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A Level Biology: Biological molecules MCQs — Biology

38 multiple-choice questions on A Level Biology: Biological molecules from Biology, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

1. The emulsion test for lipids gives

  1. a brick-red precipitate
  2. a blue-black colour
  3. a milky white emulsion
  4. a purple colour

Answer: C) a milky white emulsion

Explanation: Lipids form an emulsion in water. AS & A Level Biology · Topic 2 Biological Molecules · 2.1 Testing for biological molecules

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2. Cellulose is made of

  1. α-glucose with α-1,6 branches
  2. fructose and glucose
  3. β-glucose joined by β-1,4 glycosidic bonds
  4. α-glucose joined by α-1,4 bonds

Answer: C) β-glucose joined by β-1,4 glycosidic bonds

Explanation: Cellulose is a β-glucose polymer. AS & A Level Biology · Topic 2 Biological Molecules · 2.2 Carbohydrates and lipids

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3. A more objective way to measure the colour in Benedict's tests is to use

  1. a water bath
  2. a stage micrometer
  3. a colorimeter
  4. iodine

Answer: C) a colorimeter

Explanation: Colorimeters measure absorbance. AS & A Level Biology · Topic 2 Biological Molecules · 2.1 Testing for biological molecules

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4. Forming a glycosidic bond is a

  1. reduction reaction
  2. oxidation reaction
  3. condensation reaction releasing water
  4. hydrolysis reaction using water

Answer: C) condensation reaction releasing water

Explanation: Condensation removes water. AS & A Level Biology · Topic 2 Biological Molecules · 2.2 Carbohydrates and lipids

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5. Glycogen is suited to energy storage in animals because it is

  1. a straight chain with no branches
  2. made of β-glucose
  3. highly branched, so glucose can be released rapidly
  4. soluble and affects water potential

Answer: C) highly branched, so glucose can be released rapidly

Explanation: Many ends allow fast hydrolysis. AS & A Level Biology · Topic 2 Biological Molecules · 2.2 Carbohydrates and lipids

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6. Amylopectin differs from amylose because it has

  1. α-1,6 glycosidic branches
  2. β-glucose
  3. no α-1,4 bonds
  4. peptide bonds

Answer: A) α-1,6 glycosidic branches

Explanation: Amylopectin is branched. AS & A Level Biology · Topic 2 Biological Molecules · 2.2 Carbohydrates and lipids

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7. Why do lipids release more energy per gram than carbohydrates?

  1. They have more C–H bonds
  2. They are polar
  3. They are polymers of glucose
  4. They contain more oxygen

Answer: A) They have more C–H bonds

Explanation: More hydrogen to be oxidised. AS & A Level Biology · Topic 2 Biological Molecules · 2.2 Carbohydrates and lipids

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8. The test for a non-reducing sugar requires boiling with dilute acid first because

  1. the acid denatures proteins
  2. the acid hydrolyses glycosidic bonds to release reducing sugars
  3. the acid makes Benedict's blue
  4. the acid emulsifies lipids

Answer: B) the acid hydrolyses glycosidic bonds to release reducing sugars

Explanation: Hydrolysis forms monosaccharides that reduce Benedict's. AS & A Level Biology · Topic 2 Biological Molecules · 2.1 Testing for biological molecules

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9. Glycine is important in collagen because it

  1. is small, allowing the three chains to pack tightly
  2. carries iron
  3. is hydrophobic only
  4. forms disulfide bonds

Answer: A) is small, allowing the three chains to pack tightly

Explanation: Glycine every third position allows close packing. AS & A Level Biology · Topic 2 Biological Molecules · 2.3 Proteins

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10. In a semi-quantitative Benedict's test, which variable must be standardised?

  1. Final colour
  2. Concentration of the unknown
  3. Volume of Benedict's solution
  4. The precipitate mass

Answer: C) Volume of Benedict's solution

Explanation: Volumes, temperature and time must be constant. AS & A Level Biology · Topic 2 Biological Molecules · 2.1 Testing for biological molecules

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11. Which is a non-reducing sugar?

  1. Fructose
  2. Sucrose
  3. Glucose
  4. Maltose

Answer: B) Sucrose

Explanation: Sucrose is non-reducing. AS & A Level Biology · Topic 2 Biological Molecules · 2.2 Carbohydrates and lipids

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12. Why is sodium hydrogencarbonate added after acid hydrolysis?

  1. To make a precipitate
  2. Benedict's solution only works in alkaline conditions
  3. To remove starch
  4. To hydrolyse sucrose

Answer: B) Benedict's solution only works in alkaline conditions

Explanation: The solution must be neutralised. AS & A Level Biology · Topic 2 Biological Molecules · 2.1 Testing for biological molecules

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13. In α-glucose, the hydroxyl group on carbon 1 is

  1. absent
  2. on carbon 6
  3. above the ring
  4. below the ring

Answer: D) below the ring

Explanation: In β-glucose it is above. AS & A Level Biology · Topic 2 Biological Molecules · 2.2 Carbohydrates and lipids

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14. Globular proteins are soluble because

  1. they contain no R groups
  2. hydrophilic R groups face outwards
  3. they are very long
  4. they have many disulfide bonds

Answer: B) hydrophilic R groups face outwards

Explanation: Polar groups interact with water. AS & A Level Biology · Topic 2 Biological Molecules · 2.3 Proteins

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15. The biuret test detects

  1. peptide bonds
  2. hydrogen bonds
  3. glycosidic bonds
  4. ester bonds

Answer: A) peptide bonds

Explanation: Biuret reacts with peptide bonds. AS & A Level Biology · Topic 2 Biological Molecules · 2.1 Testing for biological molecules

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16. Starch is a good storage molecule because it is

  1. a protein
  2. made of β-glucose
  3. soluble and easily transported
  4. insoluble and does not affect water potential

Answer: D) insoluble and does not affect water potential

Explanation: Insoluble stores do not cause osmosis. AS & A Level Biology · Topic 2 Biological Molecules · 2.2 Carbohydrates and lipids

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17. Which bond is formed between the R groups of two cysteine molecules?

  1. Peptide bond
  2. Disulfide bond
  3. Glycosidic bond
  4. Ester bond

Answer: B) Disulfide bond

Explanation: Cysteine contains sulfur. AS & A Level Biology · Topic 2 Biological Molecules · 2.3 Proteins

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18. Water's high specific heat capacity is important because

  1. it resists rapid temperature change
  2. it dissolves glucose
  3. it allows sweating to cool
  4. it forms ice

Answer: A) it resists rapid temperature change

Explanation: Lots of energy is needed to raise its temperature. AS & A Level Biology · Topic 2 Biological Molecules · 2.4 Water

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19. Which result shows the highest concentration of reducing sugar?

  1. Brick-red precipitate
  2. Green
  3. Yellow
  4. Blue

Answer: A) Brick-red precipitate

Explanation: Brick-red indicates most sugar. AS & A Level Biology · Topic 2 Biological Molecules · 2.1 Testing for biological molecules

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20. The bond formed between two monosaccharides is a

  1. phosphodiester bond
  2. ester bond
  3. glycosidic bond
  4. peptide bond

Answer: C) glycosidic bond

Explanation: Condensation forms a glycosidic bond. AS & A Level Biology · Topic 2 Biological Molecules · 2.2 Carbohydrates and lipids

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21. The α-helix and β-pleated sheet are held by

  1. peptide bonds only
  2. disulfide bonds
  3. ionic bonds only
  4. hydrogen bonds

Answer: D) hydrogen bonds

Explanation: Secondary structure uses H-bonds in the backbone. AS & A Level Biology · Topic 2 Biological Molecules · 2.3 Proteins

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22. Which property of water is most important in transport in the blood plasma?

  1. Ice floating
  2. Low viscosity only
  3. High latent heat
  4. Solvent action

Answer: D) Solvent action

Explanation: Substances dissolve and are carried. AS & A Level Biology · Topic 2 Biological Molecules · 2.4 Water

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23. Amylose has a helical structure, which makes it

  1. strong for cell walls
  2. branched
  3. soluble in water
  4. compact for storage

Answer: D) compact for storage

Explanation: The coil packs many glucose units. AS & A Level Biology · Topic 2 Biological Molecules · 2.2 Carbohydrates and lipids

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24. Water is an excellent solvent because

  1. polar molecules and ions dissolve in it
  2. it has a low specific heat capacity
  3. it forms covalent bonds with all solutes
  4. it is non-polar

Answer: A) polar molecules and ions dissolve in it

Explanation: Polar water surrounds charged particles. AS & A Level Biology · Topic 2 Biological Molecules · 2.4 Water

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25. Collagen is a fibrous protein because it

  1. is a hormone
  2. is insoluble and has a structural role
  3. carries oxygen
  4. is soluble and an enzyme

Answer: B) is insoluble and has a structural role

Explanation: Fibrous proteins are structural. AS & A Level Biology · Topic 2 Biological Molecules · 2.3 Proteins

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