Classification and the three-domain systemEdexcel International A Level Biology: Mind map

Exam questions on Classification and the three-domain system

1. Two populations of small beetles live on different islands. They look very similar, but the males of one population make a different courtship sound. Biologists want to decide whether the two populations are the same species or different species.
   Beetles from the two islands are brought together, and they mate and produce offspring, but all the offspring are sterile. Explain what this suggests about whether the beetles are the same species.2 marks
2. Biologists have discovered three new single-celled organisms, P, Q and R, in a hot spring. None of them has a nucleus. The biologists compare the base sequences of the genes for ribosomal RNA (rRNA) in the three organisms. The sequences of P and Q are similar to each other, but both differ greatly from the sequence of R.
   Suggest why using molecular evidence is more reliable than using observable features alone for classifying organisms such as P, Q and R.2 marks
3. Before 1977 living organisms were classified into kingdoms using observable features. In 1977 Carl Woese and his colleagues compared the sequences of ribosomal RNA from many organisms, and the results led to a new system in which all living organisms are placed in one of three domains.
   State the three domains, and give two features of cells in the domain Eukarya that distinguish them from cells in the other two domains.3 marks