3.7.5Additional lessons
White Blood Cells — IB Biology HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 4 of 101
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Phagocytes
Origin
- Origin Phagocytes are produced continuously in the bone marrow and travel in the blood before moving into tissues.
Movement
- Movement They crawl towards infection by amoeboid movement, attracted by chemicals released by damaged cells and microbes.
Phagocytosis
- Phagocytosis The cell engulfs a pathogen into a vesicle called a phagosome, which fuses with lysosomes containing digestive enzymes.
Antigen presentation
- Antigen presentation Fragments of the digested pathogen are displayed on the phagocyte surface so that lymphocytes can recognise them.
Non-specific
- Non-specific A phagocyte will engulf many kinds of foreign particle, so it forms part of the innate response.
Part 2 of 4T Lymphocytes
T Lymphocytes
Maturation
- Maturation T cells form in the bone marrow and finish maturing in the thymus gland, which gives them their name.
T cell receptors
- T cell receptors Each mature T cell carries receptors of one shape that fit one specific antigen.
Helper T cells
- Helper T cells When activated by a presented antigen, these divide by mitosis and release signals that activate B cells and phagocytes.
Cytotoxic T cells
- Cytotoxic T cells These destroy body cells that are infected, for example by a virus, by releasing substances that kill the cell.
Part 3 of 4B Lymphocytes and Memory
1
B cells made in the bone marrow each carry surface antibodies of a single type.
2
When a B cell meets its matching antigen and receives signals from a helper T cell, it is activated.
3
The activated B cell divides by mitosis to form a clone of identical cells with the same antibody specificity.
4
Most of the clone become plasma cells with extensive rough endoplasmic reticulum that secrete large amounts of antibody.
5
A smaller number become memory cells that stay in the blood and give a rapid response to a later infection.
| Cell | Site of maturation | Main role |
|---|---|---|
| Phagocyte | Bone marrow | Engulfs and digests pathogens |
| Helper T cell | Thymus | Activates B cells and other cells |
| Cytotoxic T cell | Thymus | Kills infected body cells |
| B cell / plasma cell | Bone marrow | Secretes specific antibodies |
Part 4 of 4Exam Checklist & Tips
3.7.5 – Key Points for the Exam
- Phagocyte A white blood cell that engulfs and digests pathogens.
- Lymphocyte A white blood cell, either B or T, that carries out specific immunity.
- Plasma cell An activated B cell that secretes large quantities of antibody.
- Clone A group of genetically identical cells formed by mitosis.
- Thymus The gland in which T lymphocytes complete their maturation.
Common Mistakes
- Writing that B cells mature in the thymus; they mature in the bone marrow.
- Saying plasma cells divide forever, when most live only a short time after the infection.
- Mixing antibodies with receptors; T cell receptors are not antibodies but have a similar structure.
- Forgetting that clonal expansion occurs by mitosis, not meiosis.
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Cambridge 9700 AS Biology
Core Formula
Magnification Triangle & Unit Conversion
Formula: M = I / A ⇔ A = I / M ⇔ I = M × A
Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.