Starch is only made by plant cells.
Molecules of both types of starch are hydrophilic but are too large to be soluble in water.
Starch does not affect the osmotic balance of cells,
It is easy to add or remove extra glucose molecules to starch
Therefore starch is useful in cells for glucose, and consequently energy, storage.
In seeds and storage organs such as potato cells glucose is held as starch.
Starch is made as a temporary store in leaf cells when glucose made faster by photosynthesis than it can be exported to other parts of the plant.