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.
The testicle or testis is the male gonad in animals. Like the ovaries to which they are homologous, the testicles (testes) are components of both the reproductive system and the endocrine system. The primary functions of the testes are to produce sperm (spermatogenesis) and to produce androgens, primarily testosterone. Both functions of the testicle are influenced by gonadotropic hormones produced by the anterior pituitary. Luteinizing hormone (LH) results in testosterone release.