Classification and identification keys

1. Which statement best describes how organisms are first placed into classification groups?

Answer A: They are grouped using features that they share.

Classification begins by comparing shared features. Habitat, mass and common-name spelling can vary or mislead, whereas a set of identifiable biological features can support a meaningful grouping.

2. Which description matches the biological definition of a species used in this course?

Answer C: Organisms that can reproduce with one another to produce fertile offspring

Members of a species can reproduce with one another and produce fertile offspring. Members may vary in appearance, and unrelated species may share a habitat or food source.

3. Which name uses the correct two-word order and capitalisation?

Answer B: Homo sapiens

A binomial has two words: the genus first with an initial capital and the species part second in lower case. When typed, both words should be italicised; the capitalisation and order shown in Homo sapiens are correct.

4. What makes an identification key dichotomous?

Answer D: Each step presents two alternative statements.

A dichotomous key repeatedly offers two contrasting alternatives. One choice is selected at each step, leading either to another pair of statements or to an identification.

5. What relationship do modern classification systems aim to reflect?

Answer A: Evolutionary relationships between organisms

Classification systems aim to reflect evolutionary relationships. Organisms grouped more closely should, according to the evidence, share a more recent ancestor than organisms in more distant groups.

6. Equal lengths of a corresponding DNA region are compared. Species P and Q differ at 2 base positions, while P and R differ at 18. What is the best conclusion from this evidence?

Answer C: P and Q probably share a more recent ancestor than P and R.

P and Q have the more similar base sequences, so the evidence supports a more recent shared ancestor for P and Q. The data do not show direct descent, prove species identity or remove all relationship between P and R.

7. An organism has a mycelium made of hyphae, no chloroplasts and obtains soluble nutrients after external digestion. To which kingdom does it belong?

Answer B: Fungus

A mycelium of hyphae and nutrition by external digestion followed by absorption are characteristic fungal features. The absence of chloroplasts also separates this organism from a photosynthetic plant.

8. A unicellular organism has circular DNA free in its cytoplasm and has no nucleus. Which kingdom contains it?

Answer D: Prokaryote

Prokaryotes lack a nucleus, so their main circular DNA molecule lies free in the cytoplasm. Protoctist cells, like animal, plant and fungal cells, contain nuclei.

9. A microscopic single-celled organism has a nucleus and chloroplasts. Which kingdom is the best placement?

Answer A: Protoctist

Many protoctists are microscopic single cells with nuclei, and some are plant-like with chloroplasts. A prokaryote has no nucleus, while animals and fungi lack chloroplasts.

10. Which feature provides the clearest evidence that an unfamiliar vertebrate is a mammal?

Answer C: It has hair and females produce milk.

Hair and milk production are diagnostic mammalian features. Four limbs, air breathing and life on land are shared with members of other vertebrate groups and are therefore less specific.

11. An animal has feathers, a beak and lays hard-shelled eggs. Which vertebrate group is it in?

Answer B: Birds

Feathers are the decisive bird feature, supported here by the beak and hard-shelled eggs. Reptiles have dry scales rather than feathers, and mammals have hair or fur.

12. A vertebrate has dry scaly skin and lays eggs with leathery shells on land. How should it be classified?

Answer D: Reptile

Dry scaly skin and leathery-shelled eggs are characteristic reptile features. Amphibians have moist skin and typically lay jelly-coated eggs in water, while birds have feathers and hard-shelled eggs.

13. Which set of features is most characteristic of an amphibian?

Answer A: Moist skin and jelly-coated eggs laid in water

Amphibians characteristically have moist skin and commonly lay jelly-coated eggs in water. The other option pairs identify birds, mammals and reptiles respectively.

14. An adult vertebrate lives in water and has fins, scales and gills. Which group does it belong to?

Answer C: Fish

Fins and gills, together with scales and an aquatic habitat, identify the vertebrate as a fish. Habitat alone is not decisive, but this combination of features is.

15. An arthropod has three body regions, three pairs of legs and one pair of antennae. Which group is it in?

Answer B: Insects

Three pairs means six legs, and the combination of six legs, three body regions and one pair of antennae identifies an insect. Wings are not required because some insects are wingless.

16. An arthropod has two main body regions, four pairs of legs and no antennae. Which group is it in?

Answer D: Arachnids

Arachnids have four pairs of legs, two main body regions and no antennae. Insects have three pairs of legs, while crustaceans and myriapods have antennae and usually more legs.

17. Which combination identifies a crustacean rather than the other named arthropod groups?

Answer A: Two pairs of antennae and more than four pairs of legs

Crustaceans characteristically have two pairs of antennae and commonly have more than four pairs of legs. The other combinations describe arachnids, insects and myriapods.

18. A land arthropod has many similar body segments, many legs and one pair of antennae. How is it classified?

Answer C: Myriapod

Many similar segments with many legs and one pair of antennae are characteristic of myriapods. An insect has only three pairs of legs, and an arachnid has four pairs and no antennae.

19. A plant has roots, a stem and fronds but produces no flowers or seeds. It releases spores. Which group is it in?

Answer B: Fern

Ferns have roots, stems and fronds and reproduce by spores rather than flowers and seeds. Monocotyledons and dicotyledons are both flowering plant groups.

20. A flowering plant has one cotyledon, parallel leaf veins and flower parts in multiples of three. How is it classified?

Answer D: Monocotyledon

One cotyledon, parallel veins and flower parts commonly in multiples of three are monocotyledon features. Dicotyledons have two cotyledons and branching net-like veins.

21. Which feature combination supports identifying a flowering plant as a dicotyledon?

Answer A: Two cotyledons and branching net-like leaf veins

Dicotyledons have two cotyledons and typically show branching, net-like leaf veins. One cotyledon with parallel veins describes a monocotyledon, while the other options describe a fern and a prokaryote.

22. Which description states the required structural features of a virus?

Answer C: Genetic material surrounded by a protein coat

A virus consists of genetic material surrounded by a protein coat. It is not a cell and therefore is not described by a nucleus, cytoplasm, chloroplasts or the prokaryotic cell arrangement.

23. Use this key: 1a wings present — go to 2; 1b wings absent — species R. 2a one pair of wings — species S; 2b two pairs of wings — species T. A specimen has wings, with two pairs. What is its identification and route?

Answer B: Species T by route 1a → 2b

Wings are present, so the specimen follows 1a to step 2. It has two pairs of wings, so it then follows 2b and is identified as species T.

24. An unfamiliar organism is multicellular, has cellulose cell walls and chloroplasts, and makes organic nutrients by photosynthesis. What is the best classification from these features?

Answer D: Plant, because the combined features match the plant kingdom

The combined features—multicellularity, cellulose cell walls, chloroplasts and photosynthesis—match the plant kingdom. One shared feature alone would be weaker evidence, but the full set is diagnostic here.