AQA AS Level Biology Paper 1, June 2022: Question 7

9 marks · Medium difficulty · Practical Techniques & Data Analysis

Define a tumour, describe how to determine a reliable mitotic index from tissue observed with an optical microscope, and evaluate the conclusion that mitotic index > 5 is a reliable indicator of cancer seriousness using data from a graph and table.

Practise this question

Question

Question text

07.1 What is a tumour?

[2 marks]

07.2 Describe how you would determine a reliable mitotic index (MI) from tissue observed

with an optical microscope.

Do not include details of how you would prepare the tissue observed with an

optical microscope.

[3 marks]

Tumours detected under the skin can be a symptom of cancer.

Scientists investigated the link between the MI of tumours and skin cancer in dogs.

They found the MI of tumours in many dogs and recorded:

1. the tumour grade

2. the median survival time after the tumour is detected.

Tumour grade can be measured using this scale:

• grade 1 – low level cancer

• grade 2 – medium level cancer

• grade 3 – high level cancer.

The scientists used a statistical test to calculate the probability (P) of the difference

between median survival time in dogs with MI < 5 and dogs with MI > 5 being caused

by chance.

Figure 8 and Table 4 show the scientists’ results.

*15* Figure 8 Table 4

07.3 The scientists concluded that MI > 5 is a reliable indicator of how serious the cancer is

in a dog.

Use information from Figure 8 and Table 4 to evaluate this conclusion.

[4 marks]

Mark scheme

Show the mark scheme

Question Marking Guidance Mark Comments

07.1 1. Mass of cells/tissue 1. Accept idea of large

number of cells in a

2 lump/clump/cluster for

Abnormal cells/tissue; (2 x AO1) ‘mass’

2. Uncontrolled mitosis/cell division; 2. Ignore growth

07.2 1. Count cells in mitosis in field of view; 1. and 2. Max 1 if

2. Divide this by total number of cells in field of ‘field of view’ not

view; mentioned

3. Repeat many/at least 5 times 3 3. Accept ‘multiple’ for

(3 x AO1) ‘many’

OR 3. Ignore ‘several’

Select (fields of view) at random; Ignore conversion of

MI into a percentage.

07.3 Good indicator 1. Accept dogs with

MI > 5 only survive 2

1. Dogs with MI > 5 have shorter survival time;

months

1. Accept converse for

2. (P value shows) difference is significant MI < 5

1 and 2. Accept for 2

(P value shows) difference has low probability of marks, dogs with MI >

being due to chance; 5 have a significantly

shorter survival time

4 max 2. Accept Difference

(4 x AO3) not due to chance

3. Dogs with MI > 5 have grade 2 or grade 3

tumours/medium or high level cancer;

2. Ignore ‘results are

4. Dogs with grade 1 tumours all have MI < 5; significant’ or ‘results

are not due to chance’

But

5. (Some) dogs with MI < 5 could have any 5. Accept grade 2 or

tumour grade/cancer level; 3 for ‘any’

6. So serious cancers missed;

3 max if none of

7. Only know median survival time (not the points 5, 6 or 7

range); awarded

How to answer it

Tumours, Mitotic Index and Data Evaluation

What this question tests

This question assesses your understanding of cell division (mitosis and tumours), practical techniques for measuring mitotic index using an optical microscope, and your ability to critically evaluate experimental data, statistical significance (P values), and correlational findings.

Question 07.1

What is a tumour? [2 marks]

✅ Correct Answer

1. A mass of cells / abnormal cells (Accept large number of cells in a lump/clump/cluster).
2. Caused by uncontrolled mitosis / cell division.

💡 Key Knowledge

Tumours result from mutations in genes that regulate the cell cycle (proto-oncogenes and tumour suppressor genes).
Loss of cell cycle control leads to rapid, repeated, unregulated cell division forming a distinct mass (neoplasm).

❌ Common Errors

Using imprecise terminology like "abnormal growth" without mentioning cells or tissue (Examiners strictly require reference to cells or tissue for mark 1).
Failing to specify uncontrolled cell division.

Question 07.2

Determining a Reliable Mitotic Index [3 marks]

Describe how you would determine a reliable mitotic index (MI) from tissue observed with an optical microscope.

✅ Correct Answer

1. Count the cells in mitosis in the field of view.
2. Divide this by the total number of cells in the field of view.
3. Repeat for multiple fields of view (at least 5 times) / select fields of view at random.

🧠 Exam Technique

To score full marks for reliability, you must emphasize sampling technique and calculation structure. Mentioning random selection or counting multiple fields of view ensures your method yields representative data.

❌ Common Errors

Omitting the phrase "field of view" (caps a maximum of 1 mark for points 1 and 2 combined).
Including irrelevant tissue preparation steps (e.g., staining with toluidine blue, pressing down firmly with a coverslip) which were explicitly barred by the stem ("Do not include details of how you would prepare the tissue").

Question 07.3

Evaluating Data and Conclusions [4 marks max]

Use information from Figure 8 and Table 4 to evaluate the conclusion that MI > 5 is a reliable indicator of serious cancer in a dog.

✅ Correct Answer (Supporting the conclusion - max 3)

1. Dogs with MI > 5 have a shorter survival time (median survival time of only 2 months vs 70 months).
2. The P value (< 0.001) shows the difference is significant / has a very low probability of being due to chance.
3. Dogs with MI > 5 all have grade 2 or grade 3 tumours (medium/high level cancer).
4. Dogs with grade 1 tumours all have MI < 5.

✅ Correct Answer (Challenging/Limitations - max 3)

5. Some dogs with MI < 5 could have any tumour grade (grades 1, 2, or 3 represented).
6. Therefore, serious cancers can be missed if relying solely on MI < 5.
7. Data only shows median survival time, not the spread or range of survival times.

🧠 Exam Technique

This is a classic evaluate question requiring a balanced argument. To achieve full marks, you must provide points both supporting and questioning the conclusion (limitations). Notice the mark scheme caps certain points if you only look at one side of the data.

Topics

Biology · Practical skills · Required Practicals · 3.2 Cells · Experimental design · Data analysis · AS practicals (1–6)

Question and mark scheme from the AQA AS Level Biology examination, Paper 1, June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.