The immune system
Cambridge A-Level Biology (9700) · Unit 11: Immunity · 9 flashcards
The immune system is topic 11.1 in the Cambridge A-Level Biology (9700) syllabus , positioned in Unit 11 — Immunity , alongside Antibodies and vaccination. In one line: An antigen is a molecule (usually a protein or polysaccharide) that triggers an immune response. Self-antigens are molecules on the surface of the body's own cells that do not trigger an immune response, while non-self antigens are foreign molecules that the immune system recognizes as 'non-self' and attacks.
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 9 flashcards — 1 definition and 8 key concepts — covering the precise wording mark schemes reward. Use the definition card to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
'antigen' and differentiate between self and non-self antigens
An antigen is a molecule (usually a protein or polysaccharide) that triggers an immune response. Self-antigens are molecules on the surface of the body's own cells that do not trigger an immune response, while non-self antigens are foreign molecules that the immune system recognizes as 'non-self' and attacks.
What the Cambridge 9700 syllabus says
2025-2027 syllabus, in our words · AS LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Describe how phagocytes, both neutrophils and macrophages, carry out their action against pathogens.
- Explain the meaning of the term antigen (see 4.1.3), and state how self antigens differ from non-self antigens.
- Describe the order of events in a primary immune response, covering the part played by: macrophages; B-lymphocytes, plasma cells included; T-lymphocytes, only T-helper and T-killer cells.
- Explain how memory cells contribute to long-term immunity and to the secondary immune response.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9700 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in The immune system
- › Distinguish clearly between T-cells (cell-mediated) and B-cells (humoral). Mention killer T-cells, cytokines, and antigen presentation for T-cell questions.
- › Distinguish between phagocytes like neutrophils and lymphocytes; T-killer cells specifically target and destroy infected 'self' cells.
Describe the process of phagocytosis by macrophages and neutrophils.
Phagocytes engulf pathogens through endocytosis, forming a phagosome. Lysosomes fuse with the phagosome, releasing enzymes that digest the pathogen. The digested products are then absorbed into the phagocyte's cytoplasm.
Define 'antigen' and differentiate between self and non-self antigens.
An antigen is a molecule (usually a protein or polysaccharide) that triggers an immune response. Self-antigens are molecules on the surface of the body's own cells that do not trigger an immune response, while non-self antigens are foreign molecules that the immune system recognizes as 'non-self' and attacks.
Outline the sequence of events in a primary immune response.
Macrophages engulf the pathogen and present its antigens to T-helper cells. The B and T lymphocytes with matching receptors are selected (clonal selection) and divide by mitosis (clonal expansion). T-helper cells release cytokines that stimulate the B cells to become plasma cells, which secrete antibodies, and activate T-killer cells, which destroy infected cells. Some of the B and T cells become memory cells.
What is the role of macrophages in initiating the primary immune response?
Macrophages engulf pathogens via phagocytosis and then act as antigen-presenting cells (APCs). They present processed antigens on their surface, bound to MHC class II molecules, to T-helper cells, initiating the adaptive immune response.
Describe the role of plasma cells in the primary immune response.
Plasma cells are differentiated B-lymphocytes that produce and secrete large quantities of antibodies specific to the antigen that triggered the immune response. These antibodies circulate in the blood and lymph, targeting and neutralizing the pathogen.
Explain the function of T-helper cells in the immune response.
T-helper cells recognize antigens presented by antigen-presenting cells (APCs) like macrophages. Once activated, they release cytokines that stimulate B-lymphocytes to differentiate and produce antibodies, and also activate T-killer cells.
Describe the role of T-killer cells in the immune response.
T-killer cells (also known as cytotoxic T cells) recognize and kill infected or cancerous cells by binding to antigens presented on the cell surface via MHC class I molecules. They release cytotoxic substances like perforin, which creates pores in the target cell membrane, leading to cell lysis.
Explain the role of memory cells in the secondary immune response.
Memory cells are long-lived B and T lymphocytes produced during the primary immune response. Upon subsequent exposure to the same antigen, memory cells rapidly differentiate into plasma cells (B memory cells) and T-killer cells (T memory cells), resulting in a faster and stronger immune response than the primary response.
How do memory cells contribute to long-term immunity?
Memory cells persist in the body for a long time after the primary infection is cleared. They provide immunological memory, enabling a rapid and effective secondary immune response upon re-exposure to the same antigen, thus conferring long-term immunity to that specific pathogen.
Review the material
Read full revision notes on The immune system — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 11 — Immunity
The immune system sits alongside these A-Level Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this The immune system deck
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