In this chapter, the reader is introduced to a number of different cell types, including red blood cells, white blood cells and brain cells. Red blood cells are responsible for delivering oxygen to the retina, which is a part of the body that contains photoreceptors, or cells that produce light. Brain cells, on the other hand, are involved in the process of sending signals to other cells in the body, including the brain. The reader is also introduced to the concept of induced pluripotent stem, or iPS, a type of stem cell that can be used to create many different kinds of cells, including those that make up the body's organs.