AQA AS Level Biology Paper 2, November 2021: Question 3

8 marks · Medium difficulty · Short Answer

Answer questions on taxonomy, mutagenic agents, chromosome numbers during speciation of Spartina species, types of mutation, and sources of genetic variation.

Practise this question

Question

A multi-part exam question about taxonomy, mutations, and genetic variation. Question 03.1 asks to name the method of naming organisms using species and genus names. Question 03.2 defines a mutagenic agent. Question 03.3 features Figure 4 showing the production of Spartina townsendii from Spartina alterniflora and Spartina maritima, requiring completion of chromosome numbers in empty boxes. Figure 5 shows chromosome numbers in leaf cells of S. townsendii and S. anglica. Question 03.4 asks to name the mutation type and explain the chromosome number change from S. townsendii to S. anglica. Question 03.5 asks for another way genetic variation is increased apart from crossing over, independent segregation, and mutation.
Question text

03.1 In taxonomy, an organism is identified by referring to the species name and the genus

name.

What term is used to describe this method of naming organisms?

[1 mark]

03.2 Define the term mutagenic agent.

[1 mark]

03.3 Figure 4 shows how the species Spartina townsendii is produced.

The number of chromosomes in cells is shown in some of the boxes.

Figure 4

Complete Figure 4 by giving the correct number of chromosomes in each of the

boxes. 9

[1 mark]

A mutation in the number of chromosomes in a S. townsendii cell produced a new

species, Spartina anglica.

Figure 5 shows the number of chromosomes in leaf cells of these species.

Figure 5

03.4 Name the type of mutation that changed the number of chromosomes in S. townsendii

to produce S. anglica. Explain your answer.

[3 marks]

Name of mutation

Explanation

03.5 Genetic variation within a species is increased during meiosis by crossing over and

the independent segregation of homologous chromosomes.

Apart from mutation, explain one other way genetic variation within a species is

increased.

[2 marks]

Mark scheme

Show the mark scheme A mark scheme table showing acceptable answers for questions 03.1 to 03.5. Question 03.1 requires 'Binomial'. Question 03.2 requires 'A factor that increases the rate of mutations'. Question 03.3 accepts 60, 31, and 30 for the respective boxes. Question 03.4 awards marks for 'Non-disjunction', referencing meiosis, and chromosomes not separating or staying in one cell. Question 03.5 accepts 'Random fusion of gametes' or 'Random fertilisation' producing new allele combinations.

Question Marking Guidance Mark Comments

03.1 Binomial; 1

03.2 1

(A factor that) increases (the rate of) mutations;

03.3 Correct answer - 60, 31 and 30;

03.4 Name of mutation Ignore

homologous

1. Non-disjunction;

2. Accept

Explanation reference to

first division

2. (In) meiosis; or second

division as

3. Chromosomes not separated indicating

meiosis

OR 2. Ignore

mitosis

All chromosomes stay in one cell

3. Accept

OR 'move to

one side'

Chromosomes do not form (homologous) pairs; OR 'move to

one pole'

3.5 1. Random fusion of gametes – LOGY – 1. Accept for–JUNE2021

2 ‘gametes’,

OR

Reproductive

Random fertilisation;

cells

2. (Produces) new allele combinations

2. Ignore

genes

OR

(Produces) new maternal and paternal chromosome

combinations;

TOTAL 8

How to answer it

Taxonomy, Mutations, and Genetic Variation Study Guide

What this question tests

This exam question evaluates your understanding of biological classification systems (binomial nomenclature), mutagenic agents, chromosome behaviour during meiosis and speciation (specifically polyploidy and non-disjunction), and the cellular processes that generate genetic variation within populations (such as random fertilization).

Question 03.1

Naming Organisms in Taxonomy

✅ Correct Answer

Binomial (system)

💡 Key Knowledge

The binomial system uses two Latinized names to identify an organism: the genus (capitalized) and the species (lowercase). Universal naming prevents confusion caused by common regional names.

Awarded: [1 mark]

Question 03.2

Defining a Mutagenic Agent

✅ Correct Answer

A factor that increases the rate of mutations.

❌ Common Errors

Students often lose this mark by stating that a mutagenic agent "causes mutations". Mutations occur spontaneously anyway; examiners specifically look for the key concept that it increases the rate of mutation.

Awarded: [1 mark]

Question 03.3

Chromosome Halving in Gamete Formation

📐 Step-by-Step Breakdown

  1. Top right box (Diploid cell of Spartina maritima): Must be 60 . (Meiosis halves diploid chromosome numbers to form gametes).
  2. Left gamete box: Half of 62 is 31 .
  3. Right gamete box: Half of 60 is 30 .

🧠 Exam Technique

Read the diagram carefully. Spartina townsendii has 61 chromosomes because it is formed by the fusion of a gamete with 31 chromosomes and a gamete with 30 chromosomes ( 31 + 30 = 61 ). Working backwards from this total helps verify your chromosome math!

Awarded: [1 mark] for all three correct numbers ( 60, 31, 30 ).

Question 03.4

Chromosome Mutations and Polyploidy

✅ Correct Answer

Name of mutation: Non-disjunction

Explanation: During meiosis, chromosomes / chromatids fail to separate properly, meaning all chromosomes pass into a single cell, or homologous pairs fail to form.

💡 Key Knowledge

When gametes or cells double their chromosome number unexpectedly (such as going from 61 to 122 in Spartina anglica), it is due to non-disjunction during cell division. Examiners accept reference to the first or second division of meiosis.

Awarded: [3 marks] (1 for name, up to 2 for explanation details).

Question 03.5

Mechanisms Generating Genetic Variation

✅ Correct Answer

Random fusion of gametes OR Random fertilisation, which produces new allele / maternal and paternal chromosome combinations.

❌ Common Errors

Do not confuse genetic variation with mutation. Ensure you use precise biological terminology—saying "random mixing of genes" is too vague; examiners specifically reward reference to alleles or maternal and paternal chromosome combinations.

Awarded: [2 marks] (1 for naming the process, 1 for explaining the outcome).

Topics

Biology · 3.4 Genetic information, variation and relationships between organisms

Question and mark scheme from the AQA AS Level Biology examination, Paper 2, November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.