All living things are composed of cells, from just one to many trillions, whose details usually are visible only through a microscope. As multicellular organisms develop, their cells differentiate. A typical cell of any organism contains genetic instructions that specify its traits. Those traits may be modified by environmental influences.
Sexual reproduction produces offspring that inherit half their genes from each parent.
DNA is the genetic material of living organisms, and is located in the chromosomes of each cell. Biological evolution accounts for the diversity of species developed through gradual processes over many generations. Evidence from rocks allows us to understand the evolution of life on Earth. Rocks are often found in layers with the oldest generally on the bottom. The anatomy and physiology of plants and animals illustrate the complementary nature of structure and function.