Cells and the immune system flashcards

Cells and the immune system covers how the body recognises and destroys pathogens and abnormal cells. Students must understand the structure and roles of phagocytes and lymphocytes, including how B cells produce antibodies and how T cells coordinate responses and destroy infected cells. The concept of antigens as molecules that trigger immune responses is central, as is the distinction between the non-specific and specific immune responses. Clonal selection and clonal expansion explain how the body mounts a targeted attack, while immunological memory accounts for faster secondary responses. Students should also understand vaccination, the structure of antibodies, the antigen-antibody interaction, and how autoimmune conditions arise when the immune system fails to distinguish self from non-self.

1. Card 1

   What is an antigen?

   An antigen is a molecule, usually a protein or glycoprotein, on the surface of a cell or pathogen that triggers an immune response.

2. Card 2

   What is the role of a phagocyte in the immune response?

   Phagocytes engulf and digest pathogens by phagocytosis, forming a phagosome that fuses with a lysosome to destroy the pathogen with enzymes.

3. Card 3

   How does a phagocyte act as an antigen-presenting cell?

   After digesting a pathogen, a phagocyte displays antigen fragments on its surface using MHC proteins, activating T helper cells.

4. Card 4

   What is the difference between B cells and T cells?

   B cells produce antibodies (humoral immunity), while T cells coordinate the immune response or directly kill infected cells (cell-mediated immunity).

5. Card 5

   Describe the process of clonal selection and clonal expansion.

   A lymphocyte with a complementary receptor binds its specific antigen (clonal selection), then divides rapidly by mitosis to produce many identical clones (clonal expansion).

6. Card 6

   What is the structure of an antibody?

   An antibody is a Y-shaped glycoprotein with four polypeptide chains. The variable regions form the antigen-binding sites, which are specific to one antigen.

7. Card 7

   How do antibodies help destroy pathogens?

   Antibodies cause agglutination by binding to antigens on multiple pathogens, clumping them together so phagocytes can engulf them more efficiently.

8. Card 8

   What are memory cells and why are they important?

   Memory cells are long-lived B and T cells produced during a primary response. They enable a faster, larger secondary response if the same antigen is encountered again.

9. Card 9

   What is the difference between active and passive immunity?

   Active immunity involves the body producing its own antibodies and memory cells. Passive immunity involves receiving ready-made antibodies, giving no lasting memory.

10. Card 10

    How does a vaccine stimulate immunity without causing disease?

    A vaccine introduces antigens (from dead, weakened or fragmented pathogens) to stimulate a primary immune response and the formation of memory cells.

11. Card 11

    What is the role of T killer cells (cytotoxic T cells)?

    Cytotoxic T cells recognise and bind to infected or cancerous cells displaying foreign antigens on MHC proteins, then release perforin to destroy them.

12. Card 12

    What causes autoimmune diseases?

    Autoimmune diseases occur when the immune system fails to distinguish self from non-self, producing antibodies or T cells that attack the body's own healthy tissues.

• Students often confuse plasma cells with memory cells, forgetting that plasma cells are short-lived antibody factories while memory cells are the long-lived cells responsible for immunological memory.
• A common error is stating that vaccines contain antibodies, when in fact they contain antigens that stimulate the body to produce its own antibodies and memory cells.
• Many students incorrectly describe all T cells as having the same function, failing to distinguish between T helper cells, which coordinate the response, and cytotoxic T cells, which directly kill infected cells.

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