Biology and Human Welfare
Biology and Human Welfare connects pathogens, immunity, microbes, and food production. Questions often ask you to identify a disease agent, explain an immune failure, or match a microbe to an industrial or agricultural use.
Core rules and concepts
- Pathogens: typhoid is caused by Salmonella typhi, pneumonia by Streptococcus pneumoniae, and malaria by Plasmodium species transmitted by female Anopheles mosquitoes.
- Immunity: innate immunity is non-specific; acquired immunity has antibody-mediated and cell-mediated branches. Antibodies are produced by plasma cells. Colostrum is rich in IgA and protects the infant gut.
- HIV is a retrovirus that binds CD4 helper T cells. Their destruction weakens cell-mediated immunity and causes opportunistic infections; CD4 count is used to monitor progression.
- Microbes in welfare: Lactobacillus in curd, Saccharomyces in baking and fermentation, Penicillium for penicillin, methanogens for biogas, and activated sludge in sewage treatment.
- Food production includes apiculture, poultry, fisheries, plant breeding, tissue culture, and somatic hybridisation.
Worked example
A patient with advanced HIV develops rare fungal and bacterial infections. Reasoning: HIV infects CD4 helper T cells and destroys them. Helper T cells activate B cells and cytotoxic T cells, so their loss collapses both antibody and cell-mediated responses. The opportunistic infections are secondary consequences, not direct fungal toxins.
Traps that cost marks
Antibiotics do not treat viral infections such as influenza or HIV. Malaria is transmitted by the female Anopheles mosquito, not by contaminated water. Bt cotton uses a toxin gene from Bacillus thuringiensis, not from a virus. Colostrum's main protective antibody is IgA.