1. Glucose: This is the primary fuel source for cellular respiration. It's a simple sugar that's broken down to release energy. Animals obtain glucose from their food, either directly (like eating fruit) or indirectly (by breaking down carbohydrates like starch into glucose).

2. Oxygen: Oxygen acts as the final electron acceptor in the electron transport chain, the stage of cellular respiration where the majority of ATP (energy) is produced. Animals obtain oxygen from breathing air or through their skin (in aquatic animals).

3. Water: Water is required for various reactions within cellular respiration. It's also a product of the process. Animals get water from drinking or from the food they eat.

In addition to these three main substances, cellular respiration also requires:

* Enzymes: These proteins act as catalysts, speeding up the various chemical reactions within the process.

* Coenzymes: These molecules assist enzymes in carrying out their functions. Examples include NAD+ and FAD.

Let me know if you'd like more details about how these substances are used in cellular respiration!