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CAIE A Level Biology 9700

Biological molecules questions

Exam-style questions on Biological molecules, ordered from foundation to challenge. Pick one, write your answer the way you would in the exam, and it comes back marked against the mark scheme, point by point.

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Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.

  1. Explain4 marksStandardA student tested an unknown food sample using four biochemical tests. The results are shown in the table. Test Result Benedict's test (on original sample) Blue solution remains after heating Benedict's test after acid…
  2. Define5 marksStandardDefine what is meant by a fibrous protein. Using collagen as an example, describe how the arrangement of collagen molecules into fibres is suited to its role in providing strength and support in connective tissues.
  3. Describe5 marksStandardA student is testing three fruit juice samples (X, Y, and Z) for reducing sugar content using a semi-quantitative Benedict's test. The student first prepares a set of glucose standard solutions of known concentrations…
  4. Outline4 marksStandardA student is given a solution suspected to contain sucrose, a non-reducing disaccharide. Describe how the student could confirm the presence of a non-reducing sugar in the solution, explaining the role of acid…
  5. Compare4 marksStandardA researcher is studying two proteins from a mammal: haemoglobin and collagen. Both have quaternary structure but differ in many ways. Compare the structure and function of haemoglobin and collagen with reference to…
  6. Define5 marksStandardDefine the term 'denaturation' as it applies to proteins. In your definition, state which types of chemical bonds are broken and which are not affected during denaturation.
  7. Describe5 marksStandardDescribe how the structures of starch and cellulose are related to their functions in plants.
  8. Describe5 marksStandardA student placed two beakers, each containing 100 cm³ of liquid, on a hot plate and heated them for 5 minutes. The initial and final temperatures were recorded as shown in the table. Liquid Initial temperature / °C…
  9. Compare4 marksStandardA student is comparing two triglycerides isolated from different sources. Triglyceride A: All fatty acid tails are saturated, meaning every carbon–carbon bond in the hydrocarbon chains is a single bond. This…
  10. Describe5 marksStandardDescribe how hydrogen bonds form between water molecules and explain how the following properties of water are important in living organisms: solvent action, high specific heat capacity, and high latent heat of…
  11. Describe4 marksStandardHaemoglobin is a globular protein with quaternary structure. Describe the four levels of protein structure, from primary to quaternary, and state the types of bond or interaction that stabilise each level.
  12. Describe4 marksStandardA botanist compares starch extracted from potato tubers and from maize seeds. Both are mixtures of amylose and amylopectin, but the proportions differ. Describe how the structures of amylose and amylopectin are adapted…
  13. Explain4 marksStandardTable 1 shows two properties of water and their roles in the body of a mammal. Property of water Role in the body High specific heat capacity Buffers temperature fluctuations to maintain a stable internal environment…
  14. Compare4 marksStandardCompare the structure and properties of globular and fibrous proteins. In your answer, refer to at least one named example of each type.
  15. Explain4 marksStandardThe table below lists two properties of water and a biological role that depends on each property. Property of water Biological role High specific heat capacity Helps aquatic organisms maintain a constant internal body…
  16. Outline5 marksStandardOutline how you would test a solution for the presence of protein using the biuret test. Include in your answer the expected results for a negative control and a positive control.
  17. Outline5 marksStandardA student is using the biuret test to identify whether three unknown solutions contain protein. The student also sets up a positive control and a negative control. Outline the purpose of each control and state the…
  18. Explain4 marksStandardDuring intense exercise, a mammal produces sweat, which evaporates from the skin, cooling the body. Explain how the hydrogen bonding between water molecules is responsible for water's high latent heat of vaporisation…
  19. Explain4 marksStandardThe blood plasma of mammals contains dissolved ions such as Na+ and Cl−, and glucose. Mammals also maintain a constant body temperature. Using your knowledge of the structure of water, explain how hydrogen bonding…
  20. Explain5 marksStandardIron deficiency reduces the oxygen-carrying capacity of blood. Explain the role of iron in the haem group of haemoglobin and how this relates to the function of haemoglobin in oxygen transport.
  21. Explain4 marksStandardA student prepares a solution of glucose and fructose and carries out a condensation reaction to form the disaccharide sucrose. Explain how the sucrose molecule is formed and why the resulting solution does not give a…
  22. Describe4 marksStandardThe table below lists the four levels of protein structure. For each level, write a description of the structure and state the main bonds or interactions that stabilise it. Level of protein structure Description and…
  23. Explain5 marksStandardBamboo shoots grow rapidly and need strong cell walls to support their height. The primary cell walls of bamboo are rich in cellulose. Explain how the molecular structure of cellulose enables it to provide mechanical…
  24. Explain4 marksStandardExplain how a molecule of sucrose is formed from molecules of glucose and fructose. In your answer, describe the reaction type, the bond formed, and why sucrose is classified as a non-reducing sugar.
  25. Explain5 marksStandardA patient diagnosed with iron deficiency anaemia has a low haemoglobin concentration and experiences fatigue. Explain the importance of iron in the structure of haemoglobin and how a lack of iron affects the function…
  26. Describe4 marksStandardThe table below shows some features of two proteins, haemoglobin and collagen. Feature Haemoglobin Collagen Solubility in water Soluble Insoluble Number of polypeptide chains 4 (two α, two β) 3 (each a long chain…
  27. Explain4 marksStandardDuring exercise, a person sweats to cool down. The evaporation of sweat from the skin helps to lower body temperature. Explain how the structure of water molecules and the resulting hydrogen bonding give water…
  28. Explain5 marksStandardA student wants to estimate the concentration of reducing sugars in an unknown solution. They first prepare standard glucose solutions of known concentrations: 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 g dm⁻³. To each standard…
  29. Compare5 marksStandardA student observes that oil droplets (triglycerides) form spherical droplets in water, whereas phospholipids spontaneously form a bilayer. Compare the structures of a triglyceride and a phospholipid, and explain how…
  30. Compare4 marksStandardA student compares a saturated triglyceride from butter with an unsaturated triglyceride from olive oil. The saturated triglyceride is solid at room temperature, while the unsaturated one is liquid. Compare the…
  31. Describe4 marksStandardA student performed biochemical tests on four unknown solutions (P, Q, R, and S). The results are shown in the table below. Solution Benedict's test (before hydrolysis) Benedict's test (after acid hydrolysis) Iodine…
  32. Describe5 marksStandardA student carries out a semi-quantitative Benedict's test on solutions of known glucose concentration and on an unknown fruit juice sample. She adds Benedict's reagent to each solution, heats them in a boiling water…
  33. Explain4 marksStandardA student is given a sample of a white powder. They dissolve a small amount in water and carry out the following tests: Benedict's test: solution turns orange after 2 minutes. Biuret test: solution turns purple. Iodine…
  34. Describe5 marksStandardA biologist is studying a temperate lake. She notes that the water temperature in the lake changes very little between day and night, while the air temperature can vary by more than 10°C. She also observes that many…
  35. Describe5 marksStandardWater is a molecule with unique properties essential for life. Describe how hydrogen bonding occurs between two water molecules. Then, explain how this hydrogen bonding gives water its solvent action and its high…
  36. Describe5 marksChallengeDescribe how hydrogen bonding occurs between water molecules and describe two properties of water that result from this bonding, explaining their importance in living organisms.
  37. Explain6 marksChallengeExplain why maltose is a reducing sugar while sucrose is not. In your answer, refer to the monosaccharides involved, the type of reaction that forms disaccharides, and the structure of the glycosidic bonds.
  38. Describe6 marksChallengeWater is essential for life due to its unique properties arising from hydrogen bonding between water molecules. A marine biologist monitors a coral reef lagoon and a nearby shallow tide pool. The lagoon's water…
  39. Explain6 marksChallengeWater has several properties that are important for life. The table below lists three biological roles of water. Biological role Property of water Sweating cools the body Many metabolic reactions occur in aqueous…
  40. Outline7 marksChallengeA student is investigating the sugar content of a honey sample. Honey contains reducing sugars (glucose and fructose) and a small amount of sucrose, which is a non-reducing sugar. The student wishes to estimate the…
  41. Explain5 marksChallengeHaemoglobin is a globular protein with quaternary structure. When a solution of haemoglobin is heated above 60°C, it loses its ability to bind oxygen and becomes insoluble. Explain the changes in bonding that occur…
  42. Compare5 marksChallengeHaemoglobin transports oxygen in the blood, while collagen provides structural support in connective tissues. Compare the structures of these two proteins and explain how their structural features relate to their…
  43. Explain6 marksChallengeA student investigates the effect of placing plant cells in a concentrated salt solution. The cells lose water and their cytoplasm shrinks, but the cell walls do not collapse. Instead, the cell walls retain their shape…
  44. Describe5 marksChallengeDescribe how the structures of amylose and amylopectin differ, and explain how each structural feature contributes to the suitability of starch as a storage polysaccharide in plants.
  45. Explain5 marksChallengeThe fennec fox is a small desert mammal with a high metabolic rate. Its blood plasma contains dissolved glucose and ions. Despite extreme daytime heat, the fennec fox maintains a stable internal body temperature and…
  46. Explain6 marksChallengeIn tendons, collagen fibres are aligned parallel to the direction of tensile force. Explain how the molecular structure and arrangement of collagen fibres make it suitable for this structural role.
  47. Describe5 marksChallengeA student carried out biochemical tests on four colourless solutions, P, Q, R and S. The results are shown in the table. Test P Q R S Benedict's test Blue → brick-red precipitate after 1 min Blue → brick-red…
  48. Describe5 marksChallengeFour unknown solutions, labelled P, Q, R and S, were tested using Benedict's test (before and after acid hydrolysis), iodine test, emulsion test and biuret test. The results are shown in the table below. Test P Q R S…
  49. Compare7 marksChallengeCompare the structure of a phospholipid molecule with that of a triglyceride. In your answer, explain how the structural differences relate to the roles of these molecules in cell membranes and in energy storage.
  50. Describe7 marksChallengeA student placed equal volumes of water and ethanol in two identical beakers on the same hotplate. The temperature of each liquid was recorded every 60 seconds for 3 minutes. The results are shown in the table. Time…
  51. Explain6 marksChallengeA student is given a sample of a food labelled 'fruit nectar'. They suspect it contains both reducing sugars and the disaccharide sucrose (a non-reducing sugar). They have access to Benedict's solution, dilute…
  52. Describe7 marksChallengeTable 1 shows some physical properties of water and of ethanol. Table 1 Property Water Ethanol Specific heat capacity / J g⁻¹ °C⁻¹ 4.18 2.44 Enthalpy of vaporisation / J g⁻¹ 2260 846 Boiling point / °C 100 78 Describe…
  53. Compare6 marksChallengeA researcher studies two proteins from a species of Antarctic fish. Protein X is found in the blood and transports oxygen. Protein Y forms long fibres in the skin, providing tensile strength. The table shows some…
  54. Describe5 marksChallengeTable 1 shows two molecules found in living organisms and their functions. Molecule Function A polysaccharide from a plant cell wall Provides strength and rigidity to the cell A lipid found in cell membranes Forms a…
  55. Explain6 marksChallengeA student carries out a semi-quantitative Benedict's test to estimate the concentration of reducing sugar in an unknown solution. They first prepare a set of glucose standards with known concentrations (g dm⁻³) and…
  56. Outline7 marksChallengeA student wants to test an unknown solution for the presence of protein using the biuret test. They set up three test tubes: Tube A: 2 cm³ of distilled water Tube B: 2 cm³ of a 1% egg albumen solution (known protein)…
  57. Describe5 marksChallengeDescribe the quaternary structure of haemoglobin and explain how this structure is related to its role in oxygen transport in mammals.
  58. Define7 marksChallengeA biology student is studying the structure of haemoglobin and collagen. Haemoglobin is a globular protein with quaternary structure, consisting of four polypeptide chains (two alpha and two beta), each containing a…
  59. Describe5 marksChallengePotato tubers store starch, which is a mixture of two polysaccharides: amylose and amylopectin. Describe how the molecular structures of amylose and amylopectin are adapted for their function as storage molecules.