LQB186 Lecture Notes - Lecture 4: Lipid Bilayer, Turgor Pressure, Osmotic Concentration

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Cellular membranes possess two key qualities: they are semi-permeable. Only certain materials may freely cross large and charged substances are typically blocked: they are selective. Membrane proteins may regulate the passage of material that cannot freely cross. Movement of materials across a biological membrane may occur either actively or passively. Passive transport involves the movement of material along a concentration gradient high concentration low concentration. Because materials are moving down a concentration gradient. Does not require the expenditure of energy (atp hydrolysis) There are three main types of passive transport: Simple diffusion movement of small or lipophilic molecules (e. g. o2, co2, etc. ) Osmosis movement of water molecules (dependent on solute concentrations) Facilitated diffusion movement of large or charged molecules via membrane proteins (e. g. ions, sucrose, etc. ) Active transport: active transport involves the movement of materials against a concentration gradient low concentration high concentration. Because materials are moving against the gradient. It requires the expenditure of energy (e. g. atp hydrolysis)

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