Anatomy & Physiology

Anatomy & Physiology Study Guide

©2018 Achieve Page 58 5.10 Chapter Five Review Atoms are the basic particles of matter: • Atoms are the smallest units of matter. They consist of protons, neutrons, and electrons. • The number of protons in an atom is its atomic number. Each element includes all the atoms that have the same number of protons and thus the same atomic number. • Within an atom, an electron cloud surrounds the nucleus. • The mass number of an atom is the total number of protons and neutrons in its nucleus. Isotopes are atoms of the same element whose nuclei contain different numbers of neutrons. • Electrons occupy an orderly series of energy levels, commonly illustrated as electron shells. Chemical bonds are forces formed by atom interactions: • Atoms combine through chemical reactions creating chemical bonds. A molecule is any chemical structure consisting of atoms held together by covalent bonds. A compound is a chemical substance made up of atoms of two or more elements. • An ionic bond will result from the attraction between ions, or atoms that have gained or lost electrons. Cations are positively charged; anions are negatively charged. • Atoms that share electrons to form a molecule are held together by covalent bonds. The sharing of one pair of electrons is a single covalent bond; the sharing of two pairs is a double covalent bond. A bond with equal sharing of electrons is a nonpolar covalent bond; a bond with unequal sharing of electrons is a polar covalent bond. • Matter can exist as a solid, a liquid, or a gas, depending on the nature of the interactions among the component atoms or molecules. Decomposition, synthesis, and exchange reactions are important chemical reactions in physiology: • A chemical reaction occurs when reactants are rearranged to form one or more products. Collectively, all the chemical reactions in the body constitute its metabolism. • Kinetic energy is the energy of motion. Potential energy is stored energy that results from the position or structure of an object. • A chemical reaction is classified as a decomposition, a synthesis, or an exchange reaction. • Cells gain energy to power their functions by catabolism, the breakdown of complex molecules. Much of this energy supports anabolism, which is the synthesis of new molecules. Enzymes catalyze specific biochemical reactions by lowering a reaction’s activation energy: • Exergonic (exothermic) reactions release energy; endergonic (endothermic) reactions absorb energy. • Activation energy is the amount of energy required to start a reaction. Enzymes are catalysts— compounds that accelerate chemical reactions without themselves being permanently changed or consumed. Enzymes promote chemical reactions by lowering the activation energy requirements. • Inorganic compounds usually lack carbon, and organic compounds always contain carbon: of 368