The diagram below represents a DNA nucleotide.

Identify the phosphate group and deoxyribose.

Phosphate group: .................................................
Deoxyribose: ........................................................

Draw a labelled diagram to show how four nucleotides are joined together to form a double-stranded DNA molecule with two base pairs.

State two differences between RNA and DNA nucleotides.

Phosphate: I
Deoxyribose: III
Both correct for one mark.

two sugar-phosphate strands shown connected through bases;
a sugar-phosphate bond labeled as a covalent bond;
hydrogen bonds labeled on line between bases;
boxes labeled as (nitrogenous) bases;
complementary base pairing/A–T/G–C;
(5'–3') linkages correctly shown; (no label required)

RNA nucleotides contain ribose and DNA nucleotides contain deoxyribose;
(some) RNA nucleotides contain uracil and (some) DNA nucleotides contain thymine;

Most candidates had no problem identifying the phosphate group and deoxyribose in a diagram of a DNA nucleotide.
 

Although many drawings were dreadful in appearance, at least three marking points could be found to earn maximum credit.  Surprisingly, the nucleotide diagram that appeared in the previous question was not used by many candidates as the first nucleotide in their DNA drawings which eventually had to show four nucleotides arranged in a double strand connected through two bases.

Astute candidates who spotted the word “nucleotide” in the question earned an easy two marks by stating that RNA nucleotides contain ribose and uracil whereas DNA contains deoxyribose and thymine. Those candidates who thought in terms of a helix talked about single and double strand molecules without earning any mark. In this question, names were expected rather than letters to identify the nitrogenous bases.