Red blood cells in hypotonic, isotonic and hypertonic solutions

An example figure from the Osmosis and Tonicity generator.

Three red blood cells, each in a box of salt solution with gray NaCl particles and blue water particles: A in a hypotonic 0.45% solution, swollen round, with water arrows pointing in; B in an isotonic 0.9% solution, a normal disc with arrows both ways and the words No net movement; C in a hypertonic 1.8% solution, shrunken with spiky edges, with water arrows pointing out — The same red blood cell, 0.9% NaCl inside, in three salt solutions. In the hypotonic solution (0.45% NaCl) water moves in and the cell swells; in the isotonic solution (0.9%) water crosses equally both ways, so there is no net movement and it stays a normal biconcave disc; in the hypertonic solution (1.8%) water moves out and the cell shrinks and crenates. Solute particles are drawn as crowded as their concentration, with water particles in the room they leave.

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Answer key

A: hypotonic, water moves in, the cell gains water and swells
B: isotonic, no net water movement, the cell stays the same size
C: hypertonic, water moves out, the cell loses water and shrinks (crenates)

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