AQA AS Level Biology Paper 2, June 2019: Question 7

9 marks · Medium difficulty · Practical Techniques & Data Analysis

Evaluate whether an investigation on fish populations in tanks with different artificial selection regimes supports the use of mesh nets in sea fishing.

Practise this question

Question

An investigation showing changes in the mean mass of removed fish from three tanks (Tank A putting back largest, Tank B random, Tank C putting back smallest) over 4 years, followed by four sub-questions involving types of selection, control purpose, ratio calculations, and an evaluation.
Question text

07 Scientists investigated changes in the mass of fish from three populations of the same

species. The fish they used had a life cycle of one year.

The scientists set up three fish tanks, each containing a separate population. Each

year the scientists removed all the fish from each tank and determined the mean mass

of the fish removed. They then put back 10% of each population in the following way.

Tank A – put back only the largest fish.

Tank B – put back fish at random.

Tank C – put back only the smallest fish.

During each year the fish were left to grow and reproduce.

The scientists’ results are shown in Figure 8.

Figure 8

07.1 What type of selection were the scientists modelling in this investigation by putting

back only the largest or only the smallest fish in Tank A and Tank C? Give a reason

why.

[2 marks]

Type of selection

Reason

07.2 Explain the purpose of Tank B (on page 21).

[2 marks]

07.3 Calculate the ratio of the mean mass of fish removed from Tank A (on page 21) to the

mean mass of fish removed from Tank C (on page 21) at 1 year and at 4 years.

How much greater is the ratio at 4 years compared with the ratio at 1 year?

[2 marks]

Ratio at 1 year =

Ratio at 4 years =

How much greater at 4 years =23

07.4 Sea fishing is regulated in law. The size of the mesh used in some fishing nets is

controlled so that small fish can escape but large fish are captured. This regulation is

designed to protect populations of wild fish.

Using all the information in this question, evaluate whether the scientists’ investigation

supports the use of these types of nets in sea fishing.

[3 marks]

[Extra space]

Mark scheme

Show the mark scheme Mark scheme providing answers for four parts: identifying directional selection and reason for 0.7.1, control baseline purpose for 0.7.2, ratio calculations for 0.7.3, and evaluation points supporting or not supporting sea fishing mesh nets for 0.7.4.

Question Marking Guidance Mark Comments

Type of selection 2 2. Ignore

1. Directional; references to

adaptations/

07.1 Reason: natural selection

2. One extreme selected/removed/favoured/

2. Accept large

chosen fish/small fish for

OR ‘extreme’

One extreme allowed to breed;

1. As a baseline/control; 2 2. Ignore reference

to type of selection

2. To show effect of no selection

2. Accept not

OR

removing/not

To show what happens in a normal

catching/not fishing

population/naturally

for ‘selection’

OR

To show effect of/ compare with tank A/tank 2. Accept genetic

C; drift for ‘no

07.2 selection’

2. Accept no

fishing/no

selection/no caught

fish for ‘normal

population’

2. Accept to

compare with other

results

Correct answer for 2 marks 2 5

Accept 3 for 2

(How much greater) 1.6 to 1.7;; marks

Accept for 1 mark,

07.3

1.2 : 1 and 2 : 1

Accept for 1 mark,

4.1 : 3.4 and 4.8 : 2.4

3 max

Not supported because 2 max for “But”

1. (Sea) fishing reduces (mean) mass of fish;

2. Because large fish removed

OR

Because small fish escape/put back

OR

Because fishing (model) like Tank C;

But

3. Information from (only) one species

OR

Sea fishing catches other/different (types of)

species;

07.4 4. No statistical test;

5. Size of tank may affect fish growth;

6. Fish in tanks are all same age/sea fish not all

the same age;

7. No measure of number of fish (removed)/

only measured mean mass

OR

No measure of (total) yield of fish

OR

No measure of reproductive success of fish;

8. Removal of 90% of population is unlikely to

be replicated in the sea fishing;

9.Sea fish do not have life cycle of one year

OR

Sea fish do not reproduce all at the same

time;

TOTAL 9

How to answer it

Selection Pressures and Sea Fishing Investigation

What this question tests

This exam question evaluates your understanding of evolutionary selection pressures (specifically directional selection), the design and necessity of control groups in biological investigations, multi-step ratio calculations using graphical data, and the ability to critically evaluate whether a laboratory model accurately reflects complex real-world ecological practices like commercial sea fishing.

Question 07.1

Types of Selection and Breeding Success

✅ Correct Answer

  • Type of selection: Directional (selection).
  • Reason: One extreme is selected/removed/favoured/chosen, OR one extreme is allowed to breed.

💡 Key Knowledge

  • Directional selection occurs when an environmental pressure favours one phenotype at one extreme of a population distribution.
  • In Tank A, only large fish breed (removing small); in Tank C, only small fish breed (removing large). Both represent directional selection.

🧠 Exam Technique

Be precise with evolutionary terminology. Avoid using vague terms like "survival of the fittest" unless defined. Explicitly state that an extreme phenotype is being favoured or removed.

❌ Common Errors

  • Stating "natural selection" instead of specifying directional selection.
  • Confusing directional selection with stabilizing or disruptive selection.
  • Referring to "adaptations" rather than phenotypic characteristics (mass).
Maximum Marks: 2
Question 07.2

The Purpose of Control Tanks

✅ Correct Answer

Tank B acts as a control / baseline to show the effect of no artificial selection, or to demonstrate what happens in a normal/natural population, allowing comparison with Tanks A and C.

💡 Key Knowledge

In experimental biology, controls isolate the independent variable. Tank B removes random fish (returning 10% randomly), meaning no directional selection pressure is applied based on mass, establishing a natural baseline.

🧠 Exam Technique

When asked for the purpose of a control, always use a two-part structure: state what the control is (baseline/normal conditions) and why it is needed (to compare against experimental tanks and show the effect of the variable).

❌ Common Errors

  • Stating the control is "to make the experiment fair" without explaining baseline comparison.
  • Failing to link Tank B back to how it contrasts with Tanks A and C.
Maximum Marks: 2
Question 07.3

Data Analysis and Ratio Calculations

📐 Step-by-Step Calculation

  1. Read values from Figure 8 at Year 1:
    Tank A mean mass = 3.8 g | Tank C mean mass = 3.4 g
    Ratio at 1 year = 3.8 : 3.4 (simplifies to 1.12 : 1 or fraction 1.1 : 1 to 1.2 : 1 ).
  2. Read values from Figure 8 at Year 4:
    Tank A mean mass = 4.8 g | Tank C mean mass = 2.4 g
    Ratio at 4 years = 4.8 : 2.4 = 2 : 1 .
  3. Calculate how much greater the ratio is at 4 years:
    Method A (Subtraction): 2 - 1.2 = 0.8 (Accept range 0.8 to 0.9 )
    Method B (Division/Proportion): Ratio expressed as fractions (5/3 or 1.6 to 1.7 times greater).

✅ Final Answer Summary

  • Ratio at 1 year: 1.1 : 1 to 1.2 : 1
  • Ratio at 4 years: 2 : 1
  • How much greater: 1.6 to 1.7 (or 5/3 )

❌ Common Calculation Traps

  • Reading the wrong grid lines off the graph axes for Year 1 or Year 4.
  • Inverting the ratio (placing Tank C over Tank A instead of A to C).
  • Failing to calculate the final comparison ("how much greater") and leaving only the two individual ratios.
Maximum Marks: 2
Question 07.4

Evaluating Scientific Investigations

✅ Correct Answer (Balanced Evaluation)

  • Not supported because: Sea fishing reduces the mean mass of fish and resembles Tank C (catching large fish/allowing small fish to escape), which the graph shows drastically drives down mean fish mass over time.
  • But limitations apply: The investigation only used one species, lacked statistical tests, used fixed tank sizes, tested fish of identical age/life cycle of one year, and removed 90% of the population annually—conditions unrealistic for wild sea environments.

💡 Key Knowledge

An "evaluate" question requires a structured argument looking at evidence for and against a conclusion. Top marks require citing specific trends from Figure 8 alongside valid biological limitations of laboratory models.

🧠 Exam Technique

Always structure evaluation questions explicitly: state your overall stance ("Not supported because..."), use data from the stimulus/graphs as evidence, and then balance your answer with limitations ("However..."). Note that the mark scheme caps answers at 2 marks if you only argue one side ("But").

❌ Common Errors

  • Only writing points supporting or only writing limitations (limiting your score to a maximum of 2 marks).
  • Vague criticisms like "it's not accurate" without specifying variables such as tank size, species diversity, or reproductive synchrony.
Maximum Marks: 3 (Max 2 for one-sided arguments)

Topics

Biology · Practical skills · 3.4 Genetic information, variation and relationships between organisms · Experimental design · Data analysis

Question and mark scheme from the AQA AS Level Biology examination, Paper 2, June 2019. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.