Maintaining Isotonic Conditions in Cell Culture

Steps:

• Animal cells lack a cell wall and are sensitive to osmotic changes.
• In culture, the external solution must match the cell's internal solute concentration.
• Salt solutions provide ions to achieve this balance, mimicking physiological fluids.
• This equilibrium stops osmosis, preserving cell integrity and viability.

Why B is correct:

• An isotonic solution has equal solute concentrations inside and outside the cell, preventing net water movement by osmosis (definition of isotonicity).

Why the others are wrong:

• A: Facilitated diffusion of salts occurs naturally via channels, but the solution's role is osmotic balance, not promoting influx.
• C: Diffusion of salts is not prevented; equal concentrations result in no net salt movement, but individual molecules diffuse.
• D: Salts provide ions for membrane function, not energy; active transport uses ATP.

Final answer: B