By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium.[6] At standardized conditions for temperature and pressure, two atoms of the element bind to form dioxygen, a diatomic gas that is colorless, odorless, and tasteless, with the formula OMany major classes of organic molecules in living organisms, such as proteins, nucleic acids, carbohydrates, and fats, contain oxygen, as do the major inorganic compounds that are constituents of animal shells, teeth, and bone. Most of the mass of living organisms is oxygen as it is a part of water, the major constituent of lifeforms (for example, about two-thirds of human body mass).[citation needed] Elemental oxygen is produced by cyanobacteria, algae and plants, and is used in cellular respiration for all complex life.
đang được dịch, vui lòng đợi..