Recall questions

• Describe the structure of a starch molecule and explain how starch is adapted for its function in cells. [6]

  1. a polysccharide made from alpha glucose
  2. joined by condensation / removing a molecule of water / glycosidic bond
  3. Mainly 1 : 4 glycosidic bonds
  4. Some 1 : 6 glycosidic bonds form branches
  5. Chains are helical SO they are compact
  6. Starch is insoluble SO it doesn't affect the water potential
  7. Starch is a large molecule SO it cannot leave the cell
• Describe the structure of a glycogen molecule and explain how glycogen is adapted for its function in cells. [6]

  1. A polysaccharide made from alpha glucose
  2. joined by condensation / removing a molecule of water / glycosidic bonds
  3. Mainly 1 : 4 glycosidic bonds
  4. Lots of 1-6 glycosidic bonds to form many branches
  5. Chains are coiled so they are compact
  6. Glycogen is insoluble so it does not affect osmotic pressure
  7. Highly branched, allowing it to be hydrolysed to release glucose for respiration.
• Describe the structure of a cellulose molecule and explain how cellulose is adapted for its function in cells. [6]

  1. A polysaccharide made from beta glucose that forms long straight chains
  2. joined by condensation / removing a molecule of water
  3. Forms 1 : 4 glycosidic bonds
  4. "flipping over" of alternate molecules
  5. MANY hydrogen bonds link chains together forming fibrils
  6. cellulose makes cell walls strong/ cellulose fibres are strong
  7. can resist turgor pressure / osmotic pressure / pulling forces
  8. bonds are difficult to break
  9. resists digestion / action of microorganisms / enzymes
• Describe how the structures of starch and cellulose molecules are related to their functions. [6]

  Starch (3):

  Helical/spiral shape SO compact

  large molecule/insoluble SO osmotically inactive

  Branched SO glucose is easily released for respiration

  Cellulose (3):

  Long, straight, unbranched chains of beta glucose

  joined by many hydrogen bonding

  To form micro/ macro fibrils

  Provides rigidity / strength
• Describe the properties of water and explain the biological importance of each property (10)

  1. Polar due to hydrogen bonding
  2. SO Dissolves charged particles / acts as a (universal) solvent
  3. A metabolite
  4. SO involved in metabolic/ cell reaction / condensation / hydrolysis
  5. Water molecules stick together / cohesion between water molecules
  6. SO provides surface tension / prevents columns from breaking
  7. High (specific) heat capacity
  8. SO reduces fluctuations in temperature (of water bodies)
  9. High latent heat of vaporisation
  10. SO evaporation of small amount of water cools organisms
• Explain how a change in the primary structure of a globular protein may result in a different three-dimensional structure.

  1. sequence of amino acids changes;
  2. so different bonds form
  3. between R groups in different places
  4. so the tertiary structure changes/ folds in a different way
• Describe the structure of proteins (NOTE: for each structure include how it forms and the bonds present)

  1. a protein is a polymer of amino acids;
  2. joined by peptide bonds;
  3. formed by condensation
  4. The primary structure is the order / sequence of amino acids
  5. The secondary structure is the folding of the polypeptide chain due to hydrogen bonding (alpha helix and beta pleated sheet)
  6. The tertiary structure is the 3D folding due to hydrogen bonding and ionic and disulphide bonds
  7. The quaternary structure is two or more polypeptide chains
• Describe how you would use colorimetry to identify the concentration of glucose in an unknown solution (part 1)

  1. Carry out the benedict's test on samples of glucose with known concentrations of glucose
  2. Use a colorimeter to find the percentage light transmission of known samples of glucose
  3. Draw a graph with glucose concentration of the x-axis and % light transmission on the y-axis.
  4. Plot the points on the graph and draw a calibration curve
• Describe how you would use colorimetry to identify the concentration of glucose in an unknown solution(part 2)

  
  

  5. Carry out the Benedict's test on the solution of glucose with an unknown glucose concentration

  6. Find the percentage light transmission for this sample using the colorimeter

  7. Find this percentage light transmission on the y-axis and draw a horizontal line until you reach the calibration curve. Then draw a vertical line down and read the concentration of glucose off of the x-axis.