Water enters cells primarily through two mechanisms: simple diffusion and aquaporins. Because of its small size, water can diffuse directly across the cell membrane, but this process is relatively slow due to water's polarity. The majority of water transport occurs through aquaporins, which are specialized protein channels that facilitate rapid water movement across the cell membrane.
Here's a breakdown of the two mechanisms:
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Simple Diffusion: Water molecules, due to their small size, can squeeze between the phospholipids that make up the cell membrane. This is a slow process because water is polar and the interior of the cell membrane is hydrophobic (water-repelling).
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Aquaporins: These are integral membrane proteins that form pores in the cell membrane. These pores are specifically designed to allow water molecules to pass through quickly and efficiently. They significantly increase the rate at which water can enter and exit the cell.
In summary, while some water can passively diffuse across the cell membrane, the primary and most efficient method is through aquaporins, specialized channels that facilitate rapid water transport.
