1 DNA is a polymer. 2  Individual monomer units are called nucleotides. 3  The DNA polymer is composed of: 4  a backbone of molecules of the sugar deoxyribose (a 5 carbon sugar). 5  phosphate groups linking the deoxyribose sugar molecules together in a chain. The DNA polymer is composed of: 2  a backbone of molecules of the sugar deoxyribose (a 5 carbon sugar). 3  phosphate groups linking the deoxyribose sugar molecules together in a chain. 4  four principal bases (2 are pyrimidines and 2 are purines):
Rods and cones function as photoreceptors in the retina of the eye, turning visible light into neuronal signals, which are sent to the brain. This process is called transduction. Rods and cones perform at different wavelengths and sensitivities allowing detailed perception of light and color.
Rods work at very low levels of light. We use these for night vision because only a few bits of light (photons) can activate a rod. Rods don't help with color vision, which is why at night, we see everything in a gray scale. The human eye has over 100 million rod cells. Cones require a lot more light and they are used to see color.