Heterotrophs & Autotrophs

Biology: IB Diploma Higher Level, topic 8.2.4

Autotrophic organisms synthesize organic molecules from carbon dioxide. In contrast, heterotrophic organisms obtain carbon from organic compounds.

Photosynthetic and chemosynthetic organisms are both grouped into a category known as autotrophs.
Autotrophs are organisms capable of synthesizing their own food.
More specifically, they are capable of using inorganic carbon as a carbon source.
Autotrophs are critical for all ecosystems.
Without these organisms, energy would not be available to other living organisms and life itself would not be possible.

Photoautotrophs, such as plants, algae, and photosynthetic bacteria, serve as the energy source for a majority of the world’s ecosystems.
These ecosystems are often described by grazing food webs.
Photoautotrophs harness the solar energy of the sun by converting it to chemical energy in the form of ATP (and NADP).
The energy stored in ATP is used to synthesize complex organic molecules, such as glucose.

Chemoautotrophs are primarily bacteria that are found in rare ecosystems where sunlight is not available.
An example of such an ecosystem would be the dark caves or hydrothermal vents at the end of the oceans.
Many chemoautotrophs in hydrothermal vents use hydrogen sulfide released from the vents as a source of chemical energy.
This allows chemoautotrophs to synthesize complex organic molecules, like glucose, for their own energy and in turn supply energy to the rest of the ecosystem.
This process can be done in the abscence of oxygen.

Heterotrophs acquire the high-energy carbon compounds from autotrophs by consuming them.
Heterotrophs then break the organic molecules present in autotrophs down through respiration to obtain cellular energy, such as ATP.
These organic molecules can include carbohydrates, lipids, and proteins.
The heterotroph hydrolyzes these organic molecules before they are metabolized through respiration.

Test yourself on Heterotrophs & Autotrophs