The environment means surroundings in which people, animals and plants develop and exist. The branch of biology investigating relation ships between living beings and their environment is called ecology. Science reflects the concern about the balance of nature. Ecologists and environmentalists are very well aware of the bad state of the environment and the necessity of its protection. The most serious ecological problems of today are the pollution of air, water and soil, disappearance of many species of animal and plants, the weather changes, acid rains, the warning up of the Earth surface, the destruction of tropical rain forests and the breaking of the ozone layer.