The Chemical Level of Organization – Study Notes for Anatomy & Physiology

The Chemical Level of Organization

Introduction to Chemistry and Matter

Chemistry is fundamental to understanding the structure and function of living organisms. At its core, chemistry deals with matter, which is anything that occupies space and has mass.

• Chemistry: The science that studies the composition, structure, properties, and changes of matter.

• Matter: Anything that takes up space and has mass; includes solids, liquids, and gases.

Atoms and Atomic Structure

Subatomic Particles and Atomic Organization

Atoms are the smallest stable units of matter and are composed of subatomic particles. The arrangement and interactions of these particles determine the chemical properties of elements.

• Atom: The basic unit of matter, consisting of a nucleus and an electron cloud.

• Subatomic particles:

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

  • Neutrons (n): Neutral, located in the nucleus.

  • Electrons (e-): Negatively charged, orbit around the nucleus.

• Nucleus: Central region of the atom containing protons and neutrons.

• Electron cloud: Area surrounding the nucleus where electrons are found.

Atomic Number, Electron Shells, and Atomic Models

The atomic number is the number of protons in an atom and determines the element. Electrons occupy specific energy levels or shells around the nucleus.

• Atomic number: Number of protons in the nucleus; unique to each element.

• Electron shell: Two-dimensional representation of the electron cloud; shells hold a limited number of electrons.

• First shell: Holds up to 2 electrons.

• Second shell: Holds up to 8 electrons.

• Valence shell: Outermost shell; determines chemical reactivity.

Elements in the Human Body

Principal Elements and Their Significance

The human body is composed of several key elements, each with specific roles in physiological processes.

Element (% of total body weight)	Significance
Oxygen, O (65)	Component of water and other compounds; essential for respiration
Carbon, C (18.6)	Found in all organic molecules
Hydrogen, H (9.7)	Component of water and most other compounds in the body
Nitrogen, N (3.2)	Found in proteins, nucleic acids, and other organic compounds
Calcium, Ca (1.8)	Found in bones and teeth; important for membrane function, nerve impulses, muscle contraction, and blood clotting
Phosphorus, P (1.0)	Found in bones and teeth, nucleic acids, and high-energy compounds
Potassium, K (0.4)	Important for proper membrane function, nerve impulses, muscle contraction

Element (% of total body weight)	Significance
Sodium, Na (0.2)	Important for blood volume, membrane function, nerve impulses, and muscle contraction
Chlorine, Cl (0.2)	Important for blood volume, membrane function, and water absorption
Magnesium, Mg (0.06)	A cofactor for many enzymes
Iron, Fe (0.004)	Essential for oxygen transport and energy capture
Iodine, I (0.0002)	A component of hormones of the thyroid gland
Trace elements	Some function as cofactors; the functions of many trace elements are poorly understood Additional info: Trace elements include silicon (Si), fluorine (F), copper (Cu), manganese (Mn), zinc (Zn), selenium (Se), cobalt (Co), molybdenum (Mo), cadmium (Cd), chromium (Cr), tin (Sn), aluminum (Al), boron (B), and vanadium (V).

Key Terms

• Element: Pure substance composed of only one kind of atom; cannot be broken down by ordinary means.

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

• Mass number: Number of protons plus neutrons in an atom.

• Radioisotope: Isotope with an unstable nucleus; undergoes radioactive decay.

Example: Carbon-12 and Carbon-14 are isotopes of carbon, differing in their number of neutrons.

*Additional info: The atomic structure and elemental composition are foundational for understanding physiological processes such as respiration, nerve conduction, and muscle contraction.*