Write a short paragraph to explain why the sugar could get through the membrane, but the starch could not?

Selective permeability. When many glucose molecules combine they form one large molecule called starch. Due to starch being a larch molecules they have difficulty passing through the membrane. Glucose molecules are smaller in size therefore they can pass easily through  the membrane.

Explanation:

Selective permeability the the process whereby the cell membrane allows for selective molecules to pass through its membrane, in order to obtain internal equilibrium.

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.

the endomembrane system i think