Science often means different things to different people. to many it means bodies of knowledge about the physical world grouped under different subjects; to some it means research or the pursuit of truth; to some it means the development of technology intended to benefit mankind; and to others it means finding out. experimenting, measuring. these are all different aspects of science, as the knowledge, experimenting, technology, etc., have all been produced by what could be called the "processes of science". environmental problems are just one aspect of life to which science can be applied, but they are quite urgently in need of solution. some science concepts are particularly relevant in the solving of environmental issues. among them are 1. energy (types of energy, law of conservation of energy, and law of energy degradation); 2. ecosystem (energy flow in ecosystems, law of conservation of matter, nutrient cycling in ecosystems, evolution of ecosystems); 3. resources (the nature of resources: inexhaustible, renewable, irreplaceable); 4. food (production, nutrition, energy use); 5. pollution (pollutant, threshold, synergy, persistence, biological magnification); 6. human population (growth and control, birth rate, death rate, fertility rate, marriage age, density, and distribution).