transport across membranes

• what do cell membranes consist of

  phospholipid bilayer

  proteins
• what type of molecules can pass through the membrane

  • non polar
  • hydrophobic
  • uncharged
• role of phospholipids 


  control movement of substances across cell membrane
• role of cholesterol

  • binds to fatty acid tails
  • regulates fluidity of membrane
  • more cholesterol = less fluid
  • prevents water and ions leaking out of cell
• role of glycolipids

  • phospholipid that is attached to a carbohydrate
  • act as a recognition cell
• fluid mosaic model

  • fluid= phospholipids and proteins can move in their layer
  • mosaic = scattering of proteins
• osmosis 


  the net movement of water molecules from an area of high water potential to an area of low water potential through a partially permeable membrane
• water potential 


  pressure created by water molecules

  measure in kPa
• what is the water potential of pure water

  0kPa
• how does increasing the solute in water affect the water potential

  lower water potential (negative number)
• what type of transport is osmosis

  passive
• what occurs when a cell has a water potential lower than the surrounding fluid

  • animals - swelling leads to lysis
  • plants - becomes turgid
• what occurs when a cell has a higher water potential than surrounding fluid

  • animal - shrivels
  • plant - plasmolysed
• diffusion 


  spreading out of particles (solution or gas) resulting in a net movement of particles from an area of high concentration to an area of low concentration
• when does diffusion stop

  when the particles are spread evenly inside and outside the cell
• what is facilitated diffusion 


  diffusion with the help of a transporter protein. allows the movement of polar, hydrophilic, large, and charged molecules
• what does passive transport rely on 


  random movement of particles and diffusion
• what particles can pass by simple diffusion 


  a particle that is hydrophobic and non-polar and uncharged
• effect of unsaturated fatty acids

  • bent chains
  • cannot be packed tightly together
  • form gaps in membrane
  • small molecules move through these gaps
• examples of molecules that can pass through using faciliated diffusion

  • chloride ion
  • water molecule
  • glucose molecule
• factors that affect rate of diffusion

  • concentration gradient (can be in terms of water potential
  • short diffusion pathway
  • surface area : volume
  • more transport proteins in a given area (facilitated diffusion only)
• active transport 


  transport of particles against a concentration gradient from an area of low concentration to an area of high concentration
• what does active transport require

  transport proteins