6 Microbial Physiology Module 6: Microbial growth

Which is not true about bacterial cell division?

• There is increase in cellular constituents

• Bacteria divide by binary fission

• There is increase in cellular structure

• Daughter cells can be distinguished from mother cells

Answer explanation

Answer is D. When organisms divide by binary fission, it is not possible to distinguish the resulting cells from the mother cell.

Reference:

Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A.

(2018). Brock biology of microorganisms. Pearson Higher Education.

https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_%28Boundless%29/06%3A_Culturing_Microorganisms/6.06%3A_Microbial_Growth/6.6A%3A_Binary_Fission

The lag phase is characterized by:

• Production of new enzymes and protoplasmic constituents

• Increase in cell number or mass

• Decrease in cell number or mass

• Production of secondary metabolites

Answer explanation

Answer is A. During lag phase, there is synthesis of new protoplasmic constituents and enzymes while there is no immediate increase in cell number or mass.  

Reference:

Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A.

(2018). Brock biology of microorganisms. Pearson Higher Education.

https://microbiologynotes.org/bacterial-growth-curve-definition-phases-and-measurement/

The generation time of a bacterium is defined as:

• The length of time of the exponential phase

• The length of time it takes for a population to double

• The length of time it takes to reach the log phase

• The length of time it takes to reach the stationary phase

Answer explanation

Answer is B. Generation time (g) is defined as the length of time it takes for a population to double.

Reference:

Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A.

(2018). Brock biology of microorganisms. Pearson Higher Education.

White, D., Drummond, J., Drummond, J. T., & Fuqua, C. (2012). The physiology

and biochemistry of prokaryotes. Oxford University Press, USA.

Yu, L., Yan, X., Ye, C., Zhao, H., Chen, X., Hu, F., & Li, H. (2015). Bacterial Respiration and Growth Rates Affect the Feeding Preferences, Brood Size and Lifespan of Caenorhabditis elegans. PLoS ONE, 10(7), e0134401. https://doi.org/10.1371/journal.pone.0134401

Superoxide ion is toxic to strict anaerobes because:

• They lack oxidase

• They lack peroxidase

• They lack catalase

• They lack dismutase

Answer explanation

Answer is B. Superoxide ions are highly reactive oxygen species that can be toxic to strict anaerobes since they lack the enzyme peroxidase. Peroxidase helps neutralize reactive oxygen species, such as superoxide ions, by catalyzing the conversion of hydrogen peroxide (H2O2) into water (H2O) and oxygen (O2), which is essential for maintaining the anaerobic environment that strict anaerobes require for their metabolic processes.When peroxidase is absent, superoxide ions accumulate and damage the cellular components of anaerobes, leading to the disruption of their metabolic pathways and eventually cell death. In contrast, organisms with peroxidase, like many facultative anaerobes and aerobes, can efficiently neutralize superoxide ions and other reactive oxygen species, allowing them to thrive in the presence of oxygen. 

Reference:

Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A.

(2018). Brock biology of microorganisms. Pearson Higher Education.

White, D., Drummond, J., Drummond, J. T., & Fuqua, C. (2012). The physiology

and biochemistry of prokaryotes. Oxford University Press, USA.

The electron source used by chemolithoheterotrophs is:

• Light

• Carbon dioxide

• Organic molecules

• Inorganic compounds

Answer explanation

Answer is D. Chemolithoheterotrophs use inorganic compounds as electron source.

Reference:

Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A.

(2018). Brock biology of microorganisms. Pearson Higher Education.

http://www.greeninglab.com/wp-content/uploads/2016/05/Lecture-4-1.pdf