4 Microorganisms in Their Natural Envts (Soil, Water, Air)

Refers to the community of organisms that inhabit the surface layer of water bodies, particularly at the air-water interface.

• Pleuston

• Neuston

• Littoral zone

• Benthos

• 
  Neritic zone

Answer explanation

Answer: Neuston

The term neuston refers to the group of organisms associated with the surface layer of lakes, oceans, and slow-moving sections of streams. This assemblage includes species living just beneath the water surface (hyponeuston), those above but still immersed in the water (epineuston), and organisms that move across the surface on hydrophobic structures (superneuston), which is more accurately considered a form of epineuston.

References:

Thorp, J. H. (2014). Functional relationships of freshwater invertebrates. In Elsevier eBooks (pp. 65–82). https://doi.org/10.1016/b978-0-12-385026-3.00004-8

Toleukhanov, A. (2012). Bio-reactive two-phase transport and population dynamics in underground storage of hydrogen: natural self-organisation. Proceedings. https://doi.org/10.3997/2214-4609.20143214

Generally, when the altitude increases, what happens to the atmospheric pressure, temperature, and concentration of available oxygen?

• decrease, increase, decrease

• increase, increase, increase

• decrease, decrease, increase

• decrease, decrease, decrease

• increase, decrease, increase

Answer explanation

Answer: decrease, decrease, decrease

With increasing height in the atmosphere, the atmospheric pressure declines and the concentration of the available oxygen decrease to a point that precludes aerobic respiration.

Image from:

https://kids.britannica.com/students/assembly/view/107829

Which of the following is not a reason why spores are better adapted in the atmosphere?

• Metabolically active

• 
  Produced in very high numbers

• Relatively of small size and low density

• With protective structures

Answer explanation

Answer: Metabolically active

The correct answer is “Metabolically active” because bacterial spores are not metabolically active; rather, they are in a dormant state. This dormancy is what makes them highly resistant and well adapted to harsh atmospheric conditions. Active metabolism would require constant nutrient supply and environmental stability, which are not guaranteed in the atmosphere. In contrast, dormancy allows spores to conserve energy and survive extreme stresses such as UV radiation, desiccation, heat, and nutrient limitation.

References:

Setlow, P. (2016). Spore Resistance Properties. Microbiology Spectrum, 4(2). https://doi.org/10.1128/microbiolspec.TBS-0003-2016

https://biologyease.com/endospore/

Which of the following is true about the atmo-ecosphere?

• Substantial microorganisms in the upper troposphere

• Several viral and bacterial (not fungal) diseases are spread through the atmosphere

• No known autochthonous microorganisms

• There are no reports on temporary locations in the troposphere that may provide habitats for microorganisms

Answer explanation

Answer: No known autochthonous microorganisms

There are no known autochthonous (native) microorganisms in the atmosphere because it is an extremely hostile environment lacking the necessary water and nutrients for continuous growth and reproduction. The atmosphere is not a suitable habitat, instead serving as a transport medium where microbes are passive travelers, originating from surfaces like soil and plants. They are dispersed by air currents and undergo a continuous cycle of exposure to harsh conditions such as dehydration, strong UV radiation, and oxidants, leading to high mortality rates. 

Reference:

Gupta A, Gupta R, Singh RL. Microbes and Environment. Principles and Applications of Environmental Biotechnology for a Sustainable Future. 2016 Oct 15:43–84. doi: 10.1007/978-981-10-1866-4_3. PMCID: PMC7189961.

https://kids.frontiersin.org/articles/10.3389/frym.2022.629355

Which soil horizon does maximal accumulation of materials such as iron oxides, aluminum oxides, and silicate clays occur?

• A

• B

• O

• C

• R

Answer explanation

Answer: B

The soil horizon where the maximal accumulation of materials like iron oxides, aluminum oxides, and silicate clays occurs is the B horizon. The B horizon, often called the "subsoil," is the zone where clay, iron, and other minerals leached from upper horizons accumulate due to a process called illuviation. 

Reference:
Hartemink, A., Zhang, Y., Bockheim, J., Curi, N., Silva, S., Grauer-Gray, J., Lowe, D., & Krasilnikov, P. (2019). Soil horizon variation: A review. Advances in Agronomy, 125–185. https://doi.org/10.1016/bs.agron.2019.10.003

Which of the following is NOT true about soil microflora?

• Very few microorganisms are free in the soil solution

• Most microorganisms reside in microcolonies attached to the soil particles

• Microorganisms are autochthonous

• All groups of microorganisms are represented in the soil.

Answer explanation

Answer:

Soil microflora are indeed not solely native (autochthonous) but also include zymogenous (transient, stimulated by sudden nutrient increases) and allochthonous (foreign, imported) populations, creating a dynamic and diverse community that adapts to changing conditions. Autochthonous microbes utilize native soil organic matter, while zymogenous microbes require external nutrients for growth and allochthonous microbes originate from other environments. 

Reference:

Langer, U., Böhme, L., & Böhme, F. (2004). Classification of soil microorganisms based on growth properties: a critical view of some commonly used terms. Journal of Plant Nutrition and Soil Science, 167(3), 267–269. https://doi.org/10.1002/jpln.200421362

Madigan, M. T., Martinko, J. M., Bender, K. S., Buckley, D. H., Sattley, W.M. & Stahl, D. A. (2018). Brock biology of microorganisms (Fifteenth edition.). Boston: Pearson.

Which of the following factors DOES NOT affect soil microflora?

• Moisture

• Temperature

• Oxygen concentration

• pH

• All of the aforementioned effect soil microflora

Answer explanation

Answer: All of the aforementioned effect soil microflora

Factors affecting soil microflora include temperature, soil moisture, soil pH, oxygen availability, soil organic matter, soil texture, vegetation and plant root exudates, and microbial interactions.

References:

https://microbiologyclass.net/factors-that-affect-microbial-population-in-the-soil/#:~:text=Posted%20on%20August%2029%2C%202023,ion%20concentration%20of%20any%20environment.

https://www.fao.org/agriculture/crops/thematic-sitemap/theme/spi/soil-biodiversity/soil-organisms/physical-factors-affecting-soil-organisms/en/#:~:text=Temperature,to%20around%20121%C2%B0C.

Which DOES NOT describe the limnetic zone of lakes? 

• It is the region of the lake where light penetrates to the bottom.

• The dominant primaryproducers are planktonic algae.

• It is an area of open wateraway from the shore

• The compensation depth of this zone is the lowest level of effective light penetration

• None of the aforementioned

Answer explanation

Answer: It is the region of the lake where light penetrates to the bottom.

The statement "It is the region of the lake where light penetrates to the bottom" does not describe the limnetic zone because this feature characterizes the littoral zone, where light reaches the lakebed and supports rooted plants. In contrast, the limnetic zone refers to the open water away from the shore, extending only to the depth of effective light penetration, where phytoplankton serve as the main primary producers. Thus, the given description confuses the limnetic zone with the littoral zone.

Reference:

Wetzel, R. G. (2001). Limnology: Lake and River Ecosystems. 3rd Edition. Academic Press.

Which is NOT a characteristic of oligotrophic lakes? 

• They have low concentrations of nutrients

• Typically, they are deep, have a larger hypolimnion than epilimnion.

• They have relatively lowprimary productivity

• Oxygen concentrations are usually lower in oligotrophic lakes due to low primary productivity.

• None of the choices

Answer explanation

Answer: Oxygen concentrations are usually lower in oligotrophic lakes due to low primary productivity.

Oligotrophic lakes, despite their low nutrient levels and low primary productivity, typically have higher oxygen concentrations, especially in deeper waters. Their clear, cold, and well-mixed conditions allow oxygen to penetrate and remain throughout the hypolimnion, unlike eutrophic lakes where decomposition depletes oxygen at depth.

Reference:

Knoll, L. B., Williamson, C. E., Pilla, R. M., Leach, T. H., Brentrup, J. A., & Fisher, T. J. (2018). Browning-related oxygen depletion in an oligotrophic lake. Inland Waters, 8(3), 255–263. https://doi.org/10.1080/20442041.2018.1452355

https://guides.nynhp.org/oligotrophic-dimictic-lake/#:~:text=Oligotrophic%20lakes%20are%20low%20in,and%20have%20good%20water%20clarity.

https://www.pearson.com/channels/biology/learn/jason/ecology/freshwater-aquatic-biomes

Which of the following is NOT a function of freshwater microorganisms?

• Decompose dead organic matter

• Assimilate and introduce dissolved organic matter

• Perform mineral cycling activities

• Contribute to secondary but not primary productivity

• Food source

Answer explanation

Answer: Contribute to secondary but not primary productivity

Freshwater microorganisms significantly contribute to primary productivity by converting inorganic nutrients into organic matter through photosynthesis and chemosynthesis. These microscopic primary producers, including various microalgae and cyanobacteria, form the base of aquatic food webs, supplying energy and organic compounds for other organisms in the ecosystem.

References:

D’Costa, P. M., & Naik, R. K. (2019). Advances in sampling strategies and analysis of phytoplankton. In Elsevier eBooks (pp. 501–521). https://doi.org/10.1016/b978-0-12-817497-5.00031-8

https://www.eolss.net/sample-chapters/c03/E6-59-88-00.pdf

https://fiveable.me/limnology/unit-4