IB Diploma · Biology C3.2

IB Biology C3.2: Def. against Dis. — Practice Questions & Answers

IB Biology C3.2 Defence against infectious disease study notes: barriers, innate and adaptive immunity, antibodies, vaccination and antibiotics.

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Practice questions with answers

1 Multiple choice

What are pathogens?

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WhyPathogens are disease-causing agents, including bacteria and viruses among the listed categories.
2 Multiple choice

Which of the following is NOT typically considered a pathogen?

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WhyArchaea are generally not pathogenic and are not classified among the recognised human disease-causing groups.
3 Multiple choice

What is the primary role of the skin in defence against disease?

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WhyThe skin defends by forming a physical barrier, secreting protective chemicals, and hosting beneficial microbiota.
4 Multiple choice

What is the role of platelets in blood clotting?

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WhyPlatelets adhere to damaged walls, aggregate into a plug, and provide a surface for the clotting cascade.
5 Multiple choice

What protein is converted to fibrin during blood clotting?

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WhySoluble fibrinogen is cleaved by thrombin into insoluble fibrin threads that form the clot mesh.
6 Multiple choice

What is the role of phagocytes in infection control?

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WhyPhagocytes engulf pathogens by endocytosis and digest them with lysosomal enzymes.
7 Multiple choice

What is the movement of phagocytes from blood to sites of infection called?

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WhyPhagocytes crawl from blood into infected tissue by amoeboid movement, extending pseudopodia.
8 Multiple choice

What are lymphocytes?

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WhyLymphocytes are adaptive immune cells; B-lymphocytes in particular produce antibodies.
9 Multiple choice

Where are lymphocytes found?

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WhyLymphocytes circulate in blood and are also concentrated in lymph nodes and lymphoid tissue.
10 Multiple choice

What are antigens?

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WhyAntigens are molecular structures recognised by lymphocyte receptors that trigger an adaptive immune response.

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Key terms in Def. against Dis.

Pathogen: An organism or agent, such as a bacterium or virus, that causes infectious disease.
Mucous membrane: A lining of tracts open to the environment that traps pathogens in mucus as a non-specific barrier.
Phagocyte: A white blood cell that engulfs and digests pathogens by phagocytosis as part of the innate response.
Innate immunity: Fast, non-specific defence that acts the same way against any pathogen, including phagocytosis and inflammation.
Adaptive immunity: Slower, highly specific defence carried out by lymphocytes that target particular antigens and form memory.
Antigen: A molecule, often a surface protein of a pathogen, recognised by the immune system as foreign.
Antibody: A protein made by B-lymphocytes that binds specifically to one antigen, marking or neutralising the pathogen.
Memory cell: A long-lived lymphocyte that enables a rapid secondary response on re-exposure to the same antigen.

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Practise other IB Biology topics

A1.1 Water A1.2 Nucleic Acids A2.1 Orig. of cells A2.2 Cell Structure A2.3 Viruses A3.1 Div. of Org. A3.2 Clas. & Clad. A4.1 Evo. & Spec. A4.2 Cons. of Biodiv. B1.1 Carb. & Lipids B1.2 Proteins B2.1 Mem. & Mem. Trans. B2.2 Org. & Compart. B2.3 Cell Spec. B3.1 Gas Exchange B3.2 Transport B3.3 Muscle & Motility B4.1 Adapt. to Envir. B4.2 Eco. niches C1.1 Enzy. & Meta. C1.2 Cell Resp. C1.3 Photosynthesis C2.1 Chem. Signal. C2.2 Neu. Signal. C3.1 Int. of Body Sys. C4.1 Pop. & Commu. C4.2 Tran. of En. & Mat. D1.1 DNA Replication D1.2 Protein Syn. D1.3 Mut. & Gene Edit. D2.1 Cell & Nuc. Div. D2.2 Gene Exp. D2.3 Water potential D3.1 Reproduction D3.2 Inheritance D3.3 Homeostasis D4.1 Nat. Select. D4.2 Stab. & Change D4.3 Climate Change DIAG Diagnostic Questions