The correct option is
B. Osmosis.
Detailed Explanation:
- Definition of Osmosis:
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Osmosis is the process by which water molecules move 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, as it regulates the internal environment of cells.
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Concentration Gradient:
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In osmosis, water moves against the concentration gradient of solutes. This means that water will flow from a region where there are fewer solutes (more water) to a region where there are more solutes (less water). This movement continues until equilibrium is reached, meaning the solute concentrations on both sides of the membrane become equal.
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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. Without osmosis, cells could become dehydrated or overly swollen, leading to cell damage or death.
Why Other Options Are Incorrect:
- A. Diffusion:
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Diffusion refers to the movement of particles (solutes) from an area of higher concentration to an area of lower concentration. While diffusion can occur with water molecules, it does not specifically describe the movement of water across a membrane in relation to solute concentrations. Therefore, diffusion is not the correct answer in this context.
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C. Active Transport:
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Active transport is the process by which cells move substances against their concentration gradient, using energy (usually from ATP). This process is not applicable to the movement of water, which occurs passively in osmosis. Active transport is more about moving solutes rather than water.
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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 it does not require energy, it still refers to solutes moving from high to low concentration, not the movement of water from low to high solute concentration. Thus, it does not describe the process of osmosis.
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 and aims to equalize solute concentrations on both sides of the membrane.
- Diffusion involves solute movement from high to low concentration, while active transport requires energy to move substances against their gradient.
- Facilitated diffusion involves solutes moving through transport proteins, not water movement in relation to solute concentration.
This understanding of osmosis is crucial for grasping how cells interact with their environment and maintain homeostasis.