Free Response

How could the pineal gland, the brain structure that plays a role in annual cycles, use visual information from the suprachiasmatic nucleus of the hypothalamus?


The pineal gland could use length-of-day information to determine the time of year, for example. Day length is shorter in the winter than it is in the summer. For many animals and plants, photoperiod cues them to reproduce at a certain time of year.

How is the relationship between photoreceptors and bipolar cells different from other sensory receptors and adjacent cells?


The photoreceptors tonically inhibit the bipolar cells, and stimulation of the receptors turns this inhibition off, activating the bipolar cells.

Cataracts, the medical condition where the lens of the eye becomes cloudy, are a leading cause of blindness. Describe how developing a cataract would change the path of light through the eye.


The purpose of the lens in the eye is to focus the light beams on the retina so that the image seen by the eye can be transmitted to the optic nerve and interpreted. When the lens becomes cloudy instead of clear, it scatters the light over the back of the retina. The vision system cannot interpret the image then.