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Fluid Mosaic Model
• http://www.susanahalpine.com/anim/Life/memb.htm
• http://www.youtube.com/watch?v=ULR79TiUj80
Roles of the membrane proteins
• Move stuff across the membrane that can’t get across on its own
• Recognition – like nametags
• Receptors – trigger cellular responses
• Enzymes
Back to your homework…
• What kinds of molecules can cross the cell membrane, according to the diagram?
Make some predictions about your lab…
• What do you think will happen to the mass of your cell? Why?
• Which way do you think substances will move? Why?
Cell Membrane
• Cell Membrane Animation • Made of phospholipids and proteins• Molecules move into and out of a cell through the
cell membrane• The cell membrane is selectively permeable• How certain molecules move through the cell is
called cell transport– Passive Transport– Active Transport
Questions
• What happens when you spray air freshener or perfume?
• What happens when you put food coloring in water?
• THIS IS DIFFUSION!!!! Diffusion is also one way things are transported across the cell membrane
What is concentration?
• Amount of solute in a certain amount of solvent…think about kool-aid…– Solvent – what does the dissolving (liquid)– Solute – what is dissolved in the solvent– Which is more concentrated?
Make a hypothesis….
• Will the glucose move? Which way? Why or why not?
• Will the iodine move? Which way? Why or why not?
• Will the starch move? Which way? Why or why not?
Selectively permeable
Selectively permeable
Definition Illustrate
Explain your illustration
What qualities might affect how easily a molecule can move through a membrane?
Sizes of Molecules…
• Water (H2O)
• Iodine (I2K)
• Glucose (C6H12O6)
• Food Coloring (~450 atoms)
• Starch (~1000 atoms)
So…how big are the pores of the membrane? Make an estimate
• Lipid bi-layer
• Fluid mosaic model– http://www.youtube.com/watch?
v=Rl5EmUQdkuI
– http://www.youtube.com/watch?v=GW0lqf4Fqpg
Passive Transport
• Particles move from high concentration to low concentration
• Does NOT require extra cell energy• Includes simple diffusion, osmosis,
facilitated diffusion
SIMPLE DIFFUSION
• Movement of molecules from areas of high concentration to areas of low concentration
• Does not require energy (PASSIVE)– Because molecules are in constant, random,
motion!
• Will diffuse until reaches equilibrium (equal concentrations)
• Dynamic equilibrium (still moving!)
Simple Diffusion in Cells
Diffusion Animation
Diffusion Across a Membrane
http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter38/diffusion_through_cell_membranes.html
What kinds of things diffuse through the membrane?
• SMALL AND UNCHARGED– Like carbon dioxide and oxygen.
OSMOSIS
• The diffusion of water across a membrane from an area of high concentration to low concentration
• No energy required (PASSIVE TRANSPORT)
• Occurs until reaches DYNAMIC EQUILIBRIUM– Equal concentrations on both sides of
the membrane
Tonicity of solutions
• Used to compare the relative concentrations• Hypertonic
– solution with a higher concentration of solute – So lower water concentration
• Hypotonic – solution with a lower concentration of solute– So higher water concentration
• Isotonic – solutions with equal concentrations of solute
• Water diffuses from hypotonic solutions to hypertonic solutions!
Hypotonic Solution
• Water moves into the cell
• Cell swells– Animal cell – can burst
– Plant cell – builds up pressure on cell wall, but rigid cell wall keeps it from bursting
HYPOTONIC
Hi
Lo
Isotonic Solution
• Water moves in and out of the cell
• Cell stays the same size
• Dynamic Equilibrium
ISOTONIC
Pumping Water
• Some organisms have vacuoles that pump out excess water that enters the cell
• Too much water in the cell = vacuole works hard pumping out water!
• http://www.linkpublishing.com/video-transport.htm#Brownian_Movement
FACILITATED DIFFUSION
• Particles move from high concentration to low concentration
• No energy needed (PASSIVE)• Cells use proteins to “help”
– Transport Proteins– Channel proteins
http://www.stolaf.edu/people/giannini/biological%20anamations.html
FRAYER MODEL BREAK!
Passive Transport
defineDraw example
Explain your example
Name two examples of
things that can cross the
membrane passively
Active Transport
• Particles move from low concentration to high concentration (against the concentration gradient)
• DOES REQUIRE ENERGY!!• Requires transport proteins• Includes pumps, endocytosis,
exocytosis, etc.
The sodium-potassium pump
• Active Transport = requires energy!
• Sodium is pumped out
• Potassium is pumped in
• Animation
Active transportActive transport
Examples: Pumping Na+ (sodium ions) out and K+ (potassium ions) in against strong concentration gradients.
Called Na+-K+ Pump
Sodium-Potassium Sodium-Potassium PumpPump
3 Na+ pumped in for every 2 K+ pumped out; creates a membrane
potential
Pumps
• Some animals use salt pumps to maintain a constant concentration of salt in their bodies
• This requires energy! ACTIVE TRANSPORT!
•Large substances enter the cell
•Cell membrane forms a “pit” and wraps around substance
•Cell membrane pinches off – forms a vesicle
ExocytosisExocytosis The opposite of endocytosis is exocytosis. The opposite of endocytosis is exocytosis. Large moleculesLarge molecules that are manufactured in that are manufactured in
the cell are the cell are releasedreleased through the cell through the cell membranemembrane..
Inside Cell Cell environment
FRAYER MODEL BREAK!
Active transport
defineDraw example
Explain your example
Does it require energy?
Examples
Pom-Pom Potential
• Modeling passive and active transport along a cell membrane in a NERVE CELL
• What do nerves do?
• How do they do it?
Questions
• How did this activity model passive transport?
• How did this activity model active transport?
• Why do the membranes “work” to keep the charges on either side of the membrane “balanced”?
Moving the “Big Stuff”Moving the “Big Stuff”
Molecules are Molecules are moved outmoved out of the cell by of the cell by vesiclesvesicles that that fusefuse with the plasma membrane. with the plasma membrane.
ExocytosExocytosisis-
moving things out.
This is how many This is how many hormoneshormones are secreted and how are secreted and how nerve cellsnerve cells communicate with one another communicate with one another.
ExocytosisExocytosisExocytic Exocytic vesicle vesicle immediately immediately after fusion after fusion with plasma with plasma membrane.membrane.