An atom is the smallest component of an element that still retains the properties of the element.

Animal cells are surrounded by a semipermeable membrane which allows for the transfer of water and oxygen to and from the cell. In plant cells, the cell membrane is surrounded by a somewhat rigid cell wall which provides the cell structure and support.

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.

Found in both animal sources (meat, fish, eggs, cheese) and vegetables (beans, nuts, some grains), proteins are important for the body's maintenance, growth, and repair.

Food is mixed with gastric acid and pepsin in the stomach to help break down protein.