Skip to content
Biology journal Cambridge IGCSE 0610

Pupil sheet · Food tests

The structure of DNA — questions

Name ______________________ Date ____________

Try every question before you use a nudge. Write in full sentences where you are asked to explain.

1. complete

Complete the sentences about DNA.

A DNA molecule is made of two …

coiled together to form a double …

Each strand contains chemicals called …

Bonds between pairs of … hold the strands together.

Nudge (only if you are stuck): Look at the diagram of DNA: the unwound ladder and the coiled shape.

2. identify

Match each base to the base it always pairs with.

Write the number of the matching option.

  1. A
  2. T
  3. C
  4. G
  • A: ______
  • T: ______
  • C: ______
  • G: ______

Nudge (only if you are stuck): There are two pairs, and the pairs never swap partners.

3. identify

What holds the two strands of a DNA molecule together?

Circle one answer.

  • Bonds between pairs of bases
  • Chains of glucose units
  • The ends of the strands, joined end to end
  • Amino acids between the strands

Nudge (only if you are stuck): Look at the rungs of the ladder in the diagram.

4. deduce

One strand of a piece of DNA has the bases A C G T T A. Write the order of bases on the other strand, opposite them.

Nudge (only if you are stuck): Work along the strand one base at a time: swap A for T, T for A, C for G and G for C.

5. identify

Which of these base pairs are found in DNA? Choose all that apply.

Tick every correct statement.

  • A with T
  • A with C
  • G with C
  • T with G

Nudge (only if you are stuck): Only two kinds of pair ever form.

6. identify

Which statements describe the structure of DNA? Choose all that apply.

Tick every correct statement.

  • Two strands are coiled together to form a double helix
  • It is a single strand coiled into a helix
  • Each strand contains chemicals called bases
  • Bonds between pairs of bases hold the strands together
  • Any base can pair with any other base

Nudge (only if you are stuck): Picture the ladder, then the twist.

7. calculate

In a DNA molecule from a bacterium, 30 % of the bases are A. Calculate the percentage of the bases that are T, C and G.

T: ______________ unit ________

C: ______________ unit ________

G: ______________ unit ________

Nudge (only if you are stuck): Every A has a T partner. The rest of the bases are C and G, in equal numbers.

8. evaluate / explain

A short piece of DNA has 10 base pairs. On one strand, 4 of the 10 bases are G. A student says: "So the other strand must also have 4 G bases." Explain whether the student is right.

Nudge (only if you are stuck): What is opposite each G on the first strand?