in such a way that its cutting ends remain towards the stem of the funnel. Water should be poured in the beaker in such a way that the stem of the funnel kept beneath the water level. A test tube completely filled with water should be inverted over the stem of the funnel. At this position the experimental set should be placed in Sunlight (or underelectric   light   in   the   laboratory).Water Observation: After sometimes it will be Bubble seen that bubbles are coming out from the        Test-tube Hydrilla plant and are accumulating in the Beaker test tube. After accumulation of some gas Funel the test tube should be taken out carefully  Hydrilla plant and a glowing splinter of wood be thrusted      into the test tube, it will burst into flame.

Conclusion: As the gas helps theglowing splinter to flame so the gas is Oxygen, because Oxygen does not flame itself but helps other to flame.

 

 

2. Experiment to show that photosynthesis do not occur      without chlorophyll:

 

Requirements: A Variegated leaf of an Ornamental plant, Alcohol, Iodine solution, and a Beaker.

Observation: After immersing in the Iodine solution it will be seen that onlythe green portion of the leaf become blue (deep violet or black).

 

Conclusion: Due to presence of chlorophyll only the green portionsmanufactured carbohydrate by photosynthesis. Having no chlorophyll orange or yellow regions did not manufacture carbohydrate. As there was carbohydrates in green portion, that portion become blue (deep violet or black).

 

3. Experiment to show that light is essential for Photosynthesis: Requirements: 

A potted plant with green leaves, Black paper, Alcohol,Iodine solution, and clips, (the plant should keep in dark for a long time before experiment).

Procedure : Cover both side of a leaf withblack paper and clip so that Sunlight cannot reach inside. Then let the pot with the plant be kept in Sunlight. After one hour tear the leaf and boil in alcohol so that the leaf becomes chlorophyll free. Now let the leaf be immersed in iodine solution.

 

Observation : On taking out from the iodine solution it will be seen that allthe area except the covered area became blue (deep violet or black).

 

Conclusion: Carbohydrate react with iodine solution turns to blue (deepviolet or black). Sunlight did not reach the area covered with black paper photosynthesis did not occur there, that is carbohydrate did not produce. As carbohydrate did not produce there the area did not turn blue (deep violet or black). Thus it is proved that Sunlight is essential for photosynthesis so to say for manufacture of carbohydrate.

 

4. Experiment to show that photosynthesis cannot occur without CO2 : Requirements 

A potted plant, a widemouthed glass-bottle, a splitted cork, caustic potash (KOH) solution Alcohol, Iodine solution and Vaseline.

Procedure: The potted plant should be kept.48 hours in darkness so that the leaves do not have any starch. One-fourth of the wide mouthed bottle should be filled with caustic potash solution.

 

Now take out the potted plant from darkness and insert half of a leaf in the bottle through a splitted cork, and fix tightly the cork to the bottle. Care should be made taken that a part of the leaf is placed inside the bottle. The bottle should be air tight with vaseline so that no air from out side can enter into the bottle. The CO2 present in the air inside the bottle will be absorbed by caustic potash (KOH) solution. Now the experimental set should be placed in Sunlight. After 34 hours take that leaf and after boiling in alcohol immerse it in iodine solution.

 

Observation: On taking out of the iodine solution it will be seen that theportion of the leaf that was out side the bottle become blue (deep violet or black, and rest portion becomes yellow or brownish yellow.

Conclusion: The outside portion of the leaf absorbed CO2and manufacturecarbohydrate by photoynthesis. Carbohydrate turns blue in iodine soulution. The portion of the leaf kept inside the bottle did not manufacture carbohydrate, as there was no CO2. (CO2 present inside the bottle was absorbed by KOH solution). Thus it is proved that CO2 is essential for Photosynthesis. The portion of the leaf inside did not get both CO2 and Light so it could not take part in photosynthesis.

 

5. Evolution of O2 during photosynthesis :

 

In non-cyclic stage of photosynthesis in the light phage, O2 evolved from splitted water. If O2 was not relesed in the atmospher in the photosynthesis process, then there would be a great scarcity of O2 in the atmosphere. As a result the entire living creature would have perished because our respiratory system stops functioning for want of O2.

 

Production of Carbohydrate during Photosynthesis:

 

Carbohydrate is produced during photosynthesis. Plant reserved the excess carbohydrate after their requirements. For example: Paddy, Wheat, Maize, Barley, Potato, Sweet Potato, Sugarcane etc. We took these as food. If green plants do not manufacture carbohydrate in photosynthesis, then for want of food all of the members of Animal Kingdom including human beings would have been destroyed.

 

 

What would happen if there were no Sunlight

 

If there were no Sunlight on the Earth there will have no Photosynthesis. Without photosynthesis there would be no movement of energy. The earth would become motionless. Without Sunlight no living being could exist.

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