Crossing Membranes
- Created by: Eleanor Izzard
- Created on: 10-12-12 20:14
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- Crossing Membranes
- Diffusion
- the net movement of molecules from a region of high concentration to a region of low concentration
- molecules possess kinetic energy so no enery is required from the cell
- DOWN a concentration gradient
- EQUILIBRIUM - when molecules are distrubuted evenly, they still move but there is no overall movement
- Rate of Diffusion
- Conc. Gradient - greater = increased rate
- Temperature - increase= more kinetic energy to molecules = increased rate
- Stirring - increases the movement of molecules and rate of diffusion
- Surface Area - greater = increased rate
- Distance/Thickness - thick membranes - greater distance for molecules to travel - decreased rate
- Size of molecule - smaller = quicker rate
- In Membranes
- lipid molecules can pass through the phospholipid bilayer by diffusing down the conc. gradient
- CO2 and O2 are small enough to pass through the bilayer between phospholipid molecules
- Facilitated Diffusion
- Channel Proteins - form pores in the membrane, often complementry shaped/gated - can be opened-closed
- Ions .E.G. Na/Ca
- Carrier Proteins - complementry shape- proteins changes shape when the specific molecule fits to allow molecule through
- Large Molecules .E.G. glucose
- Different Membranes can have different carrier/channel proteins so that they can have some control over what can get in/out
- Channel Proteins - form pores in the membrane, often complementry shaped/gated - can be opened-closed
- Active Transport
- the net movement of a molecule from a low concentration to a high concentration using ATP
- Some Carrier Proteins act as pumps. They have complmentry shapes and carry larger molecules or ions
- they carry molecules ONE way across the membrane, using ATP tomove them against the conc. graidient
- the changing shape ensures a one way flow - the molecule cannot re-enter the protein as it is a different shape
- quicker than diffusion
- .E.G. Ca Ions in muscles
- they carry molecules ONE way across the membrane, using ATP tomove them against the conc. graidient
- Endo/Exocytosis - the bulk transport of materials into/out of a cell
- Bulk Transport is possible because membranes are able to easily fuse, separate and pinch off
- Requires enery - ATP, used to move the membranes / vesicles around
- Endo -inwards Exo -outwards Phago -solids Pino -liquids
- Diffusion
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