Biology and Human Welfare
Scope
This domain covers pathogens and disease, immunity and vaccines, cancer, drug and alcohol abuse, and the use of microbes in food processing, industrial products, sewage treatment and biofertilisers.
Core rules
- Pathogens: Plasmodium causes malaria, Salmonella typhi causes typhoid, HIV causes AIDS, Wuchereria causes filariasis. Malaria is transmitted by female Anopheles.
- Innate immunity is non-specific and present at birth; acquired immunity is specific and has memory, mediated by B and T lymphocytes.
- Vaccines produce memory cells; they can be live attenuated, killed, subunit or toxoid.
- Cancer arises from uncontrolled division; benign tumours stay local, malignant tumours invade and metastasise.
- Biofertilisers include Rhizobium (legume nodules), Azotobacter (free-living), Anabaena (rice fields) and mycorrhizae (phosphorus uptake).
Worked example
A patient has low CD4 count and repeated opportunistic infections. Explain the likely diagnosis and why CD4 matters. Reasoning: HIV infects helper T cells, which carry CD4 receptors. Loss of CD4 cells cripples both cell-mediated and antibody responses, so opportunistic infections appear. The diagnosis is AIDS when severe immunodeficiency or indicator infections occur. CD4 count is a marker of immune status, not the virus load itself.
Traps
- AIDS is caused by HIV; AIDS is the syndrome, not the virus.
- Colostrum is rich in IgA and gives passive immunity to the infant.
- Antibiotics such as penicillin target bacterial cell walls and do not treat viral infections.
- Cancer cells lose contact inhibition but do not always secrete toxins.