B3.1 Movement of molecules in and out of cells

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Diffusion & Active Transport

  • The process by which particles of a substance spread out from one another- Moving from a place where they are in high concentration to a place where they are low concentration.
  • Allows substances to pass in or out of cells through the cell membrane.
  • But they must be dissolved and there must be a different conecentration gradient on either side of the cell membrane 

Active Transport:

  • Sometimmes substances need to be moved against their concentration graident and this requires energy( from respiration) - Active Transport
  • There are special protiens in the cell membrance that help the substances move up the concentration gradient (which is the opposite to usual direction of diffusion)
  • The energy changes the shape of the protien which allows the protien to release the substance onto the opposide size of the cell membrane

Diffusion - Transports substances from low concentration to high concentration, Requires no additional energy output, Does not require protien carriers in cell membrane

Active Transport- Transports dissolved substances from high concentration to low concentration, Requires energy from respiration, Requires protien carriers in cell membrane.

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The movement of water molecules across a partially perimable membrane (e.g. cell membrane) to a more concentrated solution. 

A partially permiable membrane allows small, soluable solutions e.g water to pass through it freely and prevents larger molecules doing so.

If a cell is in contact with more dilute solution that water the molecules will move into the cell:

  • In a plant cell the water enters until the cell contents are pressed against the strong cell wall. (it is turgid) 
  • In an animal cell, the cell swells up until it bursts (because there is no cell wall)

If a cell is in contact with a more concentrated solution then water molecules with move out of the cell:

  • In a plant cell the loses water and the contents of the cell no longer press against the cell wall,, (it goes limp)
  • In an animal cell the cell contents shrink and it looses its normal shape.
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Organ Systems

All living organisms rely on exchanges with the environment to survive. 

Diffusion only works is the distance in which it has to diffuse is small and it has a large surface area in comparision to its volume. (This is the case for small organisms) 

For larger, more complex organisms diffusion is a lot more difficult. The larger organisms had to evolve so that substances could be exchanged more efficently - they made speicalised organ systems. 

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Sports Drinks

Athletes... Use up most of their glucose during respiration, Generates heat as they respire more, and sweat to cool themselves down (this sweatin results in loss of water and mineral ions)

If the body doesnt maintain the correct amount of mineral ions or the water and ion content of the body gets too low it can cause to much water to move in and out of the cells therefore damaging them.

During prolonged exercise water and ions are lost and it happens at a faster rate which can cause dehydration.

Water can rehydrate the body but cant replace the ions and glucose which were lost 

Sports drinks contain water, sugar and mineral ions at levels which are most effective at maintaining performance 

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