cell membranes osmosis and diffusion functions of membranes 1.protect cell 2.maintain homeostasis 3....
TRANSCRIPT
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Cell MembranesOsmosis and Diffusion
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Functions of Membranes
1. Protect cell
2. Maintain homeostasis
3. Selectively permeable - allows some molecules in, others are kept out
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Homeostasis
•Balanced internal condition internal condition of cellsof cells
• Also calledAlso called equilibrium•Maintained by cell
membrane controlling what controlling what enters & leaves the cellenters & leaves the cell
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Polar heads are hydrophilichydrophilic “water loving”Nonpolar tails are hydrophobichydrophobic “water fearing”
Phospholipid Bilayer
Makes membrane “Selective” in what crosses
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Fluid Mosaic Model:“Proteins floating in a sea of lipids”
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Proteins Are Critical to Proteins Are Critical to Membrane FunctionMembrane Function
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Blood-Brain Barrier•Allows some substances into
the brain, but screens out toxins and bacteria
•Substances allowed to cross include: water, CO2, Glucose, O2, Amino
Acids, Alcohol, and antihistamines. HIV and bacterial meningitis can cross the barrier.
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Solutions
• Solutions are made of solute and a solvent
• Solvent – The liquid part. It does the dissolving.
• Solute – The thing being dissolved. Salt and sugar are solutes.
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Methods of Transport Across Membranes
1. Diffusion
2. Osmosis
3. Facilitated Diffusion
4. Active Transport
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Methods of Transport Across Membranes
1. Diffusion -passive transport - no energy used
2. Osmosis - Passive transport of water across membrane
3. Facilitated Diffusion – Needs a helper to get things across
4. Active Transport- requires energy to transport molecules against a concentration gradient – energy is in the form of ATP
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Diffusion• Movement of molecules from
an area of high concentration to an area of low concentration.
• Movement from one side of a membrane to another, without help.
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Diffusion
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Diffusion of Liquids
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Diffusion through a Diffusion through a MembraneMembrane
Cell membrane
Solute moves DOWN concentration gradient (HIGH to LOW)
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Facilitated DiffusionFacilitated Diffusion• Does NOT require energy
• Uses transport proteins to move things from high to low concentration
Examples: Examples: GlucoseGlucose or or amino acidsamino acids moving from moving from blood into a cell.blood into a cell.
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Facilitated Diffusion
Molecules will randomly move Molecules will randomly move through the through the porespores in in Channel Channel ProteinsProteins..
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Facilitated Diffusion
• This is a helper.
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Active TransportActive Transport
• Requires energy (ATP)
• Moves materials from LOW to HIGH concentration AGAINST the concentration gradient.
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Osmosis
• Diffusion of water across a membrane.
• Moves from HIGH water amount (low solute) to LOW water amount (high solute).
Diffusion across a membrane
Semipermeable
membrane
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You could think of it this way…
• In osmosis, water FOLLOWS salt!! This is sometimes an easier way to remember this concept.
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Salt
Where is the water moving?
• The water is moving out of the cell.
• Why?• Remember
wherever salt is water follows!
SALTSALT
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Light blue = SaltDark blue = water
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There is a lot of salt outside of the cell. What will happen?
Why?
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What will happen if there is a lot of salt inside of the cell?
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Red Onion Cells• Normal • In Salt Water
• What happened to the cytoplasm and cell membrane?
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Diffusion of H2O Across A Membrane
High H2O potential (amount) andLow solute concentration
Low H2O potential (amount) andHigh solute concentration
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Osmosis: Draw this
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Three Forms of Transport Across the MembraneThree Forms of Transport Across the Membrane
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Question• Why does eating
popcorn make you thirsty?
• Popcorn is very salty and may cause water to leave the cells of your mouth and through due to diffusion. This makes a person thirsty.
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When a sea urchin egg is removed from the ocean and placed in freshwater, the egg swells and bursts. Which of these
causes water to enter the egg?
A. Coagulation
B. Sodium Pump
C. Active Transport
D. Osmosis
D
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The picture shows a cell model and the solutions associated with it. In this
situation the cell model will —
A. Gain mass
B. Shrink
C. Increase in solute content
D. Start to vibrate
B
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Which of these best explains why a freshwater aquarium would be a
dangerous habitat for saltwater fish?
A The tissues of the saltwater fish would absorb too much acid.
B The cells of the saltwater fish would lose too much water.
C The organ systems of the saltwater fish would consume too much energy.
D The cells of the saltwater fish would gain too much water.
D
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On a hot summer day, a road-crew worker perspires and then feels thirsty as her
body temperature increases. This response is an example of –
A. Releasing enzymesB. Maintaining homeostasisC. Decreasing respirationD. Assimilating proteins
B
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Think/Pair/Share
• Work with a partner to create different situations that can be classified as diffusion.
• Do the same for osmosis.
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Another Video:http://www.youtube.com/watch?v=ML-SWe5bRaE
Active Transport Video: http://www.iteachbio.com/Life%20Science/LifeFunctionsandTheCell/ActiveTransport.mov
Diffusion Video: http://www.iteachbio.com/Life%20Science/LifeFunctionsandTheCell/Diffusion.mov