IB Biology SL A1.2 Nucleic acids Questions

Practise IB Biology SL A1.2 with questions on nucleotide structure, DNA and RNA, complementary base pairing and genetic information.

54 questions in this syllabus scope, with question parts counted together.

Syllabus
First assessment 2025
Course
Biology SL
Level
SL

Exam analysis

SL · 2010–2025
Papers with this topic45 / 141in the analysed sample
Latest appearanceNovember 2025
Tagged question parts53
Paper types5

Most tested objectives

  1. A1.2.7—Differences between DNA and RNA9 papers
  2. A1.2.2—Components of a nucleotide8 papers
  3. A1.2.3—Sugar-phosphate bonding8 papers
  4. A1.2.6—DNA as a double helix8 papers
  5. A1.2.10—Conservation of genetic code8 papers

Common question formats

  • Diagram interpretation
  • Definition or recall
  • Structured response
  • Data analysis
  • Calculation
  • Comparison
  • Graph interpretation

Recent exam appearances

November 2025Paper 2 SL · TZ3Q2(a), 2(c)[ 4 ]
May 2025Paper 2 SL · TZ1Q5(b)[ 2 ]
May 2025Paper 1A SL · TZ3Q2[ 1 ]

141 papers analysed · Tagging incomplete

Exam points

  • Identify phosphate, pentose and nitrogenous-base components; show the covalent phosphate–sugar backbone and use nucleotide counts to infer phosphate totals.
  • Compare DNA and RNA using pentose sugar, thymine or uracil, strand organisation and typical length, and identify a molecule from a sequence or diagram.
  • Draw or interpret a DNA double helix with antiparallel sugar–phosphate strands, complementary A–T/G–C pairs and hydrogen bonds; distinguish these from covalent backbone links and use base-pair data to calculate missing percentages.
  • Relate the order of DNA bases and genome size to stored information, and use universal-code evidence to explain gene transfer and conserved protein sequences.
  • Use transformation, genome-source and cloning evidence to identify DNA as genetic material and distinguish nuclear from mitochondrial inheritance.

Covered syllabus points

A1.2.1—DNA as genetic materialA1.2.2—Components of a nucleotideA1.2.3—Sugar-phosphate bondingA1.2.4—Bases form the basis of a codeA1.2.5—RNA as a polymerA1.2.6—DNA as a double helixA1.2.7—Differences between DNA and RNAA1.2.8—Complementary base pairingA1.2.9—Diversity of DNA base sequencesA1.2.10—Conservation of genetic code

Exam points

  • State that DNA is the genetic material of living organisms and occurs in chromosomes, mitochondria and chloroplasts.
  • Recognise that some viruses use RNA as genetic material and are not considered living organisms.

Question 1

[Maximum number: 1]

The Human Genome Project completed the sequencing of the human genome by the year 2003. Which could have been a source of the entire genome in humans?

A

The contents of a red blood cell

B

The nucleus and mitochondria of a skin cell

C

The nucleus and acrosome of a sperm cell

D

The nucleus and ribosomes of any somatic cell

Exam points

  • Identify the phosphate group, pentose sugar and nitrogenous base that make up a nucleotide.
  • Distinguish deoxyribose in DNA from ribose in RNA, and classify A/G as purines and C/T/U as pyrimidines.

Question 1

[Maximum number: 1]

What are components of DNA and RNA?

DNA

RNA

Both DNA and RNA

ribose

deoxyribose

uracil

ribose

deoxyribose

adenine

deoxyribose

ribose

uracil

deoxyribose

ribose

adenine

Exam points

  • Explain how condensation reactions link nucleotides through sugar-phosphate bonds to form a continuous covalent backbone.
  • Describe how bases project from the sugar-phosphate backbone and carry sequence information.

Question 1

[Maximum number: 1]

What is the correct arrangement for the components of one strand in a DNA molecule?

A

- phosphate - deoxyribose - base - phosphate - deoxyribose - base -

B

- base - deoxyribose - base - deoxyribose - base - deoxyribose - phosphate phosphate phosphate

C

- phosphate - deoxyribose - phosphate - deoxyribose - phosphate - deoxyribose -

D

- phosphate - base - phosphate - base - phosphate - base deoxyribose deoxyribose deoxyribose

No public sample questions are available for this syllabus point yet.

Exam points

  • Describe RNA as a single-stranded polynucleotide formed by condensation, containing ribose and the bases A, U, G and C.
  • Distinguish the roles of mRNA, tRNA and rRNA in protein synthesis.

Question 1

[Maximum number: 1]

What is a similarity between DNA and RNA?

A

Both are polymers of nucleotides.

B

Both are composed of antiparallel strands.

C

Both contain adenine, cytosine and thymine.

D

Both contain ribose sugar.

Exam points

  • Describe DNA as a double helix formed by two antiparallel polynucleotide strands.
  • Explain complementary base pairing by hydrogen bonds: A–T and G–C.
  • Draw DNA bases attached to sugars rather than to phosphate groups.

Question 1

[Maximum number: 1]

Watson and Crick worked out the three-dimensional structure of DNA.

What did the model they built show for the first time?

A

DNA is a polynucleotide.

B

DNA contains equal quantities of adenine and thymine.

C

DNA molecules have a helical shape.

D

DNA is a double helix with antiparallel sugar-phosphate backbones.

Exam points

  • Compare the usual strand number and molecule length of DNA and RNA: DNA is usually double-stranded, while RNA is usually single-stranded and much shorter.
  • Distinguish DNA deoxyribose and thymine from RNA ribose and uracil.

Question 1

[Maximum number: 2]

The percentage of cytosine in the genome of the common octopus (Octopus vulgaris) is 17.6 %.

Distinguish between the structure of the nucleotides in DNA and RNA.

Exam points

  • State the complementary base pairs: A–T in DNA, A–U in RNA, and C–G.
  • Explain how complementary base pairing enables accurate DNA replication, transcription and translation in gene expression.

Question 1

[Maximum number: 1]

Whole genome sequencing has allowed scientists to compare the genetic content of different organisms. The table shows the genome sizes of some plants and animals.

Table for Question 1 — IB Biology SL

There are 64 million adenine-thymine base pairs in the genome of the nematode worm. Deduce the number of cytosine-guanine base pairs in the genome.

Exam points

  • Describe how DNA length and base sequence vary and how genome size and gene number differ widely between organisms.
  • Explain how diversity in DNA base sequences gives DNA a large information-storage capacity.

Question 1

[Maximum number: 1]

A human cell has between 20000 and 25000 genes whereas an E. coli cell has approximately 4000 genes. Which of the following statements is true?

A

The human genome is larger than the E. coli genome.

B

There are more genes on each human chromosome than on the E. coli chromosome.

C

The human cell and the E. coli cell produce approximately the same variety of proteins.

D

The DNA in both organisms is associated with histones (proteins).

Exam points

  • Explain that the 64 codons have nearly the same meanings across life.
  • Use conserved genes for transcription, translation and ribosomes as evidence supporting common ancestry.
  • Explain how synonymous mutations can preserve an amino acid sequence.

Question 1

[Maximum number: 1]

Research has shown that the genetic code is not entirely universal. Which research finding has shown this?

A

Some amino acids are coded for by more than one codon.

B

There are differences between the base sequences of genes in different species.

C

In some organisms the genetic code for mitochondria differs from the genetic code for the nucleus.

D

Some codons code for the addition of an amino acid and some code for the termination of translation.