Microbiology Practice Exam

A chemoheterotroph is defined by its mode of nutrition, which involves obtaining carbon from organic compounds rather than from carbon dioxide, as is the case with autotrophs. These organisms rely on consuming other living or dead organisms, or their byproducts, which are rich in organic materials, for both energy and carbon. This characteristic distinguishes chemoheterotrophs from other types of organisms, such as photoautotrophs that use sunlight for energy or those that fix carbon directly from inorganic sources.

The choice that states organisms derive carbon from carbon dioxide refers to autotrophs, which produce their own organic material from inorganic sources. Meanwhile, the option about living without oxygen describes anaerobic organisms rather than defining a chemoheterotroph, which can still require oxygen for metabolic processes depending on the specific strains or conditions. Therefore, the defining feature of chemoheterotrophs is their dependence on organic material for both energy and carbon sources.