Chapter 4 -

• osmosis

  movement of water across a partially permeable membrane from a high to low water potential.
• which transports use membrane proteins

  active transport - carrier

  facilitated diffusion - channel
• simple diffusion and osmosis go through

  a phospholipid bilayer
• phospholipid bilayer

  phosopholipid - hydrophilic head and a hydrophobic tail

  channel proteins - tubes that go through the bilayer

  carrier proteins - bind to molecules and change shape

  cholesterol - prevents loss of water, reduces movement of other molecules

  glycolipid - maintains stability, act as recognition sites

  glycoprotein - allows cells to recognise each other, helps cells attach
• simple diffusion

  net movement of particles from a high to low concentration

  all particles are constantly in motion due to their kinetic energy

  have random motion

  distribute themselves evenly in space
• facilitated diffusion

  charged ions and polar molecules do not diffuse easily because of the hydrophobic nature of the phospholipids

  movement is made easier by channel proteins

  occurs from high to low concentration gradient

  relies on natural kinetic energy
• co-transporters

  a type of carrier protein that can transport 2 things at once
• how active transport works

  1. molecules bind to a carrier protein
  2. the P in ATP binds to the carrier protein causing it to change shape
  3. molecules travel through the newly opened channel
  4. a P molecule is released and it bind to ADP to reform ATP
  5. carrier protein returns to its original shape
• osmosis practical method

  1. make a series of dilutions of 1M sucrose solution and distilled water
  2. measure 5cm3 into each test tube
  3. use a cork borer to cut 6 equally sized potato chips
  4. weigh each potato
  5. place potato in each test tube for 20 mins
  6. remove and dab dry and weigh the potatoes
  7. calculate percentage mass change for each sucrose solution
• active transport is useful in

  reabsorbsion of useful molecules into the blood after filtration by the kidneys.

  loading sugar from photosynthesizing cells into the phloem

  loading ions from the soil to root hair cells
• how co transporters work

  1. sodium ion co transports glucose by simple diffusion into the epitheluim cell as conc is lower
  2. then the glucose can be transported into the blood by facilitated diffusion
  3. the sodium ion has to be actively transported as conc is higher in the blood
• permeability of cell membranes required practical method

  1. use extract and water to prepare a series of 6 test tubes containing 5cm3 of different conc of extracts and label them
  2. set up a water bath at 30 degrees
  3. create test tubes with different concs of alcohol solution and a bung and label them
  4. put the test tubes of alcohol in the water bath until temp of the alcohol reaches 30 degrees
  5. blot 30 discs of beetroot with towel to remove excess water
  6. put 5 beetroot discs in each test tube
  7. leave the tubes in the water bath for 5 mins and shake every minute
  8. pour each solution into a clean test tube and label them
  9. compare with the color standards you made in the first step
  10. record the absorbance reading with a colorimeter
• functions of phospholipids in membranes

  allow lipid soluble substances to enter and leave

  prevent water soluble substances entering and leaving

  make the membrane flexible and self sealing