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4. Cells And Tissues eLearn.Punjab

Water balance problems are somewhat different for plant cells because of their rigid cell walls. Most
plant cells live in hypotonic environment i.e. there is low concentration of solutes in extracellular
fluids than in cells. As a result, water tends to move first inside cell and then inside vacuole. When
vacuole increases in size, cytoplasm presses firmly against the interior of cell wall, which expands a
little. Due to strong cell wall, plant cell does not rupture but instead becomes rigid. In this condition,
the outward pressure on cell wall exerted by internal water is known as turgor pressure and the
phenomenon is turgor. In isotonic environment, the net uptake of water is not enough to make
the cell turgid and it is flaccid (loose / not firm). In a hypertonic environment a plant cell loses water
and cytoplasm shrinks. The shrinking of cytoplasm is called plasmolysis.

Figure 4.23: Effect of tonicity on animal and plant cell V: 1.1

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