Rhodopsin is defined as

• A. The final adjustment and alignment of an aircraft and its flight control system that provides the proper aerodynamic characteristics.
• B. The four fundamental risk elements in aviation: the pilot, the aircraft, the environment, and the type of operation that comprise any given aviation situation.
• C. The photosensitive pigments that initiate the visual response in the rods of the eye.
• D. The rough, milky, opaque ice formed by the instantaneous freezing of small supercooled water droplets.

Answer: (C)

Rhodopsin is the photosensitive pigment in the rods of the retina that initiates the visual response in low-light conditions. It is a molecule made of a protein (opsin) bound to a light-sensitive component (retinal). When light hits rhodopsin, the retinal changes shape, starting a signaling cascade through a G-protein pathway. This cascade reduces the concentration of cyclic GMP, causing ion channels to close, which hyperpolarizes the rod cell and sends a signal to the brain. This mechanism underpins night vision and motion detection in dim light, though color vision relies on different pigments in the cone cells. The other options describe flight controls, a four-element risk model, and a type of ice—none of which relate to the pigment in the retina.