Final answer:
The solvent density inversely affects the diffusion rate of a molecule; the denser the solvent, the slower the diffusion. Other factors influencing diffusion include molecule mass and temperature.
Step-by-step explanation:
The factor that inversely affects the diffusion rate for a molecule across a membrane is the density of the solvent. As the solvent becomes denser, the rate of diffusion decreases because the molecules have a harder time moving through the denser medium. Thus, if a cell is dehydrated and loses water, its cytoplasm becomes denser, leading to a slower diffusion rate and impaired cell function. The mass of the diffusing molecules also plays a role in diffusion, with heavier molecules diffusing more slowly than lighter ones. Temperature is another important factor; higher temperatures lead to an increase in molecular movement and diffusion rate, whereas lower temperatures reduce this movement.