What is true regarding an isotonic solution?

An isotonic solution is defined by having equal solute concentrations on both sides of a cell membrane. This means that the concentration of solutes (like salts or sugars) in the solution outside the cell is the same as inside the cell. As a result, there is no net movement of water into or out of the cell; water molecules move in and out at equal rates, maintaining cell shape and size. This equilibrium is crucial for cell health because it prevents excessive swelling or shrinking of the cell.

In this context, the other choices do not accurately describe an isotonic solution. For instance, a higher solute concentration inside the cell would indicate a hypertonic solution, leading to water moving out of the cell. Claiming that only water moves across the membrane does not capture the concept of isotonic balance correctly, as both solute and solvent concentrations are considered. Referring to isotonic solutions as a type of active transport misplaces the context; isotonic conditions are passive and do not require energy input, contrasting with active transport processes that involve energy to move substances against their concentration gradient.