Transport methods

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  • Created by: chxrwest
  • Created on: 14-01-16 08:43

Diffusion

Net or overall movement of particles form a region of higher concentration to a region of lower concentration.

Due to particles having  kinetic energy and is random and an unequal distribution will occur until an equlibrium is met.

Short diffusion distance is faster because there is less chance of collisions of particles.

The higher the temperature the higher the rate of difffusion - due to an increase in kinetic energy.

The greater the concentrration gradient the faster the rate of diffusion.

The larger the area of an exchange surface, the higher the rate of diffusion.

THe thinner the exhange surface, the higher the rate of diffusion.

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Facilitated Diffusion

Diffusion across a membrane through protein channels.

Passive process, down a concentration gradient.

The more protein channels the higher the rate of overall diffusion.

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Active Transport

The movement of molecules or ions into or out of a cell from a region of lower to higher concentration.

Requires energy and carrier proteins.

Carrier Proteins:

  • Molecule or ion being transported binfs ro receptors in the carrier protein on the outside of the cell.
  • On the inside ATP binds to the protein and is hydrolised to form ADP and phosphate.
  • The binding of the phoosphate to the protein causes it to change shape so the molecule can then travel through.
  • The phosphate is released, the carrier protein returns to its original chape, and combines back with ADP to form ATP.
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Bulk Transport

Endocytosis: movement of materials into cells.

  • phagocytosis - solds pinocytosis - liquid
  • The cell surface membrane invaginates when it comes into contact with the material.
  • The membrane enfolds the material until eventually the membrane fuses, forming a vesicle.
  • The vesicle pinches off and moves into the cytoplasm.

Exocytosis: movement of materials out of cells.

  • Vesicles, usually formed by the golgi apparatus, move towards and fuse with the cell surface membrane.
  • The contents are then released.

Energy in the form of ATP is needed for movement of vesicles along the cytoskeleton, changing the shape of cells and the fusion of cell membranes.

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Osmosis

The net movement of water from a higher water potential to more negative water potential.

Passive process

The movement of water into a soloution will increase the volume of the soloution and if it's in a closed system will increase the hydrostatic pressure.

Plant cells have strong cell walls so an increase in hydrostatic pressure will make the cell more turgid. If the cell looses water it will become flaccid or in extrem plasmolised as it starts to shrink so much it pulls away from the cell wall.

Animal cells however can easily burst, cytolysis/haemolysed, before this the cell will swell in a hypotonic soloution. The opposite is the cell shrinking in hypertonic soloution resulting in crenation.

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