Overview
This lecture introduces the core levels of biological organization, focusing on atoms, elements, and atomic structure as foundations for understanding human biology and key chemical principles relevant to biological processes.
Levels of Biological Organization
- Life is organized in hierarchical levels: atoms, molecules, organelles, cells, tissues, organs, organ systems, and the organism.
- Atoms (e.g., carbon, hydrogen, oxygen) combine to form molecules (e.g., water, DNA).
- Molecules form organelles (e.g., nucleus, mitochondria), which perform specific functions within cells.
- Cells are the smallest living units and display all characteristics of life.
- Tissues are groups of similar cells performing common functions (e.g., muscle, nerve tissue).
- Organs consist of two or more tissues working together (e.g., stomach, heart).
- Organ systems are groups of organs functioning together (e.g., cardiovascular, nervous system).
- The organism level encompasses the entire human body, made up of 11 organ systems.
Matter, Elements, and Essential Elements
- Matter is anything with mass and volume; it exists in solid, liquid, or gas states.
- Matter is composed of elements, substances that cannot be broken down by normal physical means.
- Elements are represented on the periodic table by symbols (e.g., C for carbon, O for oxygen).
- 92 naturally occurring elements exist; 25 are essential to life, with four (O, C, H, N) making up 96% of the human body.
- Trace elements are required in small amounts (e.g., iodine, iron) but are vital for body functions.
Atomic Structure and Subatomic Particles
- Atoms consist of protons (positive charge), neutrons (no charge), and electrons (negative charge).
- Protons and neutrons are found in the nucleus (center) of the atom; electrons orbit in energy shells.
- Atomic number (smaller number) equals number of protons and electrons in a neutral atom.
- Atomic mass (larger number) equals number of protons plus neutrons; neutrons = atomic mass – atomic number.
Isotopes and Radioactivity
- Isotopes are atoms of the same element with different numbers of neutrons, resulting in different atomic masses.
- Some isotopes are radioactive and decay over time; they are used in medicine and dating fossils.
Electron Shells and the Octet Rule
- Electrons occupy energy shells: first shell holds 2, second 8, third 18 electrons.
- The outermost shell is the valence shell; atoms are stable when this shell is full (octet rule: 8 electrons).
- Atoms not meeting the octet rule are reactive and will gain, lose, or share electrons to achieve stability.
- Noble gases are stable, while most atoms (e.g., sodium, chlorine) are reactive.
Practice: Atomic Diagrams and Stability
- Determine protons, neutrons, and electrons using atomic number and atomic mass.
- Diagram atoms by placing protons and neutrons in the nucleus; distribute electrons in shells.
- Stability is based on a full valence shell: helium is stable (full first shell), sodium and chlorine are reactive (incomplete outer shells).
Key Terms & Definitions
- Atom — Smallest unit of an element, made of protons, neutrons, and electrons.
- Molecule — Two or more atoms bonded together.
- Organelle — Structure within a cell performing specific functions.
- Element — Pure substance made of only one kind of atom.
- Proton — Positively charged subatomic particle in the nucleus.
- Neutron — Neutrally charged subatomic particle in the nucleus.
- Electron — Negatively charged subatomic particle in shells around the nucleus.
- Atomic Number — Number of protons in an atom; defines the element.
- Atomic Mass — Total number of protons and neutrons in an atom’s nucleus.
- Isotope — Atoms of the same element with different numbers of neutrons.
- Valence Shell — The outermost electron shell of an atom.
- Octet Rule — Atoms tend to be stable with 8 electrons in their valence shell.
- Trace Element — Essential element needed in small amounts.
Action Items / Next Steps
- Review and answer study guide questions for atoms and atomic structure.
- Practice drawing atomic diagrams and applying the octet rule.
- Read textbook sections on chemical and biological organization and atomic structure.
- Use provided practice questions and solutions to prepare for quizzes and exams.