Evidence of organic matter (starch) formation in leaves when exposed to light.

You can make sure that starch is formed in the leaves in the light by experiment.

Plant in the dark
Place the houseplant (pelargonium, begonia) in a dark place, such as a closet.
After two or three days, we cut off one leaf and put it in boiling water for 2-3 minutes, and then in hot alcohol. The leaf will lose its green color: the chlorophyll contained in the chloroplasts will dissolve in alcohol.
Rinse the sheet in water, place it in a glass cup and fill it with a weak iodine solution. In this case, the leaf practically does not change color, but only partially turns yellow from iodine.
Consequently, no starch was formed in the leaves of a plant placed in a dark place.
Conclusion: organic matter in a plant is formed only in the light.

Plant in the light
Let’s continue the experiment. On one of the leaves of the same plant, we fix a strip of thick paper on both sides. Let’s expose the plant to sunlight. Cut off the experimental leaf in a day. Immerse it in boiling water for 2-3 minutes, then in hot alcohol. Rinse the leaf in water, and then fill it with a weak iodine solution in a glass cup.
In this case, most of the leaf will turn blue. The area of ​​the leaf that has not been exposed to light will only turn slightly yellow from iodine.
Conclusion: the formation of starch occurs in the leaves only in the light.

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