The heart is the organ that drives the circulatory system. In humans, it consists of four chambers with two that collect blood called atria and two that pump blood called ventricles. The heart's valves prevent blood pumped out of the ventricles from flowing back into the heart.

Force is applied to change an object's speed or direction of motion.

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

After air enters through the nose, it passes through the nasal cavity which filters, moistens, and warms it. Further filtering takes place in the pharynx, which also helps protect against infection, and then in the trachea which is just past the epiglottis, responsible for preventing food from entering the airway.

The cell nucleus contains the genetic material of the cell and is where DNA replication takes place.