aktiivne hapnikuühend mis organismides kahjustab teisi ühendeid, eriti lipiide, oksüdeerides neid, Singlet oxygen is a high-energy form of oxygen which in organisms damages other substances, especially lipids in a cell by oxydaiting them. it is also is linked to a oxidation of LDL cholesterol and resultant cardiovascular effects. In photosynthesis, singlet oxygen can be produced from the light-harvesting chlorophyll molecules.