Cell Membranes Osmosis and Diffusion. Functions of Membranes. Protect cell Maintain homeostasis 3. Selectively permeable - allows some molecules in, others are kept out. Homeostasis. Balanced internal condition of cells Also called equilibrium
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3. Selectively permeable - allows some molecules in, others are kept out
Polar heads arehydrophilic“water loving”
Nonpolar tails arehydrophobic“water fearing”
Makes membrane“Selective”in what crosses
“Proteins floating in a sea of lipids”
water, CO2, Glucose, O2, Amino Acids, Alcohol, and antihistamines. HIV and bacterial meningitis can cross the barrier.
3. Facilitated Diffusion
4. Active Transport
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
Solute moves DOWNconcentration gradient (HIGH to LOW)
Molecules will randomly move through the pores in Channel Proteins.
Diffusion across a membrane
High H2O potential (amount) andLow solute concentration
Low H2O potential (amount) andHigh solute concentration
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 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.
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 –
Active Transport Video: http://www.iteachbio.com/Life%20Science/LifeFunctionsandTheCell/ActiveTransport.mov
Diffusion Video: http://www.iteachbio.com/Life%20Science/LifeFunctionsandTheCell/Diffusion.mov