The Chemical Context of Life Chapter 2 Matter consists of chemical elements in pure form and in combinations called compounds Organisms are composed of matter Matter is anything that takes up space and has mass ? 2011 Pearson Education, Inc. Elements and Compounds Matter is made up of elements An element is a substance that cannot be broken down to other substances by chemical reactions A compound is a substance consisting of two or more elements in a fixed ratio A compound has characteristics different from those of its elements ? 2011 Pearson Education, Inc. Figure 2.3 Sodium Chlorine Sodium chloride The Elements of Life About 20?25% of the 92 elements are essential to life, but it varies among organisms Humans need 25 elements while plants only need 17 elements