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3.2.4 Cell recognition and the immune system

AQA A-level Biology 3.2.4 practice on Cell recognition and the immune system, with free MCQs, clues and worked explanations drawn from the Cells section of specification 7402.

Specification route
3.2.4
Question bank
23 questions
Course stage
AS / Year 12

Sample questions

QUESTION 1 · 3.2.4 · LEVEL 1

How is an antigen defined in the context of the immune system?

  • Specific molecules on the cell surface that enable the immune system to identify it.
  • White blood cells that engulf and destroy pathogens via phagocytosis.
  • Proteins produced by plasma cells that bind to specific pathogens.
  • Enzymes inside lysosomes that digest abnormal body cells.
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These are usually proteins that generate an immune response.

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Answer: Specific molecules on the cell surface that enable the immune system to identify it.

Each type of cell has specific molecules on its surface that identify it. These molecules enable the immune system to identify pathogens... Definition of antigen.

QUESTION 2 · 3.2.4 · LEVEL 1

Which immune cells are primarily responsible for the cellular response to a foreign antigen?

  • T lymphocytes
  • B lymphocytes
  • Plasma cells
  • Red blood cells
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These cells respond to antigen-presenting cells.

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Answer: T lymphocytes

The response of T lymphocytes to a foreign antigen is known as the cellular response.

QUESTION 3 · 3.2.4 · LEVEL 2

What is the specific role of helper T cells in the immune system?

  • They stimulate cytotoxic T cells, B cells, and phagocytes.
  • They release monoclonal antibodies to destroy antigens.
  • They differentiate into plasma cells to provide active immunity.
  • They form a capsule around the pathogen to prevent replication.
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They act as coordinators for both the cellular and humoral responses.

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Answer: They stimulate cytotoxic T cells, B cells, and phagocytes.

The role of helper T cells is stimulating cytotoxic T cells, B cells and phagocytes.

QUESTION 4 · 3.2.4 · LEVEL 2

What does the humoral response involve?

  • The response of B lymphocytes to a foreign antigen, clonal selection, and the release of monoclonal antibodies.
  • The response of T lymphocytes, phagocytosis, and the destruction of abnormal body cells.
  • The injection of a vaccine to provide herd immunity to a population.
  • The replication of viruses within helper T cells and subsequent cell death.
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This response focuses on fluids ('humors') using antibodies.

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Answer: The response of B lymphocytes to a foreign antigen, clonal selection, and the release of monoclonal antibodies.

The humoral response involves the response of B lymphocytes to a foreign antigen, clonal selection and the release of monoclonal antibodies.

QUESTION 5 · 3.2.4 · LEVEL 3

What processes follow the formation of an antigen-antibody complex to destroy bacterial cells?

  • Agglutination and phagocytosis
  • Lysis and binary fission
  • Osmosis and active transport
  • Clonal selection and replication
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Antibodies clump pathogens together so they can be easily engulfed.

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Answer: Agglutination and phagocytosis

The formation of an antigen-antibody complex leads to the destruction of the antigen, limited to agglutination and phagocytosis of bacterial cells.

QUESTION 6 · 3.2.4 · LEVEL 1

Which cells are responsible for producing a rapid secondary immune response upon reinfection?

  • Memory cells
  • Plasma cells
  • Helper T cells
  • Phagocytes
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These cells remain in the blood for years, 'remembering' the specific antigen.

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Answer: Memory cells

The roles of plasma cells and of memory cells in producing primary and secondary immune responses. Memory cells specifically drive the secondary response.

QUESTION 7 · 3.2.4 · LEVEL 2

Which specific cell type does the HIV virus replicate within?

  • Helper T cells
  • B lymphocytes
  • Cytotoxic T cells
  • Phagocytes
Show clue

HIV attacks the cells that coordinate the immune system.

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Answer: Helper T cells

Structure of HIV and its replication in helper T cells.

QUESTION 8 · 3.2.4 · LEVEL 3

Why are antibiotics ineffective in treating a viral infection such as HIV?

  • Viruses lack their own metabolic pathways and cell structures, which antibiotics typically target.
  • Viruses constantly mutate their attachment proteins to resist the antibiotics.
  • Antibiotics only target the secondary immune response, which viruses evade.
  • Viruses undergo binary fission too rapidly for antibiotics to work.
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Antibiotics disrupt bacterial cell walls and bacterial ribosomes.

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Answer: Viruses lack their own metabolic pathways and cell structures, which antibiotics typically target.

Why antibiotics are ineffective against viruses. Viruses use the host's machinery, so there are no specific viral metabolic pathways or unique cell walls for the antibiotic to target without harming the host.

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