Why do erythrocytes swell and burst when placed in water?
(A) Since water concentration is higher outside the cell, water moves inward by passive diffusion.
(B) Since hemoglobin concentration is higher inside the cell, hemoglobin moves outward by exocytosis.
(C) Since potassium ions are more concentrated inside the cells, potassium ions move outward by osmosis.
(D) Erythrocytes pump water inward by active transport to balance osmotic gradients.
(E) Water is a universal solvent and simply dissolves the erythrocyte membranes.

A.
There is more sodium inside the cell than outside. There is a saying that "water follows salt". It is found in the case of osmosis and the semipermeable membrane around the cell. In this case there is more salt inside so water will move inside. The cell can break with too much water.

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