뒤로Membrane Transport and Diffusion in Cells
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Membrane Transport and Diffusion
Introduction to Membrane Transport
Cell membranes regulate the movement of substances into and out of the cell. This process is essential for maintaining homeostasis and supporting cellular functions. The movement of molecules across membranes can occur through several mechanisms, including diffusion, facilitated diffusion, and active transport.
Diffusion: The passive movement of molecules from an area of higher concentration to an area of lower concentration.
Facilitated Diffusion: The passive movement of molecules across the membrane via specific transport proteins.
Active Transport: The movement of molecules against their concentration gradient, requiring energy (usually in the form of ATP).
Diffusion and Concentration Gradients
Diffusion is driven by the concentration gradient, which is the difference in the concentration of a substance between two regions. Molecules move down their concentration gradient until equilibrium is reached.
Concentration Gradient: The difference in the concentration of a substance across a space or a membrane.
Equilibrium: The state in which the concentration of a substance is equal throughout a space.
Example: Oxygen diffuses from areas of high concentration (outside the cell) to areas of low concentration (inside the cell) until equilibrium is reached.
Osmosis
Osmosis is a specific type of diffusion involving water molecules. It is the movement of water across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration.
Hypertonic Solution: Higher solute concentration outside the cell; water moves out, causing the cell to shrink.
Hypotonic Solution: Lower solute concentration outside the cell; water moves in, causing the cell to swell.
Isotonic Solution: Equal solute concentration; no net movement of water.
Equation for Osmotic Pressure:
= osmotic pressure
= van 't Hoff factor (number of particles the solute dissociates into)
= molarity of the solution
= gas constant
= temperature in Kelvin
Visual Representation: Diffusion Across Membranes
The provided image appears to show diagrams of cells in different solutions, illustrating the effects of osmosis:
Solution Type | Direction of Water Movement | Effect on Cell |
|---|---|---|
Hypertonic | Out of cell | Cell shrinks (crenation in animal cells) |
Isotonic | No net movement | Cell remains the same size |
Hypotonic | Into cell | Cell swells (may burst in animal cells) |
Key Terms
Selective Permeability: The property of cell membranes that allows some substances to pass through while blocking others.
Transport Proteins: Proteins that assist in the movement of substances across the cell membrane.
ATP (Adenosine Triphosphate): The energy currency of the cell, used in active transport.
Summary
Membrane transport is essential for cell survival and function.
Diffusion and osmosis are passive processes driven by concentration gradients.
Active transport requires energy to move substances against their gradients.
Additional info: Some content and context have been inferred based on standard General Biology curriculum and the visible structure of the provided material.
