AS Biology F211 Membranes and Transport

Revision Cards of AS Biology F211 Membranes and Transport

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  • Created by: Pheebie
  • Created on: 17-09-11 09:58

Membrane Structure- Fluid Mosaic Model.


A membrane structure seperates a cell from its external environment.

It's on the out side of every cell.

It's made of a phospholipid bilayer, in which proteins are.

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Parts of a Cell Membrane

  • Phospholipids- Act as a barrier to most molecules.
  • Glycoproteins and Glycoproteins- Involved in cell recognition and cell attachments.
  • Integral Proteins- Transport molecules across the membrane or catalyse reactions.
  • Cholesterol- Helps control membrane fluidity.
  •                       (
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Functions of a Cell Membrane

  • Control what goes in and out of the cell.
  • Separate compartments with in the cell.
  • Important in cell signalling.
  • Allow electrical signal to pass through.
  • Provide attachments to enzymes and other molecules involved in metabolism.
  • Provides support for cells.
  • Allow recognition by other cells- Antigens.


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Cell Membranes use in Cell Signalling

  • Help cell to react to changes in the environment by picking up signals at the surface- they coordinate hormones and impulses.
  • Let ions through channels into and out of the cells.
  • The receptors in the cell react with G-proteins which activates an enzyme causing a reaction inside the cell.
  • The third is a receptor- enzyme which is made up of 2 parts. The reactor cell slots its self between them and it becomes an enzyme forcing a chemical reaction.


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Active Transport

  • Moves from a low to a high concentration.
  • Carried out by transporter proteins in the plasma membranes.
  • Active transport is used to change the shape of transporter proteins.
  • It's used where we need Potassium and need less Sodium but it's going against the concentration gradient to take it in and out of our cells.


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  • Particles move from a high to a low concentration.
  • Result of random movement.
  • Substance has free moving particles , there movement will be down the concentration gradient.
  • This is how particles move when they're being sprayed form an aerosol.
  • Facilitated diffusion uses carrier proteins.


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  • Only water can be moved by osmosis.
  • It must be across a partially permeable  membrane.
  • Moves from a High water potential to a Low water potential.
  • Water moves in and out of a plant cell to make them turgid and give them support.


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  • Process of moving a substance into a cell through the cell membrane.
  • Active process which requires energy.
  • Puts out fingers of cytoplasm around the substance, creating a ring (vesticle.) Enzymes are sent out from the vacuole to digest the vesticle and then the substance is absorbed into the cytoplasm.


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  • Substances produced with in the cell need to be released from cell.
  • Opposite to Endocytosis.
  • Vesticle surrounds what needs to be moved out cell. Once in the vesticle it moves up the microtubles.
  • It then fuses with the with the plasma membrane and empties out of the cell.


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Water Potential

  • Water diluted in a solution can move more easily than water in a concentrated solution.
  • Pure water has a water potential of 0kPa
  • Therefore water in a solution has a negative water potential because it moves more freely.
  • A dilute solution will be less negative (-100kPa) than a more concentrated solution (-300kPa)
  • Hypotonic:- A high water potential (less negative)
  • Isotonic:- Same water potential (0)
  • Hypertonic:- A low water potential (more negative)
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Hey, could you make notes on the whole bit abt Lungs surface area/vol ratio?



I agree with Lollypop...

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