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upload3 - Chemical Context of Life-Atoms Atomic Bonds...

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Chemical Context of Life--Atoms, Atomic Bonds 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 At each successive level of organization, from atoms to molecules to cells to organs and systems, additional emergent properties appear. A. Elements and Compounds 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 such as H for hydrogen, or Ca for calcium. Some of the symbols are derived from Latin or German names such as Na for sodium or Fe for iron. 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. Pure sodium and chlorine are awful; but the combination in NaCl is ordinary table salt. This change in behavior is an example of emergent properties , new behaviors emerge when nature combines elements. 2. 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).
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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. B. Atoms and Molecules 1. Atomic structure determines the behavior of an element. Each element consists of unique atoms. An atom is the smallest unit of matter that still retains the properties of an element. ° Atoms are composed of even smaller parts, called subatomic particles. There are many subatomic particles, but in biology we are concerned with only three stable 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 moving about the nucleus can be visualized as forming a cloud of negative charge around the nucleus.
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