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Transcript
CELL TRANSPORT Chapter 5 1. Cells must keep a biological balance with their environment to stay alive & healthy. This condition is called homeostasis. 2. The cell membrane is able to maintain homeostasis by being selectively permeable - allowing some molecules into cell while keeping others out. 3. Structure of the cell membrane: a) there are 2 layers of phospholipid molecules - the fatty acid tails inside the membrane are non-polar & avoid water (hydrophobic) & the phosphate heads on the outer boundaries are polar & allow interaction with cell’s watery environment (hydrophilic) b) transport proteins within the phospholipid layers form channels to allow materials to move across 4. When molecules can move easily across the cell membrane without the help of cellular energy, this is called passive transport. 5. Diffusion requires only a concentration gradient. This means that molecules move from an area of greater concentration to an area of lesser concentration to reach equilibrium. The diffusion of water is called osmosis. 6. Sugars & amino acids use carrier proteins to cross the membrane. This form of passive transport is called facilitated diffusion. 7. A solution is composed of a solute (sugar) dissolved in a solvent (water). The direction water will move across a membrane depends on the concentration of the 2 substances. A solution may be: a) hypotonic - concentration of solute molecules outside cell is lower than in cell - water will diffuse into cell b) hypertonic - concentration of solute molecules outside cell is greater than inside - water will diffuse out of cell c) isotonic - concentration of solutes outside & inside cell are equal - water will not diffuse in either direction 8. Ions (sodium, potassium) move across the membrane against the concentration gradient (lesser to greater) with the help of carrier proteins. This requires energy from ATP molecules in the cell & is called active transport. 9. Some cells use active transport to take in & release large molecules, groups of molecules, or even whole cells. a) endocytosis - cell surrounds material from environment & encloses it in a vacuole where it’s digested by enzymes (food & microscopic organisms) b) exocytosis - cell expels matter from its interior to the exterior environment (waste, hormones, proteins)