Microbiology Practice Exam 2025 - Free Microbiology Practice Questions and Study Guide

Chemoautotrophs are a unique group of organisms that obtain energy through the oxidation of inorganic substances, such as hydrogen sulfide, ammonia, or ferrous iron, rather than from sunlight. This is the primary distinction between them and photoautotrophs, which harness energy from sunlight through photosynthesis.

Both chemoautotrophs and photoautotrophs are classified as autotrophs because they utilize carbon dioxide as their carbon source. While photoautotrophs utilize sunlight for energy and fix carbon dioxide in the process of photosynthesis, chemoautotrophs utilize chemical reactions involving inorganic molecules to extract energy, which they then use to fix carbon dioxide into organic compounds.

In contrast to the correct choice, the other responses do not accurately describe the relationship between these types of organisms. Chemoautotrophs do not gain energy from sunlight; instead, their energy comes from chemical reactions. Photoautotrophs do not rely on consuming organic compounds; rather, they synthesize their own organic compounds from carbon dioxide using energy derived from sunlight. Both groups do not use organic material for energy—chemoautotrophs rely on inorganic compounds while photoautotrophs use sunlight. Hence, the clear distinction of