뒤로Chapter 2: The Chemical Context of Life – Study Notes
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Chapter 2: The Chemical Context of Life
Concept 2.1: Matter Consists of Chemical Elements in Pure Form and in Combinations Called Compounds
All living organisms are composed of matter, which is anything that occupies space and has mass. Understanding the nature of matter is fundamental to biology, as it underlies the structure and function of all biological molecules.
Element: A pure substance that cannot be broken down into other substances by chemical reactions. Each element is defined by its unique atomic structure.
Compound: A substance consisting of two or more elements combined in a fixed ratio. Compounds have emergent properties that are different from those of their constituent elements.
Example: Sodium (Na) is a reactive metal, and chlorine (Cl) is a poisonous gas. When combined, they form sodium chloride (NaCl), or table salt, which is safe to consume.
Elements and Compounds
Matter is made up of elements and compounds, each with distinct properties and roles in biological systems.
Emergent Properties: Compounds often exhibit properties that are not present in their individual elements.
Example: The formation of NaCl from sodium and chlorine demonstrates how new properties arise from chemical combination.
The Elements of Life
Of the 92 naturally occurring elements, only a small subset is essential for life. These elements are required for the structure and function of biological molecules.
Essential Elements: About 20–25% of elements are essential for life. The four most abundant are carbon (C), hydrogen (H), oxygen (O), and nitrogen (N), making up approximately 96% of living matter.
Other Important Elements: Calcium (Ca), phosphorus (P), potassium (K), and sulfur (S) contribute to the remaining 4%.
Trace Elements: Elements required in minute quantities, such as iron (Fe) and iodine (I), are vital for specific biological functions.
Table: Elements in the Human Body
Element | Symbol | Percentage of Body Mass (including water) |
|---|---|---|
Oxygen | O | 65.0% |
Carbon | C | 18.5% |
Hydrogen | H | 9.5% |
Nitrogen | N | 3.3% |
Calcium | Ca | 1.5% |
Phosphorus | P | 1.0% |
Potassium | K | 0.4% |
Sulfur | S | 0.3% |
Sodium | Na | 0.2% |
Chlorine | Cl | 0.2% |
Magnesium | Mg | 0.1% |
Additional info: Trace elements (less than 0.01% of mass) include boron (B), chromium (Cr), cobalt (Co), copper (Cu), fluorine (F), iodine (I), iron (Fe), manganese (Mn), molybdenum (Mo), selenium (Se), silicon (Si), tin (Sn), vanadium (V), and zinc (Zn).
