Substance R is too large to diffuse across the cell membrane or to be transported across by a protein. Molecules of Substance R can, however, cross the membrane and exit the cell. By which of the listed processes do they cross?

A. Active transport

B. Facilitated diffusion

C. Osmosis

D. Diffusion

B

Explanation:

. facilitated Diffusion is the form of assisted diffusion through special protein channels in the membrane of cells. It is a passive form of diffusion because it still depends on the movements of the particular substance down the concentration gradient. It is the transport methods for large polar molecules e. g amino acids, glucose and ions to reach the inside of the cells.

The special proteins involved are the carrier, gated channels, and channels protein. These proteins provides hydrophylic medium for theses molecules to reach the cells.

Generally the channels proteins are fixed in shape, while the carrier proteins can change between the two shapes

A. Active transport

Explanation:

The process is called Exocytosis which falls under the Active transport system.

Active Transport describes the processes of moving materials through the cell membrane that requires the use of energy. Substance R was said to be too large to diffuse so it will certainly need some form of energy to make it pass through the membranes. This makes Active transport the correct choice.