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:
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:
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:
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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