Transport through the Cell Membrane

Passive Transport Movement across a cell membrane that does not require energy 2 examples: Diffusion Osmosis

Diffusion Movement of a substance from areas of higher concentrations to areas of lower concentrations Ex. Food coloring in water

Concentration Gradient Difference in the concentration of a substance

Equilibrium Concentration of a substance is equal throughout an area

Facilitated Diffusion Type of passive transport that uses proteins to move substances down their concentration gradient. Ex: There are specific proteins that help move sugars into the cell

Ion Channels

Osmosis Diffusion of water http://www.watchknow.org/Video.aspx?VideoID=5165 - Osmosis in lettuce Why should you gargle with salt water when you have a sore throat?

Answer Pain caused by swelling of throat tissues (these contain water) Salt water has a lower concentration of water than the throat tissues. When a person gargles with salt water, the water from the throat tissues moves to the salt water. Loss of water from throat tissue results in less swelling and pain.

Question Why do plants along side of the road die after a winter where roads were heavily salted? Explain in terms of osmosis.

Answer The higher than normal amount of salt in the plants’ environment causes their cells to lose water through osmosis. Their leaves begin to look they have been through a very hot, dry summer. Eventually the plants die because they do not have enough water to live.

Question Why do wooden drawers of a dresser become sticky after a rain storm or a high humidity day? Explain in terms of osmosis.

Answer On very wet days, wooden drawers in dressers absorb water from the air because of osmosis. This absorption warps the wood, making the opening and closing of drawers difficult. In drier weather water is lost from the wood, and the drawers return to their normal size.

Movement of Water Solute: the substance that is dissolved in a solution, the smaller amount. Solvent: dissolves the solute in a solution, the larger amount Ex: Make a solution of saltwater. Solute: Salt Solvent: Water Water is the universal solvent.

Hypertonic solution: solution is more concentrated (more solute), water moves out of the cell

Hypotonic solution: solution has a lower concentration (less solute) water moves into the cell

Isotonic: concentration is equal (equal amts of solute), no water movement

Hypertonic, Hypotonic and Isotonic Solutions If the fluid outside the cell has…… Then Outside Fluid is…… Water diffuses…… Effect on Cell Higher solute concentration than the inside Hypertonic Out of cell Cell Shrinks Lower concentration than the inside Hypotonic Into cell Cell swells Equal concentration to the inside Isotonic Equally Cell stays the same size

Questions Why are green leafy vegetables sprinkled with water at the supermarket? Why is salt sometimes used to preserve food? Why should you not drink sea water?

Answers This prevents them from wilting due to water loss Because a salt solution is hypertonic , the microorganisms present on the foods shrink and die. Sea water contains high concentrations of solutes. Cells in the body lose water because of osmosis, possibly causing death.

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Active Transport Chapter 4.2

Active Transport Transport of substances against their concentration gradient, uses energy Energy is in the form of ATP Adenosine Triphosphate Carrier proteins help move substances

Sodium-Potassium Pump Transports sodium and potassium Ions against their concentration gradient

Sodium-potassium pump Chapter 4 Cells and Their Environment Sodium-potassium pump pumps three pumps two sodium ions potassium ions out of the cell into the cell

Sodium Potassium Pump http://highered.mcgraw- hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/s ites/dl/free/0072437316/120068/bio03.swf::Sodium- Potassium%20Exchange%20Pump

Movement in Vesicles Many substances, such as proteins and polysaccharides, are too large to be transported by carrier proteins. These substances are moved across the cell membrane by vesicles.

Movement in Vesicles Endocytosis: movement of a substance into the cell. Cell membrane forms a pouch and pinches off Exocytosis: movement of a substance out of the cell Vesicles fuse with the cell membrane and empty their contents outside the cell.

Endocytosis

Exocytosis

Review of Cell Processes http://highered.mcgraw- hill.com/olc/dl/120068/bio02.swf Exo and Endo animation http://www.classzone.com/cz/books/bio_07/get_chap ter_group.htm?cin=2&rg=animated_biology&at=anim ated_biology&var=animated_biology http://www.northland.cc.mn.us/biology/Biology1111/ animations/transport1.html