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

The nervous system consists of the brain and spinal cord (central nervous system) and the peripheral nervous system which is the network of nerve cells (neurons) that collect and distribute signals from the central nervous system throughout the body.

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

Small quantities of certain minerals like iron, calcium, magnesium, and salt are important for nutrition and health.

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