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C3.2.6—Lymphocytes

Lymphocytes explains how a specific barrier, pathogen interaction, immune mechanism, treatment response or population process contributes to protection against infectious disease.

Syllabus
First assessment 2025
Objective
C3.2.6
Level
SL

Exam analysis

Chance of appearing2%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper2
Typical marks1–3

Common command terms

  • Explain
  • Outline
  • Identify

Scoring notes

Common mistake
Confusing plasma cells, memory cells and helper T-cells in the activation sequence.

Recent exam appearances

November 2025Paper1A ["SL"] · TZ117[ 1 ]C3.2.6—Lymphocytes
May 2019Paper2 ["SL"] · TZ13(d)[ 2 ]C3.2.6—Lymphocytes
May 2014Paper2 ["SL"] · TZ12(c)(ii)[ 3 ]C3.2.6—Lymphocytes
Practice this objective

Coverage 2014–2025 · Updated 16 Jul 2026

Lymphocytes provide specific immune recognition

Lymphocytes are adaptive immune cells that circulate in blood and are also concentrated in lymph nodes, where antigen-specific cells cooperate to produce antibodies.

An individual has a very large number of B lymphocytes with different receptors. Each B-cell clone is capable of making one specific type of antibody, so the population collectively recognizes many antigens.

Location: blood and lymph nodes. Diversity: many B-cell specificities. Cooperation: antigen-specific helper T cells help activate matching B cells, which can form antibody-secreting cells.

Only the small B-cell population with receptors complementary to a viral surface antigen is selected to produce antibodies against that antigen.

One B cell does not make every antibody. Large population diversity plus cooperation between lymphocytes creates the adaptive repertoire.

Lymphocytes exam focus

Assessment in practice

1–7 marks
How it is assessed

This objective is assessed through structured response, commonly using Explain / Outline / Identify.

Command terms

Explain / Outline / Identify

What earns marks

Mark schemes repeatedly reward named details, correct sequence and clear distinctions between similar processes.

Watch for

Confusing plasma cells, memory cells and helper T-cells in the activation sequence.

Representative question

Question 1

[Maximum number: 7]

Explain how cells in the bloodstream cause a specific immune response.

Defence Against Disease

  • Skin, mucus, cilia, lysozyme and clotting form primary barriers against pathogens.
  • Innate immunity is rapid and broad: phagocytes recognize, engulf and digest pathogens. Adaptive immunity is antigen-specific and forms memory.
  • Helper T-cells coordinate responses; activated B-cells undergo clonal selection, producing antibody-secreting plasma cells and memory cells. A second exposure therefore triggers a faster, stronger response.
  • HIV infects CD4 helper T-cells; their loss weakens immune coordination and can lead to AIDS.
  • Antibiotics target bacterial processes, not viruses. Antibiotic exposure selects resistant variants, which can spread by reproduction or plasmid transfer.
  • Vaccination creates active artificial immunity; high population immunity can indirectly protect susceptible people.
  • Evaluate disease and vaccine claims using reliable sources, trends, controlled comparisons, incidence and efficacy—not raw totals alone.

Concept essentials

  • Lymphocytes has to be linked to the exact pathogen, cell, molecule or population process involved.
  • The biological effect of lymphocytes depends on the sequence from trigger to protective outcome.
  • Clear distinctions within lymphocytes prevent confusion with neighbouring immune responses.
  • Evidence for lymphocytes is strongest when mechanism and consequence are explained together.