Question

A bacterium obtains energy from a chemical source by the oxidation of reduced \({NO}_2^{-}\), with \({CO}_2\) as the principal carbon source. Which one of the following nutritional groups does this bacterium belong to?

• A. Photoautotroph.
• B. Photoheterotroph.
• C. Chemautotroph.
• D. Chemoheterotroph.

Hint:

Chemoautotrophs are organisms that obtain energy from the oxidation of inorganic compounds, such as reduced nitrogen or sulfur, and use \({CO}_2\) as their carbon source. This is in contrast to photoautotrophs, which rely on light for energy.

Answer 1

The Correct Option is C

The bacterium described in the question obtains its energy by the oxidation of a chemical source, specifically the reduction of \({NO}_2^{-}\), and uses \({CO}_2\) as its carbon source. This indicates that the bacterium is using chemical energy (from the oxidation of \({NO}_2^{-}\)) and inorganic carbon (from \({CO}_2\)) for its metabolic needs. This type of organism is classified as a chemoautotroph. Chemotrophs obtain energy from chemical compounds, and autotrophs use inorganic carbon sources like \({CO}_2\). Therefore, the correct answer is (C).
- (A): Photoautotrophs obtain their energy from sunlight (photosynthesis) and use \({CO}_2\) as a carbon source. Since this bacterium uses chemical energy, statement (A) is incorrect.
- (B): Photoheterotrophs obtain their energy from light but use organic carbon sources (not \({CO}_2\)) for carbon. This is not the case for the described bacterium, so statement (B) is incorrect.
- (D): Chemoheterotrophs obtain energy from chemical sources and use organic carbon sources. This bacterium uses \({CO}_2\), an inorganic carbon source, so it cannot be classified as a chemoheterotroph. Hence, statement (D) is incorrect.
Thus, the correct answer is (C), chemoautotroph.