Question

1. selectively permeable membranes allow ______.

no molecules to pass through
all molecules to pass through
concentrated molecules to pass through
only certain molecules to pass through

Explanation:

Selectively permeable membranes, like cell membranes, have a property that they do not allow all molecules to pass freely. They have specific mechanisms (such as protein channels, carrier proteins etc.) that control the entry and exit of substances. Molecules pass based on factors like size, charge, solubility in lipid (for lipid - based membranes). So they do not allow no molecules (as cells need to exchange substances like oxygen, water), not all molecules (as some harmful or unnecessary large molecules are restricted), and not just concentrated molecules (concentration gradient is one factor but not the only determinant). Only certain molecules can pass through based on the membrane's selective criteria.

Answer:

only certain molecules to pass through