[Solved] Phenylalanine is a(n)____ and the starting point for a network of metabolic pathways. A) lactase precursor molecules B) carbohydrate by-products of respiration C) essential amino acid D) sub-types of hemoglobin E) phenylthiocarbamides Stage and Light Source: Key components of a microscope that support the specimen and provide necessary illumination for viewing. Objective and Ocular Lenses: Components of a microscope, where the objective lens is close to the object being observed for magnification, and the ocular lens or eyepiece is what the viewer looks through at the magnified image. Upside Down: Oriented in the opposite direction to the usual, with the top or upper part turned toward the bottom. Naked Eye: Refers to the observation of objects without the use of magnification instruments.