Write down the biological importance of $Na$ and $K$ in the human body and give a brief note on the sodium-potassium pump.

(N/A) typical $70 \ kg$ human contains about $90 \ g$ of $Na$ and $170 \ g$ of $K$,compared with only $5 \ g$ of iron and $0.06 \ g$ of copper. Sodium ions are found primarily on the outside of cells,located in blood plasma and in the interstitial fluid surrounding the cells.
These ions participate in the transmission of nerve signals,in regulating the flow of water across cell membranes,and in the transport of sugars and amino acids into cells.
Sodium and potassium,although chemically similar,differ quantitatively in their ability to penetrate cell membranes,in their transport mechanisms,and in their efficiency to activate enzymes. Potassium ions are the most abundant cations within cell fluids,where they activate many enzymes,participate in the oxidation of glucose to produce $ATP$,and,along with sodium,are responsible for the transmission of nerve signals.
There is a considerable variation in the concentration of sodium and potassium ions on opposite sides of cell membranes. For example,in blood plasma,sodium is present at $143 \ mmol \ L^{-1}$,whereas the potassium level is only $5 \ mmol \ L^{-1}$. Within red blood cells,these concentrations change to $10 \ mmol \ L^{-1}$ for $Na^{+}$ and $105 \ mmol \ L^{-1}$ for $K^{+}$.
These ionic gradients demonstrate that a discriminatory mechanism,called the sodium-potassium pump,operates across cell membranes. This pump consumes more than one-third of the $ATP$ used by a resting animal and about $15 \ kg$ of $ATP$ per $24 \ h$ in a resting human.