Cell Membranes Movement Across Them Regents Biology 2006
Cell Membranes & Movement Across Them Regents Biology 2006 -2007
Cell Membrane § Substances move in and out of the cell in § § order for the cell to function properly and maintain homeostasis. Homeostasis -- the ability of an organism to maintain a constant internal balance even when the conditions around it change. Regents Biology
Cell (plasma) membrane § Cells need an inside & an outside… u separate cell from its environment u cell membrane is the boundary IN food - sugars - proteins - fats salts O 2 H 2 O Regents Biology OUT waste - ammonia - salts - CO 2 - H 2 O products - proteins cell needs materials in & products or waste out
Semi-permeable membrane § Cell membrane controls what gets in or out § Need to allow some materials — but not all — to pass through the membrane u semi-permeable § only some material can get in or out So what needs to get across the membrane? sugar lipids Regents Biology aa O 2 H 2 O salt waste
Building a membrane § How do you build a barrier that keeps the watery contents of the cell separate from the watery environment? FATS LIPIDS Remember: oil & water don’t mix!! What substance do you know that doesn’t mix with water? Regents Biology
Lipids of cell membrane § Membrane is made of special kind of lipid u u phospholipids “split personality” “attracted to water” § Membrane is a double layer u phospholipid bilayer phosphate inside cell lipid outside cell Regents Biology “repelled by water”
Crossing the cell membrane § What molecules can get through the cell membrane directly? u fats and oils can pass directly through inside cell waste outside cell Regents Biology lipid salt sugar aa H 2 O but… what about other stuff?
Cell membrane channels § Need to make “doors” through membrane u protein channels allow substances in & out § specific channels allow specific material in & out § H 2 O channel, salt channel, sugar channel, etc. inside cell salt waste. Biology Regents H 2 O aa sugar outside cell
How do you build a semi-permeable cell membrane? § Channels are made of proteins u proteins both “like” water & “like” lipids bi-lipid membrane Regents Biology protein channels in bi-lipid membrane
Protein channels § Proteins act as doors in the membrane u channels to move specific molecules through cell membrane HIGH LOW Regents Biology
Movement through the channel § Why do molecules move through membrane if you give them a channel? HIGH ? LOW ? Regents Biology
Molecules move from high to low § Diffusion u move from HIGH to LOW concentration Regents Biology
Diffusion § Move from HIGH to LOW concentration passive transport u no energy needed u EXAMPLE diffusion of water diffusion osmosis u Regents Biology
Facilitated Diffusion § Move from HIGH to LOW through a channel sugar inside cell sugar LOW Which way will sugar move? HIGH outside cell sugar Regents Biologysugar sugar
Diffusion § Move from HIGH to LOW concentration u directly through membrane § simple diffusion § no energy needed u help through a protein channel § facilitated diffusion (with help) § no energy needed HIGH Regents Biology LOW
Osmosis Movement of Water Across Cell Membrane Regents Biology 2006 -2007
Osmosis § Water is very important, so we talk about § water separately Osmosis u diffusion of water from HIGH concentration of water to LOW concentration of water § across a semi-permeable membrane Regents Biology
Keeping water balance § Cell survival depends on balancing water uptake & water loss freshwater Regents Biology balanced saltwater
1 Keeping right amount of water in cell § Hypotonic KABOOM! freshwater high concentration of water around cell u cell gains water u u Cell swells u Example § a cell in fresh water Regents Biology No problem, here
2 Keeping right amount of water in cell § Hypertonic Solution I’m shrinking, I’m shrinking! low concentration of water around cell u cell loses water u Cell Shrinks u u Example § Cells in salt water Regents Biology I will survive! saltwater
3 Keeping right amount of water in cell § Isotonic Solutions That’s better! no difference in concentration of water between cell & environment u No change in the size of cell u u See these solutions in action Regents Biology I could be better… balanced
Simple vs. facilitated diffusion simple diffusion inside cell lipid facilitated diffusion inside cell H 2 O protein channel outside cell Regents Biology outside cell H 2 O
Active transport § Cells may need molecules to move against concentration “hill” u need to pump “uphill” § from LOW to HIGH using energy u requires energy (ATP) ATP Regents Biology
ANALOGY: ENERGY NEEDED: Active Transport NO ENERGY NEEDED: Diffusion Osmosis Facilitated Diffusion Regents Biology
• Endocytosis and Exocytosis is the mechanism by which very large molecules (such as food and wastes) get into and out of the cell Food is moved into the cell by Endocytosis Wastes are moved out of the cell by Exocytosis animation Regents Biology
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