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3.6.5Additional lessons

White Blood Cells — IB Biology SL Revision Notes & Topical Questions

5 min read 5 parts Lesson 74 of 142

📚 IB Biology SL Hub / Topical Revision
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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.
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Part 1 of 5Phagocytes

Phagocytes are the first white blood cells to arrive at an infection.

Role
  • Role Phagocytes engulf and destroy pathogens and form part of both the non-specific defence and the start of the specific response.
Phagocytosis
  • Phagocytosis The cell membrane extends round the pathogen and takes it in by endocytosis, forming a phagocytic vacuole.
Digestion
  • Digestion Lysosomes fuse with the vacuole and release enzymes that digest the pathogen inside the phagocyte.
Antigen presentation
  • Antigen presentation After digestion, some phagocytes display pathogen antigens on their surface to show them to lymphocytes.

Part 2 of 5Lymphocytes

Origin
  • Origin All lymphocytes are made from stem cells in the bone marrow.
B cells
  • B cells They mature in the bone marrow and, when activated, become plasma cells that secrete antibodies.
T cells
  • T cells They mature in the thymus, which gives them their name, and carry receptors for specific antigens.
Specificity
  • Specificity Each lymphocyte has receptors for one antigen, so the body holds a vast range of different lymphocytes.
FeaturePhagocyteLymphocyte
Response typeNon-specificSpecific
Main actionEngulfs pathogensMakes antibodies or kills infected cells
MemoryNoYes

Part 3 of 5Helper T Cells and B Cells

1
A phagocyte or other antigen-presenting cell displays an antigen on its surface.
2
A helper T cell with a complementary receptor binds to the presented antigen and is activated.
3
The activated T cell divides by mitosis to produce a clone of identical T cells.
4
Helper T cells activate B cells that carry matching antigen receptors.
5
The B cells divide and differentiate into plasma cells and memory cells.

Part 4 of 5Functions of the Cells

Functions of the Cells
Plasma cells
  • Plasma cells These have much rough endoplasmic reticulum for making and secreting large amounts of antibody.
Cytotoxic T cells
  • Cytotoxic T cells They kill body cells infected by a virus by releasing substances that cause the target to die.
Memory cells
  • Memory cells They persist for years and allow rapid action if the antigen reappears.

Part 5 of 5Exam Checklist & Tips

3.6.5 – Key Points for the Exam

  • Phagocyte A white blood cell that engulfs and digests pathogens.
  • Lymphocyte A white blood cell, either B or T cell, that gives a specific response.
  • Plasma cell An activated B cell that secretes antibodies.
  • Thymus The organ in which T cells mature.
  • Antigen-presenting cell A cell that displays foreign antigen to lymphocytes.

Common Mistakes

  • Thinking T cells mature in the bone marrow; B cells mature there while T cells mature in the thymus.
  • Saying phagocytes make antibodies.
  • Stating that one B cell makes antibodies against many antigens.
  • Using exocytosis for how a phagocyte takes in a pathogen; this is endocytosis.

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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.

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