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How does water help cells maintain their volume and shape?

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water rapids, Niagara Falls, Canada — water Water is the most plentiful compound on Earth and is essential to life. Although water molecules are simple in structure (H₂O), the physical and chemical properties of water are extraordinarily complicated.

Water is essential for maintaining the volume and shape of cells, though the mechanisms differ between plant and animal cells.

Animal Cells

In animal cells, water constitutes 70 to 80 percent of the cell volume. Water moves in and out of the cell via osmosis through specialized channels in the cell membrane known as aquaporins. This movement balances cellular fluid levels, which prevents the cell from shrinking or swelling and maintains its proper volume and shape. Maintaining this balance is critical for vital processes such as nerve impulse conduction and the transport of nutrients.1

Plant Cells

In plant cells, shape and rigidity are primarily maintained through turgor pressure. Plant cells contain a large central vacuole that stores a solution of salts and sugars. The high concentration of these solutes draws water into the vacuole through osmosis. As the vacuole expands, it exerts hydrostatic pressure against the cell wall, pressing the cell membrane firmly against it. This turgor-induced stiffening provides the structural support necessary for plant tissues to remain upright. When a plant loses water, the resulting drop in turgor pressure causes the cells to lose their rigidity, leading to wilting.234