Syllabus Edition

First teaching 2023

First exams 2025

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White Blood Cells (SL IB Biology)

Revision Note

Ruth

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Ruth

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Phagocytes

What do phagocytes do?

  • Phagocytes are white blood cells that are produced continuously in the bone marrow
  • They are responsible for removing dead cells and invasive microorganisms; a non-specific immune response
  • Phagocytes move in an amoeboid movement to the site of infection and attach to pathogens
    • The cell surface membrane of the phagocyte extends out and around the pathogen, engulfing it by endocytosis
  • They then digest the pathogen using enzymes which are stored within lysosomes (in their cytoplasm)

Phagocytosis diagram

Phagocytic white blood cells

Phagocytic cells ingest pathogens and digest them using enzymes

Lymphocytes

What are lymphocytes?

  • There are two types of lymphocyte that play a particular role in the specific immune response
    • T cells
    • B cells
  • Note that lymphocytes are a type of white blood cell found both in the lymph nodes and circulating in the blood

T cells

  • T cells, sometimes known as T lymphocytes, are produced in the bone marrow and finish maturing in the thymus, which is where the T in their name comes from
  • Mature T cells have specific cell surface receptors called T cell receptors
  • These receptors have a similar structure to antibodies and are each specific to a particular type of antigen

Production of T cells diagram

_The maturation of T-lymphocytes

Mature T cells have many different types of receptor on the cell surface membrane; these receptors will bind to different antigens on antigen presenting cells

  • T cells are activated when they encounter and bind to their specific antigen on the surface of an antigen-presenting cell 
    • This antigen-presenting cell might be a macrophage, an infected body cell, or the pathogen itself
  • These activated T cells divide by mitosis to increase in number
    • Dividing by mitosis produces genetically identical cells, or clones, so all of the daughter cells will have the same type of T cell receptor on their surface

B cells

  • B cells, also known as B lymphocytes, are a second type of white blood cell in the specific immune response
    • B cells remain in the bone marrow as they mature, hence the B in their name
  • B cells have many specific receptors on their cell surface membrane
    • The receptors are in fact antibodies, and are known as antibody receptors
    • Each B cell has a different type of antibody receptor, meaning that each B cell can bind to a different type of antigen

Production of B cells diagram

The maturation of B lymphocytes

Mature B cells each have different types of antibody receptors on their cell surface membrane

  • If the corresponding antigen enters the body, B cells with the correct cell surface antibodies will be able to recognise it and bind to it 
    • When the B cell binds to an antigen it forms an antigen-antibody complex
  • The binding of the B cell to its specific antigen, along with the cell signalling molecules produced by T helper cells, activates the B cell
  • Once activated, the B cells divide repeatedly by mitosis, producing many clones of the original activated B cell
  • There are two main types of B cell
    • Effector cells, which differentiate into plasma cells
      • Plasma cells produce specific antibodies to combat non-self antigens
    • Memory cells
      • Remain in the blood to allow a faster immune response to the same pathogen in the future

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Ruth

Author: Ruth

Expertise: Biology

Ruth graduated from Sheffield University with a degree in Biology and went on to teach Science in London whilst also completing an MA in innovation in Education. She gained 10 years of teaching experience across the 3 key science disciplines and physical education. Ruth decided to set up a tutoring business to support students in her local area. Ruth has worked with several exam boards and loves to use her experience to produce educational materials which make the mark schemes accessible to all students.