Which scientist crystallised the tobacco mosaic virus and showed it to be largely protein?

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.