This work is devoted to the discussion of the peculiarities of studying the optical and photovoltaic properties of plants in order to increase the effectiveness of the study of the biological potential of plants and their protection. In the article we try to analyze the validity of our conclusions, citing proven experimental methods of solid state physics for studying plants. These studies were conducted on a wide range of plants. The analysis of the obtained results allows us to conclude that the main the result obtained in the studies of photoelectrical properties with the application of the methods developed and improved by us can actually serve to control the condition of the plant, acting as a kind of markers in the study of their biological potential. © Published under licence by IOP Publishing Ltd.