As muscle contracts, the overlap between the thin and thick filaments increases, decreasing the length of the sarcomere—the contractile unit of the muscle—using energy in the form of ATP. At the molecular level, this is a cyclic, multistep process that involves binding and hydrolysis of ATP, and movement of actin by myosin.

Alleles are different forms of the same gene. Humans and other diploid organisms inherit two alleles of every gene, one from each parent.

The Integral Test is a method for determining whether an infinite series converges or diverges by comparing the series to an improper integral. It is especially useful when the terms of a series are difficult to add directly, but they follow the values of a related continuous function. Instead of summing infinitely many discrete terms one by one, the test studies the area under a curve that represents the same pattern of decrease.A glow stick provides a useful example of this idea. After...