What does the designation ‘autotroph’ imply about an organism’s mode of obtaining carbon?
A It obtains carbon via photosynthesis.
B It obtains carbon from organic molecules formed by other organisms.
C It obtains carbon from inorganic sources such as CO2.
D It can only grow and survive in the presence of 02.
The correct answer and explanation is:
The correct answer is C: It obtains carbon from inorganic sources such as CO2.
Autotrophs are organisms that can produce their own food from inorganic substances. The term “autotroph” comes from the Greek words “auto,” meaning self, and “troph,” meaning nourishment. This designation refers to an organism’s ability to synthesize organic molecules, particularly carbohydrates, from inorganic carbon sources. The primary source of carbon for autotrophs is carbon dioxide (CO2) from the environment.
There are two main types of autotrophs based on how they obtain energy to drive the process of carbon fixation:
- Photoautotrophs use light as an energy source to convert CO2 into organic molecules. This process is most commonly seen in plants, algae, and some bacteria. They use sunlight to power the process of photosynthesis, where CO2 and water are converted into glucose (C6H12O6) and oxygen.
- Chemoautotrophs obtain energy from chemical reactions, often involving inorganic compounds such as hydrogen sulfide or ammonia. This type of autotrophy is found in certain bacteria and archaea, which live in extreme environments like deep-sea vents.
In contrast, heterotrophs (such as animals, fungi, and most bacteria) obtain their carbon by consuming organic molecules formed by other organisms. Heterotrophs cannot fix carbon from inorganic sources, so they depend on autotrophs or other heterotrophs for their carbon source.
The ability of autotrophs to obtain carbon from inorganic sources allows them to be at the base of ecological food webs. By producing their own organic compounds, they serve as primary producers, supporting the rest of the ecosystem. This characteristic also distinguishes them from organisms like heterotrophs, which rely on other organisms for their carbon and energy needs.