The reason red blood cells burst in freshwater while plant cells do not is due to differences in their structure and the concept of osmosis.
Red Blood Cells:
Red blood cells (RBCs) are surrounded by a flexible plasma membrane that is not resistant to osmotic pressure. When RBCs are placed in freshwater, the concentration of solutes (like salts) outside the cells is much lower than the concentration inside the cells. This creates a situation where water moves into the cells by osmosis, as water moves from an area of lower solute concentration (the freshwater) to an area of higher solute concentration (inside the RBCs).
As water enters the RBCs, they swell because of the increased internal pressure. Since RBCs do not have a rigid cell wall to withstand this pressure, they eventually reach a point where the membrane cannot cope with the volume of water, leading to the cells bursting, a process called hemolysis.
Plant Cells:
In contrast, plant cells have a rigid cell wall made of cellulose that provides structural support. When plant cells are placed in freshwater, the same osmotic effect occurs—the water moves into the cells due to the lower external solute concentration. However, as water enters, the cell's vacuole fills, and the internal pressure (turgor pressure) increases.
The rigid cell wall of the plant cell provides a counterforce to this pressure, allowing the cell to maintain its shape and resist bursting. As the vacuole expands, the pressure against the cell wall increases until it reaches a balance—the plant cell becomes turgid (firm and full) but does not burst.
Summary:
- Red Blood Cells: No cell wall, so they burst under osmotic pressure when placed in freshwater (hemolysis).
- Plant Cells: Have a rigid cell wall that provides structural integrity and can accommodate increased internal pressure from water uptake, preventing bursting even in freshwater.
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