Classification of Living Organisms: Five Kingdoms and Taxonomy

The correct answer is B, Carolus Linnaeus. The Swedish naturalist Carl von Linne, known in Latin as Carolus Linnaeus, arranged plants and animals in a hierarchy of ranks and gave biology the two-word system of scientific names in his works Systema Naturae and Species Plantarum, so he is called the father of taxonomy. A is wrong because Charles Darwin explained how species change by natural selection in On the Origin of Species, which is the foundation of evolutionary biology rather than of naming and ranking. C is wrong because Ernst Haeckel added the kingdom Protista for single-celled organisms, an important step but long after the system of naming had been settled. D is wrong because Robert Hooke first saw and named cells in a thin slice of cork and belongs to the history of cytology.

The correct answer is C, R. H. Whittaker. Robert Harding Whittaker proposed the five kingdoms Monera, Protista, Fungi, Plantae and Animalia in 1969, using cell structure, body organisation, mode of nutrition, reproduction and evolutionary relationships as the criteria of division. A is wrong because Ernst Haeckel proposed a three-kingdom system by adding Protista to Plantae and Animalia. B is wrong because Carl Woese came later and, working from the chemistry of ribosomal nucleic acid, proposed the three domains Archaea, Bacteria and Eukarya, splitting the old Monera. D is wrong because Herbert Copeland proposed a four-kingdom system in which the bacteria were separated from the Protista, a step between Haeckel and Whittaker. Remember the sequence of systems as two kingdoms by Linnaeus, three by Haeckel, four by Copeland, five by Whittaker and three domains by Woese, because questions are often set on who came after whom.

The correct answer is C, Chlamydomonas. Chlamydomonas is a unicellular, flagellated member of the Chlorophyceae, the green algae, in which chlorophyll a and b give the plant its grass-green colour and the food is stored as starch. A is wrong because Laminaria is a kelp and belongs to the Phaeophyceae or brown algae, in which the pigment fucoxanthin masks the chlorophyll and the stored food is laminarin and mannitol. B is wrong because Sargassum is also a brown alga, the floating weed that gives the Sargasso Sea its name. D is wrong because Fucus, the rockweed of cold shores, is again a brown alga. Of the four, only Chlamydomonas carries the green pigments without a masking one, so only it is a green alga. A quick rule for the paper is that a name ending in the Chlorophyceae group is green, while kelps and rockweeds of cold seas are brown and are stored as laminarin rather than starch.

The correct answer is C, species. A species is a group of organisms that resemble one another in all essential characters and that can interbreed to produce fertile offspring; it is the smallest and the basic unit of classification, and all higher ranks are built by grouping species together. A is wrong because a genus is a group of closely related species, as Panthera holds the lion, the tiger and the leopard, so it stands one rank above the basic unit. B is wrong because a family is a group of related genera and is therefore wider still. D is wrong because an order is a group of related families, standing two ranks above family and far from being the basic unit of classification. A simple test in the examination hall is that the basic unit must be the group that cannot be divided further into smaller named groups of interbreeding organisms, and that description fits only the species.

The correct answer is B, chitin. The wall of a fungal cell is built of chitin, a nitrogen-containing polysaccharide that is also found in the exoskeleton of insects, and it is one of the main reasons fungi were taken out of the plant kingdom and given a kingdom of their own. A is wrong because cellulose is the wall material of plant cells and of some algae, and fungi have very little of it. C is wrong because peptidoglycan, also called murein, is the wall material of bacteria, that is of the kingdom Monera, and it is the target of antibiotics such as penicillin. D is wrong because lignin is not a wall-forming polysaccharide at all but the substance that stiffens the woody tissue of higher plants.

The correct answer is A, Mycoplasma. Mycoplasmas are the smallest living cells known, they lack a cell wall altogether, and because of that they can change shape and are not affected by antibiotics that act on the wall; they cause diseases in plants and animals and are placed in the kingdom Monera. B is wrong because Escherichia coli is a normal rod-shaped bacterium with a well-developed peptidoglycan wall and is much larger than a mycoplasma. C is wrong because yeast is a unicellular fungus with a chitin wall and a true nucleus, so it is both walled and eukaryotic. D is wrong because Chlorella is a green alga, a walled eukaryotic cell with chloroplasts, used as a food supplement and in studies of photosynthesis. Candidates should also note that a mycoplasma is often called the smallest known organism capable of independent life, which is why it is the standard answer to questions on the smallest living cell.

The correct answer is B. Mosses and liverworts grow on damp soil, rocks and tree trunks, that is on land, but they have no vascular tissue and their male gametes must swim through a film of water to reach the female gamete, so reproduction fails without water; living on land and breeding in water is exactly the position of amphibians among animals. A is wrong because bryophytes are not aquatic plants; the truly aquatic members of the plant kingdom are the algae. C is wrong because tolerance of salt and fresh water describes certain fishes and some algae, not the bryophytes. D is wrong because a seasonal change of form is common to many plants and has nothing to do with the name amphibians of the plant kingdom.

The correct answer is B, an alga and a fungus. In a lichen the algal partner, called the phycobiont, photosynthesises and supplies food, while the fungal partner, the mycobiont, gives shelter and absorbs water and minerals; lichens grow on bare rock as pioneers and die in polluted air, so they serve as indicators of air pollution. A is wrong because an association of a fungus with a bacterium is not a lichen and has no such standard name. C is wrong because a fungus living with the root of a higher plant is a mycorrhiza, another famous symbiosis but a different one. D is wrong because the nitrogen-fixing partnership of an alga with a bacterium, as in a rice field, is not a lichen either.

The correct answer is C, Arthropoda. Arthropoda is the largest phylum of the animal kingdom, holding more described species than all the others together, because it contains the insects along with the crustaceans, spiders, scorpions and centipedes; its members have a chitinous exoskeleton and jointed legs. A is wrong because Chordata, the phylum of animals with a notochord, contains the fishes, amphibians, reptiles, birds and mammals but is far smaller in number of species. B is wrong because Mollusca, with the snails, bivalves, squids and octopuses, is the second largest phylum. D is wrong because Annelida, the segmented worms such as the earthworm and the leech, is smaller still. A useful figure to carry into the hall is that more than two thirds of all described animal species are arthropods, most of them insects, which is why no other phylum can be the answer to this question.

The correct answer is B, genus. In binomial nomenclature the first word of the name is the generic name, the genus to which the organism belongs, and the second is the specific epithet; thus Panthera is the genus that also holds the lion as Panthera leo and the leopard as Panthera pardus, while tigris is the epithet of the tiger. A is wrong because the species is named by the second word, and in any case a species name is meaningful only along with its genus. C is wrong because the family of the cats is Felidae, a rank above the genus and never part of the two-word name. D is wrong because the class here is Mammalia, several ranks higher and also never written in the binomial name.

The correct answer is C, W. M. Stanley. Wendell Meredith Stanley crystallised the tobacco mosaic virus and showed that the crystals were made chiefly of protein, work that proved a virus could be handled like a chemical substance and won him a share of a Nobel Prize. A is wrong because Dmitri Ivanovsky, in 1892, only showed that the sap of a diseased tobacco plant stayed infectious after being passed through a filter that held back bacteria. B is wrong because Martinus Beijerinck repeated and extended that experiment and called the agent a living infectious fluid, without isolating it. D is wrong because Edward Jenner developed vaccination against smallpox nearly a century earlier and never worked on plant viruses. Keep the three names in order as Ivanovsky in 1892, then Beijerinck, then Stanley, because questions often ask which of them came first or who gave the agent its name.