Which of the following types of microorganisms uses CO2 as a carbon source and H2 as an energy source?

• A. Chemoautotrophs
• B. Photoheterotrophs
• C. Chemoheterotrophs
• D. Photoautotrophs

Answer: (A)

Verified step by step guidance

1. Understand the terms involved: 'carbon source' refers to where the microorganism obtains carbon for building cellular components, and 'energy source' refers to how it obtains energy to drive metabolic processes.
2. Identify the meaning of 'autotroph' and 'heterotroph': autotrophs use CO2 as their carbon source, while heterotrophs use organic compounds as their carbon source.
3. Recognize the energy sources: 'chemo-' means the organism obtains energy from chemical compounds, and 'photo-' means it obtains energy from light.
4. Match the given options with their definitions: Chemoautotrophs use inorganic chemicals (like H2) as an energy source and CO2 as a carbon source; Photoheterotrophs use light for energy but organic compounds for carbon; Chemoheterotrophs use chemical compounds for energy and organic compounds for carbon; Photoautotrophs use light for energy and CO2 for carbon.
5. Conclude that the microorganism using CO2 as a carbon source and H2 as an energy source fits the definition of chemoautotrophs.