The correct option is
B. Facilitated diffusion.
Detailed Explanation:
- Understanding Osmosis:
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Osmosis is the movement of water across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration. This process aims to equalize solute concentrations on both sides of the membrane.
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Role of Aquaporins:
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Aquaporins are specialized protein channels embedded in the cell membrane that facilitate the rapid transport of water molecules. They are crucial for maintaining water balance in cells, especially in tissues that require quick water movement, such as kidney cells.
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Facilitated Diffusion:
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Facilitated diffusion is a type of passive transport that allows substances to cross membranes with the assistance of special proteins. In this case, aquaporins act as the transport proteins for water. Since this process does not require energy (ATP), it is classified as passive transport.
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Why Option B is Correct:
- Water moves through aquaporins via facilitated diffusion because it relies on the concentration gradient of water (from high to low concentration) without the need for energy input. The presence of aquaporins increases the permeability of the membrane to water, allowing it to move more efficiently compared to simple diffusion.
Why the Other Options are Incorrect:
- A. Active Transport:
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Active transport involves the movement of substances against their concentration gradient, which requires energy (usually in the form of ATP). Since osmosis through aquaporins occurs along the concentration gradient (from high to low), this option is not applicable.
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C. Simple Diffusion:
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Simple diffusion refers to the movement of molecules directly through the lipid bilayer of the cell membrane without the aid of proteins. While water can move through the membrane this way, the presence of aquaporins significantly enhances the rate of water transport, making facilitated diffusion the more accurate description of the process in this context.
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D. Endocytosis:
- Endocytosis is a process by which cells engulf substances to bring them into the cell, typically involving the formation of vesicles. This process is not related to the movement of water across the membrane in response to solute concentration gradients, making it irrelevant to the question.
Summary of Key Points:
- Osmosis is the movement of water across a membrane in response to solute concentration gradients.
- Aquaporins are protein channels that facilitate the rapid transport of water.
- Facilitated diffusion is a passive transport mechanism that does not require energy and allows water to move through aquaporins.
- Other processes like active transport, simple diffusion, and endocytosis do not accurately describe the movement of water through aquaporins in this context.