Aquaporins are selective for water molecules o 3

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aquaporins are selective for water molecules o 3- Osmosis = diffusion of water across membranes Water diffuses from a region of high to low water concentration across a membrane Another way of saying that: water moves from a region of low solute (e.g. salt) to high solute to dilute it & reach equilibrium net movement of water from where it is more available (because of lower solute concentration) to where is is less available (because of higher solute concentration) - Energy requiring o 1- Active transport : membrane proteins use energy (ATP) to move molecules across plasma membranes against their concentration gradients Active transport proteins span the entire membrane They often have a molecule binding site (recognition site) & ATP binding site o 2- Endocytosis -Cells engulf particles or fluids by endocytosis (into the cell) 3 types of endocytosis Pinocytosis (“cell drinking”) moves liquids into the cell Receptor-mediated endocytosis moves specific molecules into the cell Phagocytosis (“cell eating”) moves large particles into the cell o 3- Exocytosis moves material out of the cell Cell uses energy to dispose of waste or secrete substances Vesicles containing the material move to the cell surface, fuse with the cell membrane, then allow contents to diffuse/empty into the outside fluid Isotonic, hypertonic, & hypotonic solutions - Isotonic= no net flow of water- equilibrium o solutions: equal concentrations of water and dissolved substances on either side of a membrane - Hypertonic= water flows out of cell and it shrivels up o Hypertonic solution is one with a greater solute (e.g. salt) concentration
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o Water moves across a membrane (osmosis) toward hypertonic solution to reach equilibrium - Hypotonic= water flows into cell and it expands and bursts o solution has a lower solute concentration o Water moves across a membrane (osmosis) away from the hypotonic solution Diffusion vs. osmosis- which will occur & in which direction?
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