Question

In which case would facilitated diffusion be needed?

Answer 1

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:

    A and C. Passive transport, as facilited diffusion,  implies movement in favor of a concentration gradient.

    B and C. Non-polar small or very small molecules can cross the membrane by simple diffusion.