Transcript Cell Membranes Osmosis and Diffusion

Cell Membranes
Osmosis and Diffusion
Functions of Membranes
1. Protect cell
2. Control incoming and outgoing substances
3. Maintain concentrations of various
substances
4. Selectively permeable - allows some
molecules in, others are kept out
Methods of Transport Across
Membranes
1) Two types of Passive Transport (uses no energy to move
substances)
• Diffusion – the moving of particles from areas of higher
concentration to those of a lower concentration (no
energy used; like going down a hill)
• Osmosis - diffusion of water across a membrane
2) Active Transport- requires energy to transport
molecules against a concentration
gradient (like up a hill)
Diffusion
Osmosis
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.
Plant and Animal Cells put into
various solutions
Questions:
1. Which picture represents the carrot in the plain
water? Why?
2. Which picture represents the carrot in the salt
water? Why?
3. How does the human body
maintain homeostasis using
diffusion? (Hint: think about
what happens when you eat a
whole bag of sunflower seeds?)
• http://www.youtube.com/watch?v=AYNwy
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