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.
Special cells called Rods and Cones are used to process light, in a human eye, their number is estimated to be 5-7 million Cones and 110-130 million Rods. Cones are found mainly in the central area of the Retina (Fovea), while Rods are found in the Peripheral Retina. The Photoreceptors respond to light, it causes the activation and consequent breakdown of a photo-sensitive pigment, bound in large quantities to the membranes of the outer segment.