Part of the peripheral nervous system, the autonomic nervous system regulates involuntary activity in the heart, stomach, and intestines.

An ecosystem is a biological community of interacting organisms and their physical environment. This includes both the biotic (living) and abiotic (non-living).

The columns of the Periodic Table are called groups and all elements in a group have the same number of electrons in their outer electron shell. The group that an element occupies generally determines its chemical properties as the number of outer shell electrons establishes the way it reacts with other elements to form molecules. So, because each element has the same number of electrons in its outer shell, each has similar reactivity.

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

Weight is a force that describes the attraction of gravity on an object. Force is measured in newtons (N) with 1 N being the force required to impart an acceleration of 1 m/s² to a mass of 1 kg.