Microbial bioenergetics — Organisms that use organic compounds specifically as their electron donors are called:

Difficulty: Easy

Correct Answer: organotrophs

Explanation:


Introduction / Context:
Microbes can be categorized by their energy source, electron source, and carbon source. This nomenclature (photo/chemo, litho/organo, auto/hetero) is essential for understanding ecological niches and designing culture media. The question focuses on the electron donor classification when the donor is organic carbon.


Given Data / Assumptions:

  • “Electron donor” is the substance oxidized in catabolism.
  • Organic compounds include carbohydrates, lipids, and many reduced organics.
  • We must choose the correct “-troph” term for electron donor origin.


Concept / Approach:
Organotrophs obtain electrons from organic compounds; lithotrophs obtain electrons from reduced inorganic substances (e.g., H2, NH3, NO2−, Fe2+, H2S). Phototrophs use light as their energy source (not an electron donor designation), while chemotrophs use chemicals for energy (either organic or inorganic). Therefore, the most precise term for organisms using organic electron donors is “organotrophs.”


Step-by-Step Solution:

Identify the classification axis: electron donor source.Map organic electron donors to the “organo-” designation.Select “organotrophs” as the accurate term and reject energy-source-only labels.


Verification / Alternative check:
Typical heterotrophic bacteria are chemoorganoheterotrophs: they use chemicals for energy (chemo-), organic compounds as electron donors (organo-), and organic carbon as the carbon source (hetero-).


Why Other Options Are Wrong:

  • Lithotrophs: use inorganic electron donors.
  • Phototrophs: describes energy source (light), not electron donor source.
  • Chemotrophs: describes energy source (chemicals), not specifically organo versus litho.


Common Pitfalls:
Confusing the three axes (energy, electrons, carbon). Remember: photo/chemo (energy), organo/litho (electrons), hetero/auto (carbon).


Final Answer:
organotrophs

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