* Size: Starch molecules are large and complex carbohydrates. They are significantly bigger than the pores in a partially permeable membrane.
* Solubility: Starch is not soluble in water. It forms a colloid, meaning it is dispersed but not dissolved in water. This lack of solubility prevents it from easily passing through the membrane's pores.
Partially permeable membranes are designed to allow the passage of small molecules, like water, oxygen, carbon dioxide, and some dissolved nutrients. They are often found in cells, where they control the movement of substances in and out.
Think of it like this: Imagine a sieve with small holes. Sand grains (small) can pass through, but pebbles (large) get stuck. Starch molecules are like the pebbles, too big to pass through the membrane's "holes."
Instead of passing through the membrane directly, starch can be broken down into smaller molecules. Enzymes like amylase can digest starch into smaller sugar molecules (like glucose), which are small enough to pass through the membrane.
