Answer:
The case in which facilitated diffusion would be needed is in the transport of large non-polar molecules moving down the concentration gradient.
Explanation:
Facilitated diffusion (FD) involves a form of passive transport, that is, it does not require energy and mobilizes substances across the cell membrane in favor of a concentration gradient.
The passive transport mechanism of FD is necessary only in the case of transport of very large molecules or polar molecules that:
- Cannot be transported by simple diffusion, due to the selective permeability of the membrane
- They follow a concentration gradient, from the place with the highest concentration to the one with the lowest concentration.
For FD to occur, it requires the use of a protein, which acts as a carrier of the molecules to be mobilized.
The other options are not correct because:
<em> A and C. Passive transport, as facilited diffusion, implies movement in favor of a concentration gradient.</em>
<em> B and C. Non-polar small or very small molecules can cross the membrane by simple diffusion.</em>
