[Campbell Biology P.1169] Compare the state of a photoreceptor cell in the dark versus in the... | Practice Question
Compare the state of a photoreceptor cell in the dark versus in the light, according to Figure 50.18 and the accompanying text.
A: In the dark, cGMP levels are high, keeping Na+ channels open, leading to depolarization and continuous glutamate release. In the light, cGMP levels fall, Na+ channels close, causing hyperpolarization and cessation of glutamate release.
B: In the dark, the cell is hyperpolarized and releases glutamate. In the light, it depolarizes and ceases glutamate release.
C: Glutamate is released continuously in both dark and light conditions, but its effect on bipolar cells changes.
D: Na+ channels are always closed in the dark and open in the light, regardless of cGMP levels.
Explanation
Figure 50.18a and its description state that in the dark, high cGMP levels keep Na+ channels open, leading to depolarization and continuous glutamate release. Figure 50.18b and its description show that in the light, cGMP levels fall, causing Na+ channels to close, which results in hyperpolarization and cessation of glutamate release.