The following is some practice reading and using the term "react" or "reaction."

This course is concerned with the chemical reactions that are fundamental to basic biological functions, such as:

• heredity (how enzymes build DNA molecules to pass traits on to offspring)
• emotions have their physical basis in chemical reactions
• reproduction (how cells divide their genetic material and their cellular contents when one cell splits into two cells)
• growth (how cells produce new organic molecules as cells enlarge)
• photosynthesis (how solar energy is stored in organic molecules of plant tissue)
• cellular respiration (how cells breakdown food molecules and use the energy)

Chemistry can be defined as the study of how atoms "react" for form molecules.  For atoms to join together to form a molecule, a chemical reaction must occur; and for a molecule to break a part, a chemical reaction must occur.

Some reactions are spontaneous under normal earth conditions, such as two oxygen atoms forming oxygen gas (O₂) or two hydrogen atoms joining with an oxygen to produce a water (H₂O) molecule.

Other reactions, especially those involving organic molecules (carbohydrates, fats, proteins and nucleic acids), normally require the enzymes of living cells to occur.  However, early in the 1900's chemists learned how to use high temperatures and chemical catalysts to cause these organic reactions to occur in a test tube.