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Biology journal Cambridge IGCSE 0610
Contains the answers

Answers · Food tests

Food tests — return questions key

Check meaning, not exact wording. These are teaching points, not official Cambridge marks.

1. BR1 · Return

Model answer. b. Starch, glycogen and cellulose are all made from glucose. They differ only in how the glucose units are joined and arranged.

A full answer includes

  • I chose b.

Also accept

  • b

Watch for

  • “Glycogen and cellulose are made from different sugars.” — All three are made from glucose.

2. BR2 · Return

Model answer. Proteins are made from amino acids. Fats and oils are made from fatty acids and glycerol. As well as carbon, hydrogen and oxygen, proteins contain nitrogen.

A full answer includes

  • g1: amino acids.
  • g2: fatty acids.
  • g3: glycerol.
  • g4: nitrogen.

Also accept

  • amino acids; fatty acids; glycerol (either order with fatty acids); nitrogen

Watch for

  • “Proteins contain only carbon, hydrogen and oxygen.” — The last gap asks for a fourth element. Go back to the first gap: proteins are built from amino acids, and every amino acid contains nitrogen.

3. FR1 · Return

Model answer. b. Benedict's solution must be heated in a water bath (about 80 °C for 5 minutes) for the colour change to happen.

A full answer includes

  • I chose b.

Also accept

  • b

Watch for

  • “Benedict's works straight away, like iodine.” — Benedict's only changes colour when heated.

4. FR2 · Return

Model answer. Iodine solution turns blue-black with starch. Biuret solution turns purple with protein. DCPIP loses its blue colour with vitamin C, and, with the same DCPIP and the same drop size, the fewer drops of sample needed, the more vitamin C it contains.

A full answer includes

  • g1: blue-black.
  • g2: purple.
  • g3: blue.
  • g4: more.

Also accept

  • blue-black; purple; blue; more

Watch for

  • “The blue biuret reagent is a positive result.” — Positive is purple.
  • “Fewer drops means less vitamin C.” — With the same DCPIP and drop size, fewer drops means more.

5. FR3 · Return

Model answer. The liquid turns evenly cloudy white, like milk. Fat dissolves in ethanol but not in water, so when the ethanol meets the water the fat comes out as millions of tiny droplets spread evenly through the liquid: an emulsion. The droplets scatter light, which makes the liquid look cloudy.

A full answer includes

  • The liquid turns evenly cloudy white (milky) all the way through.
  • The fat comes out of solution as tiny droplets spread through the water (an emulsion), which scatter light.

Also accept

  • evenly cloudy white; tiny fat droplets spread through the water (emulsion)

Watch for

  • “A positive emulsion test is a white solid at the bottom, or a layer of oil on top.” — It is tiny droplets spread evenly through the whole liquid.

6. NR1 · Return

Model answer. d. C always pairs with G (and A with T).

A full answer includes

  • I chose d.

Also accept

  • d

Watch for

  • “Any base can pair with any other base.” — Recall the two pairs, A–T and C–G: the base in the same pair as C is G.

7. NR2 · Return

Model answer. A DNA molecule is two strands coiled together to form a double helix. Each strand contains chemicals called bases. The bases form pairs across the two strands, and bonds between the bases of each pair hold the strands together.

A full answer includes

  • Two strands coiled together to form a double helix.
  • Each strand contains bases.
  • Bonds between pairs of bases hold the strands together.

Also accept

  • two strands, double helix; bases on each strand; bonds between base pairs hold the strands

Watch for

  • “DNA is one long chain.” — DNA has two strands coiled round each other.