cell membrane

• describe the structure of a phospholipid

  one glycerol molecule, two fatty acids and one phosphate head group
• is the head of a phospholipid hydrophilic or hydrophobic?

  hydrophilic
• is the tail of a phospholipid hydrophilic or hydrophobic?

  hydrophobic
• state three factors that can affect the permeability of the cell membrane

  • solvent concentration
  • temperature
  • pH
• define diffusion

  the net movement of particles from an area of high concentration to an area of low concentration
• define facilitated diffusion

  the movement of molecules through a channel/carrier protein from an area of high concentration to an area of low concentration
• what kind of process if facilitated diffusion?

  passive
• what kinds of molecules do channel proteins allow through the membrane?

  polar molecules

  e.g. water
• what kinds of molecules do carrier proteins allow through the membrane?

  large molecules
• how do carrier proteins facilitate diffusion?

  they change shape
• state five factors that affect the rate of diffusion

  • concentration gradient
  • temperature
  • membrane surface area
  • thickness of diffusion membrane
  • the number of channel/carrier proteins
• define osmosis

  the diffusion of water through a partially permeable membrane from a high concentration of water (high WP) to a low concentration of water (low WP)
• define active transport

  the movement of particles from an area of low concentration to an area of high concentration, against the concentration gradient
• what kind of process is active transport?

  active (requires energy)
• describe the sodium-potassium co-transport mechanism

  1. sodium ions are transported into the blood by sodium-potassium ATPase, from the epithelium cells in the ileum
  2. this makes the concentration of Na+ lower inside the cell than outside
  3. two Na+ ions from the ileum bind to the sodium-glucose cotransporter protein, a molecule of glucose also binds at they move into the cell