Final answer:
Decreasing temperature leads to a reduced rate of diffusion across a cell's plasma membrane both by decreasing the kinetic energy of molecules, slowing their movement, and by reducing the fluidity of the membrane, making it less permeable. (option d)
Step-by-step explanation:
When considering how decreasing temperature would affect the rate of diffusion of molecules across a cell’s plasma membrane, two main effects can be expected:
- Firstly, a decrease in temperature would decrease diffusion rate because molecules have less kinetic energy at lower temperatures, leading to slower movement.
- Secondly, this reduced molecular motion also results in a decrease in membrane fluidity as lipid molecules in the biomembrane move more sluggishly, making it harder for other molecules to pass through.
Therefore, the correct answer to how decreasing temperature affects the rate of diffusion across a cell’s plasma membrane is option d: Decrease diffusion rate, decrease fluidity.
Hence, the answer is option d