Molecule: A group of atoms bonded together representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction.
Combustion: A high-temperature exothermic redox chemical reaction between a fuel and an oxidant, usually atmospheric oxygen, that produces oxidized products like water and carbon dioxide.
Hemoglobin:The protein molecule in red blood cells that carries oxygen from the lungs to the body's tissues and returns carbon dioxide from the tissues back to the lungs.