Anatomy & Physiology

Anatomy & Physiology Study Guide

Chapter 5: The Chemical Level of Organization 5.1 Atoms Chemistry is the study of the structure, composition, and interactions of matter. Matter is defined as anything that takes up space and has mass. Mass, the amount of material in matter, is a physical property that determines the weight of an object. The mass of an object is similar to weight; however, weight depends on the gravitational force exerted, whereas mass does not. Energy is matter in motion. There are two types of energy: kinetic (energy in action) and potential (stored energy). Energy can take many forms depending on how it is converted. Some of these forms include chemical, electrical, mechanical, and electromagnetic energy. The smallest units of matter are called atoms . The unique characteristics of each object, living or nonliving, result from the types of atoms it is composed of and how they interact with each other. Atoms are composed of subatomic particles: protons, neutrons, and electrons. • Protons and neutrons are similar in size and mass, but protons ( + ) have a positive electrical charge. • Neutrons ( or 0 ) are electrically neutral. • Electrons ( − ) are much lighter than protons and hold a negative electrical charge. An equal number of protons and neutrons are normally found within atoms. The atomic number represents the number of protons in an atom. Hydrogen (H) has an atomic number of 1 and is the simplest atom. Thus, an atom of hydrogen contains one proton and one electron. Electrons travel around the nucleus at high speed, forming an electron cloud . Electrons travel in “shells” around the nucleus within the cloud. An electron tends to remain in its electron shell because the negatively charged electron is attracted to the positively charged proton. This electrical force of attraction between opposite electrical charges is involved in many physiological processes. Elements and Isotopes An element is a pure substance composed of atoms of only one kind. Only 92 elements exist in nature. About two dozen additional elements have been created through nuclear reactions in research laboratories. Every element has a chemical symbol, an abbreviation recognized by scientists everywhere. Most of the symbols are easily connected with the English names of the elements (i.e., O for oxygen, H for hydrogen, P for phosphorus), but a few are abbreviations of their Latin names. For example, the symbol for sodium, Na, comes from the Latin word natrium. Atoms of the same element, whose nuclei contain the same number of protons but different numbers of neutrons, are called isotopes . The nuclei of some isotopes spontaneously give off and let go of subatomic particles or radiation. Such isotopes are called radioisotopes , and the emission process is called radioactive decay . Strongly radioactive isotopes are dangerous because the emissions can break molecules apart, destroy cells, and otherwise damage living tissues.

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