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

Hard bones provide primary support for the endoskeleton while more flexible cartilage is found at the end of all bones, at the joints, and in the nose and ears. In addition to providing support and protecting bodily organs, bones also produce blood cells and store minerals like calcium.

The carbon cycle represents the ciruit of carbon through Earth's ecosystem. Carbon dioxide (CO₂) in the atmosphere is absorbed by plants through photosynthesis. Plants then die and release carbon back into the atmosphere during decomposition or are eaten by animals who breathe (respiration) the carbon into the atmosphere they exhale and produce waste which also releases carbon as it decays.

A neutron is a subatomic particle found in the nucleus of an atom. It is neutral as it carries no electric charge.

A population is a group of organisms of the same species who live in the same area at the same time. A community is a group of populations living and interacting with each other in an area.