Your body has a layer of skin that protects it from the environment. This layer of skin is made up of many individual skin cells. Explain where all the cells came from and how two individual cells share the same traits.

Stratum Corneum This layer is composed of the many dead skin cells that you shed into the environment—as a result, these cells are found in dust throughout your home. This layer helps to repel water.

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.