Classification of living organisms – GCSE Biology exam questions with mark scheme

1Grade 1–3Foundation4 marks

Carl Linnaeus developed a system for classifying living organisms into groups.

(a) The list shows the groups in order, from the largest group to the smallest group. Three of the groups are missing.

kingdom → ____________ → class → ____________ → family → ____________ → species

Complete the list. [3]

(b) What did Linnaeus use to sort organisms into groups?

Tick (✓) one box.

☐ The chemicals in their cells
☐ Their DNA base sequences
☐ Their fossil records
☐ Their structure and characteristics

[1]

(a) phylum (second box, between kingdom and class)
allow phyla; allow phonetic spelling, e.g. 'filum'(1)
(a) order (fourth box, between class and family)(1)
(a) genus (sixth box, between family and species)
allow genera; each word must be in the correct position to score(1)
(b) Their structure and characteristics
if more than one box ticked, 0 marks(1)
Answer: (a) phylum, order, genus (b) Their structure and characteristics
Examiner tip: Use a memory sentence such as 'King Prawns Curl Over Flaming Gas Stoves' – a word in the wrong gap earns nothing even if it is spelt perfectly.

2Grade 1–3Foundation4 marks

The table shows the common names and binomial names of five types of tree found in British woodland.

Common name	Binomial name
English oak	Quercus robur
Sessile oak	Quercus petraea
Turkey oak	Quercus cerris
Beech	Fagus sylvatica
Sweet chestnut	Castanea sativa

(a) Give the genus of the beech tree. [1]

(b) How many different genera are shown in the table? (Genera is the plural of genus.) [1]

(c) Explain how the binomial names show that the English oak is more closely related to the Turkey oak than to the beech. [2]

(a) Fagus
ignore lack of capital / italics; do not accept sylvatica or Fagus sylvatica(1)
(b) 3 / three(1)
(c) English oak and Turkey oak are in the same genus / both have Quercus as the first part of their name
allow 'same first name'(1)
(c) the beech is in a different genus (Fagus)
allow organisms in the same genus share more features / have a more recent common ancestor(1)
Answer: (a) Fagus (b) 3 (c) English and Turkey oak are both in genus Quercus; beech is in a different genus, Fagus.
Examiner tip: The first word of a binomial name is the genus; the second word is the species – students often give the whole name when only the genus is asked for.

3Grade 4–55 marks

Carl Woese suggested that all living organisms should be divided into three domains.

The table describes four organisms, P, Q, R and S.

Organism	Description
P	Single-celled; no nucleus; lives in hot springs at 90 °C; its genes and cell membrane chemicals are very different from those of bacteria
Q	Single-celled; no nucleus; lives in the human large intestine
R	Single-celled; has a nucleus and chloroplasts; lives in ponds
S	Made of thread-like hyphae; cells have a nucleus; grows on rotting wood

(a) Name the domain that each organism belongs to. [3]

(b) Before Woese's system, organisms P and Q were classified in the same group.

Suggest why. [1]

(a) P – Archaea
allow archaebacteria(1)
(a) Q – Bacteria
allow true bacteria / eubacteria(1)
(a) R and S – Eukaryota (both needed)
allow eukaryotes(1)
(b) both are single-celled / prokaryotic / have no nucleus
allow they look similar (under a microscope); ignore 'both are bacteria'(1)
(c) (evidence from) chemical analysis
allow analysis of genes / DNA / RNA / cell membrane chemicals; ignore 'microscopes'(1)
Answer: (a) P Archaea, Q Bacteria, R and S Eukaryota (b) both single-celled with no nucleus (c) chemical analysis
Examiner tip: Archaea are not just 'bacteria in extreme places' – the key point is that chemical analysis showed they are fundamentally different from true bacteria.

4Grade 4–55 marks

The diagram shows an evolutionary tree for six species, A to F.

(a) Which species is most closely related to species A? [1]

(b) Which species in the tree is extinct? Give a reason for your answer. [2]

(d) Scientists used data from living organisms to place most species on the tree.

What type of data would they have used to place the extinct species? [1]

(a) B(1)
(b) D(1)
(b) its line / branch does not reach the present day
allow its branch stops / ends before the others; allow it has no living members (present day)(1)
(c) a common ancestor (of species C, D, E and F)
allow the most recent common ancestor of C, D, E and F; do not accept 'common ancestor of all six species'(1)
(d) fossil data / fossils / fossil record(1)
Answer: (a) B (b) D – its branch ends before the present day (c) the common ancestor of C, D, E and F (d) fossils
Examiner tip: A branch that stops short of the present-day line means extinction; a branching point is always a common ancestor, not a living species.

5Grade 6–7Higher6 marks

Scientists compared the base sequence of the same section of DNA in humans and in four other primates.

The table shows the percentage of bases that are different from the human sequence.

Primate	Percentage of bases different from human DNA (%)
Chimpanzee	1.2
Gorilla	1.6
Orangutan	3.1
Rhesus macaque	6.4

(a) The section of DNA is 5000 bases long.

Calculate the number of bases that are different between the human and the orangutan sequence. [2]

(b) A student said: 'These data show that humans evolved from chimpanzees.'

Explain why the student is wrong. [2]

Suggest two reasons why comparing DNA gives a more reliable classification. [2]

(a) $\dfrac{3.1}{100} \times 5000$(1)
(a) 155
correct answer with no working scores 2 marks(1)
(b) the data show humans and chimpanzees are (the most) closely related / have the most similar DNA(1)
(b) because they share a (recent) common ancestor
allow both species evolved from the same ancestor / chimpanzees have also been evolving; ignore 'humans did not evolve from apes' unqualified(1)
(c) any two from: organisms that are not closely related can have similar physical features (allow similar features can evolve separately because organisms live in similar environments); closely related organisms can look very different (e.g. because they live in different environments)(1)
(c) …DNA differences can be measured / counted / give a numerical comparison, whereas physical features are judged subjectively; DNA is inherited, so the number of DNA differences shows directly how closely related organisms are (allow more DNA differences means a longer time since the common ancestor)(1)
Answer: (a) 155 bases (b) the data only show that humans and chimpanzees are the most closely related – they share a recent common ancestor (c) e.g. unrelated organisms can look similar; DNA differences can be counted objectively.
Examiner tip: Never write that humans evolved from chimpanzees or any living ape – close relatives share a common ancestor.

6Grade 6–7Higher4 marks

Linnaeus classified mushrooms and other fungi in the plant kingdom.

Today, fungi are classified in their own kingdom.

(a) Suggest one reason why Linnaeus classified fungi as plants. [1]

(b) Explain why fungi are no longer classified as plants. [3]

(a) any one from: fungi do not move (around) / grow in one place; fungi have cell walls; fungi grow out of the soil / on wood like plants
ignore 'they look like plants' unqualified(1)
(b) fungi do not contain chloroplasts / chlorophyll
ignore 'fungi are not green' unless linked to having no chlorophyll(1)
(b) so fungi cannot photosynthesise / must get their food from other (dead or living) organisms
allow fungi feed by digesting material outside their cells and absorbing it(1)
(b) any one from: fungal cell walls are not made of cellulose (allow made of chitin); new evidence from better microscopes / chemical (DNA) analysis showed these differences; DNA shows fungi are more closely related to animals than to plants(1)
Answer: (a) e.g. fungi do not move and have cell walls (b) no chloroplasts, so cannot photosynthesise; cell walls not made of cellulose / DNA evidence shows they are not closely related to plants.
Examiner tip: 'Fungi are not green' scores nothing on its own – say they have no chlorophyll / chloroplasts, so they cannot photosynthesise.

7Grade 4–54 marks

The bird called a 'robin' in Britain has the binomial name Erithacus rubecula.

The bird called a 'robin' in North America has the binomial name Turdus migratorius.

(a) Explain why scientists use binomial names instead of common names. [2]

(b) The British blackbird has the binomial name Turdus merula.

What does this tell you about the British blackbird and the North American robin? [1]

Suggest why classifying organisms only by their appearance can be misleading. [1]

(a) common names can differ between countries / languages
allow the same common name can be used for different species (e.g. robin)(1)
(a) each species has only one binomial name / binomial names are used by scientists everywhere, so there is no confusion (about which organism is meant)
allow so scientists can communicate (internationally) about the same species(1)
(b) they are in the same genus (Turdus)
allow they are closely related; do not accept 'same species'(1)
(c) organisms that look similar may not be closely related
allow two different species can share a feature (by chance / because of a similar environment)(1)
Answer: (a) Common names vary and can refer to different species; a binomial name is unique to one species and understood worldwide. (b) Same genus, Turdus – closely related. (c) Similar-looking organisms may not be closely related.
Examiner tip: For 'explain', state the problem with common names AND how a binomial name solves it – one side alone scores one mark.

8Grade 8–9Higher6 marks

The way scientists classify living organisms has changed since the 1700s, when Carl Linnaeus developed his system.

Describe the Linnaean system and the three-domain system.

In your answer, explain why the classification system has changed. [6]

Linnaeus classified organisms using their structure and (observable) characteristics(1)
hierarchy of groups: kingdom, phylum, class, order, family, genus, species(1)
organisms given a binomial name made of genus and species(1)
microscopes improved, so scientists could see internal / cell structures (e.g. presence of a nucleus)(1)
understanding of biochemical processes improved(1)
chemical analysis (e.g. of genes / DNA / RNA) gave new evidence about how closely organisms are related(1)
Carl Woese proposed the three-domain system(1)
three domains: Archaea, Bacteria and Eukaryota(1)
archaea were previously thought to be bacteria but chemical analysis showed they are very different(1)
archaea often live in extreme environments (e.g. hot springs, salty lakes)(1)
Eukaryota includes protists, fungi, plants and animals(1)
domains are a level above kingdoms(1)
evolutionary trees now show how organisms are thought to be related, using classification data and fossil data(1)
some organisms have been reclassified as new evidence was found(1)

Level	Marks	What it looks like
Level 3	5–6	Clear, logically linked description of both systems with accurate detail (e.g. the ranks and the three named domains). Changes are explained by linking them to specific new evidence, such as better microscopes and chemical analysis showing archaea differ from bacteria.
Level 2	3–4	Relevant description of both systems, or detailed description of one, with at least one reason for change given. Some links between evidence and change but the explanation may be incomplete or lack detail.
Level 1	1–2	Some simple, relevant statements about one or both systems (e.g. names some ranks or domains). Little or no explanation of why classification changed.
No relevant content	0	Nothing worthy of credit.

Answer: Linnaeus: hierarchy kingdom→species based on observable structure, binomial names. Improved microscopes and chemical (genetic) analysis revealed hidden differences, so Woese proposed three domains – Archaea, Bacteria, Eukaryota – with archaea separated from bacteria.
Examiner tip: Top-level answers link each change to the evidence that caused it – a list of the ranks and domains with no 'because' stays in Level 1–2.

9Grade 6–7Higher5 marks

The table shows how four mammals are classified.

Group	Grey wolf	Red fox	Brown bear	House mouse
Kingdom	Animalia	Animalia	Animalia	Animalia
Phylum	Chordata	Chordata	Chordata	Chordata
Class	Mammalia	Mammalia	Mammalia	Mammalia
Order	Carnivora	Carnivora	Carnivora	Rodentia
Family	Canidae	Canidae	Ursidae	Muridae
Genus	Canis	Vulpes	Ursus	Mus
Species	lupus	vulpes	arctos	musculus

(a) Give the binomial name of the brown bear. [1]

(b) Name the smallest group that both the red fox and the brown bear belong to. [1]

Use information from the table to explain your answer. [2]

(d) The coyote has the binomial name Canis latrans.

Which family does the coyote belong to? Give a reason for your answer. [1]

(a) Ursus arctos
ignore lack of italics / capitals; both words needed(1)
(b) (the order) Carnivora
allow order; do not accept Canidae or Mammalia(1)
(c) house mouse(1)
(c) it is in a different order (Rodentia) / shares only kingdom, phylum and class with the wolf
allow it shares the fewest groups with the wolf; the other two are both in Carnivora(1)
(d) Canidae and it is in the same genus as the grey wolf (Canis), so it must be in the same family
both parts needed(1)
Answer: (a) Ursus arctos (b) Carnivora (c) house mouse – different order, shares only kingdom, phylum and class (d) Canidae, because it is in genus Canis like the wolf.
Examiner tip: 'Smallest group' means the lowest shared rank – read down the table and stop at the last row where both columns still match.

10Grade 6–7Higher7 marks

The diagram shows an evolutionary tree for six species, P, Q, R, S, T and U.

The time scale shows millions of years ago.

(a) How many millions of years ago did the most recent common ancestor of species S and T live? [1]

(b) Calculate how much longer species R and S have been evolving separately than species P and Q. [2]

For how many million years did species U exist? [1]

(d) A scientist states that species P is more closely related to species Q than to species S.

Use the tree to explain why. [2]

(e) Suggest why scientists are less certain about the position of species U on the tree than about the position of species S. [1]

(a) 5 (million years ago)(1)
(b) 30 (million years ago) and 15 (million years ago) read correctly from the tree(1)
(b) 15 million years
correct answer with no working scores 2 marks; allow ecf from their readings(1)
(c) 10 (million years)
allow 25 − 15(1)
(d) P and Q share a more recent common ancestor (15 million years ago)(1)
(d) the common ancestor of P and S lived longer ago / 45 million years ago
allow P and Q have been evolving separately for less time than P and S(1)
(e) only fossil data is available for U / DNA cannot be compared for U (but can for S)
allow the fossil record is incomplete / fossils may be damaged or only parts of the organism are preserved(1)
Answer: (a) 5 million years ago (b) 30 − 15 = 15 million years (c) 25 − 15 = 10 million years (d) P and Q share a common ancestor 15 million years ago; P and S's common ancestor was 45 million years ago (e) U is known only from incomplete fossils – no DNA to compare.
Examiner tip: Read branching points against the time axis carefully: the further back (left) two lines join, the less closely related the species are.

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