The answer is C. Mollusks. Hope this helps. :)
<span>The sequence is as follows:
c, d, a, b, f, g, e
The impulse starts at the SA node that has its own contraction rhythm (but can be faster or slower depending on other impulses or hormones). That impulse travels then through the atria and is slowed down by the atrioventricular septum except for a region in the right atrium called AV node where the impulse has continuity. The impulse travels then to the ventricles through the AV bundle. The impulse continues through bundle branches to other fibers: Purkinje fibers. These Purkinje fibers cause then a contraction that goes from the apex of the heart and rapidly through the ventricles.</span>
Out of the following given choices;
<span>A. </span>The sodium channels would open and close randomly, regardless of the presence of light.
<span>B. </span>The sodium channels would remain closed in the light and the dark, even when cGMP decreases after light stimulation.
<span>C. </span>The sodium channels would remain open in the dark and close rapidly to the light.
<span>D. </span>The sodium channels would remain open longer, even when cGMP decreases after light stimulation.
The answer is D. cGMP maintain the sodium channels open when there is no light stimulation. This ensures that there is high intracellular Ca2+ concentration due to the Na+/Ca2+-K+ exchanger. When cGMP is hydrolyzed in light stimulation cascade, the channels close causing hyperpolarization of the rod cells.