Final answer:
The reactants for cellular respiration are provided by breathing in oxygen and eating food, which supplies oxygen and glucose required for energy production in the form of ATP.
Step-by-step explanation:
The two activities that provide the reactants for cellular respiration are breathing in oxygen and eating food. When we breathe in, oxygen enters our body and is transported through the blood to all our cells, where it is used in cellular respiration. Eating food provides glucose and other nutrients that are broken down to release energy. Glucose, specifically, is the main fuel used in cellular respiration. Thus, it is the combined action of inhaling oxygen and consuming food that supplies the essential reactants needed for the production of ATP, which is the energy currency of cells.