Chemistry of Life

This chapter introduces the fundamental chemical principles that underlie the structure and function of living organisms, providing a foundation for understanding Anatomy & Physiology.

Atoms

Atoms are the smallest units of matter that retain the properties of an element. They are composed of subatomic particles and form the basis of all chemical substances in the body.

• Protons (p+): Positively charged particles located in the nucleus.

• Neutrons (n0): Uncharged (neutral) particles also found in the nucleus.

• Electrons (e-): Negatively charged particles that orbit the nucleus in electron shells.

• Example: A carbon atom has 6 protons, 6 neutrons, and 6 electrons.

Elements

Elements are pure substances that cannot be broken down into simpler substances by ordinary chemical means. Each element is defined by its atomic number.

• Atomic Number: The number of protons in the nucleus of an atom, unique to each element.

• Mass Number: The sum of protons and neutrons in the nucleus.

• Isotopes: Atoms of the same element with different numbers of neutrons.

• Periodic Table: Organizes elements by increasing atomic number and similar chemical properties.

• Major Elements in the Human Body: Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N) make up about 96% of body mass.

Additional info: Trace elements are required in very small amounts but are essential for health (e.g., iron, iodine).

Mixtures

Mixtures are combinations of two or more substances that are physically blended but not chemically bonded. The components retain their original properties.

• Suspensions: Heterogeneous mixtures with large particles that settle out over time (e.g., blood with red blood cells).

• Colloids: Mixtures with small particles that do not settle out and are not visible to the naked eye (e.g., milk).

• Solutions: Homogeneous mixtures where one substance (solute) is dissolved in another (solvent). The particles do not settle out (e.g., salt water).

• Solute: The substance that is dissolved.

• Solvent: The substance in which the solute dissolves (in biological systems, water is the most common solvent).

• Example: Blood plasma is a solution; milk is a colloid; blood with cells is a suspension.

Table: Types of Mixtures