Question

Most systemic capillary exchange of solutes occurs via __________.

a. Simple diffusion
b. transcytosis
c. Active transport
d. Sodium-potassium pump
e. Sodium symporters

Answer 1

Systemic capillary exchange of solutes primarily occurs via facilitated diffusion, which uses specific transport proteins but does not directly consume energy like active transport mechanisms.

Step-by-step explanation:

The most common method for systemic capillary exchange of solutes is via facilitated diffusion. This process involves the passive and spontaneous transfer of molecules or ions across cell membranes through specific transmembrane proteins. Facilitated diffusion is similar to passive diffusion but is distinguished by its saturation kinetics, similar to enzyme catalysis, meaning the rate of transport approaches a maximum when all available transport proteins are being utilized. Sodium symporters utilize secondary active transport, where the active transport of one molecule, like sodium ions, creates a concentration gradient that is then used to drive the transport of another molecule, such as glucose, into cells. However, once molecules are transported by a symport mechanism on the apical membrane, they are transported by facilitated diffusion on the basal membrane, moving down their concentration gradient without the direct use of ATP.

While ion pumps such as the sodium-potassium pump and processes like phagocytosis require active transport, facilitated diffusion is the primary mechanism for solute exchange in systemic capillaries.

Answer 2

Most systemic capillary exchange of solutes occurs via a) simple diffusion.

Step-by-step explanation:

Most systemic capillary exchange of solutes occurs via simple diffusion. Simple diffusion allows for the passive movement of substances from an area of higher concentration to an area of lower concentration. While symport mechanisms, active transport, and facilitated diffusion all play roles in the transport of substances across the cell membrane, it is the process of simple diffusion that is primarily responsible for the exchange of solutes in systemic capillaries.

An example of facilitated diffusion is the way glucose is transported into the cell in the kidneys, using a symporter with sodium on the apical membrane, and then moving out of the cell on the basolateral side by facilitated diffusion to the bloodstream.

Hence, the correct answer is Option A.