* Cell membranes are selectively permeable: They control what substances can enter and exit the cell. This selective permeability is crucial for maintaining the cell's internal environment.
* Sugar molecules are too large: Sugar molecules are relatively large compared to the pores in most cell membranes. They cannot simply diffuse through the membrane like smaller molecules (like water or oxygen) can.
* Active transport is needed: To move sugar molecules across the membrane, cells need to use active transport mechanisms. This requires energy and specialized proteins embedded in the membrane.
In summary: In a simple bag, without any active transport mechanisms, sugar molecules would not be able to pass through the membrane.
