Biology and Human Welfare (Health, Disease, Microbes, Biotechnology Applications)
Biology and Human Welfare tests pathogens and disease, immunity and vaccines, the industrial uses of microbes, and the tools and applications of biotechnology.
Disease and immunity
- Malaria is caused by Plasmodium, transmitted by female Anopheles; dengue by a virus transmitted by Aedes aegypti; tuberculosis by Mycobacterium tuberculosis; typhoid by Salmonella typhi and diagnosed by the Widal test; AIDS by HIV and detected by ELISA.
- Innate immunity is non-specific; acquired immunity is specific and includes B cells and T cells. Active immunity follows infection or vaccination; passive immunity follows antibody transfer.
- Antibodies are immunoglobulins IgA, IgD, IgE, IgG and IgM; the secondary response is faster and larger.
Microbes and biotechnology
- Microbes in food and industry: Lactobacillus in curd, Saccharomyces cerevisiae in bread and beer, Aspergillus niger for citric acid, Penicillium notatum for penicillin, methanogens for biogas.
- Wastewater treatment has primary, secondary (activated sludge) and anaerobic sludge digestion stages.
- Recombinant DNA uses restriction enzymes such as EcoRI, DNA ligase and vectors such as pBR322.
- PCR uses Taq polymerase: denaturation near 94 °C, annealing near 50–60 °C, extension near 72 °C.
- Applications include DNA fingerprinting, gene therapy for ADA deficiency, Bt cotton using cry genes, Golden Rice and human insulin produced in bacteria.
Worked example
Starting with one DNA molecule, PCR doubles the target each cycle, so after n cycles there are 2ⁿ copies. After 30 cycles, 2³⁰ ≈ 1.07 × 10⁹ copies. The reasoning is exponential amplification, which is why even trace DNA can be analysed.
Traps
Antibiotics do not treat viral infections; malaria is caused by a protozoan, not a virus; Taq polymerase is heat-stable; passive immunity involves ready-made antibodies; the Bt toxin gene is cry, not a plant gene.