Question

What is the biological importance of $N{a^ + }$ and ${K^ + }$ ions in cell fluids like blood plasma?
(A) They participate in transmission of nerve signals
(B) They regulate the number of red and white blood corpuscles in the cell
(C) They can be present in any amount in the blood since they are absorbed by the cells
(D) They regulate the viscosity and color of the blood

Answer 1

Sodium and potassium ions both have different ability to penetrate the cell membrane. Their concentration difference around cell membranes can actually regulate such physiological processes in the body.

Complete answer:
Generally, sodium ions are found in the blood plasma outside the cell and in the interstitial fluids which is found in the surroundings of the cells. Potassium ions are the most abundant cations found in the cell fluids.
- They both participate in the transmission of nerve signals. Let’s see their other functions.
- Sodium and Potassium are chemically very similar but they have very different ability to penetrate certain types of cell membranes, they differ in their transport mechanism and also in their efficiency to activate such types of biological catalysts-enzymes.
- They also help to regulate the flow of water across cell membranes. Transportation of sugars and amino acids is also done with the help of sodium and potassium ions.
- We have found that there is notable variation of the concentration of sodium and potassium ions on the opposite sides of the cell membranes. As an example, if concentration of sodium ions in blood plasma is 150 $mmol{L^{ - 1}}$ and potassium ions in red blood cells is 7 $mmol{L^{ - 1}}$ at a time and this may change to 10 $mmol{L^{ - 1}}$ and 145 $mmol{L^{ - 1}}$ at another time. This ionic gradient suggests that there is some kind of mechanism working which is known as sodium-potassium pump. This helps nerves to send signals.

Note: Remember that as sodium and potassium ions have concentration differences that will not alter the viscosity of fluid at all. Remember the fact that across the cell membranes, the side where sodium concentration is low, potassium concentration will be high there and vice-versa.