Which statement best describes the outer segment's role in photopigment localization?

• A. The inner segment houses photopigments
• B. The outer segment contains mitochondria and ribosomes
• C. The outer segment houses photopigments in disc membranes
• D. The synaptic terminal houses photopigments

Answer: (C)

Photoreceptors detect light using photopigments that are located in the outer segment. These pigments sit in the membranes of stacked discs, which creates a large surface area to hold many pigment molecules and maximize light absorption. When light hits the pigment, the retinal molecule changes shape, triggering a chemical cascade that alters the cell’s membrane potential and signals the brain. The inner segment, by contrast, is rich in mitochondria and ribosomes for energy production and protein synthesis, while the synaptic terminal handles neurotransmitter release to downstream neurons. This structural arrangement makes it clear why the outer segment houses photopigments in disc membranes is the best description.