chemical A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
chemical reaction A process that involves the rearrangement of the molecules or structure of a substance, as opposed to a change in physical form (as from a solid to a gas).
dairy Containing milk or having to do with milk. Or a building or company in which milk is prepared for distribution and sale.
digest (noun: digestion) To break down food into simple compounds that the body can absorb and use for growth. Some sewage-treatment plants harness microbes to digest — or degrade — wastes so that the breakdown products can be recycled for use elsewhere in the environment.
lactose A type of sugar found in milk and other dairy products.
lactose intolerance An inability to easily digest lactose, a sugar found in milk and other dairy products. People with this condition do not produce an enzyme (or enough of this enzyme) to break lactose down into two simpler sugars: glucose and galactose. These are more readily absorbed into the bloodstream for use in cells. The condition generally does not occur until after age 2. People — especially adults — that make too little of the enzyme lactase may develop abdominal pain, gas, bloating and diarrhea shortly after eating foods containing relatively large amounts of lactose.
molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
Stone Age A prehistoric period when weapons and tools were made of stone or of materials such as bone, wood, or horn. This period lasted millions of years and came to an end around 10,000 to 12,000 years ago.
