Question

Photo lithotrophic autotroph organisms use

• A. Light energy, inorganic electron source and CO\(_2\) as its carbon source
• B. Chemical energy, organic electron source and CO\(_2\) as its carbon source
• C. Light energy, organic electron source and organic compounds as its carbon source
• D. Chemical energy, inorganic electron source and CO\(_2\) as its carbon source

Hint:

• Breakdown of metabolic classification terms:
  • Energy: Photo- (light), Chemo- (chemical).
  • Electrons: -litho- (inorganic), -organo- (organic).
  • Carbon: -autotroph (CO\(_2\)), -heterotroph (organic C).
• Plants are photolithoautotrophs (using H\(_2\)O as the electron donor).

Answer 1

The Correct Option is A

Organisms can be classified based on their sources of energy, electrons, and carbon:

• Energy Source:
  • Photo-: Light energy
  • Chemo-: Chemical energy (from oxidation of chemical compounds)
• Electron Source (Reducing Power):
  • -litho-: Inorganic electron donor (e.g., H\(_2\)O, H\(_2\)S, NH\(_3\), Fe\(^{2+}\))
  • -organo-: Organic electron donor (e.g., glucose, acetate)
• Carbon Source:
  • -autotroph: Uses inorganic carbon (primarily CO\(_2\)) as its main carbon source.
  • -heterotroph: Uses organic compounds as its main carbon source.

The term "Photo lithotrophic autotroph" (or photolithoautotroph) describes an organism that:

• Photo-: Uses light as its energy source.
• -litho-: Uses inorganic compounds as its electron source.
• -autotroph: Uses CO\(_2\) (inorganic carbon) as its primary carbon source.

This matches option (a): "Light energy, inorganic electron source and CO\(_2\) as its carbon source". Examples include plants, algae, and cyanobacteria (which use H\(_2\)O as the electron donor, producing O\(_2\)) and some photosynthetic bacteria like purple sulfur bacteria and green sulfur bacteria (which may use H\(_2\)S or other inorganic donors as electron sources). \[ \boxed{\text{Light energy, inorganic electron source and CO}_2 \text{ as its carbon source}} \]