ANSWERS TO REVIEW QUESTIONS – CHAPTER 31
1. (a) What proportion of the world’s biodiversity is found in Australia?
Australia has 7–8% of the world’s total species diversity; over 800,000 species occur here. Of these
species, over 80% are endemic—that is, they are found in Australia and nowhere else.
(b) In terms of discovering, describing and naming species, about which groups of
organisms do we know the least? (p. 741)
Insects and fungi have low proportions of named species. It is estimated that only 10% of Australia’s
250,000 species of fungi and 30% of the 225,000 species of insects have been named.
2.
Approximately what proportion of Australia’s (1) insects, (2) marsupials (3) vascular plants
are considered to be endemic? (Make sure that you know what the terms ‘biodiversity’ and
‘endemic’ mean). (Box 34.1)
Biodiversity is the variety of all forms of life, the diversity of genes they contain and the ecosystems of
which they are components. Species are said to be endemic to Australia when they are found in
Australia and nowhere else.
1.
2.
3.
Many are endemic but the proportion has not been estimated, presumably because so many are
undescribed.
90%
85%
3.
a) Distinguish between the terms ‘homologous’ and ‘analogous’, giving examples. (pp. 745–
750)
Homologous characters are characters that occur across two or more related species because they were
present in the ancestral species. Homologous characters are thus identical by descent. Analogous
characters are characters occurring across two or more species that were not present in a common
ancestor, and are identical or similar because of convergence, not by descent.
(b) What sort of features of similarity are the most useful for discovering evolutionary
relationships? (pp. 745–750)
Synapomorphic (shared, advanced) characters are the most useful for discovering evolutionary
relationships, since they define branch points on phylogenetic trees.
(c) Give one example of homology at the level of morphology and one at the level of DNA.
(pp. 745–750)
The skeletal structures of the forelimb of a crocodile, bird, bat and whale are homologous. The three
nucleotides in positions 1156, 2311 and 3257 of the 28 S ribosomal gene in the frog Xenopus and the
fruitfly Drosophila also represent an homologous character.
4.
What is a vestigial organ and how is it evidence of evolutionary relationship? Give an
example. (p. 744)
A vestigial organ is a rudimentary organ with no apparent function. Vestigial organs were likely
present in ancestral organisms and are therefore an indication of evolutionary phylogeny. For example,
humans have a vestigial tail (coccyx) which is similar to the prehensile tail of the monkey. Adult
baleen whales lack teeth but develop them when they are an embryo.
5.
Flowers of some grevilleas (Grevillea) and waratahs (Telopea) are red, which attracts birds
as pollinators. Is this colouration an example of convergent or divergent evolution? Why?
(p. 745)
This is an example of convergent evolution. Both groups include species that do not have red flowers
and are not primarily pollinated by birds. Insect vision tends to utilise higher wavelengths than
vertebrate vision, and insect-pollinated flowers tend to use blues and whites or, indeed, reflect most
strongly in the UV. Insects do not see red well. The red colour is visually striking and sends an
attractive signal to birds, and has probably arisen independently in both groups.
6.
Why is it useful to have a classification of organisms? Why is it most useful to have a
classification that is based on phylogeny? (pp. 742–743)
Having a classification of organisms helps us to systematise information on organisms and, given there
are an estimated ten million species, this is clearly necessary. Having a classification based on
phylogeny means that we can use data in a predictive manner. We can infer properties and
characteristics of a large number of species on the basis of the characteristics of related species without
having to subject them to intense study. Again, this is clearly very important when we are dealing with
ten million species.
7. What is meant by the terms ‘taxon’ and ‘taxonomy’? (p. 752)
A taxon is a formally recognised group of organisms in a system of classification—e.g. the genus
Homo and the species H. sapiens are both taxa in the Linnaean system. The principles by which the
organisms are grouped reflect the classification system. Taxonomy is both the practice of classification
and the principles or theory underlying the classification system.
8.
1.
2.
3.
4.
5.
6.
7.
List the order from highest to lowest the ranks commonly used in biological classification.
(p. 752)
Kingdom
Division (or Phylum)
Class
Order
Family
Genus
Species
9.
In the eighteenth century, before the time of Charles Darwin, the French zoologist Ětienne
Geoffroy Saint-Hilaire had the idea of a ‘unity of plan’ among animals. What did this mean
to him? (p. 744)
Refer to Box 31.2.
10. (a) How is the Kingdom Protista problematic as a taxon?
(b) Given the phylogenetic tree in Figure 31.10, and by only naming monophyletic groups,
how many kingdoms would you recognise? What groups of organisms would they
include? (Try making a case for recognising three ‘super kingdoms’ instead of five
kingdoms). (pp. 756–757)
The kingdom Protista is probably polyphyletic, in that microsporidia and metamonads are included in
it, but these groups are not true eukaryotes in that they appear primitively to lack mitochondria. They
may well have a different common ancestor within the archaeobacteria than the other protists. If the
kingdom is not polyphyletic, it is, at least, paraphyletic, since the Fungi, Plantae, and Animalia
kingdoms all appear to have arisen from within the protists. It is thus a ‘dustbin’ for eukaryotic and
eukaryote-like organisms that cannot conveniently be located elsewhere.
The obvious solution would be to raise the eubacteria and archaeobacteria to the status of kingdoms,
and make the third kingdom the eukaryota. The status of microsporidians and metamonads would still
be ambiguous.