Autotrophs are organisms that can produce their own food from the substances available in their surroundings using light (photosynthesis) or chemical energy (chemosynthesis). Heterotrophs cannot synthesize their own food and rely on other organisms — both plants and animals — for nutrition. Technically, the definition is that autotrophs obtain carbon from inorganic sources like carbon dioxide (CO2) while heterotrophs get their reduced carbon from other organisms. Autotrophs are usually plants; they are also called "self feeders" or "primary producers".
Comparison chart
| Autotroph | Heterotroph | |
|---|---|---|
| Produce own food | Yes | No |
| Food chain level | Primary | Secondary and tertiary |
| Types | Photoautotroph, Chemoautotroph | Photoheterotroph, Chemoheterotroph |
| Examples | Plants, algae, and some bacteria | Herbivores, omnivores, and carnivores |
| Definition | An organism that is able to form nutritional organic substances from simple inorganic substances such as carbon dioxide. | Heterotrophs cannot produce organic compounds from inorganic sources and therefore rely on consuming other organisms in the food chain. |
| What or How they eat ? | Produce their own food for energy. | They eat other organisms to get proteins and energy. |
Energy Production
Autotrophs produce their own energy by one of the following two methods:
- Photosynthesis - Photoautotrophs use energy from sun to convert water from the soil and carbon dioxide from the air into glucose. Glucose provides energy to plants and is used to make cellulose which is used to build cell walls. E.g. Plants, algae, phytoplankton and some bacteria. Carnivorous plants like pitcher plant use photosynthesis for energy production but depend on other organisms for other nutrients like nitrogen, potassium and phosphorous. Hence, these plants are basically autotrophs.
- Chemosynthesis - Chemoautotrophs use energy from chemical reactions to make food. The chemical reactions are usually between hydrogen sulfide/methane with oxygen. Carbon dioxide is the main source of carbon for Chemoautotrophs. E.g. Bacteria found inside active volcano, hydrothermal vents in sea floor, hot water springs.
Heterotrophs survive by feeding on organic matter produced by or available in other organisms. There are two types of heterotrophs:
- Photoheterotroph – These heterotrophs use light for energy but cannot use carbon dioxide as their carbon source. They get their carbon from compounds such as carbohydrates, fatty acids and alcohol. E.g. purple non-sulfur bacteria, green-non sulfur bacteria and heliobacteria.
- Chemoheterotroph – Heterotrophs that get their energy by oxidation of preformed organic compounds, i.e. by eating other organisms either dead or alive. E.g. animals, fungi, bacteria and almost all pathogens.
| Type of organism | Energy source | Carbon source |
|---|---|---|
| Photoautotroph | Light | Carbon dioxide |
| Chemoautotroph | Chemicals | Carbon dioxide |
| Photoheterotroph | Light | Carbon from other organisms |
| Chemoheterotroph | Other organisms | Other organisms |
Food Chain
Autotrophs do not depend on other organism for their food. They are the primary producer and are placed first in the food chain. Heterotrophs that depend on autotrophs and other heterotrophs for their energy level are placed next on the food chain.
Herbivores that feed on autotrophs are placed in the second trophic level. Carnivores that eat meat and omnivores that eat all types of organisms are placed next in the trophic level.
Photosynthesis 
Aerobic 
Mold 
Mildew 
Eukaryotic Cell 
Mitosis
Comments: Autotroph vs Heterotroph