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AS · Practice questions · Lymphocytes and the immune response

Select, clone, remember.

Six original Cambridge-style questions on the primary and secondary immune responses, including data to interpret.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Every step has a named cell.

01
Recall
[5 marks]

Describe the sequence of events in a primary immune response to a bacterium, from the bacterium entering the blood to the secretion of antibodies.

  • A macrophage engulfs the bacterium and presents its antigens on its cell surface membrane. ✓
  • A T-helper cell with complementary receptors binds to the presented antigen (clonal selection). ✓
  • The T-helper cell divides by mitosis (clonal expansion) and releases cytokines. ✓
  • A B-lymphocyte with complementary receptors binds the antigen and, stimulated by cytokines, divides by mitosis into a clone. ✓
  • The clone differentiates into plasma cells, which secrete specific antibodies, and memory cells. ✓
02
Explain
[3 marks]

Plasma cells contain large amounts of rough endoplasmic reticulum, many Golgi bodies and many mitochondria. Explain how these features relate to their function.

  • Antibodies are proteins, made by ribosomes on the rough ER. ✓
  • The Golgi body modifies and packages the antibodies into vesicles for exocytosis. ✓
  • Mitochondria supply ATP for protein synthesis and for the secretion of large amounts of antibody. ✓
03
Data
[4 marks]

A person's blood was tested after two exposures to the same antigen, 40 days apart. After the first exposure, antibody was first detected on day 7 and peaked at 10 arbitrary units on day 14. After the second exposure, antibody was detected within 2 days and peaked at 100 arbitrary units on day 46. Describe and explain the differences between the two responses.

  • Second response starts sooner (2 days compared with 7 days). ✓
  • Second response peaks ten times higher (100 compared with 10 units) and antibody stays high for longer. ✓
  • Memory B cells made in the first response are present in much larger numbers than the original matching lymphocytes. ✓
  • So clonal selection is immediate and memory cells divide rapidly into many plasma cells. ✓
04
Explain
[3 marks]

Explain why a person with an infection usually feels ill for several days before they start to recover during a primary immune response.

  • Only a few lymphocytes have receptors complementary to the new antigen. ✓
  • Clonal selection, clonal expansion and differentiation into plasma cells take several days. ✓
  • During this time the pathogen multiplies and damages tissues, causing symptoms. ✓
05
Analysis
[3 marks]

Compare the roles of T-helper cells and T-killer cells.

  • Both are T-lymphocytes with specific receptors that are selected and cloned in response to an antigen. ✓
  • T-helper cells release cytokines that stimulate B cells to divide and form plasma cells, and activate T-killer cells and macrophages. ✓
  • T-killer cells bind to and destroy infected body cells displaying the antigen; they do not stimulate B cells. ✓
06
Explain
[2 marks]

Explain the role of memory cells in long-term immunity.

  • Memory cells are long-lived and remain in the blood for years after the infection. ✓
  • On re-infection with the same antigen they give a rapid secondary response, so the pathogen is destroyed before it causes disease. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.