MYP Biology: Microorganisms & Disease FAQ

You need to classify microorganisms — bacteria, viruses, fungi, protozoa — and explain how each causes disease. You also need transmission routes (direct contact, vectors, water, air), the body's defences, and how antibiotics differ from vaccines. The MYP: Sciences guide places this under the key concept 'Systems', often within the global context 'Globalisation and sustainability'.

MYP Biology covers four main groups: bacteria (single-celled, no nucleus), viruses (non-living, need a host cell to reproduce), fungi (some single-celled like yeast, others multicellular moulds), and protozoa (single-celled, have a nucleus). Each causes disease through a different mechanism, which is exactly what markers check for.

Pathogens spread through direct contact (touch, bodily fluids), indirect contact (contaminated surfaces or water), airborne droplets (coughing, sneezing), and vectors — an organism like a mosquito that carries a pathogen between hosts. Malaria is the classic vector example IB examiners return to again and again.

Defence happens in three stages: physical barriers stop entry (skin, mucus, stomach acid); a non-specific response follows if a pathogen gets in (white blood cells engulfing invaders, inflammation); then a specific immune response kicks in, where lymphocytes produce antibodies matched to that exact pathogen's antigens.

Antibiotics treat an existing bacterial infection by killing bacteria or stopping them reproducing — they do nothing against viruses. Vaccines work before infection, training your immune system to recognise a pathogen's antigens so it responds faster if you're exposed later. Confusing these two is the single most common exam mistake in this unit.

This unit usually assesses Criterion A (Knowing and understanding) through explanation of pathogens and disease, and Criterion D (Reflecting on the impacts of science) through discussions of antibiotic resistance or public health. If your unit includes a practical, Criteria B and C — Inquiring and designing, and Processing and evaluating — get assessed too.

Pick a testable question — comparing how different concentrations of an antibacterial soap affect bacterial growth on agar plates works well. State your hypothesis, control variables (temperature, incubation time, agar type), follow aseptic technique, then evaluate reliability against your controlled variables and suggest one genuine improvement.

The three I see every year in class: students say antibiotics kill viruses (they don't), they describe vaccines as 'curing' disease rather than preventing it, and they confuse vectors with the pathogen itself — a mosquito is the vector, the Plasmodium parasite is the pathogen.

Level 7-8 answers use precise terminology (antigen, antibody, pathogen, vector — not 'germ'), justify every claim with a specific mechanism, and connect the biology to a real-world issue like antibiotic resistance or a named disease outbreak. Vague, generic answers rarely clear level 5, however accurate they sound.

Microorganisms & disease in MYP 4-5 lays the groundwork for DP Biology topics on viruses (Structure 2.2) and the immune response (Physiology). According to the IB, first exams for the current DP Biology guide were in 2025, and it treats immunity in far more molecular detail — antibody structure, monoclonal antibodies, HIV replication — than MYP does.

Look for resources that mix concise notes with practice questions rather than dense textbook chapters — this topic rewards recall of specific examples and mechanisms over long prose. RevisionPrep's MYP Biology Revision Notes and Topical Worksheets are built around exactly this unit, with a question bank for self-testing before the unit assessment.