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O Level Biology: Biological Molecules MCQs — Biology

14 multiple-choice questions on O 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. Which test needs heating?

  1. Benedict's test
  2. Ethanol emulsion test
  3. Iodine test
  4. Biuret test

Answer: A) Benedict's test

Explanation: Benedict's solution is heated in a water bath. O Level Biology · Topic 4 Biological Molecules · 4.1 Biological molecules

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2. Which element is present in DNA but not in proteins?

  1. Hydrogen
  2. Nitrogen
  3. Carbon
  4. Phosphorus

Answer: D) Phosphorus

Explanation: DNA contains phosphorus in its nucleotides. O Level Biology · Topic 4 Biological Molecules · 4.1 Biological molecules

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3. What is the positive result for the biuret test?

  1. Blue-black
  2. Cloudy white
  3. Purple
  4. Brick-red

Answer: C) Purple

Explanation: Biuret turns purple with protein. O Level Biology · Topic 4 Biological Molecules · 4.1 Biological molecules

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4. Which element is found in proteins but NOT in carbohydrates?

  1. Carbon
  2. Nitrogen
  3. Hydrogen
  4. Oxygen

Answer: B) Nitrogen

Explanation: Proteins contain nitrogen; carbohydrates contain only C, H and O. O Level Biology · Topic 4 Biological Molecules · 4.1 Biological molecules

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5. A food is heated with Benedict's solution and turns brick-red. It contains

  1. starch
  2. protein
  3. fat
  4. a reducing sugar

Answer: D) a reducing sugar

Explanation: Brick-red precipitate = reducing sugar. O Level Biology · Topic 4 Biological Molecules · 4.1 Biological molecules

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6. Lipids are made from

  1. fatty acids and glycerol
  2. amino acids
  3. nucleotides
  4. glucose

Answer: A) fatty acids and glycerol

Explanation: Fats and oils are made of fatty acids and glycerol. O Level Biology · Topic 4 Biological Molecules · 4.1 Biological molecules

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7. Proteins are made from

  1. fatty acids
  2. amino acids
  3. nucleotides
  4. glucose

Answer: B) amino acids

Explanation: Amino acids are the building blocks of proteins. O Level Biology · Topic 4 Biological Molecules · 4.1 Biological molecules

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8. Starch, glycogen and cellulose are all made of

  1. nucleotides
  2. glucose
  3. amino acids
  4. fatty acids and glycerol

Answer: B) glucose

Explanation: All three are polymers of glucose. O Level Biology · Topic 4 Biological Molecules · 4.1 Biological molecules

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9. Cellulose is used by plants to

  1. build cell walls
  2. make enzymes
  3. store energy in seeds
  4. transport sugar

Answer: A) build cell walls

Explanation: Cellulose forms plant cell walls. O Level Biology · Topic 4 Biological Molecules · 4.1 Biological molecules

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10. Which reagent is used to test for starch?

  1. Ethanol
  2. Iodine solution
  3. Biuret solution
  4. Benedict's solution

Answer: B) Iodine solution

Explanation: Iodine turns blue-black with starch. O Level Biology · Topic 4 Biological Molecules · 4.1 Biological molecules

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11. Which carbohydrate is stored in the liver and muscles of animals?

  1. Cellulose
  2. Glycogen
  3. Sucrose
  4. Starch

Answer: B) Glycogen

Explanation: Animals store glucose as glycogen. O Level Biology · Topic 4 Biological Molecules · 4.1 Biological molecules

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12. A green colour in the Benedict's test means

  1. a small amount of reducing sugar
  2. a large amount of reducing sugar
  3. no sugar
  4. starch is present

Answer: A) a small amount of reducing sugar

Explanation: Green shows a low concentration; brick-red shows a high one. O Level Biology · Topic 4 Biological Molecules · 4.1 Biological molecules

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13. The ethanol emulsion test shows a cloudy white layer. The food contains

  1. glucose
  2. starch
  3. protein
  4. lipid

Answer: D) lipid

Explanation: A white emulsion indicates fat or oil. O Level Biology · Topic 4 Biological Molecules · 4.1 Biological molecules

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14. A solution gives a blue colour with Benedict's after heating and stays orange-brown with iodine. It contains

  1. both reducing sugar and starch
  2. reducing sugar only
  3. starch only
  4. neither reducing sugar nor starch

Answer: D) neither reducing sugar nor starch

Explanation: Both tests are negative. O Level Biology · Topic 4 Biological Molecules · 4.1 Biological molecules

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