Like the respiratory system, the circulatory system serves to transport oxygen throughout the body while removing carbon dioxide. In addition, the circulatory system transports nutrients from the digestive system.

The Kuiper Belt is similar to the asteroid belt but much larger. Extending beyond the orbit of Neptune, it contains objects composed mostly of frozen methane, ammonia, and water. Most notably, the Kuiper Belt is home to Pluto, a dwarf planet that, until a 2006 reclassification, was considered the ninth planet of the solar system.

The rows of the Periodic Table are called periods and contain elements that have the same number of electron shells ordered from lower to higher atomic number.

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.

The water (hydrologic) cycle describes the movement of water from Earth through the atmosphere and back to Earth. The cycle starts when water evaporates into a gas from bodies of water like rivers, lakes and oceans or transpirates from the leaves of plants.