Biology Topic 6

Pathogens are disease-causing micro-organisms, including bacteria, viruses, protists, and fungi.
Bacteria: One of the oldest life forms; structure includes cell wall, cell membrane, cytoplasm, and circular DNA (no nucleus). They reproduce by dividing into clones.
Viruses: Smaller ( $0-1\,\mu m$ - $1\,\mu m$ ) than bacteria; consist of a protein coat and genes. They must reproduce inside a host cell, destroying it upon release.
Transmission methods: Contact, aerosol, body fluids, water, insects, and contaminated food.

First Line: The skin provides a barrier of dead cells and skin flora to prevent pathogen establishment.
Second Line: Platelets clot blood at cuts to form scabs, blocking microbe entry.
Third Line: White blood cells defend via: - Phagocytes: Detecting, engulfing, and digesting microbes. - Lymphocytes: Producing antitoxins to counteract bacterial toxins and antibodies to inactivate pathogens.

Antibiotics: Substances like Penicillin (from Penicillium) that kill bacteria or prevent their growth; they do not affect viruses.
Resistance: The ability of organisms to survive lethal doses of poison. Overuse in animal feed and over-prescription by doctors lead to resistant strains.
MRSA: Methicillin resistant Staphylococcus aureus is a widespread resistant strain; hospitals control it through hand washing, alcohol gels, thorough cleaning, and screening.

Health Factors: A state of physical and mental fitness affected by diet, genes, lifestyle, living conditions, and infection contact.
Drug Testing: New drugs require large-scale testing for side effects. Animal testing is supported by scientists to model complex biological processes but opposed by animal-rights groups for ethical and physiological reasons.

Vaccination: Introduces dead or inactive pathogens to trigger antibody and memory cell production without causing disease.
Edward Jenner: In $1796$ , he performed the first vaccination by using cowpox to protect a boy from smallpox.
MMR Story: Dr Andrew Wakefield's $1998$ paper in The Lancet suggested a link between the vaccine and autism based on only $12$ children. Despite a conflict of interest ( $£55\,000$ payment), vaccine uptake fell from $92\%$ to $75\%$ by $2001$ . Subsequent large-scale studies proved no link between MMR and autism.