AQA AS Level Biology Paper 2, November 2020: Question 7

✅ Correct Answer Structure

• Point 1: Less or no antibody is produced.
• Point 2: Because HIV destroys helper T cells.
• Point 3: Therefore, few or no B cells are activated/stimulated (or few/no B cells undergo mitosis/differentiate into plasma cells).

💡 Key Knowledge

Helper T cells play a crucial coordinating role in the adaptive immune response. When antigen-presenting cells present antigens, helper T cells must stimulate B cells via cytokines and direct cell contact to trigger clonal expansion and differentiation into antibody-producing plasma cells.

🧠 Exam Technique

Ensure you show the logical chain of events: Virus destroys T cells → Lack of T cell stimulation → B cells fail to activate → Fewer/no antibodies produced. Missing out the intermediary step (B cell activation) often costs students marks.

❌ Common Errors

Students frequently lose marks by stating that HIV destroys B cells or plasma cells directly, or claiming that HIV destroys antibodies. Remember: HIV specifically targets and infects cells bearing CD4 receptors, primarily helper T cells.

✅ Correct Answer / Marking Points

Not effective because:

• T cell count drops below 200 cells per mm³ at month 4 (AIDS symptoms occur).
• Drug does not remove all HIV particles (levels remain fairly constant or slightly increase over 16 months).
• Methodological limitations: No statistical test, only 16 months of data, single test subject (only one person), unknown side effects, and no control group.

Effective because:

• T cell count rises above 200 cells per mm³ after 5 months (or increases after month 4).
• Shows long-term recovery/relief of AIDS symptoms as T cells recover.

💡 Key Knowledge & Data Interpretation

An evaluation question requires a balanced argument using both supporting and contradicting evidence from the provided graph, alongside scientific critique of the experimental design (sample size, controls, duration).

🧠 Exam Technique

To access top-level marks (Max 5), you must include at least one limitation regarding the study's design (e.g., no control group, only one person tested) alongside data points read directly from the graph. Look out for the constraint: "Max 4 marks if not one of points 9 or 10" (meaning you must balance both sides or include specific indicators of recovery).

❌ Common Errors

Confusing the two data lines on the dual-axis graph is a major trap. Always double-check which axis corresponds to T cells (left axis, scale up to 600) versus HIV particles (right axis, scale up to 120). Vague answers like "the drug works because cells go up" without citing specific months or threshold values (200 cells per mm³) will not gain credit.