Blood is created in bone marrow and is made up of cells suspended in liquid plasma. Red blood cells carry oxygen, white blood cells fight infection, and platelets are cell fragments that allow blood to clot.

The broadest classification of life splits all organisms into three groups called domains. The three domains of life are bacteria, archaea and eukaryota.

A substance undergoes a phase transition when it moves from one state of matter to another, for example, when water freezes or boils.

Radiation occurs when electromagnetic waves transmit heat. An example is the heat from the Sun as it travels to Earth.

During intercourse, the penis ejaculates sperm, produced in the testes, into the vagina. Some of the sperm makes their way to the uterus where, if they encounter an egg to fertilize, unite with the ovum to form a fertilized egg or zygote. The zygote then may implant in the uterus and eventually develop into a fetus.