BackChapter 2: The Chemical Context of Life – Study Notes
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Chapter 2: The Chemical Context of Life
Introduction
This chapter explores the fundamental chemical principles that underlie biological processes. Understanding the chemical context of life is essential for studying how living organisms function at the molecular level.
Concept 2.1: Matter Consists of Chemical Elements in Pure Form and in Combinations Called Compounds
Definition of Matter
Matter is anything that takes up space and has mass.
All organisms are composed of matter.
Elements and Compounds
Element: A substance that cannot be broken down into other substances by chemical reactions.
Compound: A substance consisting of two or more elements in a fixed ratio.
Compounds have emergent properties that are different from those of their constituent elements.
Example: Sodium (Na) and chlorine (Cl) combine to form sodium chloride (NaCl), which has properties distinct from either element.
Elements Essential for Life
About 20-25% of the 92 natural elements are essential for life.
Major elements: Carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) make up about 96% of living matter.
Other important elements: Calcium (Ca), phosphorus (P), potassium (K), and sulfur (S) constitute most of the remaining 4%.
Trace elements: Required in minute quantities (e.g., iron, iodine).
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% |
Trace elements | - | <0.01% |
Adaptation to Toxic Elements
Some elements can be toxic to organisms.
Certain species can adapt to environments containing toxic elements (e.g., plants adapted to serpentine soils).
What Determines the Properties of a Compound?
A compound is made of atoms joined by bonds.
The number of protons determines an atom’s identity.
An atom’s electron distribution determines its ability to form bonds.
A compound’s properties depend on its atoms and how they are bonded together.
Example: Formic acid (HCOOH) has properties determined by its atomic composition and structure.
*Additional info: The introductory images and diagrams illustrate the importance of chemical structure in determining biological function, such as the role of formic acid in ants.*
