A pathogen is an organism or virus that causes a disease. Most, but not all, are microorganisms.
6.3.2 Explain why antibiotics are effective against bacteria but not against viruses
Antibiotics are naturally occuring substances that slow down or kill microorganisms. They are obtained mainly from fungi or bacteria, and are substances which such organisms manufacture in their natural habitats.
Most antibiotics are so extremely effective at disrupting bacterial metabolism that whole populations are quickly suppressed. A key process here is the formation and laying down of the new dividing wall. Bacterial cells have a rigid wall containing giant, complex, molecules of amino-sugars and peptide units (polymers) rather than the polysaccharides of plant cell walls.
Virus on the other hand, are not living cells and have no metabolism of their own to be interfered with. Viruses reproduce using metabolic pathways in their host cell that are not affected by antibiotics. Antibiotics cannot be used to prevent viral diseases.
6.3.3 Outline the role of skin and mucous membranes in defense against pathogens
6.3.4 Outline how phagocytes leucocytes ingest pathogens in the blood and in blood tissues
6.3.5 Distinguish between antigens and antibodies
6.3.6 Explain antibody production
6.3.7 Outline the effects of HIV on the immune system
6.3.8 Discuss the cause, transmission and social implications of AIDs
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