Plant Stores D. Crowley, 2008

Plant Stores Tuesday, August 20, 2019 To know that plants store glucose as starch, and how to test for this

Equations The word equation for photosynthesis is carbon dioxide + water  glucose + oxygen The symbol equation for photosynthesis is 6CO2 + 6H2O  C6H12O6 + 6O2

Glucose & Starch During photosynthesis glucose is produced (a simple sugar) However, plants cannot store glucose, so they convert it into starch (many small glucose molecules are joined together) Starch is insoluble, meaning it can be stored easily (when you wash some rice you can see the starch wash off)

Starch Test How can we test for starch? How can we relate the presence of starch to the amount of photosynthesis taking place? Iodine tests for starch – it turns blue/black in the presence of starch If a plant photosynthesis a lot, then there should be more starch present (as more glucose would have been made and converted into starch)

Experiment Your task is to look at two different types of leaf –one normal leaf, and one which has been kept in the dark You need to find out how much starch is present in each leaf… Follow the leaf starch experiment worksheet

Starch Experiment

Boiling & Ethanol Why do we need to boil the leaf first, and then add it to the ethanol? Boiling the plant damages the cell wall, and the ethanol extracts the chlorophyll from the leaf allowing us to test if any starch is present

Explanation Explain your results for the leaf in the light and the leaf in the dark The leaf in the light has a good store of starch (photosynthesis has taken place, converting the glucose produced to starch) The leaf in the dark cannot photosynthesize, but has been respiring (using up the starch supply)

Storage Why store the glucose as starch? Remember, the starch is insoluble, so the plant can store it conveniently without it getting dissolved within the cell which is much more convenient than the soluble glucose