Chemosynthetic organisms are capable of manufacturing their food from simple inorganic substances through the process of?

Analyze the question The question asks which process chemosynthetic organisms use to make food from simple inorganic substances.

Explain the concept Photosynthetic organisms use light energy to make food. Chemosynthetic organisms (mostly bacteria) use chemical energy instead. They get this energy by oxidizing inorganic substances such as ammonia, nitrites, hydrogen sulphide, sulphur, or iron compounds. The energy released from this oxidation is then used to build carbohydrates from carbon dioxide and water.

Examples:

• Nitrosomonas oxidizes ammonia to nitrite.
• Nitrobacter oxidizes nitrite to nitrate.
• Sulphur bacteria oxidize hydrogen sulphide to sulphur.
• Iron bacteria oxidize ferrous (Fe²⁺) to ferric (Fe³⁺) compounds.

Solution Checking each option:

• A. Oxidation: Correct. The oxidation of inorganic compounds is the energy source that drives chemosynthesis.
• B. Denitrification: This is the conversion of nitrates to nitrogen gas by denitrifying bacteria. It is not how food is manufactured.
• C. Reduction: Carbon dioxide is reduced during food synthesis, but this is also true of photosynthesis. It is not the distinguishing process of chemosynthesis, which is defined by oxidation of inorganic substances as the energy source.
• D. Phosphorylation: This is the addition of a phosphate group (for example in ATP formation). It is not the defining process here.

Answer The correct option is A. oxidation.

Exam tip Remember: Photosynthesis = light energy; Chemosynthesis = chemical energy from oxidation. When you see "chemosynthesis", think "oxidation of inorganic compounds".