The correct option is
B. Osmosis.
Detailed Explanation:
- Definition of Osmosis:
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Osmosis is the movement of water molecules across a selectively permeable membrane. This movement occurs from an area of lower solute concentration (where there are fewer solute particles) to an area of higher solute concentration (where there are more solute particles). The goal of osmosis is to equalize solute concentrations on both sides of the membrane.
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Selectively Permeable Membrane:
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A selectively permeable membrane allows certain molecules (like water) to pass through while blocking others (like solutes). This property is crucial for maintaining cellular homeostasis.
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Concentration Gradient:
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In osmosis, water moves along its concentration gradient. When there is a higher concentration of solute on one side of the membrane, the water will move toward that side to dilute the solute, thereby reducing the concentration difference.
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Importance of Osmosis:
- Osmosis is vital for many biological processes, including nutrient absorption, waste removal, and maintaining cell turgor pressure in plants. It helps cells maintain their shape and function properly.
Why Other Options Are Incorrect:
- A. Diffusion:
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Diffusion refers to the movement of solute particles from an area of higher concentration to an area of lower concentration. While water can diffuse, the specific process of water movement across a membrane is termed osmosis, not diffusion. Therefore, diffusion does not accurately describe the movement of water in this context.
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C. Active Transport:
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Active transport is the movement of molecules across a membrane against their concentration gradient, which requires energy (usually in the form of ATP). Osmosis does not require energy; it is a passive process driven by concentration differences. Thus, active transport is not applicable to the movement of water as described in the question.
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D. Facilitated Diffusion:
- Facilitated diffusion is a type of passive transport that involves the movement of molecules across a membrane via specific transport proteins. While water can move through specialized channels called aquaporins (a form of facilitated diffusion), the fundamental process of water moving from low to high solute concentration is still classified as osmosis. Therefore, this option does not fully capture the essence of the question.
Summary of Key Points:
- Osmosis is the movement of water from an area of lower solute concentration to an area of higher solute concentration across a selectively permeable membrane.
- It is a passive process that does not require energy.
- Diffusion refers to solute movement, while active transport requires energy and moves substances against their gradient.
- Facilitated diffusion involves transport proteins but does not specifically describe the movement of water in the context of solute concentration.
By understanding these concepts, you can better grasp the mechanisms of water movement in biological systems and their significance in maintaining cellular functions.