Chapter 2

1. Growth in prokaryotes mainly refers to increase in number.

• True

• False

Answer explanation

Growth in Microbiology is defined as an increase in number. Microbial cells have a finite life span and a species is maintained only as a result of continued growth of its population.

2. Most bacteria divide by binary fission.

• True

• False

Answer explanation

Some bacteria belonging to various lineages, including antibiotic-producing Streptomyces and predatory Bdellovibrio, proliferate by nonbinary fission, wherein three or more chromosome copies are synthesized and the resulting multinucleoid filamentous cell subdivides into progeny cells.

3. Secondary metabolites are produced during log phase.

• True

• False

Answer explanation

Secondary metabolites are produced during idiophase.

4. When you want to use viable cell count as a means of measuring growth, samples can be taken in any part of the growth cycle of a bacterium.

• True

• False

Answer explanation

Exponential phase cells are typically in their healthiest state and are thus most desirable for studies of their enzymes or other cell components.

5. Length of lag phase may depend on the nutrient composition of the medium.

• True

• False

Answer explanation

Lag phase may be brief or extended depending on the history of the cells used as inocula and the composition of the growth medium and growth conditions.

6. Streak plating can also be used for quantitative observation.

• True

• False

Answer explanation

Streak plating is used only for observing cultural characteristics of the target microorganism(s).

7. Direct microscopic count can be performed for both wet and dry samples.

• True

• False

Answer explanation

Microscopic counts can be performed either on samples dried on slides or on liquid samples. Dried samples can be stained to increase contrast between cellsand their background. With liquid samples, counting chambers consisting of a grid with squares of known area etched on the surface of a glass slide are used.

8. Filtration can be used for samples with high microbial load.

• True

• False

Answer explanation

Filtration is best used for dilute aquatic samples to concentrate the cells present in an aquatic sample.

9. Turbidimetric is an indirect method of determining cell count.

• True

• False

Answer explanation

A cell suspension looks cloudy (turbid) to the eye because cells scatter light that passes through the suspension. The more cells that are present, the more light is scattered, and hence the more turbid the suspension. Because cell mass is proportional to cell number, turbidity measurements can quickly estimate cell numbers in laboratory cultures.

10. MPN method can be used to measure non-coliforms.

• True

• False

Answer explanation

Selective media can be used for specific microorganisms. This technique can be used to count the total number of microorganisms, Salmonella, Staphylococcus, Enterococcus, Vibrio parahaemolyticus, Escherichia coli, coliforms, fecal coliforms, and others. Only living microorganisms are counted from the sample in the MPN technique.