Home · A-Level Biology 9700 · Immunity · Phagocytes and antigens · Practice
AS · Practice questions · Phagocytes and antigens

Find it, engulf it, digest it.

Six original Cambridge-style questions on phagocytes and antigens, from the stages of phagocytosis to explaining transplant rejection.

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

Non-specific first, specific later.

01
Recall
[4 marks]

Describe how a neutrophil destroys a bacterium.

  • Chemotaxis: the neutrophil moves towards chemicals released by the bacterium or damaged cells. ✓
  • Receptors on the neutrophil bind to non-self antigens on the bacterium. ✓
  • The cell surface membrane extends around the bacterium and engulfs it into a phagosome (vacuole) by endocytosis. ✓
  • Lysosomes fuse with the phagosome and release hydrolytic enzymes (lysozyme) that digest the bacterium. ✓
02
Analysis
[3 marks]

Compare neutrophils and macrophages.

  • Similarities: both are phagocytes made in the bone marrow that engulf pathogens and digest them with lysosomal enzymes. ✓
  • Neutrophils have a lobed nucleus, are short-lived and arrive at an infection first in large numbers. ✓
  • Macrophages are larger and long-lived, develop from monocytes in tissues, and present antigens to lymphocytes. ✓
03
Recall
[2 marks]

Explain what is meant by an antigen.

  • A molecule (usually a protein or glycoprotein, often on a cell surface) that stimulates an immune response. ✓
  • It is recognised by complementary receptors on lymphocytes and leads to the production of specific antibodies. ✓
04
Explain
[3 marks]

A patient receives a kidney from an unrelated donor. Explain why the patient's immune system may reject the kidney.

  • The donor's cells carry surface antigens (glycoproteins) that differ from the patient's own. ✓
  • These are recognised as non-self antigens. ✓
  • Lymphocytes with complementary receptors are activated, and T-killer cells and antibodies attack the kidney cells. ✓
05
Explain
[2 marks]

Suggest why the number of neutrophils in the blood rises sharply during a bacterial infection.

  • Neutrophils are short-lived and many die after engulfing bacteria. ✓
  • The bone marrow makes more to replace them and to deal with the large number of bacteria, so the count rises. ✓
06
Explain
[3 marks]

Explain why phagocytosis is described as a non-specific response, while the response of lymphocytes is specific.

  • A phagocyte engulfs any material it recognises as non-self, whatever the pathogen. ✓
  • Each lymphocyte has receptors of one shape, complementary to only one antigen. ✓
  • So only the lymphocytes that match a particular antigen respond to it. ✓

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.