Biological membranes

• What is diffusion?


  Net movement of particles from an area of higher concentration to an area of lower concentration.

  Passive
• what 4 factors does rate of diffusion depend on?


  Temperature

  Thickness of the exchange surface

  Surface area

  Concentration gradient
• what is facilitated diffusion?


  passive process where particles move down the conc gradient with the help of carrier and channel proteins in cell membrane.
• Role of a carrier protein?


  moves larger molecules in and out of cell, down conc gradient.

  larger molecule binds to carrier protein, the protein changes shape and releases it onto the other side.
• Role of channel proteins?


  Forms pores in the membrane for ions to diffuse through.
• describe endocytosis


  for too large molecules.

  the cell surrounds the molecule with its plasma membrane.

  it pinches off to form a vesicle.

  Active process and uses ATP
• describe exocytosis


  a way of releasing substances produced by the cell.

  from the Golgi body the substances pinch off into vesicles.

  fuses with the plasma membrane and release the contents out.

  uses ATP
• what is osmosis?


  The movement of water molecules from an area of high water potential to an area of low potential across a semi-permeable membrane.
• define hypotonic


  Higher water potential out than in the cell.

  Water moves into cell via osmosis.

  Causes the cell to burst
• define isotonic


  equal water potential in and out.

  no change to cell
• define hypertonic


  lower water potential in than out of cell.

  water moves out via osmosis

  causes cell to shrink.
• how is the structure of a plasma membrane described as


  Fluid mosaic
• name the components of the membrane

  phospholipid bilayer

  cholesterol

  glycolipid

  glycoprotein

  transport proteins - carrier and channel
• describe the structure of phospholipids


  bilayer

  hydrophobic tails

  hydrophilic head
• describe the role of cholesterol


  type of lipid

  slot between the phospholipids

  bind to the tails to bring them closer together - increases rigidity.
• role of glycoproteins and glycolipids?

  stabilise the membrane by forming hydrogen bonds with the surrounding water molecules.

  binding site for larger molecules

  acts as receptors for cell signalling

  antigens
• Using beetroot describe how temperature, solvent type and solvent concentration effect the permeability of the cell membrane.


  affect of temperature:

  Cut 5 equal sized pieces and rinse

  Put in 5 different test tubes each with 5cm3 of water

  Place each in different water bath at different temp for same time

  Remove the piexes

  Use colorimeter to see how much light is absorbed
• Investigate water potential using potato cylinders


  Sucrose solutions

  Cork borer to cut equal pieces of potato

  Divide into groups of 3 and measure mass

  Place one group in each solution

  Leave for same length of time

  Remove chip and dry

  Weigh them

  Calculate % change in mass