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Human red blood cell (erythrocyte) after 1/2 minute in severely hypotonic solution (0% NaCl), less than the content of normal blood.  Water has moved into the cell and the cell has increased in size and has lost the biconcave shape. The pressure from the water has produced projections in the cell surface at weak points in the cell membrane. SEM X10,000 (based on 4" x 5")