Take a look around you! The chair you're sitting in, the tree see when you look out the window, and even you are made up of matter. Matter is anything that has mass and occupies space.

Elements are the simplest type of matter and have unique chemical and physical properties. An element is a form of matter that cannot be decomposed into simpler substances by ordinary chemical methods. As of the year 2000, there were 112 known elements, but just 6 of the elements make up more than 99% of all matter in living systems.

The elements hydrogen and oxygen are found in water, H-2-O. Water is the most abundant substance in the human body. For example, the liquid part of the blood, called plasma, is about 90% water. Most substances from "organic" or living sources, like the hemoglobin molecule we see here, contain large amounts of the element carbon. Nitrogen is found in all of the amino acids that form proteins in our body. The elements calcium and phosphorous are found in large quantities in bone. Phosphorous is also an important component of DNA, our genetic material.

Five elements are found in small amounts in living organisms: sodium, magnesium, sulfur, chlorine, and potassium.

In addition to the 6 primary elements and 5 secondary elements, living organisms also require several additional elements. A trace element is an element required in minute quantities by an organism to maintain proper physical functioning. Trace elements make up less than 0.01% of body weight, compared to the 6 primary elements that make up 99% of body weight. Trace elements include: boron, fluorine, silicon, vanadium, chromium, manganese, iron, cobalt, copper, zinc, selenium, molybdenum, tin, and iodine. All together, living organisms use just 25 of the 112 elements currently known.

Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education