Osmosis - Lecture notes 8 PDF

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Michael Hedrick...

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2/5 Osmosis ● Osmosis and Tonicity ○ Osmosis ■ Diffusion of water ■ Water moves from an area of low (solute) to an area of high (solute) ○ This is equivalent to: ■ Water moving from an area of high (H2O) to an area of low (H2O)

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● ○ Tonicity -

■ Refers to cell’s behavior in a solution (Swelling, shrinking, not changing). Solutions can be hypotonic( call swells), hypertonic (cell shrinks), isotonic (no change)

● ○ Osmotic pressure ■ is a quantitative description of the number of particles in solution. Solutions can be hypo-osmotic, hyper-osmotic, iso-osmotic ■ Osmotic pressure = i C ● I = activity coefficient ● C = concentration ■ I M = osmolarity (osmoles/liter) ■ I = number of dissociable particles ■ (eg. sucrose = 1, NaCl = 2, CaCl2 = 3) ■ Ex. 0.2 M NaCl = 0.4 Osmolar ● (0.2 X 2 = 0.4 osmolar) ● Summary of diffusion: ○ Passive – molecules move from an area of [high] to [low] ○ Depends of Permeability and Concentration • ○ Diffusion of water (Osmosis) also occurs passively across cell membranes in response to changes in solute concentrations.

● Passive diffusion ○ uses energy from concentration gradients (i.e. from high to low

○ Requires that the molecule diffusing is permeable to the membrane (both polar and nonpolar molecules) ○ Osmosis is the diffusion of water through its own concentration gradient ● Facilitated diffusion ○ Specific for a given group of chemicals or substances (e.g. sugar specific, amino acid specific)

● ○ Passive Process (depends on concentration gradient) ○ Protein carriers are necessary because some polar solutes are too large to cross the cell membrane ○ Carriers can become saturated (limited numbers)

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● Active transport ○ Requires energy (ATP) to move molecules against a concentration gradient ■ I.e. low solute to high solute ○ 1) primary active transport ■ Na - K - ATPase (sodium pump)

● ■ Pumps 3 NA out of the cell for every 2K that is pumped into the cell ■ AKA Electrogenic pump

● ○ 2) secondary active transport ■ Uses energy from ion gradients (established by primary active transport) to couple movement of ions and other molecules (eg. sugars, amino acids) against their of own concentration gradient ■ 1) co-transport (ions and molecules move in the same direction)( AKA symport)

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■ 2) counter - transport (ions and molecules move in opposite directions) (AKA antiport)

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