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 | |
|---|---|---|
| Definition | An organism that produces its own food by synthesizing organic compounds from simple inorganic substances such as carbon dioxide, using an energy source like sunlight. | An organism that cannot make its own food and obtains nutrition by consuming other organisms or organic matter. |
| Etymology | From Greek 'autos' (self) + 'trophe' (nourishment) — meaning 'self-feeding.' | From Greek 'heteros' (other) + 'trophe' (nourishment) — meaning 'other-feeding.' |
| Produce own food | Yes | No |
| Trophic role | Producer | Consumer or decomposer |
| Food chain level | First — the base of the food chain. | Second and higher (primary, secondary, and tertiary consumers). |
| Energy source | Sunlight (photoautotrophs) or energy from inorganic chemical reactions (chemoautotrophs). | Chemical energy stored in the organic compounds of the food they consume. |
| Carbon source | Inorganic carbon, mainly carbon dioxide (CO2). | Organic carbon obtained from other organisms. |
| Metabolic process | Photosynthesis or chemosynthesis to build organic molecules. | Digestion and cellular respiration to break down organic molecules. |
| Gas exchange | Photoautotrophs absorb CO2 and release O2 during photosynthesis — but they also respire, using O2, like all living cells. | Take in O2 and release CO2 through cellular respiration. |
| Pigments / chlorophyll | Photoautotrophs contain chlorophyll or other pigments to capture light. | Generally lack chlorophyll and cannot capture light energy. |
| Types | Photoautotrophs (use light) and chemoautotrophs (use chemical energy). | Photoheterotrophs and chemoheterotrophs; ecologically grouped as herbivores, carnivores, omnivores, and decomposers. |
| Dependence on others | Independent; do not rely on other organisms for food. | Dependent on autotrophs or other heterotrophs for food. |
| Role in ecosystem | Form the base of every food web; the main entry point through which energy and inorganic carbon enter living systems. Nearly all other life depends on them. | Transfer energy up the food chain; decomposers like fungi and many bacteria recycle nutrients back to soil and air for autotrophs to reuse. |
| Exceptions (mixotrophs) | Not always strict — mixotrophs like Euglena and some carnivorous plants make food by photosynthesis yet also consume organisms. | Mixotrophs blur the line, consuming food while also producing some via photosynthesis (e.g., Euglena, certain dinoflagellates). |
| Common misconception | Being non-animal doesn't make something an autotroph — fungi look plant-like but are heterotrophs. The label is about making food, not about being a plant. | A heterotroph need not ingest food — fungi and many bacteria absorb dissolved organic matter rather than swallowing it. |
| Examples | Plants, algae, cyanobacteria, and some bacteria. | Animals, fungi, protozoa, and most bacteria; includes herbivores, omnivores, and carnivores. |
| What or How they eat ? | Produce their own food for energy via photosynthesis or chemosynthesis. | They eat other organisms to obtain organic molecules for energy and growth. |
Energy Production
Monotropastrum humile, a myco-heterotroph dependent on fungi throughout its lifetime
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 |
A flowchart explaining the various types of trophs
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.
Food cycle between autotrophs and heterotrophs
Photosynthesis 
Aerobic 
Mold 
Mildew 
Eukaryotic Cell 
Mitosis
Comments: Autotroph vs Heterotroph