IP Biology Notes: Infectious Diseases in Humans (Upper Sec 09)

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.

The core idea is simple: Infectious disease answers must link pathogen, route, defence, and control.

Use it as a working check: Match each prevention method to the transmission route. Antibiotics work on bacteria, not viruses, and misuse selects resistant bacteria.

Then go one layer deeper: Example: masks and isolation help droplet spread, while clean water and proper cooking help food or water spread. Vector control fits mosquito-borne disease.

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.

Route-to-control checkpoint

When a question asks for prevention, name the route first, then choose a control that breaks that route.

Reviewed by

Ezekiel Tan·Academic Advisor (Biology)