"Photosynthesis, the process by which green plants and certain other organisms transform light energy into chemical energy. During photosynthesis in green plants, light energy is captured and used to convert water, carbon dioxide, and minerals into oxygen and energy-rich organic compounds."Source
Testing for starch in a leaf is just same as testing for starch in a food such as for iodine solution drops is used in testing for starch. The colour of iodine solution in most cases is brown but it turns into blue black colouration once it gets in touch with the starch.
Before a leaf is tested for starch, it is first of all heated in a beaker containing water in order to breakdown the cells of the leave and for effective iodine action on it.
Moreover, it is inserted in a test tube containing ethanol solution. Ethanol is a highly flammable liquid so care should be taken when handling in a place that flames are present.
The ethanol function is remove the green colouration contained on the leaves of plant just like bleaching.
After that, the leaf is inserted in a beaker containing warm water for softening and rinsing though a proper care is recommended when handling the leaf because as at this moment it is very brittle and can easily tear off as well.
Moreso, the leaf is removed gently from the break with a thong holder and placed on a white tile preferably for easy observation of the colour change.
Last but not least, two to three drops of iodine solution is added to the leaf using the dropper and a colour change is noticed.
If the leaf contains starch indicating it has photosynthesised previously then colour of the iodine solution turns blue black colour.
If there is no starch presence and no photosynthesis has taken place before then there would no observable colour change.
That's all as regards starch as a storage parameter of carbohydrate as a product of photosynthesis. More would be discussed in the subsequent post and happy blogging.
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Video from science projects YouTuber