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Chapter 2 Notes


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P a g e | 1 [ CAMPBELL BIOLOGY: CHAPTER 2 NOTES ] Overview: Chemical Foundations of Biology Living organisms and the world they live in are subject to the basic laws of physics and chemistry. Biology is a multidisciplinary science, drawing on insights from other sciences. Life can be organized into a hierarchy of structural levels. At each successive level, additional emergent properties appear. Concept 2.1 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. ° Matter is made up of elements. An element is a substance that cannot be broken down into other substances by chemical reactions. ° There are 92 naturally occurring elements. ° Each element has a unique symbol, usually the first one or two letters of the name. Some of the symbols are derived from Latin or German names. A compound is a substance consisting of two or more elements in a fixed ratio. ° Table salt (sodium chloride or NaCl) is a compound with equal numbers of atoms of the elements chlorine and sodium. ° While pure sodium is a metal and chlorine is a gas, they combine to form an edible compound. This change in characteristics when elements combine to form a compound is an example of an emergent property. 25 chemical elements are essential to life. About 25 of the 92 natural elements are known to be essential for life. ° Four elements—carbon (C), oxygen (O), hydrogen (H), and nitrogen (N)—make up 96% of living matter. ° Most of the remaining 4% of an organism’s weight consists of phosphorus (P), sulfur (S), calcium (Ca), and potassium (K). Trace elements are required by an organism but only in minute quantities. ° Some trace elements, like iron (Fe), are required by all organisms. ° Other trace elements are required by only some species. For example, a daily intake of 0.15 milligrams of iodine is required for normal activity of the human thyroid gland. Concept 2.2 An element’s properties depend on the structure of its atoms Each element consists of unique atoms. An atom is the smallest unit of matter that still retains the properties of an element.
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P a g e | 2 ° Atoms are composed of even smaller parts, called subatomic particles. ° Two of these, neutrons and protons, are packed together to form a dense core, the atomic nucleus, at the center of an atom. ° Electrons can be visualized as forming a cloud of negative charge around the nucleus. Each electron has one unit of negative charge. Each proton has one unit of positive charge. Neutrons are electrically neutral. The attractions between the positive charges in the nucleus and the negative charges of the electrons keep the electrons in the vicinity of the nucleus.
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