Which of these options is NOT a feature of isotonic solutions?

Isotonic solutions are defined by their equality in solute concentration relative to another solution, commonly in reference to the fluid inside a cell. When two solutions are isotonic, the concentration of solute particles is equal on both sides of the cell membrane, resulting in no net movement of water across the membrane. This equilibrium allows the cell to maintain its shape and function without swelling or shrinking.

The first option reflects that in an isotonic environment, the solute concentration outside the cell matches that inside, ensuring homeostasis. The second option points to the equal concentration of solvent, which follows from the equality of solute concentrations as solvent and solute ratios are inherently balanced in isotonic situations. The last option accurately states that there is no net movement of water when in an isotonic state, as the movement of water occurs equally in both directions.

The inclusion of a greater concentration of solutes inside the cell describes a hypertonic solution, which leads to osmotic movement of water out of the cell, causing it to shrink. Thus, this concept does not align with the characteristics of isotonic solutions, establishing it as the correct answer to identify the feature that does not belong to isotonicity.