Question

(a) How do some viruses cause cancer in humans ?

(b) How do benign tumours turn malignant ? How do malignant tumours harm the human body ?

Hint:

(a) Viral oncogenes or activated proto-oncogenes; (b) mutation, loss of contact inhibition and metastasis, with nutrient competition and organ damage.

Answer 1

Step 1: Understanding the Concept:
Cancer is uncontrolled cell division. Normal cells show contact inhibition, which stops growth when cells touch. Cancer cells lose this control.

Step 2: Part (a) - How viruses cause cancer:
Some viruses are called oncogenic viruses. They carry genes called viral oncogenes.
Normal cells also hold genes called proto-oncogenes (cellular oncogenes). A virus can activate these genes or insert its own oncogene into the host genome.
The cell then divides without control and turns into a cancer cell. Examples are human papilloma virus and hepatitis B virus.

Step 3: Part (b) - How a benign tumour turns malignant:
A benign tumour stays at its site and rarely spreads.
If its cells get new mutations, they lose contact inhibition, divide faster and invade the nearby tissues. They then enter blood or lymph and spread to other organs. This spread is called metastasis.

Step 4: How malignant tumours harm the body:
Malignant cells grow fast and take up nutrients from normal cells, so those cells starve.
Spread of the tumour damages tissues and organs and disturbs their function.

Final Answer:
Oncogenic viruses bring or activate oncogenes. A benign tumour turns malignant by mutation, invasion and metastasis. A malignant tumour harms the body by competing for nutrients and damaging organs.