Question

Facilitated diffusion involves molecules passing through protein channels, allowing for specific substances to be transported across the cell membrane. The limited number of protein channels available for facilitated diffusion results in a maximum rate of transport. This contrasts with simple diffusion, where molecules pass directly through the phospholipid bilayer. The graph demonstrates that as the concentration of molecules increases, the rate of transport reaches a maximum due to the saturation of available protein channels. a) Saturation of protein channels b) Increasing concentration of molecules c) Simple diffusion through bilayer d) Limited membrane permeability

Answer 1

Facilitated diffusion uses protein channels to transport specific substances across the cell membrane down their concentration gradient without energy, but has a saturation point where the rate of transport maxes out. Therefore, the correct option is A.

Step-by-step explanation:

In facilitated diffusion, specific substances are transported across the cell membrane via protein channels, allowing molecules that are generally not able to pass through the phospholipid bilayer to diffuse into or out of the cell.

This type of diffusion depends on the concentration gradient, moving substances from an area of higher concentration to one of lower concentration without the need for cellular energy.

However, since the number of transport proteins is finite, the rate of transport via this method can become saturated, meaning it reaches a maximum rate beyond which it cannot increase even if the concentration gradient becomes steeper. This contrasts with simple diffusion, where molecules pass directly through the membrane without intermediary transport proteins, and the rate of transport is not limited by the number of protein channels.

Therefore, the correct option is A.