Investigating diversityAQA A-Level Biology: Subtopic test

1. 1
   Scientists compared the amino acid sequence of the same protein, cytochrome c, from four species and counted the number of differences from the human sequence. The chimpanzee sequence had 0 differences, the rhesus monkey sequence had 1, the horse sequence had 12 and the tuna sequence had 21.

   (a)

   Which conclusion is best supported by these data?

   [1 mark]

   • AThe horse is more closely related to humans than the rhesus monkey is
   • BHumans and chimpanzees must belong to the same species
   • CThe rhesus monkey is not related to humans
   • DOf the four species, the tuna is the least closely related to humans

   (b)

   Why can differences in amino acid sequence be used to suggest how closely species are related?

   [1 mark]

   • AAmino acid sequences are unaffected by mutations
   • BSpecies with more differences are more closely related
   • CThe sequences are coded for by DNA, so fewer differences suggest a more recent common ancestor
   • DThe same protein has an identical sequence in all species

   (c)

   Explain why the human cytochrome c sequence has fewer differences from that of the rhesus monkey than from that of the tuna.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Two individuals of the same beetle species were found to differ by one base in the DNA sequence of the gene coding for an enzyme. When the amino acid sequences of the enzyme in the two beetles were compared, they were identical.

   (a)

   Which statement best explains why the enzyme amino acid sequences are identical?

   [1 mark]

   • AThe genetic code is degenerate, so the changed base may still code for the same amino acid
   • BThe enzyme is not coded for by DNA
   • CA base difference always changes the mRNA but never the DNA
   • DThe two beetles must belong to different species

   (b)

   Which investigation would show the difference between the two beetles?

   [1 mark]

   • AComparing the frequency of observable characteristics
   • BComparing the base sequence of the DNA
   • CComparing the amino acid sequence of the enzyme
   • DComparing the mean body mass of a large sample

   (c)

   Suggest why comparing the base sequences of DNA gives a more complete measure of genetic diversity than comparing amino acid sequences.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A biologist measured the wing length of 50 randomly chosen moths from each of two populations. The mean wing length of population A was 24.2 mm with a standard deviation of 1.1 mm. The mean wing length of population B was 25.0 mm with a standard deviation of 3.2 mm.

   (a)

   Explain what the standard deviations show about the wing lengths of the two populations.

   [3 marks]

   (b)

   Use the data to evaluate whether the two populations differ in mean wing length.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A conservation team is studying a rare plant species that survives in three isolated populations. Botanists have always compared the populations using observable features such as flower colour and leaf shape. The team has now also sequenced the same 600-base gene from each population and from a related species, Z. The sequences from populations 1 and 2 are identical. The sequence from population 3 differs from them at 4 bases. The sequence from species Z differs from population 1 at 38 bases.

   (a)

   Use the sequence data to deduce how the populations and species Z are likely to be related.

   [6 marks]

   (b)

   Discuss how gene technology has changed the way genetic diversity is investigated, and evaluate the value of comparing DNA sequences rather than observable features.

   [6 marks]

   Total for question 4: 12 marks

End of questions