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Transcript
Transport of materials across the cell membrane Packet 5 part 2 What is a concentration gradient? An increase or decrease in the density of a type of molecule in a given area. Which way will the molecules move? Molecules naturally spread out with their kinetic energy. Molecules move from high to low concentration naturally • Diffusion Molecules move down their concentration gradients. Osmosis • Water is very important, so we talk about water separately • Osmosis – diffusion of water from HIGH concentration of water to LOW concentration of water • across a semi-permeable membrane Passive Transport: Simple Diffusion • Move from HIGH to LOW concentration • No energy required fat inside cell LOW fat fat fat fat fat Which way will fat move? HIGH outside cell fat fat fat fat fat fat fat fat Crossing the cell membrane • What molecules can get through the cell membrane directly with simple diffusion? – Small lipids (fatty acids, glycerol) can pass directly through – small uncharged molecules like O2, CO2 and H2O (**) can also pass directly through Fatty CO2 acid O2 inside cell salt waste outside cell sugar aa H 2O but… what about other stuff? Protein channels • Proteins act as doors in the membrane – channels to allow specific molecules through cell membrane Facilitated Diffusion • Move from HIGH to LOW through a protein channel inside cell sugar sugar sugar sugar sugar sugar LOW Which way will sugar move? HIGH outside cell sugar sugar sugar sugar sugar sugar sugar Diffusion Summary • Move from HIGH to LOW concentration – directly through membrane • simple diffusion • no energy needed – help through a protein channel • facilitated diffusion (with help) • no energy needed HIGH LOW Active transport • Cells may need molecules to move against concentration gradient – need to pump “uphill” • from LOW to HIGH using energy – protein pump (transport protein) – requires energy • ATP ATP Figure 8.19 The three types of endocytosis in animal cells RME Transport summary simple diffusion facilitated diffusion No energy needed High to low concentration With the concentration gradient: Floating downstream active transport energy needed ATP Low to high concentration Against the concentration gradient: swimming against the current Tonicity 2006-200 Keeping water balance • Cell survival depends on balancing water uptake & water loss • Tonicity= the relative amount of dissolved solutes in an aqueous solution freshwater balanced saltwater Keeping water balance • • • A hypotonic solution has a concentration of solutes that is lower than inside the cell. A hypertonic solution has a concentration of solutes that is higher than inside the cell. An isotonic solution has a concentration of solutes that is equal to the concentration inside the cell. Solutions and osmosis Remember, water will diffuse from an area of high concentration to an area of low concentration. Hypotonic Hypertonic Less solute, more water The net movement is from the left side to the right side. More solute, less water Isotonic The net movement is now equal.
