Final answer:
The phototransduction cascade is triggered in the presence of light when it causes a change in the shape of the retinal in photoreceptor cells, leading to a series of events that convert light into a neural signal. The correct option is a).
Step-by-step explanation:
Phototransduction Cascade Triggering
The phototransduction cascade is triggered in the presence of light. When light strikes photoreceptor cells in the retina, such as rods and cones, it initiates a change in the shape of a light-absorbing molecule called retinal. This alteration from a bent (cis) form to a linear (trans) form activates a photopigment called rhodopsin.
The activation of rhodopsin leads to a sequence of biochemical events that ultimately result in the hyperpolarization of the photoreceptor cell, effectively converting the light signal into a neural signal that the brain can process.
During this cascade, various proteins and enzymes are involved, including a G-protein called transducin. This process is essential for vision, allowing organisms, including humans, to detect light and convert it into a form that can be interpreted by the nervous system as visual information. Option a) is the correct one.