Singlet oxygen is a name given to several higher-energy species of molecular O
2 in which all the electron spins are paired. It is much more reactive towards common organic molecules than is molecular oxygen per se. In nature, singlet oxygen is commonly formed from water during photosynthesis, using the energy of sunlight. It is also produced in the troposphere by the photolysis of ozone by light of short wavelength, and by the immune system as a source of active oxygen. Carotenoids in photosynthetic organisms (and possibly also in animals) play a major role in absorbing energy from singlet oxygen and converting it to the unexcited ground state before it can cause harm to tissues.
What is the name for a form of oxygen in which electrons are paired? To what is singlet oxygen more reactive? In what process is singlet oxygen usually formed? By what process is singlet oxygen made in the tropophere? What objects in organisms absorb singlet oxygen to prevent harm?