Chapter 2 the chemical context of life. Matter consists of chemical elements in pure forms and in combinations called compounds. Matter is anything that takes up space and has a mass: composes organisms. Matter is made of elements: elements: a substance that cannot be broken down to other substances by chemical reactions. Compound: a substance consisting of two or more different elements combined in a fixed ratio: nacl table salt. 20-25% of 92 known elements are essential elements: essential elements: a chemical element required for an organism to survive, grow and reproduce, humans need 25 while plants only need 17. Oxygen, hydrogen, carbon and phosphorus make up about 96% of living matter. Trace elements: an element indispensable for life but required in extremely minute amounts: required by an organism in small amounts, some (iron) are needed by all organisms, while others are only needed by some. Iodine is essential for animals with vertebrates: low causes thyroid gland to grow.