OCR A Level Biology A: Classification and taxonomy (H420) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover section 4.2.2(a) to (d) of the OCR A Level Biology A (H420) specification, Version 4.1 (April 2026), for first assessment in 2025. Cladistics is not required.

Read the study guide for explanations and the revision notes for quick recall. The free diagnostics cover the rest of the course.

Questions

1. The taxonomic hierarchy runs: domain, kingdom, ____, class, ____, family, ____, species. Write the three missing ranks in order. [3]

2. Pedunculate oak is Quercus robur and sessile oak is Quercus petraea.

(a) State two conventions for writing the binomial name of pedunculate oak correctly in a printed report. [2] (b) State what the two names tell you about the relationship between the two oaks. [1]

3. In Britain, “buzzard” refers to Buteo buteo, but in North America the word is often used for vultures. Explain why scientists prefer the name Buteo buteo. [3]

4. The table shows part of the classification of four insects. All four are in the domain Eukarya, kingdom Animalia, phylum Arthropoda and class Insecta.

	Honey bee	Bumblebee	Common wasp	Seven-spot ladybird
Order	Hymenoptera	Hymenoptera	Hymenoptera	Coleoptera
Family	Apidae	Apidae	Vespidae	Coccinellidae
Genus	Apis	Bombus	Vespula	Coccinella

(a) Name the lowest taxon shared by the honey bee and the bumblebee. [1] (b) Name the lowest taxon shared by the honey bee and the seven-spot ladybird. [1] (c) The common wasp shares a lower taxon with the honey bee than the ladybird does. State what this suggests about the common ancestry of the three insects. [2]

5. Two organisms were collected and examined.

• Organism J is multicellular. It consists of branching threads (hyphae) with chitin in the walls. It grows on rotting wood, secretes enzymes onto it and absorbs the products. It has no chloroplasts.
• Organism K consists of single cells about 2 µm across. It has no nucleus, its DNA is circular and lies free in the cytoplasm, and it has a peptidoglycan wall.

(a) Name the kingdom of organism J and give two features from the description that support your answer. [3] (b) Name the kingdom of organism K and give one feature that supports your answer. [2]

6. Compare the kingdoms Animalia and Fungi. Give two similarities and two differences. [4]

7. Explain how molecular evidence led to a new classification system with three domains. [4]

8. The table describes three organisms.

	Organism X	Organism Y	Organism Z
Nucleus	Absent	Absent	Present
Cell wall	No peptidoglycan	Peptidoglycan	Cellulose
Membrane lipids	Ether-linked, branched	Ester-linked	Ester-linked
DNA and histones	Circular DNA with histones	Circular DNA, no histones	Linear DNA with histones

(a) Name the domain of each organism. [3] (b) State two features that show organism X is not in the same domain as organism Y. [2]

9. Compare the five-kingdom and three-domain classification systems. [4]

10. A protein of 180 amino acids was sequenced in four species, A, B, C and D. The table shows the number of amino acid differences between each pair.

Pair	Differences
A and B	9
A and C	27
A and D	54
B and C	26
B and D	55
C and D	52

(a) Calculate the percentage of amino acids that are identical in A and C. [2] (b) State which two species are most closely related and explain your choice. [2] (c) Describe the phylogenetic tree that the data support. [3]

11. (a) Define phylogeny. [1] (b) Explain how the taxonomic hierarchy reflects phylogeny. [2] (c) Suggest why comparing DNA sequences can give a more reliable picture of relationships than comparing appearance. [2]

12. A 400-base section of a gene was compared in four species of a plant group, W, X, Y and Z. The numbers of base differences are shown.

Pair	Differences
W and X	8
Y and Z	12
W and Y	60
W and Z	62
X and Y	58
X and Z	64

An older classification, based on observable features, placed X and Y in one genus and W and Z in another.

(a) Calculate the percentage of bases that differ between X and Y. [1] (b) Describe the arrangement of the four species on a phylogenetic tree based on these data. [3] (c) Evaluate whether the data support the older classification. [4]

Answers

1. Phylum [1], order [1], genus [1]. [3] Examiner insight: Ranks must be in the correct positions; giving all three names in the wrong order does not show you know the hierarchy.

2. (a) Genus name starts with a capital letter and species name with a lower-case letter, giving Quercus robur [1]. The name is in italics (or underlined if handwritten) [1]. [2] (b) They share the same genus, Quercus, so they are relatively closely related (both are oaks) [1]. [1] Examiner insight: Part (a) asks for two separate conventions, so give capitalisation and italics or underlining as two distinct points rather than merging them.

3. The same common name can refer to different organisms in different regions or countries [1]. One species may have several common names, in different places or languages [1]. The binomial name is universal: each species has one name used by scientists worldwide, which avoids confusion [1]. [3] Examiner insight: An answer that says only “Latin is the scientific language” does not give a reason; the marks come from saying the name is the same everywhere and refers to one species.

4. (a) Family Apidae [1]. [1] (b) Class Insecta [1]. [1] (c) The wasp and honey bee share the same order, Hymenoptera, while the ladybird is in a different order [1]. This suggests that the wasp and honey bee share a more recent common ancestor than either does with the ladybird [1]. [2] Examiner insight: Quoting the lowest taxon shared is not enough in an explain or suggest question; you need to link it to how recently the ancestor lived.

5. (a) Fungi [1]. Any two from: chitin in the walls; hyphae; absorbs nutrients after secreting enzymes (extracellular digestion); no chloroplasts [2]. [3] (b) Prokaryotae [1]. Any one from: no nucleus; DNA circular and free in cytoplasm; peptidoglycan wall; very small cells [1]. [2] Examiner insight: The features must come from the description of the organism; a general statement about the kingdom that the description does not support is weaker evidence.

6. Similarities, any two: both are eukaryotic with a nucleus; both are heterotrophic; neither has chloroplasts; both store glycogen [2]. Differences, any two: fungi have cell walls of chitin, animals have no cell wall; fungi absorb nutrients after external digestion, animals ingest food and digest it internally; fungi have hyphae or are single cells, animals are multicellular with tissues and organs [2]. [4] Examiner insight: A comparison needs both organisms covered for each difference; writing only “fungi have chitin walls” without saying what animals have gains less.

7. Scientists compared the base sequences of ribosomal RNA (and other molecular evidence) from different organisms [1]. The prokaryotes fell into two distinct groups, Bacteria and Archaea [1], that differed from each other as much as each does from eukaryotes [1]. This showed that the old kingdom Prokaryotae did not reflect relationships, so a rank above kingdom was introduced with three domains: Bacteria, Archaea and Eukarya [1]. [4] Examiner insight: The question asks how the evidence led to the change, so state what was compared, what was found and what classification followed, not just the names of the domains.

8. (a) X: Archaea [1]. Y: Bacteria [1]. Z: Eukarya [1]. [3] (b) X has no peptidoglycan whereas Y has peptidoglycan [1]. X has histones with its DNA whereas Y has no histones; or X has ether-linked branched membrane lipids whereas Y has ester-linked lipids [1]. [2] Examiner insight: Absence of a nucleus does not separate X from Y, because both lack one; choose a feature from the table where the two organisms differ.

9. Any four from: domain is a higher rank than kingdom [1]; the kingdom system puts all prokaryotes in one kingdom, Prokaryotae, whereas the domain system splits them into Bacteria and Archaea [1]; the four eukaryotic kingdoms are all placed within the single domain Eukarya [1]; the kingdoms were based mainly on observable features, while the domains were based on molecular evidence such as rRNA sequences [1]. [4] Examiner insight: Comparison answers should point to a difference in each system, not describe the two separately, and the domains do not replace the eukaryotic kingdoms.

10. (a) 180 − 27 = 153 identical [1]; 153 ÷ 180 × 100 = 85.0 % [1]. [2] (b) A and B [1], because they have the fewest differences (9), so they share the most recent common ancestor [1]. [2] (c) A and B join at the most recent branch point [1]. C joins next, branching from the line leading to A and B [1]. D branches off first and is the least closely related to the others (it differs from all three by about 30 %) [1]. [3] Examiner insight: Show the subtraction before the percentage, and in part (c) describe the order of branching rather than only naming the closest pair.

11. (a) Phylogeny is the evolutionary history of a group of organisms, showing how species are related by descent from common ancestors [1]. [1] (b) Groups are nested because organisms are related by branching descent from common ancestors [1]. Organisms in the same low-rank taxon, such as a genus, share a more recent common ancestor than organisms that are only in the same higher-rank taxon [1]. [2] (c) Sequences can be compared objectively and counted [1]. Appearance can be similar in distantly related species because they live in similar ways, whereas sequence differences build up over time since the common ancestor [1]. [2] Examiner insight: “More accurate” needs a reason; say what is wrong with appearance as evidence, not just that DNA is better.

12. (a) 58 ÷ 400 × 100 = 14.5 % [1]. [1] (b) W and X are the closest pair and join at one branch point [1]. Y and Z form a second pair at another branch point [1]. The two pairs join at an older common ancestor [1]. [3] (c) X and Y are 14.5 % different, much more than X and W (2.0 %) or Y and Z (3.0 %) [1]. So the data do not support placing X and Y together in a genus [1]. X is more closely related to W, and Y to Z, so the older classification may not reflect phylogeny and may need revising [1]. This is only one gene section, so more genes or other evidence should be compared before changing it, and the similar appearance of X and Y may not come from recent common ancestry [1]. [4] Examiner insight: An evaluation gains credit for using figures from the table and for a limitation of the evidence, not only for a conclusion.

Where marks are usually lost

• Mixing up the order of the ranks, or leaving out domain.
• Giving both genus and species a capital letter, or forgetting to italicise or underline.
• Giving “Latin” as the advantage of the binomial system instead of “universal”.
• Calling Archaea bacteria, or saying domains replace the eukaryotic kingdoms.
• Forgetting to subtract the differences from the total when asked for percentage identity.
• Naming the closest pair without saying that fewer differences mean a more recent common ancestor.

Next steps

• Revise with the revision notes and the study guide.
• See the OCR A Level Biology hub and the printable checklist.
• Try all free 10-minute diagnostics to find other gaps.
• Book a free trial class for help from a teacher.

Official syllabus

OCR, A Level Biology A (H420) specification, Version 4.1 (April 2026), first assessment 2025, section 4.2.2(a) to (d).