An organism is a living thing. Multicellular organisms have multiple cells and unicellular organisms have 1 cell.

Characteristics Of Organisms (Living Things)

1. Organizations (Cells)
2. Reproduction (To make babies)
3. Stimuli
4. Homeostasis
5. Metabolism (energy)
6. Evolution & adaptations

Heterotrophs get energy from eating food and autotrophs create their own food from sunlight, carbon dioxide, and oxygen (photosynthesis).

Hope this helps!​