1. Glucose: This is the primary fuel source for cellular respiration. It's a simple sugar that cells break down to release energy. Glucose can come from:

* Food we eat: Carbohydrates in our food are broken down into glucose.

* Stored glycogen: Our bodies store glucose as glycogen in the liver and muscles.

* Other molecules: Cells can convert other molecules, like fatty acids and amino acids, into glucose if needed.

2. Oxygen: This is the final electron acceptor in the electron transport chain, the final stage of cellular respiration. Oxygen is needed to produce ATP, the energy currency of the cell. Oxygen comes from:

* Breathing: We take in oxygen through our lungs and it travels throughout the body in the blood.

While these are the main starting materials, cells also require:

* Water (H2O): Used in various steps of cellular respiration, particularly the electron transport chain.

* Enzymes: These are proteins that catalyze (speed up) the chemical reactions in cellular respiration.

Remember that cellular respiration is a complex process that involves a series of steps. These starting materials are necessary for the process to occur and for cells to generate energy.