Practice question

Microbial growth influenced by physicochemical variables reflecting physiology. Temperature controls enzyme catalysis activation energy, membrane fluidity, protein thermostability, cardinal minima optima maxima distinct per species. Oxygen availability categorizes obligate aerobes requiring cytochrome oxidases and superoxide dismutase, obligate anaerobes lacking detoxification killed by oxygen, facultative anaerobes switching via Fnr ArcAB, microaerophiles needing low oxygen. pH affects proton motive force, amino acid charge, solubility nutrients. Water activity aw controlled by osmotic solutes, halophiles adapt via compatible solutes ectoine trehalose and modified proteome rich in acidic residues. Light essential only for phototrophs using bacteriochlorophyll, not major factor for chemoheterotrophs cultured in dark incubators. Presence of mitochondria is irrelevant because bacteria are prokaryotes lacking membrane bound organelles, their energy conservation across plasma membrane via electron transport chain composed of NDH dehydrogenases quinones cytochromes, proton extrusion forming gradient driving F1Fo ATP synthase. Mitochondria originate from alphaproteobacterial endosymbiosis in eukaryogenesis, not component of bacterial cell. Hence mitochondria absence as factor distinguishes domains.