There are about 120 million rods in the human retina. The cones are not as sensitive to light as the rods. However, cones are most sensitive to one of three different colors (green, red or blue). Signals from the cones are sent to the brain which then translates these messages into the perception of color.
The concave disc shape of red blood cells Maximizes the surface area of the cell , allowing for rapid movement of oxygen or carbon dioxide to and form the hemoglobin within the cell.
