4.4 Uses of glucose from photosynthesis

Five uses of glucose

Plants make glucose by photosynthesis. They use it in five main ways.

1. Respiration: to release energy for the plant's cells.
2. Converted into starch for storage: starch is insoluble, so it does not affect the water balance of cells by osmosis, as glucose would. It is stored in leaves, roots, tubers (potatoes) and seeds, and turned back into glucose when needed.
3. Making fats and oils for storage: many seeds, such as sunflower seeds and peanuts, store energy as oil.
4. Making cellulose: cellulose strengthens the cell walls.
5. Making amino acids: glucose is combined with nitrate ions absorbed from the soil to make amino acids, which are joined to make proteins, such as enzymes.

Why plants store starch, not glucose

Glucose is soluble. A cell full of glucose would take in water by osmosis and could swell. Starch is insoluble, so it can be stored in large amounts without affecting the movement of water. This is also why the iodine test on a leaf shows where photosynthesis has happened: the leaf turns glucose into starch.