Exam Q -1 carbs

• Raffinose : three monosaccharides mixed

  Molecular formula :

  • carbon 18
  • hydrogen 32
  • oxygen 16
• Biochemical test for non reducing sugar

  1. Do Benedict’s test and it should be negative
  2. boil with acid then neutralise with an alkali
  3. heat with Benedict’s solution
  4. red precipitate colour
• Which chemical group in glucose used to form a glycosidic bond

  OH
• Other than calorimeter what can the student do to measure the quantity of reducing sugars

  1. filter and dry the precipitate
  2. find mass and weights
• Use of calorimeter would improve the repeatability of the students result calorimeter standardises the result

  colour change is subjective
• One similarity and difference between structure of lactulose and lactose

  • both contain galactose / a glycosidic bond
  • lactulose contains fructose whereas lactose contains glucose
• Describe two differences between the structure of a cellulose molecule and a glycogen molecule

  • cellulose is made up of beta glucose monomers but glycogen is made up of alpha glucose
  • cellulose molecule has straight chains but glycogen is branched
  • cellulose contains 1-4 glycosidic bonds only but glycogen contains both 1-4 and 1-6 glycosidic bonds
• Describe and unexplained two features of starch that makes it a good storage molecule

  • insoluble in water so doesn’t affect water potential
  • branched so it makes molecules compact
  • polymer of alpha glucose so provides glucose for respiration
• Suggest how glycogen acts as a source of energy

  1. hydrolysed to glucose
  2. glucose is used in respiration
• Explain one way in which starch molecule that adapted for the function in plant cells

  • Insoluble - don’t affect water potential
  • Coiled/ helical - compact
  • large molecules - can’t leave cells
• Explain how cellulose molecules are adopted for their function in plant cells

  1. long and straight chains
  2. Become link together by many hydrogen bonds to form fibrils
  3. Provides strength to the cell wall
• Glycogen is more highly branched with shorter chains

  1. Animals have a higher metabolism
  2. Needs a faster release of glucose for respiration
• suggest why ,other than colour change, in which different concentrations of reducing sugars could be estimated

  • dry the precipitate in each sample and weigh it
  • the heavier it is the more reducing sugar present
• explain why its not possible to distinguish between very concentrated sMPLES , when their concentrations are different

  • once all copper 2 sulphate has been reduced to copper 2 oxide
  • further amounts of reducing sugars can‘t make a difference
• Explain how the structure of galactose allow it to be used as a respiratory substrate

  • Bonds contain energy - broken down by respiratory enzymes
  • h Oh form hydrogen bonds with water - allows solubility
  • soluble - move within cells in the body
• What reducing sugar would you expect to produce during chewing and give a reason

  1. Maltose
  2. Salivary amylase breaks down starch
• Explain the difference in structure of starch molecules and cellular molecules shown in the diagram above

  • Starch is formed from alpha glucose cellulose is formed from beta glucose

  • position of hydrogen and hydroxyl group on carbon one is inverted
• Hydrogen bonds are important in cellulose molecules explain why

  1. Hold chains to form microfibrils which provides strength to the cell wall
  2. Hydrogen bonds are strong in large numbers
• Explain the results for beakers A and B in the table

  1. a is glucose and b is maltose
  2. because more sugar will be present after hydrolysis of maltose

  
• GOS are polymers of galactose explain why GOS are described as polysaccharides (2)

  1. galactose is a monosaccharide
  2. Polysaccharide are carbohydrate polymers
  3. Galactose are joined by condensation reactions or glycosidic bonds
• Describe structure of glycogen

  1. Polysaccharide of alpha glucose
  2. Joined by glycosidic bonds