chapter 6.3: membranes regulate the traffic of molecules college prep biology mr. martino
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Chapter 6.3: Membranes regulate the traffic of
molecules
College Prep BiologyMr. Martino
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6.3 Cell Membranes Cell membranes make
the E in chemical bonds available for metabolic reactions Kinds and amounts of
substances different on either side of membrane – membrane is selectively permeable
CO2, O2, water, and small nonpolar molecules move easily across
Large, polar molecules and ions do not move freely across
These require various proteins
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Concentration Gradients Brownian Motion –
continuous random movement of particles due to temp. differences
Concentration gradient: the difference in conc. of particles on one side of a membrane as opposed to the other
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Diffusion
Diffusion: the tendency for particles to move from areas of high concentration to areas of low conc.
Molecules naturally move “with” conc. Gradient
Diffusion is fastest when gradient is steep
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Active transport: requires E to move substances across a membrane Transport
protein pumps the substance against the conc. gradient
Usually use ATP
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Movement of Water
Osmosis: the diffusion (passive transport) of water Hypertonic
Solution: has a higher conc. of solutes than the cell
Water will leave cells and cells will shrivel
Hypotonic Solution: had a lower conc. of solutes than the cell
Water will rush into cells and cells will swell
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Turgor (hydrostatic) pressure: the internal force pushing outward in plant cells Cell wall prevents
the uptake of too much water
Isotonic Solution: the conc. of particles inside the cell is = to the conc. of the particles outside the cell Movement
continues – just no net movement
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Endocytosis and Exocytosis
Exocytosis: process of how cells export bulky materials from the cytoplasm Ex. Tear and insulin
formation Endocytosis: process of how
cells import macromolecules Phagocytosis: cellular
eating Pinocytosis: cellular
drinking Receptor-mediated
endocytosis: highly specific due to receptor proteins
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