Unit 3 Ch 7.2 Cell Membranes
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This document discusses cell membranes and movement across them. It explains that cell membranes are made of phospholipids arranged in a bilayer that acts as a semi-permeable barrier. Materials can cross the membrane through simple diffusion, facilitated diffusion using membrane channels, or active transport using protein pumps. Water specifically crosses by osmosis, moving from high to low concentration areas. Cells need to regulate water movement to avoid bursting in hypotonic solutions or shriveling in hypertonic solutions, maintaining an isotonic balance.
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Unit 3 Ch 7.2 Cell Membranes
- 1. Cell Membranes Regents Biology & Movement Across Them
- 2. Cell (plasma) membrane Cells need an inside & an outside… separate cell from its environment cell membrane is the boundary IN food - sugars - proteins - fats salts O2 H2O Regents Biology OUT waste - ammonia - salts - CO2 - H2O products - proteins cell needs materials in & products or waste out
- 3. Building a membrane How do you build a barrier that keeps the watery contents of the cell separate from the watery environment? What substance do you know that doesn’t mix with water? Regents Biology ® FATS ¬ ® LIPIDS ¬ Remember: oil & water don’t mix!!
- 4. Lipids of cell membrane Membrane is made of special kind of lipid phospholipids “split personality” Membrane is a double layer phospholipid bilayer Regents Biology inside cell outside cell phosphate lipid “attracted to water” “repelled by water”
- 5. Semi-permeable membrane Cell membrane controls what gets in or out Need to allow some materials — but not all — to pass through the membrane semi-permeable only some material can get in or out So what needs to get across the membrane? sugar lipids aa H2O salt waste Regents Biology O2
- 6. Crossing the cell membrane What molecules can get through the cell membrane directly? fats and oils can pass directly through inside cell outside cell Regents Biology lipid salt sugar aa H2O waste but… what about other stuff?
- 7. Cell membrane channels Need to make “doors” through membrane protein channels allow substances in & out specific channels allow specific material in & out H2O channel, salt channel, sugar channel, etc. inside cell Regents Biology H2O aa sugar outside cell waste salt
- 8. How do you build a semi-permeable cell membrane? Channels are made of proteins proteins both “like” water & “like” lipids bi-lipid membrane Regents Biology protein channels in bi-lipid membrane
- 9. Protein channels Proteins act as doors in the membrane channels to move specific molecules through cell membrane Regents Biology HIGH LOW
- 10. Movement through the channel Why do molecules move through membrane if you give them a channel? Regents Biology ? HIGH ? LOW
- 11. Molecules move from high to low Diffusion move from HIGH to LOW concentration Regents Biology
- 12. Diffusion Move from HIGH to LOW concentration passive transport no energy needed Regents Biology diffusion of water diffusion osmosis
- 13. Simple Diffusion Move from HIGH to LOW inside cell outside cell Regents Biology Which way will fat move? fat fat fat fat fat fat fat fat fat fat fat fat fat fat LOW HIGH
- 14. Facilitated Diffusion Move from HIGH to LOW through a channel inside cell outside cell Regents Biology sugar sugar sugar sugar sugar sugar sugar sugar sugar sugar sugar Which way will sugar move? sugar sugar LOW HIGH
- 15. Diffusion 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 Regents Biology LOW
- 16. Simple vs. facilitated diffusion simple diffusion facilitated diffusion inside cell outside cell Regents Biology lipid inside cell protein channel outside cell H2O H2O
- 17. Active transport Cells may need molecules to move against concentration “hill” need to pump “uphill” from LOW to HIGH using energy protein pump requires energy ATP Regents Biology ATP
- 18. Transport summary Regents Biology simple diffusion facilitated diffusion active transport ATP
- 19. Osmosis Movement of Water Across Cell Membrane Regents Biology
- 20. 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 Regents Biology
- 21. Keeping water balance Cell survival depends on balancing water uptake & water loss freshwater balanced saltwater Regents Biology
- 22. Keeping right amount of water in cell Freshwater KABOOM! a cell in fresh water high concentration of water around cell cell gains water example: Paramecium problem: cells gain water, swell & can burst Regents Biology water continually enters Paramecium cell solution: contractile vacuole pumps water out of cell freshwater No problem, here 1
- 23. Cell in a hypotonic solution HYPOTONIC SOLUTION A solution having a lower concentration of solute More water outside the cell than inside the cell Regents Biology
- 24. Controlling water Contractile vacuole in Paramecium Regents Biology
- 25. Keeping right amount of water in cell Saltwater I’m shrinking, I’m shrinking! a cell in salt water low concentration of water around cell cell loses water example: shellfish problem: cell loses water in plants: plasmolysis in animals: shrinking cell solution: take up water Regents Biology saltwater I will survive! 2
- 26. Cell in a hypertonic solution HYPERTONIC SOLUTION A solution having a higher concentration of solute than the cell, which causes the cell to shrink or shrivel because water leaves the cell by osmosis Regents Biology
- 27. Keeping right amount of water in cell Balanced conditions That’s better! no difference in concentration of water between cell & environment cell in equilibrium example: blood problem: none Regents Biology water flows across membrane equally, in both directions volume of cell doesn’t change balanced I could be better… 3
- 28. Cell in isotonic solution ISOTONIC SOLUTION Solution with the same concentration of water and solutes as inside the cell, resulting in the cell retaining its normal shape because there is no movement of water. Regents Biology
- 29. In summary Regents Biology
Editor's Notes
- Donuts! Each transport protein is specific as to the substances that it will translocate (move). For example, the glucose transport protein in the liver will carry glucose from the blood to the cytoplasm, but not fructose, its structural isomer. Some transport proteins have a hydrophilic channel that certain molecules or ions can use as a tunnel through the membrane -- simply provide corridors allowing a specific molecule or ion to cross the membrane. These channel proteins allow fast transport. For example, water channel proteins, aquaprorins, facilitate massive amounts of diffusion.
- Movement from high concentration of that substance to low concentration of that substance.
- Plants have nitrate & phosphate pumps in their roots. Why? Nitrate for amino acids Phosphate for DNA & membranes Not coincidentally these are the main constituents of fertilizer.