7 Transport across membranes

7 Transport across membranes - Biology141 (Physiology)...

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4/6/08 1:01 AM Biology141 (Physiology) Page 1 of 3 https://courses.bio.psu.edu/spring2008/biol141/Lecture%207(2008).htm Biology141 (Physiology) Lecture 7 M. Whim TRANSPORT ACROSS MEMBRANES. [1]. BACKGROUND. ( a ). Why is cross-membrane transport important? uptake of nutrients from extracellular environment and release of waste products. critical for the functioning of the nervous system. cells are selectively permeable (e.g. not permeable to proteins, nucleic acids, phosphorylated molecules). (b). Categories of transport. passive transport down a conc. gradient (simple diffusion; osmosis; facilitated diffusion). active transport movement against a conc. gradient. requires metabolic energy (e.g. pumps). [2]. PASSIVE TRANSPORT. ( a ). Diffusion. solution = solvent (water) + solute molecules (dissolved). molecules are in random motion (due to thermal energy) if a concentration gradient exists then the random motion will eliminate the concentration difference – this is diffusion .
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7 Transport across membranes - Biology141 (Physiology)...

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