1.4 Membrane transport. A membrane is a barrier. Almost all membranes are semi-permeable. Why?
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Transcript of 1.4 Membrane transport. A membrane is a barrier. Almost all membranes are semi-permeable. Why?
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1.4 Membrane transport
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A membrane is a barrier.
Almost all membranes are semi-permeable.
Why?
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Particles are moved across a membrane in four ways:
1.Simple diffusion2.Facilitated diffusion3.Osmosis4.Active transport
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1. Simple diffusion
Particles moving from high to low concentrations, particles moving down a concentration gradient.
Passive process. Particles move between phospholipids
Oxygen can move easily (non-polar molecule).
Small polar molecules can pass relatively easily (at a low rate) but larger polar molecules e.g. urea, pass much more slowly.
See fig. 6. pg. 36
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2. Facilitated diffusion
Particles moving through specific channels in the membrane.
These channels are typically very narrow, the diameter of the protein channel determines what type of molecule is able to pass through.
Passive process.
High to low concentration, movement down a concentration gradient.
Cells are able to control which types of channels are synthesised, which in turn controls diffusion in/out of the cell.
http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html
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3. Osmosis
Movement of water, water moves freely. The net movement of water is known as osmosis.
Intermolecular forces (e.g. hydrogen bonds) between substances dissolved in water can restrict its movement.
If something has a high concentration of solutes, it will have a low concentration of water.
Passive process. High to low centration, down the concentration gradient.
http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html
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4. Active transport
Substances absorbed against the concentration gradient.
Low to high concentration.
Active process – REQUIRES energy (uses ATP).
Globular proteins inside the membrane (pump proteins)
Fig. 10, pg. 38
http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html
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Read text book pages, find examples of passive/active transport
McGraw hill animation, endo/exocytosis? Passive/active transport
Design lab???
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PASSIVE TRANSPORT
What does passive transport mean?
Examples?
Task
How would you design an experiment to test osmosis?
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Facilitated diffusionCarrier proteins inside the membrane , carrier proteins combine with a substance/molecule and transport it across the membrane.
Does not require energy
Very specific
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Write a short paragraph to explain the difference
between Diffusion (simple), Facilitated diffusion &
Osmosis
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Active transportRequires energy
Moves molecules against the concentration gradient
Uses pumps
Read pg. 35/36. Summarise the process into a short paragraph
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EndocytosisPart of the membrane
‘pinches’ off forming a vesicle to transport incoming
molecules within the cell.
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EXOCYTOSISVesicle joining the membrane,
releasing contents into extracellular region