1. 1
   A microbiologist discovers a previously unknown single-celled organism living in a highly acidic hot spring at a temperature of 80°C. She wants to classify it and decide which broad group of life it belongs to, using both the traditional Linnaean system and modern classification methods based on chemical analysis of its cells.

   (a)

   Under the traditional Linnaean system, it would be classified into a kingdom, phylum, class, order, family, genus and species. Which of the following correctly lists three of the Linnaean groups in order from broadest to most specific?

   [1 mark]

   • AKingdom, order, genus
   • BGenus, class, kingdom
   • CSpecies, family, kingdom
   • DOrder, kingdom, phylum

   (b)

   Chemical analysis of the organism's biochemistry places it in the domain of primitive, extremophile micro-organisms rather than with true bacteria. According to the three-domain system developed by Carl Woese, which domain is this?

   [1 mark]

   • AEukaryota
   • BBacteria
   • CArchaea
   • DProtista

   (c)

   Explain why classification systems have changed since the Linnaean system was first developed, and why chemical analysis was needed to correctly place this organism.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A team of scientists is building an evolutionary tree for four living species of wild cat, using DNA sequence data collected from each living species and fossil data from an extinct ancestor species that is believed to be common to all four.

   (a)

   Which type of data would the scientists use to construct the branch of the evolutionary tree representing an ancient, extinct ancestor species that lived millions of years ago?

   [1 mark]

   • ADNA sequencing data from living descendants only
   • BFossil data
   • CCurrent geographical distribution data
   • DCurrent population size data

   (b)

   Two of the four living cat species share a more recent common ancestor with each other than either does with the other two species. On the evolutionary tree, how would this close relationship be shown?

   [1 mark]

   • ATheir names are listed in alphabetical order next to each other
   • BTheir branches are drawn in the same colour
   • CTheir branches are the same length as each other
   • DTheir branches split from a shared branch point closer to the present than the other species

   (c)

   Explain what this evolutionary tree allows the scientists to conclude about how the four living cat species are related to each other and to the extinct ancestor.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A single population of finches once lived on one large island. A rise in sea level created a channel of water that split the island into two smaller islands, isolating the finch population into two separate groups that could no longer fly between the islands. Over many thousands of generations, the two groups developed noticeably different beak shapes suited to the different food sources available on each island. Scientists studying the two groups today find that, even when individuals from each island are brought together, they can no longer interbreed to produce fertile offspring.

   (a)

   Describe the steps by which the two island populations of finches became separate species.

   [3 marks]

   (b)

   Explain how natural selection acting on genetic variation within each isolated population led to the two groups becoming increasingly different from each other over time.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   For over a century, a group of similar-looking beetles found across a mountain range was classified by taxonomists as a single genus, based entirely on their external appearance. Recent DNA sequencing and biochemical analysis of beetles from the northern and southern ends of the mountain range has revealed substantial genetic differences between the two populations, despite their near-identical outward appearance. Some scientists now argue the group should be reclassified as two separate genera, and also suggest the two populations may be in the process of becoming separate species.

   (a)

   Explain how classification systems have changed over time as new scientific evidence has emerged, and evaluate why the beetle group should now be split into two separate genera.

   [6 marks]

   (b)

   Explain the process of speciation, and discuss how it might apply to the northern and southern beetle populations described above.

   [6 marks]

   Total for question 4: 12 marks

End of questions