Material and energy metabolism takes place continuously between plants and their surrounding environment. Plants not only create biomass but also reduce technological pollutants in the environment. Temperature pulsations in the plant's gas exchange system induce thermodynamic processes that are involved in energy conversion. It has been found that during the sunny day of the day, the plant leaf is powered by a thermal jet engine (a biological prototype of a thermal engine) that generates mechanical energy. The operation of a plant leaf heat engine (biological prototype) is based on the change in pressure potential energy in the leaf gas exchange system. The generated mechanical energy in the plant leaf stimulates gas exchange with the environment and intensifies the assimilation process. Theoretical and experimental studies are presented, which show plant leaf temperature fluctuations, plant leaf stomata pressure pulsations. The thermal efficiency coefficient η_t of a plant leaf heat engine is very low. η_t = 0.003 and depends on the natural environmental conditions of the solar radiation density provided to the plant leaf, and the mechanical energy is converted from 0.06 to 0.6W/m². Energy conversion is 0.3% of the heat involved in the convective heat exchange of the sheet with the environment. The principle and possibility of transforming the thermal energy used in the vital processes of plants into mechanical energy have been used in the technique of plant leaf relatively recently.