IP Biology Notes: Infectious Diseases in Humans (Upper Sec 09)
26 Nov 2025, 00:00 Z
Reviewed by
Ezekiel Tan·Academic Advisor (Biology)
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Use this as a free IP Biology notes chapter on infectious diseases for Year 3 to Year 4. It keeps the IP pacing while reinforcing the 6093 biology foundations most schools test through DBQs, diagrams, and practical explanations.
Status: SEAB O-Level Biology 6093 syllabus (exams from 2026) checked 2025-11-30 - scope unchanged; remains the reference for this note.
What you must know
- Infectious diseases caused by pathogens (viruses, bacteria); non-infectious include genetic, lifestyle diseases.
- Virus vs bacteria: viruses are acellular, need host to replicate; bacteria are cells with cytoplasm, membrane, wall, sometimes plasmids.
- Case studies: influenza (droplet spread, fever, body aches), pneumococcal disease (bacterial, can cause pneumonia/meningitis); both preventable by vaccines, hygiene, masks, reducing crowding.
- Immunity: vaccines introduce antigens to stimulate memory cells/antibodies without causing disease.
- Antibiotics kill/inhibit bacteria (not viruses); misuse (overuse, incomplete courses) selects resistant strains.
Detailed notes
- Transmission: droplets, contact, contaminated food/water, vectors (mosquitoes), body fluids. Break chain with hygiene, clean water, cooking, masks, isolation, vector control (remove stagnant water, nets, insecticides).
- Defences: physical/chemical barriers (skin, mucus/cilia, tears, stomach acid); phagocytes engulf; lymphocytes produce antibodies and memory cells-faster secondary response.
- Vaccination: weakened/killed pathogen or antigen stimulates primary response → memory. Herd immunity helps protect those unvaccinated.
- Antibiotics: target bacteria (cell wall/ribosomes); ineffective on viruses. Misuse breeds resistance-complete courses, avoid unnecessary use.
- Distinguish infectious vs non-infectious (genetic, lifestyle) to avoid incorrect examples.
Worked walkthroughs
- Explain how vaccination leads to active immunity via memory cells; contrast with passive immunity (antibodies given, short-lived).
- Describe how vector control reduces dengue/malaria (destroy breeding sites, nets, sprays).
- Outline body response to a cut: clot forms, phagocytes act, lymphocytes produce antibodies if needed.
Pitfalls and fixes
- Saying antibiotics kill viruses-they do not.
- Confusing vaccination with passive immunity.
- Ignoring matching control to transmission route (e.g., water vs droplet vs vector).
- Saying “body becomes immune to antibiotics”-it’s bacteria that develop resistance.
