Heterotrophs primarily depend on which process for their energy source?

Heterotrophs are organisms that cannot produce their own food and must rely on consuming organic matter from other organisms to obtain their energy. This group includes animals, fungi, and many bacteria. They metabolize the organic compounds found in the food they consume to derive energy through processes such as respiration. In particular, these organisms break down the complex organic molecules into simpler substances, releasing energy stored in those molecules.

While photosynthesis is crucial for autotrophs, which use sunlight to create organic compounds, it is not a process heterotrophs utilize to obtain energy. Respiration is indeed a key process for heterotrophs, as they use it to convert the organic matter they consume into usable energy, but it follows their initial consumption of that matter. Cellular division is essential for growth and reproduction but does not directly pertain to energy acquisition. Thus, the primary method through which heterotrophs derive their energy is through the consumption of organic matter, making this the correct emphasis in the context of the question.