IBBiologySLTopic QuestionsUnity & DiversityNucleic Acids

Syllabus Edition

First teaching 2023

First exams 2025

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Nucleic Acids (SL IB Biology)

Topic Questions

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11 mark

The table below shows four biological molecules and their component elements.

Which of the rows, A to D, correctly identifies the elements in each molecule?

  Sucrose Triglyceride Insulin DNA nucleotide
A C, H, O C, H, O, N C, H, O C, H, O, N, P
B C, H, O, N C, H, O C, H, O, N, P C, H, O, N, S
C C, H, O C, H, O C, H, O, N, S C, H, O, N, P
D C, H, O, N C, H, O, P C, H, O, N, P C, H, O, N, S

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2
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The following diagram represents the structure of a nucleotide.2-5-e-2

Which row of the following table correctly identifies all the components of this nucleotide?

  1 2 3
A. Adenine Pentose sugar Phosphate group
B. Phosphate group Adenine Pentose sugar
C. Pentose sugar Phosphate group Adenine
D. Phosphate group Pentose sugar Adenine

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3
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Which of the following statements only apply to RNA?

I. The molecule is in the shape of a double helix, with antiparallel strands

II. The four bases are adenine, cytosine, guanine, thymine

III. Ribose is present as the pentose sugar in its nucleotides

IV. It is a polymer formed by the linkage of many nucleotides

  • I and III

  • I, II and IV

  • II, III and IV

  • III and IV

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4
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The following diagram shows a section of a DNA molecule.

2-5easyq3

Which of these base pairs are not correct?

  • None

  • 1

  • 2

  • 3

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1
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Which of the following would be the result of analysing a DNA molecule 14 000 base pairs in length?

  • 28 000 pentose sugars, 14 000 phosphate groups, an equal ratio of cytosine to thymine bases and an equal ratio of guanine to adenine bases

  • 28 000 pentose sugars, 28 000 phosphate groups, an equal ratio of cytosine to guanine bases and an equal ratio of thymine to adenine bases

  • 14 000 pentose sugars, 28 000 phosphate groups, an equal ratio of cytosine to thymine bases and an equal ratio of guanine to adenine bases

  • 28 000 pentose sugars, 28 000 phosphate groups, an equal ratio of cytosine to thymine bases and an equal ratio of guanine to adenine bases

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2
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Which of the following would not be considered an advantage of complementary base pairing in DNA?

  • It enables each DNA strand to act as a template for the formation of a new strand during replication

  • Hydrogen bonding between complementary bases stabilises the structure of the DNA molecule

  • It ensures genetic continuity between generations of cells so that they all contain the same genetic information as the parent cells

  • It plays an important role in maintaining the covalent bonds within the DNA molecule

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11 mark

A short piece of DNA 19 base pairs long was analysed to find the number of nucleotide bases in each of the polynucleotide strands. Some of the results are shown below.

  Number of nucleotide bases  
  A T G C
Strand 1 8 - - -
Strand 2 - 8 3 4

How many nucleotides containing adenine (A) were present in strand 2?

  • 2

  • 4

  • 6

  • 8

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21 mark

Which of the following would be a result of analysing a DNA molecule?

  • An equal ratio of pentose sugars to phosphates and an equal ratio of thymine to adenine bases.

  • Twice as many pentose sugars as phosphates and an equal ratio of guanine to cytosine bases.

  • An equal ratio of hexose sugars to phosphates and an equal ratio of thymine to cytosine bases.

  • Twice as many hexose sugars as phosphates and an equal ratio of guanine to adenine bases.

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31 mark

The approximate angle of orientation ('twist') of one nucleotide in respect to its neighbouring nucleotide in a given strand of DNA is between 35 and 40 degrees. How many base pairs are required for the double-helix to twist by one whole turn? 

  • 5

  • 8

  • 10

  • 12

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41 mark

The diagram shows part of an RNA molecule. mcq-q7-ib-hl-biology

Which row of the table below is correct?

  Uracil Phosphate Ribose Guanine

A

B

C

D

W

W

X

X

Z

Y

Z

Y

Y

Z

Y

Z

X

X

W

W

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51 mark

The table shows the percentages of bases in DNA samples from various organisms.

Source of DNA Adenine Cytosine Guanine Thymine
Human liver 30 20 20 Z
Chicken liver W 40 40 10
Dog liver 24 26 24 26
Mouse bone marrow 23 X 26 25
Sunflower leaf 10 39 Y 12


Which row of the table below correctly reflects the missing data values?

  W X Y Z
A 9 24 38 30
B 10 26 39 31
C 10 26 39 30
D 10 25 38 29

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61 mark

The simplified diagram represents a section of DNA in 2D form.

mcq-q10-ib-hl-biology

How many mistakes are there in this diagram? 

  • 0

  • 1

  • 3

  • 5

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71 mark

Which of the following drawings best represents the structure of a section of DNA?

2-6-biology-mcq-q6

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81 mark

Which of the following statements about the genetic code are correct?. 

  1. A single DNA base will always be transcribed and translated in eukaryotic organisms.
  2. A single DNA base can be part of genes that overlap each other.
  3. The genetic code allows multiple triplet codons to code for a single amino acid. 
  4. The genetic code in a eukaryotic organism's genome stays the same throughout the organism's life.

  • III only

  • I and IV

  • I, II and III

  • III and IV

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