Active vs. Passive Transport across cell membranes

MEMBRANES CONTAIN… 1. Phospholipids Heads are phosphate and glycerol hydroPHILIC hydroPHILIC “tails” are 2 fatty acids hydroPHOBIC hydroPHOBIC Makes a “sandwich” with fatty acids in the middle Called phospholipid “BILAYER”

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Membranes also contain… 2. CARBOHYDRATE CHAINS for cell-cell recognition 3. PROTEINS for channels and cell transport, and other things 4. CHOLESTEROL which makes membrane flexible

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7 Membrane structure is visible using an electron microscope. Transmission electron microscopes (TEM) can show the 2 layers of a membrane.

Check your understanding… What molecule is the main component of your cell membranes? Why is the cell membrane called a phospholipid BILAYER? What component of the cell membrane is for… making channels? flexibility? cell-cell recognition?

stuff moves in and out by… Passive transport or Active transport

10 I. Passive transport : no energy is required no energy is required moves substances in response to concentration gradient moves substances in response to concentration gradient If 2 solutions have different water concentrations… If 2 solutions have different water concentrations… Osmosis moves water toward the lower concentration (from high to low) Osmosis moves water toward the lower concentration (from high to low) Water concentration tries to “balance out” Water concentration tries to “balance out” NO energy is used NO energy is used II. Active transport: 1. requires energy (ATP) 2. moves substances against concentration gradient

11 hypertonic solution has a higher solute concentration hypotonic solution has a lower solute concentration

12 II. Active Transport requires energy – ATP is used moves substances from low to high concentration – “against the gradient”

13 Check your understanding… What are 2 different ways that cells can move substances in or out? What type of cell transport requires ENERGY? What type of transport moves substances AGAINST a concentration gradient? What is your cell’s “energy molecule”?

Videos Active Transport videoActive Transport video 1 Active Transport video Sodium-Potassium Pump Sodium-Potassium Pump