[Campbell Biology P.1169] Which of the following accurately describes the sequence of events ... | Practice Question

Which of the following accurately describes the sequence of events in a photoreceptor cell when it is exposed to light?

  • A: Light activates rhodopsin, which activates transducin. Transducin then activates phosphodiesterase, leading to cGMP hydrolysis, closure of Na+ channels, and hyperpolarization.
  • B: Light causes Na+ channels to open, leading to depolarization and cGMP synthesis.
  • C: Rhodopsin directly opens Na+ channels upon light exposure, leading to glutamate release.
  • D: Phosphodiesterase directly binds to Na+ channels, causing them to open and depolarize the cell.

Explanation

According to Figure 50.18b and the accompanying text, light triggers a cascade where rhodopsin activates transducin, which in turn activates phosphodiesterase. This enzyme hydrolyzes cGMP, causing its levels to fall. Since cGMP is required to keep Na+ channels open, their closure leads to hyperpolarization of the photoreceptor cell.