6.2.5Unit 6: Practical Skills in Biology II
Lymphocytes: Types and Roles — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 5 parts Lesson 11 of 48 Unit quiz
Section 1 of 5T Cells
Origin
- T cells are made in the bone marrow and finish maturing in the thymus, which gives them their name.
Receptors
- Each T cell has receptors on its membrane that are specific to one antigen.
Activation
- A T cell is activated when its receptor binds its antigen on an antigen-presenting cell.
Clones
- Activated T cells divide by mitosis to produce many genetically identical cells.
Antigen-presenting cell
- The cell presenting the antigen may be a macrophage, an infected body cell or the pathogen itself.
Section 2 of 5Types of T Cell
Types of T Cell
T helper cells
- These release cytokines that activate B cells and T killer cells and stimulate phagocytosis.
T killer cells
- These bind to infected body cells showing the antigen and destroy them.
T memory cells
- These stay in the blood and allow a faster response if the pathogen returns.
Cell signalling
- Chemical signals from helper T cells coordinate the other cells of the immune response.
Section 3 of 5B Cells
Follow the stages in order to see how one B cell produces a large clone.
1
B cells mature in the bone marrow, and each has antibody receptors on its surface that fit one antigen.
2
When a B cell binds its specific antigen, it forms an antigen-antibody complex.
3
Signals from T helper cells activate the B cell.
4
The activated B cell divides repeatedly by mitosis, forming a clone of cells.
5
Some become plasma cells that secrete large amounts of antibody, and others become memory cells.
6
Because the receptors are antibodies fixed to the membrane, each B cell can respond to only one antigen.
Section 4 of 5Comparison
Mature in
- T cells mature in the thymus, whereas B cells mature in the bone marrow.
Main action
- T cells coordinate and kill infected cells; B cells produce antibodies via plasma cells.
Memory
- Both T cells and B cells give rise to memory cells that remain after infection.
Selected by antigen
- Only lymphocytes with receptors matching the antigen are activated and cloned.
| Cell | Role |
|---|---|
| T helper | Activate B cells and T killer cells |
| T killer | Destroy infected body cells |
| Plasma cell | Secrete antibodies |
| Memory cell | Give a faster secondary response |
Section 5 of 5Exam Checklist & Tips
6.2.5 – Key Points for the Exam
- Lymphocyte A white blood cell, such as a T cell or B cell, involved in the specific immune response.
- Plasma cell A differentiated B cell that secretes antibodies.
- Memory cell A long-lived lymphocyte that allows a faster response to a repeated infection.
- Clone A group of genetically identical cells produced by mitosis.
- T helper cell A T cell that releases signals activating B cells and T killer cells.
Common Mistakes
- Saying B cells kill infected cells, when T killer cells do this.
- Writing that T cells produce antibodies, which are made by plasma cells.
- Forgetting that lymphocyte division is by mitosis and so produces identical cells.
- Mixing up T and B cells by where they mature.
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