Question

hypothesis: if molecules are small enough, then they will diffuse across a semipermeable membrane because they can pass through its tiny openings. the independent variable in this experiment was molecule size, and the dependent variable was molecule shape ability to diffuse rate of diffusion

Explanation:

The independent variable is what is changed in an experiment, here it's molecule size. The dependent variable is what is being measured or observed and is affected by the independent variable. Since the hypothesis is about whether molecules will diffuse based on size, the ability to diffuse is what depends on molecule size.

Answer:

ability to diffuse