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A Level Biology: Biological molecules MCQs — Biology (page 2)

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.

26. Unsaturated fatty acids contain

  1. at least one C=C double bond
  2. peptide bonds
  3. phosphate groups
  4. no double bonds

Answer: A) at least one C=C double bond

Explanation: Saturated = no double bonds. AS & A Level Biology · Topic 2 Biological Molecules · 2.2 Carbohydrates and lipids

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27. How many oxygen molecules can one haemoglobin molecule carry?

  1. One
  2. Eight
  3. Four
  4. Two

Answer: C) Four

Explanation: One O₂ per haem group. AS & A Level Biology · Topic 2 Biological Molecules · 2.3 Proteins

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28. Hydrogen bonds form in water because

  1. water molecules are polar
  2. oxygen is positively charged
  3. hydrogen is negatively charged
  4. water is non-polar

Answer: A) water molecules are polar

Explanation: δ+ H attracts δ− O. AS & A Level Biology · Topic 2 Biological Molecules · 2.4 Water

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29. Ionic bonds in proteins are easily broken by

  1. hydrolysis of glycosidic bonds
  2. adding water only
  3. changes in pH
  4. cold temperatures

Answer: C) changes in pH

Explanation: pH changes alter charges on R groups. AS & A Level Biology · Topic 2 Biological Molecules · 2.3 Proteins

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30. Haem contains an ion of

  1. copper
  2. calcium
  3. iron (Fe²⁺)
  4. magnesium

Answer: C) iron (Fe²⁺)

Explanation: Iron binds oxygen. AS & A Level Biology · Topic 2 Biological Molecules · 2.3 Proteins

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31. The primary structure of a protein is

  1. the number of polypeptides
  2. the folding into α-helices
  3. the sequence of amino acids
  4. the 3D shape

Answer: C) the sequence of amino acids

Explanation: Primary = sequence. AS & A Level Biology · Topic 2 Biological Molecules · 2.3 Proteins

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32. The peptide bond forms between

  1. two R groups
  2. two amine groups
  3. the amine group of one amino acid and the carboxyl group of another
  4. glycerol and a fatty acid

Answer: C) the amine group of one amino acid and the carboxyl group of another

Explanation: Condensation of –NH₂ and –COOH. AS & A Level Biology · Topic 2 Biological Molecules · 2.3 Proteins

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33. In cellulose, chains are held together in microfibrils by

  1. ester bonds
  2. ionic bonds
  3. hydrogen bonds
  4. disulfide bonds

Answer: C) hydrogen bonds

Explanation: Many H-bonds give tensile strength. AS & A Level Biology · Topic 2 Biological Molecules · 2.2 Carbohydrates and lipids

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34. Phospholipids form bilayers because they have

  1. hydrophilic heads and hydrophobic tails
  2. only hydrophobic regions
  3. only hydrophilic regions
  4. glycosidic bonds

Answer: A) hydrophilic heads and hydrophobic tails

Explanation: Heads face water; tails face inward. AS & A Level Biology · Topic 2 Biological Molecules · 2.2 Carbohydrates and lipids

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35. Collagen molecules are joined to form fibrils by

  1. covalent cross-links with staggered ends
  2. hydrogen bonds to haem
  3. peptide bonds only
  4. hydrophobic tails

Answer: A) covalent cross-links with staggered ends

Explanation: Cross-links and staggering give strength. AS & A Level Biology · Topic 2 Biological Molecules · 2.3 Proteins

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36. Haemoglobin is made of

  1. one polypeptide and one haem group
  2. four identical chains without haem
  3. three polypeptides in a triple helix
  4. two α-globin and two β-globin chains, each with a haem group

Answer: D) two α-globin and two β-globin chains, each with a haem group

Explanation: Haemoglobin has quaternary structure. AS & A Level Biology · Topic 2 Biological Molecules · 2.3 Proteins

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37. A triglyceride is formed from

  1. glucose and fructose
  2. glycerol and three fatty acids
  3. amino acids
  4. glycerol, two fatty acids and phosphate

Answer: B) glycerol and three fatty acids

Explanation: Three ester bonds join fatty acids to glycerol. AS & A Level Biology · Topic 2 Biological Molecules · 2.2 Carbohydrates and lipids

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38. Sweating cools the body effectively because water has a high

  1. latent heat of vaporisation
  2. density
  3. pH
  4. solvent ability

Answer: A) latent heat of vaporisation

Explanation: Evaporation removes much heat. AS & A Level Biology · Topic 2 Biological Molecules · 2.4 Water

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