IBBiologyHLExam QuestionsUnity & DiversityNucleic Acids

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First exams 2025

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Nucleic Acids (HL IB Biology)

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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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      51 mark

      Which of the following statements correctly describes a nucleosome?

      • A strand of DNA coiled around a central core of eight histone proteins.

      • A strand of DNA wrapped around a central core of four histone proteins.

      • A section of supercoiled DNA.

      • A strand of DNA wrapped around a central core of eight chromatin proteins.

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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

      DNA is described as a double-helix, antiparallel structure. Which of the following statements best explains the term, 'antiparallel'? 

      • One strand possesses deoxyribose sugar, the opposite strand possesses ribose sugars. 

      • The nitrogenous bases invert their orientation on the sense strand versus the antisense strand.

      • The alignment of the sugar-phosphate backbone of each strand runs in opposite directions.

      • The alignment of the two strands of nucleotides runs in opposite directions.

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      41 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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      51 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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        61 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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          71 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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          81 mark

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

          2-6-biology-mcq-q6

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            91 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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            101 mark

            Which of the following are correct statements about nucleosomes?

            I.

            They contain histone proteins

            II.

            They help supercoil the DNA to form a compact structure

            III.

            They are found in both eukaryotes and prokaryotes

            IV.

            They consist of both DNA and chromatin

            • I only

            • I and II

            • I, II and III

            • I, II and IV

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            111 mark

            In the 1950s, Hershey and Chase demonstrated that DNA, not protein, is a factor of heredity responsible for carrying genetic information from one generation to another. They used viruses that were labelled with either radioactive sulphur (35S) or radioactive phosphorus (32P) to infect bacteria.

            Which of these statements correctly describes the results of their experiment?

            • Only bacteria infected by 32P labelled viruses were shown to be radioactive

            • 32P was only detected in the supernatant

            • Only bacteria infected by 35S labelled viruses were shown to be radioactive

            • 35S was detected in the pellet after centrifugation

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            121 mark

            Molecular visualisation software can be used to look at the three-dimensional structure of complex macromolecules such as the nucleosome.

             Which of the following statements about molecular visualisation software are correct?

            I.

            Can help relate structure to chemical or biological behaviour.

            II.

            Can support the design of pharmaceutically active compounds.

            III.

            Can be used to study the interactions between proteins.

            IV.

            Is primarily used to identify if a DNA sequence encodes for a gene.

            • I and II

            • I, II and III 

            • I and IV

            • I, II, III and IV

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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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            3
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            Hershey and Chase carried out an experiment to determine whether the molecule of heredity was protein or DNA; their results after centrifugation are shown below.

            Note the following:

            • Extracellular material is found in the supernatant.
            • The y-axis shows the percentage of each radioactive element present in the supernatant; the remainder of each element ends up in the pellet.7-1_q5h

            Which of the following can be concluded from the results shown?

            • No viral protein enters the infected bacterial cells.

            • DNA has a greater mass than protein.

            • Around 80 % of the viral DNA enters the infected bacterial cells.

            • Most proteins are separated from the bacterial cells by the blending process.

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