BackChapter 2: The Chemical Context of Life – General Biology 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 takes up space and has mass. Understanding the nature of matter is fundamental to biology, as it underpins the structure and function of all biological molecules.
Matter: Anything that occupies space and has mass.
Element: A substance that cannot be broken down into other substances by chemical reactions.
Compound: A substance consisting of two or more elements combined in a fixed ratio.
Emergent Properties: Compounds have characteristics different from those of their constituent elements.
Example: Sodium (Na) is a reactive metal, and chlorine (Cl) is a poisonous gas, but together they form sodium chloride (NaCl), which is table salt, a safe and essential compound for life.
Elements and Compounds
Matter is made up of elements, and elements combine to form compounds. The properties of compounds are often very different from the properties of the elements that compose them.
Elements: Pure substances consisting of only one type of atom.
Compounds: Substances formed from two or more elements in a specific ratio.
Emergent Properties: New properties arise when elements combine to form compounds.
Example: Na (sodium) + Cl (chlorine gas) → NaCl (sodium chloride).
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 the 92 natural elements are required for life.
Major Elements: Carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) make up about 96% of living matter.
Minor Elements: Calcium (Ca), phosphorus (P), potassium (K), and sulfur (S) make up most of the remaining 4%.
Trace Elements: Required in minute quantities (e.g., iron, iodine).
Table: Elements in the Human Body
The following table summarizes the major elements found in the human body and their relative abundance.
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% |
Trace elements (less than 0.01% of mass): 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), zinc (Zn).
Key Terms and Concepts
Essential Elements: Elements required for an organism to survive, grow, and reproduce.
Trace Elements: Elements required by organisms in very small amounts.
Emergent Properties: New properties that arise when elements combine to form compounds, which are not present in the individual elements.
Example: Emergent Properties in Compounds
When sodium (a soft, reactive metal) and chlorine (a poisonous gas) combine, they form sodium chloride (NaCl), which is table salt—a safe and essential nutrient for humans.
Additional info: The study of elements and compounds is foundational for understanding biological molecules, cellular processes, and the chemistry of life.
