Final answer:
The osmolar activity of the body between the extracellular fluid (EF) and intracellular fluid (IF) is maintained through osmotic gradients created by differences in solute concentrations. The EF has a higher concentration of sodium and chloride ions compared to the IF, leading to the movement of water across cell membranes.
Step-by-step explanation:
The osmolar activity refers to the concentration of solutes in a solution, which affects the movement of water across cell membranes. In the human body, the extracellular fluid (EF) and intracellular fluid (IF) have different osmolar activities. The EF, which includes plasma and interstitial fluid, has a higher concentration of sodium and chloride ions compared to the IF. This difference in osmolarity creates an osmotic gradient that allows water to move between the EF and IF, maintaining osmotic balance.