Bacteria Questions and Answers

Answer: A

Correct answer: Specific receptors

Adsorption is the first step of infection: a protein on the virus surface binds a specific receptor molecule on the host cell. Which receptor a virus recognises is what determines its host range and its tissue tropism - HIV binds CD4, so it infects helper T cells.

Answer: C

Correct answer: The mechanism called viropexia

Viropexis is the engulfment of the attached virus particle by the cell membrane, which folds round it and takes it in as a vesicle - receptor-mediated endocytosis. Enveloped viruses have a second option, fusing their envelope directly with the plasma membrane.

Answer: D

Correct answer: The synthetic machinery of host cell

A virus carries no ribosomes and, in most cases, no metabolism of its own. For biosynthesis it takes over the host cell’s machinery - ribosomes, tRNAs, amino acids and ATP - to make its own proteins and nucleic acid. That total dependence is what makes viruses obligate intracellular parasites, and what makes them so hard to attack with drugs.

Answer: D

Correct answer: adsorption or attachment

The cycle begins with adsorption: a protein on the virus binds a specific receptor on the host cell. Nothing can follow until that happens, and which receptor the virus recognises is what decides its host range and the tissues it infects.

Answer: B

Correct answer: biosynthesis

The order is adsorption, penetration, uncoating, biosynthesis, maturation and release. The fourth step is where the viral genome is expressed and copied, using the host’s ribosomes and precursors.

Answer: A

Correct answer: Microorganisms increase in size of cell and metabolic rate

In the lag phase there is no increase in cell number: the organisms are adapting to the new medium, synthesising the enzymes and intermediates they need. The cells grow larger and their metabolic rate rises, and only then does division begin.

Answer: B

Correct answer: The cells start dividing and their number increase by geometric progression

In the log (exponential) phase the cells divide at a constant rate, so their number doubles at each generation - a geometric progression, which plots as a straight line on a logarithmic scale. This is the phase in which the population is most uniform and most susceptible to antibiotics, since so many cells are building walls.

Answer: C

Correct answer: Rate of multiplication and death becomes almost equal

In the stationary phase nutrients are running short and toxic products accumulating, so the rate of division falls until it exactly balances the rate of death. The viable count therefore stays level, though the cells within it are constantly being replaced. Spores and secondary metabolites are typically produced here.

Answer: D

Correct answer: Population of the cells decreases

In the decline (death) phase deaths outnumber divisions, so the viable population falls - often exponentially. Nutrients are exhausted and toxic products have accumulated; some cells lyse altogether.

Answer: A

Correct answer: differential media

Endo medium contains lactose and a fuchsin-sulphite indicator, so lactose fermenters such as E. coli grow as dark red colonies with a metallic sheen while non-fermenters stay colourless. Distinguishing organisms by their appearance on the plate is what makes a medium differential.