Oxygen gas is produced during photosynthesis by photolysis of water in the chloroplasts of algae and green plants and in the thylakoid of cyanobacteria. The chlorophyll of photosystem II absorbs light energy which leads to the excitation and knocking out of an electron within the photosystem.
The energy released as a result of returning the electrons to the ground state in an acceptor molecule is used in splitting water molecules into hydrogen and oxygen. The electron released from the splitting of water replaces the one knocked out from the photosystem II while oxygen atoms from two water molecules combine to form diatomic oxygen which is later released as oxygen gas.
The whole process of photolysis of water and the release of oxygen gas happens during the light-dependent reaction of photosynthesis.
Normal people can't breed cats by modifying their DNA, so options b and c are eliminated. Breeding cats for specific traits is not natural, so it is not choice a, either. Instead, selective breeding is d. artificial selection.
