AQA AS Level Biology Paper 2, June 2022: Question 5

10 marks · Medium difficulty · Short Answer

Analyze phylogenetic classification, relationships, and DNA base sequences of rhinoceros species across multiple structured sub-questions.

Practise this question

Question

A series of questions about rhinoceros taxonomy and phylogeny, including Table 1 showing taxonomic ranks and scientific names, Figure 4 showing nested Venn diagram taxons, Table 2 showing percentage differences in DNA base sequences of different rhinoceros species compared to a reference Indian rhinoceros, and follow-up evaluation questions.
Question text

05.1 Describe how organisms are grouped in a phylogenetic classification system.

[2 marks]

Table 1 shows some of the taxa in the phylogenetic classification of a rhinoceros

species.

Table 1

Taxon name Scientific name

Class Mammalia

Order Perissodactyla

Family Rhinocerotidae

Genus Rhinoceros

Species unicornis

Figure 4 shows the relationship between the taxa in the classification of

two rhinoceros species: Rhinoceros unicornis and Dicerorhinus sumatrensis.

Figure 4

05.2 Use information in Table 1 to give the scientific name of the taxon labelled B in

Figure 4.

*12* [1 mark]

05.3 Draw an oval on Figure 4 to show the species14 Rhinoceros sondaicus.

[1 mark]

Scientists investigated a phylogenetic relationship between individuals of five species

of rhinoceros.

The scientists:

• determined the DNA base sequence of the cyt b gene of each rhinoceros

• compared each cyt b DNA base sequence with that of one Indian rhinoceros

(called the reference rhinoceros)

• calculated the percentage difference between each cyt b DNA base sequence and

that of the reference rhinoceros.

Table 2 shows their results.

Table 2

Investigated species Percentage difference in DNA base sequences

of rhinoceros compared with the reference Indian rhinoceros

Indian 2

Javan 5

Sumatran 13

White 14

Black 14

05.4 What can you conclude about the likely phylogenetic relationships between these

species? Evaluate your conclusion.

[4 marks]

05.5 A scientist obtained a rhinoceros horn confiscated from poachers and wanted to

identify the species of rhinoceros that was killed for its horn.

He used the procedure described in Question 05.4 and calculated the difference in

cyt b DNA as 14%.

What can you conclude from this result? Explain your answer.

Suggest a change to the procedure that will more precisely identify the rhinoceros

species that provided the horn.

[2 marks]

Conclusion and explanation

Suggested change to the procedure

Mark scheme

Show the mark scheme The mark scheme providing detailed marking points for questions 05.1 through 05.5, outlining acceptable answers regarding taxonomic hierarchies, phylogenetic relationships, DNA sequence comparisons, and experimental limitations.

Question Marking Guidance Mark Comments

1. Hierarchy (of groups) with no overlaps

OR

(smaller) groups within (larger) groups with no 2

05.1 overlaps;

(2 x AO1)

2. Accept ‘common

2. (Grouped) according to evolutionary ancestry’

origins/relationships/history;

Perissodactyla; Accept incorrect

spellings provided the

word looks close to

1 Perissodactyla

05.2

(AO2) Ignore

upper/lowercase

letters

Accept ‘order’

Oval/shape drawn inside the Rhinoceros oval 1

05.3 and not overlapping the unicornus oval or the

Rhinoceros oval; (AO2)

1. (Genetic) variation/difference (exists) between

Indian rhinos;

2. Indian rhinos most/more related to Javan 2. Accept more recent

rhinos; common ancestor for

‘most/more related’

3. Indian rhinos least/less related to

White/Black rhinos;

3. Ignore ‘Sumatran’

4 max

05.4 4. Comparisons only made to one Indian rhino

(4 x AO3)

OR

4. Ignore ‘sample size

Sample size (of other rhinos) not known; too small’

5. Cannot conclude anything about relationship

between other species (with each other)

OR

(same) percentage differences may not refer

to same base sequences;

Question Marking Guidance Mark Comments 11

1. (Likely) either White or Black (rhinoceros) as

identical/same/14 percentage

OR

Not from Indian/Javan (rhinoceros) as (very)

different percentages

OR

Cannot be certain as White, Black and

Sumatran have similar percentages;

2. Use a different reference (species of) 2. Accept black/white

rhinoceros rhino, but reject

Javan/Sumatran if

OR 2 named

05.5

(2 x AO3)

Use a different gene/protein

OR

Use more than one gene

OR

Compare (DNA) base sequence (not

percentage differences)

OR

Compare amino acid sequences 2. Ignore amino acid

OR sequence of cyt b

Compare mRNA sequences;

How to answer it

Classification, Phylogeny and DNA Sequencing

What this question tests

This question evaluates your understanding of hierarchical classification systems, the interpretation of phylogenetic trees and nested Venn diagrams, and the ability to analyse DNA base sequence data to evaluate evolutionary relationships and draw valid scientific conclusions.

Question 05.1

Describe how organisms are grouped in a phylogenetic classification system. [2 marks]

✅ Correct Answer

  • Hierarchy of groups with no overlaps (smaller groups contained within larger groups).
  • Organisms grouped according to evolutionary origins, relationships, and history (or common ancestry).

💡 Key Knowledge

  • Hierarchical system: Taxa are arranged in continuous ranks (Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species) where each group is mutually exclusive.
  • Phylogeny: Reflects evolutionary descent, showing how closely related different species are based on shared common ancestors.

🧠 Exam Technique

  • This is a classic AO1 recall question. Ensure you mention both the structural arrangement (hierarchy/no overlap) and the basis of grouping (evolutionary descent).
Mark breakdown: 2 marks available (2 × AO1). 1 mark for hierarchy/no overlaps; 1 mark for evolutionary origins/relationships.

Question 05.2

Use information in Table 1 to give the scientific name of the taxon labelled B in Figure 4. [1 mark]

✅ Correct Answer

Perissodactyla

❌ Common Errors

Misspelling the taxonomic group. Examiners are usually lenient with minor spelling errors provided the word is clearly recognizable, but try to copy spelling accurately from Table 1. Ignore case sensitivity.

Mark breakdown: 1 mark available (AO2). Awarded for correctly identifying the Order from the table hierarchy.

Question 05.3

Draw an oval on Figure 4 to show the species Rhinoceros sondaicus. [1 mark]

✅ Correct Answer

An oval/shape drawn inside the larger Rhinoceros genus oval, positioned such that it does not overlap with the existing unicornis oval.

🧠 Exam Technique

In nested diagrams representing taxonomic rank, species exist within their respective genus. Draw your oval cleanly inside the genus boundary next to the other species without crossing boundaries.

Mark breakdown: 1 mark available (AO2). Validates understanding that species-level taxa sit entirely within their respective genus taxon.

Question 05.4

What can you conclude about the likely phylogenetic relationships between these species? Evaluate your conclusion. [4 marks]

✅ Correct Answer

  • Genetic variation/differences exist between Indian rhinos.
  • Indian rhinos are most closely related to Javan rhinos (lowest percentage difference of 5%).
  • Indian rhinos are least related to White and Black rhinos (highest percentage difference of 14%).
  • Evaluation points: Comparisons were only made against one Indian rhino; sample size of other rhinos is unknown; percentage differences may not refer to the exact same gene base sequences across all comparisons.

💡 Key Knowledge

Lower percentage differences in DNA base sequences indicate fewer mutations accumulated since divergence, signifying a more recent common ancestor and a closer phylogenetic relationship.

❌ Common Errors

Vague evaluation statements such as "sample size too small". Examiners specifically reward structural limitations like "comparisons only made to one Indian rhino" or "sample size of other rhinos not known".

Mark breakdown: 4 marks max (4 × AO3). Up to 3 marks for conclusions drawn from the data; 1 mark for evaluating the methodology or limitations.

Question 05.5

A scientist obtained a rhinoceros horn confiscated from poachers and wanted to identify the species... What can you conclude from this result? Explain your answer. Suggest a change to the procedure that will more precisely identify the rhinoceros species. [2 marks]

✅ Correct Answer

  • Conclusion & Explanation: The horn likely came from either a White or Black rhinoceros because they share the same percentage difference (14%). Alternatively, it is definitely not from Indian or Javan rhinos as their percentages are very different.
  • Suggested change: Use a different reference species of rhino (e.g., compare against White or Black rhino reference), use a different gene/protein, use more than one gene, compare actual DNA base sequences rather than percentage differences, or compare amino acid/mRNA sequences.

🧠 Exam Technique

When data points overlap (both White and Black rhinos show 14%), a single measurement cannot distinguish between them. Your suggested improvement must target this ambiguity—either by changing the reference standard or increasing the resolution of genetic data analysed.

Mark breakdown: 2 marks available (2 × AO3). 1 mark for conclusion/explanation; 1 mark for a valid methodological improvement.

Topics

Biology · 3.4 Genetic information, variation and relationships between organisms

Question and mark scheme from the AQA AS Level Biology examination, Paper 2, June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.