[ELI5] Why do plants store starch instead of glucose?


I know this question has been answered many times on the internet but I don’t get one thing – why is water moving to the plant cell a bad thing? The cell won’t burst since it has a wall so wouldn’t it be positive for plants to get more water? With that being said, why is storing starch instead of glucose beneficial then?

In: 2

Plant cells can only store so much water before they stretch, interfere with metabolism and nutrient balance and waste disposal. Then too much water the cell wall will break and cause cellular damage or death.

Glucose is water soluble, so it’s not good for long-term storage. Plants store energy as starch kind of similar to how humans store energy as fat.

Swelling of cells is caused by osmotic pressure, which is a colligative property – it depends on the *number* of molecules dissolved in the liquid, not the weight. Starch is a polymer of glucose; by stringing many glucose molecules together into a single molecule, it dramatically reduces the osmotic pressure, since the total number of molecules is now much lower. To the extent the starch is insoluble (depends on molecular weight and architecture) this lowers the number of molecules in solution even lower.

It’s easy to store glucose as starch since it’s more space efficient.

Also, storing glucose as starch allows you to control how much glucose is floating around. Starch can’t be readily metabolized, but glucose can. Plants need a way to limit glucose consumption in scarcity. Hiding glucose away as starch is a good way to make sure the glucose isn’t being used up too quickly