Quick questions on Pathogens and modes of disease transmission (QCE Biology Unit 2)

Bacteria. Prokaryotic, single-celled organisms with circular DNA, 70S ribosomes and (in most species) a peptidoglycan cell wall. Reproduce by binary fission. Cause disease either by damaging tissues directly or by producing toxins. - Mycobacterium tuberculosis (tuberculosis): respiratory.

Some diseases sit at the boundary: certain cancers (cervical cancer, liver cancer) are triggered by communicable infections (HPV, Hepatitis B and C) but the cancers themselves are not transmissible.

Most communicable diseases use one or more of the following routes.

Prokaryotic, single-celled organisms with circular DNA, 70S ribosomes and (in most species) a peptidoglycan cell wall. Reproduce by binary fission. Cause disease either by damaging tissues directly or by producing toxins.

Non-cellular: nucleic acid (DNA or RNA) inside a protein capsid, sometimes with a lipid envelope studded with glycoproteins. Cannot reproduce on their own; they hijack host cell machinery to replicate. - Influenza A virus (influenza): respiratory droplet.

Eukaryotic; chitin cell walls. Mostly multicellular networks of hyphae; some are single-celled yeasts. Cause disease through tissue invasion, allergic reactions or mycotoxins.

Eukaryotic, mostly unicellular. Varied structures including flagella, cilia or pseudopodia. Many have complex life cycles involving vectors.

Misfolded versions of a normal cellular protein (PrP). They convert correctly folded copies into the misfolded form, producing aggregates that damage neurons. No nucleic acid is involved.

Viruses are non-cellular and far smaller. Antibiotics that target bacteria (cell wall, ribosomes) do not work on viruses.

Prions are the smallest assessable pathogen group at QCE level; expect them to come up specifically because they are unusual.

Mode matters for control. Waterborne pathogens need clean water, vector-borne pathogens need vector control, blood-borne pathogens need safe injecting and screened blood, droplet pathogens need distance and ventilation.

Communicable diseases include all transmissible infections, including vector-borne and foodborne ones; contagious is usually reserved for highly transmissible person-to-person diseases.