AQA A-Level Biology: Characteristics of Tumours and Cancer Development — mark scheme explained

The question

Compare the characteristics of benign and malignant tumours. [Paraphrased for study — not reproduced from any exam paper.]

Mark scheme, decoded

What each mark is really for — in plain English — and the wording trap that loses it.

• S1

  Step 1: Define benign tumours.

• S2

  Benign tumours are non-cancerous growths that do not spread to other parts of the body, grow slowly, have well-defined borders, and rarely recur after surgical removal.

• S3

  Step 2: Define malignant tumours.

• S4

  Malignant tumours are cancerous growths that can spread (metastasize) to other parts of the body, grow rapidly, have irregular borders, and often recur after surgical removal.

• S5

  Step 3: Compare the characteristics.

• S6

  Benign tumours are generally less threatening and easier to treat, while malignant tumours are more aggressive and can be life-threatening due to their ability to spread.

Model answer

Worked through, with each step tagged to the mark it earns.

1. S1

   Step 1: Define benign tumours.

2. S2

   Benign tumours are non-cancerous growths that do not spread to other parts of the body, grow slowly, have well-defined borders, and rarely recur after surgical removal.

3. S3

   Step 2: Define malignant tumours.

4. S4

   Malignant tumours are cancerous growths that can spread (metastasize) to other parts of the body, grow rapidly, have irregular borders, and often recur after surgical removal.

5. S5

   Step 3: Compare the characteristics.

6. S6

   Benign tumours are generally less threatening and easier to treat, while malignant tumours are more aggressive and can be life-threatening due to their ability to spread.

7. Final answer: Benign tumours are non-cancerous, grow slowly, have well-defined borders, and rarely recur. Malignant tumours are cancerous, can spread, grow rapidly, have irregular borders, and often recur.

Common mistakes

• Confusing benign and malignant tumours. — Always remember that benign tumours are non-cancerous, grow slowly, have well-defined borders, and rarely recur. Malignant tumours are cancerous, can spread, grow rapidly, have irregular borders, and often recur.
• Misunderstanding the roles of oncogenes and tumour suppressor genes. — Oncogenes are mutated versions of proto-oncogenes that cause uncontrolled cell proliferation. Tumour suppressor genes normally prevent cells from dividing too rapidly or uncontrollably. When these genes are mutated or inactivated, they can no longer perform their protective function.
• Failing to recognize the significance of abnormal methylation. — Hypomethylation can activate oncogenes, promoting cell proliferation. Hypermethylation can silence tumour suppressor genes, leading to a loss of their protective function. Both processes are important in cancer development.
• Not understanding the role of oestrogen in breast cancer. — Increased endogenous and exogenous oestrogen levels can promote the growth of breast cancer cells by binding to oestrogen receptors. This is associated with higher risk in women who start menstruating early or enter menopause late, and exposure to external sources of oestrogen.
• Failing to evaluate evidence effectively. — Practice analyzing data and drawing conclusions based on the evidence provided. Look for patterns and trends in the data that support your explanations.
• Not providing clear and concise explanations. — Practice writing clear and concise explanations that demonstrate a deep understanding of the topic. Use specific examples and key terms to support your answers.

Where the marks go

• Full worked solution (all marking points)4 marks

Related questions

• AQA A-Level Biology: Monomers, Polymers, and Chemical Reactions in Biological Molecules — mark scheme explained →
• AQA A-Level Biology: Triglycerides and Phospholipids: Structure and Properties — mark scheme explained →