Cellular respiration is the process by which cells obtain energy from respiratory substrates. Glucose is one type of respiratory substrate. The substances needed are glucose, oxygen and water. Carbon dioxide, water and energy are produced.
Cellular respiration is represented by a chemical reaction which, when balanced, obeys the Law of Conservation of Matter:
C₆H₁₂0₆+60₂ — 6C0₂+6H₂0
The number of atoms of reactants equals the number of atoms of products: Six carbon atoms, 12 hydrogen atoms, 18 oxygen atoms. No atoms are created or destroyed in this process, they’re just rearranged into different molecules.