Question 9 of 20: Ten Microbiology Definitions

Question 9: Ten Microbiology Definitions (10 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

1.1 Heterotroph. An organism that obtains carbon and energy by consuming organic compounds produced by other organisms, rather than fixing it from an inorganic source — virtually all bacteria performing BOD removal in wastewater treatment are heterotrophs.

1.2 Function of an enzyme. A biological catalyst (almost always a protein) that lowers the activation energy of a specific biochemical reaction, speeding it up by many orders of magnitude without itself being consumed — enzymes drive every step of microbial metabolism, from substrate hydrolysis to respiration.

1.3 Autotroph. An organism that builds its own organic cell material from an inorganic carbon source (CO₂), using either light (photoautotroph, e.g. algae) or a chemical oxidation reaction (chemoautotroph, e.g. nitrifying bacteria oxidizing ammonia/nitrite) as its energy source.

1.4 Binary fission. The asexual reproduction mechanism of most bacteria: a single cell replicates its DNA and divides into two genetically identical daughter cells, the basis of the exponential (log) growth phase.

1.5 What DNA does. Deoxyribonucleic acid stores an organism’s genetic information as a sequence of base pairs, which is transcribed to RNA and translated into the proteins/enzymes that determine the cell’s structure and metabolic capability, and is copied and passed to daughter cells at each division.

1.6 Pathogenicity. The capacity of a microorganism to cause disease in a susceptible host — a qualitative property (pathogenic or not), distinct from virulence (the quantitative degree/severity of that disease-causing ability).

1.7 Synthesis. The metabolic process by which a cell builds new, complex organic cell material (proteins, nucleic acids, cell membrane) from simpler substrate molecules, consuming energy (ATP) generated by catabolism/respiration — the process responsible for biomass (sludge) production in biological treatment.

1.8 Brownian movement. The continuous, random, jittery motion of small particles (including bacteria and colloids) suspended in a fluid, caused by constant random bombardment from the thermally-agitated molecules of the surrounding liquid.

1.9 Function of ATP. Adenosine triphosphate is the universal intracellular energy-carrier molecule: energy released by catabolic (oxidative) reactions is captured by phosphorylating ADP to ATP, and that stored energy is released again (ATP→ADP) to drive synthesis, transport and motility.

1.10 MPN. Most Probable Number — a statistical estimate of viable organism (typically coliform) density in a sample, obtained from the pattern of positive/negative growth results across a set of replicate dilution tubes and read from a standard MPN probability table, reported as organisms per 100 mL.