Ecological Systems and Devices Annotation << Back Features of Development of the Population Microalgae Depending on the Concentration of Photosensitize in the Environment Dallakyan G.A. Singlet oxygen produced by photosensitizers in the light, at low concentrations, stimulates the growth of algae, increase chlorophyll content, rate of oxygen, and, conversely, in high concentrations, suppresses them. When the concentration of singlet oxygen is higher than the threshold at 5 mg/l Rose Bengal, there is suppression of all physiological parameters of a population of algae. This dramatically increases the concentration of malondialdehyde end product of lipid. What causes increased lipid peroxidation is a target for singlet oxygen. Shown that singlet oxygen changes, rare, with the aquatic environment, does not penetrate into the cell. Part of singlet oxygen enters the cell separately. Another part of the singlet oxygen formed from Rose Bengal directly in cells. Singlet oxygen at high concentrations inhibit the release of oxygen, disabling the photosystem II in chloroplasts. Extremely high reactivity of singlet oxygen, allowing them to react with different structural and functional components of cells, causing oxidative stress. It is shown that for contaminated water photosensitizers need to have a preliminary biochemical and biophysical analysis of their impact on the test object. Keywords: algae; singlet oxygen; chlorophyll; phytoplankton; Rose Bengal. Contacts: E-mail: honarisbk@.ru Pp. 52-59.