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Cell Membrane Permeability: Understanding Transport Across Cells

This chapter explains how substances can pass in and out of cells through the selectively permeable cell membrane. It covers various forms of transport, including passive and active transport, and introduces concepts like diffusion, osmosis, and endocytosis.

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Cell Membrane Permeability: Understanding Transport Across Cells

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  1. Chapter 3.2 Keep out, you big, dumb, molecule! How do things get into and out of your cells?...

  2. Both a screen and a teabag are selectively permeable. This means some things can pass, and some things cannot. Fill in the blank: The screen is permeable to _________. The teabag is permeable to _________. (What CAN pass through a screen or teabag?) Now fill in this blank: The screen is impermeable to _________. The teabag is impermeable to _________. (What CANNOT pass through a screen or teabag?)

  3. How does this relate to science class?... Because the cell membrane is selectively permeable. Name one thing it can be permeable to. Name one thing to which it may be impermeable.

  4. Remember, that last slide, and this one, are not showing the real colors of a cell! But, if you magnified it, everything else about this picture is “real”…. outside of cell inside of cell

  5. Transport Across the Membrane Passive transport means that something is going from where there’s already a lot of it to where there’s not so much of it. Because of this, no energy is required to move the material. It’s kind of like when the boys all spray Axe in the locker room and there’s a cloud of it floating around. Then, little by little, it diffuses under the door to the hallway (because there WASN’T any Axe there, so that’s where it’s naturally going to go to….)

  6. Passive Transport Across the Membrane When oxygen, water, or other similar substances move across the cell membrane, no energy is required. (The diffusion of water is specifically called osmosis.)

  7. Transport Across the Membrane If something slightly bigger needs to get across the membrane, it can still do so without using energy. It just has to use a carrier protein instead of sliding through the cracks. This is called facilitated diffusion. It’s kind of like the drive-through window at McDonald’s.

  8. Another view…

  9. Transport Across the Membrane Active transport means something is going from where there is some of it present to somewhere where there’s already a lot of it. It’s just like trying to shove that last piece of clothing into your drawer – it’s so crowded already, it takes energy to get it in there.

  10. In active transport, a carrier protein is still used, but now it has to do some work. See, now more of them are “smushing in”…. That takes energy, so it’s “active”.

  11. Finally, if something is just too big to get into the cell, a process called endocytosis is used. (Look at page 80 in your textbook for a “real” picture of endocytosis in action – that one cell is trying to take in the other one.)

  12. To get back out of the cell, exocytosis is used. It’s like how you keep all your little trash in a bigger trash bag, and eventually you take that big trash bag out to the curb.

  13. Look at pg 81 in your textbook for a better view of this picture. All of these things are happening IN YOUR BODY, IN EVERY ONE OF YOUR CELLS, RIGHT NOW (AND ALWAYS, UNTIL YOU DIE).

  14. Page 81 In ActionPick one… or watch all of them….(You’ll need sound.) http://www.youtube.com/watch?v=Pfu1DE9PK2w “rapping” http://www.youtube.com/watch?v=kfy92hdaAH0 http://www.youtube.com/watch?v=svAAiKsJa-Y Traditional Instruction http://www.youtube.com/watch?v=ovHYKlHYpyA with classical music 

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