Final answer:
Photons striking a rod cell lead to a decrease in cGMP and cause hyperpolarization of the membrane potential, due to closing of sodium channels and resulting decrease in sodium ion influx.
Step-by-step explanation:
When photons strike a rod cell in the retina, the correct answer is that there is a decrease in cGMP in the cytoplasm and hyperpolarization of the membrane potential. The process of visual transduction involves light activating the photopigment rhodopsin, which then activates the G-protein called transducin. Transducin subsequently activates phosphodiesterase, an enzyme that converts cGMP into GMP. The reduction in cGMP levels leads to the closing of sodium channels. With these channels closed, there is a reduction in the sodium ion influx, which causes the membrane to become hyperpolarized. When the membrane is hyperpolarized, the photoreceptor cell releases less neurotransmitter glutamate to the bipolar cells, signaling that light has been detected.