EXAM QUESTIONS REVIEW

• Describe a biochemical test to show that raffinose solution contains a non-reducing sugar.


  Heat with acid and neutralize; (Accept boil/water bath for heat ) Heat with Benedict's (solution); Red precipitate/color; (Accept other colors eg orange/ brown/green)
• A student carried out the Benedict’s test. Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution.

  Filter and dry (the precipitate). Find mass/weight;
• Use of a colorimeter in this investigation would improve the repeatability of the student’s results. Give one reason why.

  Quantitative. OR Standardises the method.
• What is a monomer?


  A smaller unit from which larger molecules are made .
• Glycogen and cellulose are both carbohydrates. Describe two differences between the structure of a cellulose molecule and a glycogen molecule.

  Cellulose is made up of β-glucose (monomers) and glycogen is made up of α-glucose (monomers); 2. Cellulose molecule has a straight chain and glycogen is branched; 3. glycogen has 1,4- and 1,6- glycosidic bonds and cellulose has only 1,4- glycosidic bonds.
• Starch is a carbohydrate often stored in plant cells. Describe and explain two features of starch that make it a good storage molecule.

  Insoluble (in water), so doesn’t affect water potential; 2. Starch is branched which provides a large surface area for enzymes to act on or more ends for fast breakdown.
• Describe the structure of glycogen.

  Polysaccharide/Polymer of alpha glucose. 2. Joined by glycosidic bond.
• During early pregnancy, the glycogen in the cells lining the uterus is an important energy source for the embryo. Suggest how glycogen acts as a source of energy. Do not include transport across membranes in your answer.

  Glycogen is hydrolysed to glucose. 2. Glucose is the main substrate for respirationand provides energy to the cell in the embryo.
• Name the monomers from which a maltose molecule is made.

  Glucose (and glucose).
• Name the type of chemical bond that joins the two monomers to form maltose.

  (α1,4) Glycosidic.
• Explain how you would use the graph to determine the maltose concentration with a light absorbance of 0.45 arbitrary units.

  Line of best fit drawn. Read off value at 0.45.
• Starch molecules and cellulose molecules have different functions in plant cells. Each molecule is adapted for its function. Explain one way in which starch molecules are adapted for their function in plant cells.

  Insoluble; 2. Don’t affect water potential; OR 3. Helical; (Accept form spirals) 4. Compact .
• Explain how cellulose molecules are adapted for their function in plant cells.

  Microfibrils are strong threads which are made of long cellulose chain running parallel to one another that are joined by hydrogen bonds forming strong cross-linkages. Cellulose is important in stopping the cell wall from bursting under osmotic pressure. This is because it exerts inwards pressure that stops the influx of water. 2. Providing strength to the cell wall. 3. Cellulose long and straight chain.
• Monosaccharides and disaccharides taste sweet. The lactose-free milk made after hydrolysis with lactase tastes sweeter than the cow’s milk containing lactose. Suggest why.

  (Lactose hydrolysed to) galactose and glucose; 2. (So) more sugar molecules; Tastes sweeter.
• Give two ways in which the structure of starch is similar to cellulose?

  Contain glycosidic bonds. 2. Are polymers, Have glucose or 1-4 links.
• Give two ways in which the structure of starch is different from cellulose.

  Starch contains alpha glucose whereas cellulose contains beta glucose. Starch is a branched molecule whereas cellulose is straight. Starch has 1-6 bonds whereas cellulose only has 1-4 bonds
• Using the diagram, suggest and explain one other way in which sieve cells are adapted for mass transport.

  Thicks walls so easier to resist pressure.
• Using the diagram, suggest and explain one other way in which companion cells are adapted for the transport of sugars between cells.

  Mitochondria release energy for active transport.
• What reducing sugar, or sugars, would you expect to be produced during chewing? Give a reason for your answer.

  Maltose; 2. Salivary amylase breaks down starch.
• In this model of digestion in the human gut, what other enzyme is required for the complete digestion of starch?

  Maltase
• Explain how a sports drink could provide an energy boost when running.

  Drink contain carbohydrates. Increases glucose to the muscle for respiration. More faster energy release.
• In humans, the enzyme maltase breaks down maltose to glucose. This takes place at normal body temperature. Explain why maltase: • only breaks down maltose • allows this reaction to take place at normal body temperature.

  Tertiary structure / 3D shape of enzyme (means); Active site complementary to maltose (Description of induced fit); Enzyme is a catalyst and it lowers activation energy; By forming an enzyme-substrate complex;
• Name the group represented by COOH?

  Carboxyl group
• Describe how you would test for the presence of a lipid in a liquid sample of food.

  Add ethanol/alcohol then add water and shake/mix. 2. White/milky (emulsion).
• Describe how a triglyceride molecule is formed.

  A triglyceride molecule is formed from one molecule of glycerol attached to three fatty acids joined together by an ester bond formed in a condensation reaction.
• Describe how an ester bond is formed in a phospholipid molecule.

  An ester bond is formed between glycerol and fatty acid molecule in a condensation reaction.
• The scientists expressed their results as Percentage of lipid in plasma membrane by mass. Explain how they would find these values.

  Divide the mass of each lipid by the total mass of all lipids (in that type of cell); 2. Multiply the answer by 100.
• Suggest one advantage of the different percentage of cholesterol in red blood cells compared with cells lining the ileum.

  Red blood cells free in blood / not supported by other cells so cholesterol helps to maintain shape;
• E. coli has no cholesterol in its cell-surface membrane. Despite this, the cell maintains a constant shape. Explain why.

  Cell unable to change shape; 2. (Because) cell has a cell wall; 3. (Wall is) rigid / made of peptidoglycan/murein.
• Other than ethical reasons, suggest two reasons why they chose to use cats as model organisms.

  Small enough to keep in the laboratory. 2. (Can use a) large number.
• Explain why monitoring the pH of the mixture could show whether the cat’s milk contained lipase.

  Hydrolysis of lipids produces fatty acids; 2. Which lower pH of mixture.
• A triglyceride molecule is formed by condensation. From how many molecules is this triglyceride formed?

  4
• The structure of a phospholipid molecule is different from that of a triglyceride. Describe how a phospholipid is different.

  In phospholipid one of the fatty acids is substituted with a phosphate group.
• Explain what is meant by an unsaturated fatty acid.

  Double bond(s); 2. (Bonds) between carbon;
• Scientists investigated the relationship between the amount of omega-3 fatty acids eaten per day and the risk of coronary heart disease. The graph shows their results. Do the data show that eating omega-3 fatty acids prevents coronary heart disease? Explain your answer.

  Graph shows negative correlation / (description given); 2. Correlation does not mean causation; May be due to another factor/(example given);
• Hydrogen bonds are important in cellulose molecules. Explain why.

  Forms cross-links between chains / forms microfibrils, providing strength/rigidity (to cell wall); 2. Hydrogen bonds are strong in large numbers;x
• A starch molecule has a spiral shape. Explain why this shape is important to its function in cells.

  Compact/Tightly packed
• Use the information in the figure to explain two ways in which fatty acids are important in the formation of new cells. (Used to make plasma membrane.),(Respired for energy.)

  Fatty acids used to make phospholipids; 2. Phospholipids in membranes; 3. More phospholipids more membranes made; (part2) Fatty acids respired to release energy;2. More triglycerides more energy released;
• Describe how an ATP molecule is formed from its component molecules.

  ATP is formed from the nucleotide base adenine combined with a ribose sugar and three phosphate groups. 3. ADP and Pi joined together in a condensation reaction catalysed by the enzyme ATP synthase .
• Name the two products of ATP hydrolysis.

  ADP (Adenosine diphosphate) 2. Pi (Inorganic phosphate)