AS LEVEL- Biology- Plasma membranes (3)
- Created by: Ammarah123
- Created on: 04-11-18 13:01
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- Plasma membranes (3)
- Facilitated Diffusion (Passive- No energy is required)
- Passive-Energy for movement comes from the natural/kinetic energy of molecules
- Facilitated diffusion- Particles move from a region of high to low concentration
- 1) Some large molecules eg. amino acids + polar molecules don't diffuse directly through the phospholipid bilayer of the cell membrane
- 2) Instead they diffuse through carrier or channel proteins in the cell membrane
- Carrier- Aqueous channel for ions + large polar molecules
- Channel- *A conformational change in the shape of the protein has to occur to allow the molecules/ ions to pass through *This protein generally transports
- Factors that
affect the rate
of diffusion
- Concentration gradient
- Thickness of membrane
- SA
- Temp
- Number of channel + carrier
- Active Transport (Active - Requires energy)
- Active- Requires metabolic energy in the form of ATP
- Active transport- Movement of particles from an area of low to high concentration using metabolic energy in the form of ATP
- Particles move against a concentration gradient
- 1) The molecule/ion to be transported binds tio receptors in the carrier protein
- 2) ATP binds to the protein on the other side of the membrane + is hydrolysed into ADP and inorganic phosphate
- 3) Binding of the phosphate molecule to the carrier protein causes a change in the structure of the protein meaning that the inside of the carrier protein opens
- 4) The molecule/ion is then released from the carrier protein
- 5) The phosphate molecule is released by the carrier protein + recombines with ADP to ATP
- 6) The carrier protein reverts back to its original shape
- Bulk Transport (Active - Requires energy)
- Active- Requires metabolic energy in the form of ATP
- ATP is needed as the vesicles + cell surface membrane need to fuse, vesicles are moving along the cytoskeleton + cell surface membrane changes the shape of the cell
- Endocytosis- (Enter = in)
- 1) Cell surface membrane invaginates when it comes into contact with the material
- 2) Membrane enfolds until the membrane fuses, forming a vesicle
- 3) Vesicle pinches off + movies into cytoplasm + is transferred to sites of further processing within the cell
- Exocytosis (Exit = out)
- Some substances produced by the cell eg. hormones need to be released from the cell
- 2) The vesicle + cell surface membrane fuses which leads to the contents releasing
- 1) Vesicles move to the cell surface membrane using the cytoskeleton
- Active- Requires metabolic energy in the form of ATP
- Osmosis (Passive- No energy is required)
- Passive-Energy for movement comes from the natural/kinetic energy of molecules
- Osmosis- Movement of water across a PPM from an area of high to low water potential
- 1) Water potential- pressure exerted by the water molecules as they collide with a membrane
- Units = Pascal (Pa) or Kilopascal (kPa)
- 2) Pure water has the highest water potential as it has a high concentration of water molecules and therefore a lower concentration of solute
- 3) *Very concentrated = low water potential (more negative) *Not very concentrated = high water potential (not so negative)
- How water potential affects animals cells
- Solution has the same water potential as the cell (Isotonic)
- *Water molecules pass into + out of the cell in equal amounts *The cell stays the same
- Solution has a higher water potential than the cell (Hypotonic)
- *Net movement of water molecules is into the cell *Cell bursts
- Solution has a lower water potential than the cell (Hypertonic)
- *Net movement of water molecules is out of the cell *Cell shrinks
- Solution has the same water potential as the cell (Isotonic)
- How water potential affects plant cells
- Solution has a higher water potential than the cell (Hypotonic)
- *Net movement of water molecules is into the cell *The vacoule swells *The vacuole + cytoplasm push against the cell wall *The cell becomes turgid (swollen)
- Solution has a lower water potential than the cell (Hypertonic)
- *Net movement of water molecules is out of the cell *The cell becomes flaccid (limp) *The cytoplasm + membrane pull away from the cell wall- plasmolysis
- Solution has a higher water potential than the cell (Hypotonic)
- Facilitated Diffusion (Passive- No energy is required)
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