This unit covers the processes of photosynthesis, extinction, biomimicry and bioremediation. In the first lesson on photosynthesis, students learn how engineers use the natural process of photosynthesis as an exemplary model of a complex yet efficient process for converting solar energy to chemical energy or distributing water throughout a system. In the next lesson on species extinction, students learn that it is happening at an alarming rate. Students discover that the destruction of habitat is the main reason many species are threatened and how engineers are trying to stop this habitat destruction. The third lesson introduces students to the idea of biomimicry-or looking to nature for engineering ideas. And, in the fourth and final lesson, students learn about a special branch of engineering called bioremediation-the use of living organisms to aid in the clean up of pollutant spills.