Which statement about the three regions of the photoreceptor inner segment is true?

Which statement about the three regions of the photoreceptor inner segment is true?

• A. The myoid is for protein synthesis
• B. The ellipsoid is for energy production
• C. The cilium connects outer and inner segments
• D. All of the above

Answer: (D)

Think of the photoreceptor’s inner segment as a set of specialized zones, each doing a different job that supports the outer segment where light is detected. The myoid sits near the cell body and contains the cellular machinery for making proteins, including components needed to support the outer segment’s renewal. The ellipsoid is packed with mitochondria, providing the high level of ATP that photoreceptors require to power ion pumps and the ongoing processes of phototransduction. The connecting cilium links the inner and outer segments and serves as a transport highway, moving newly synthesized proteins and membranes from the inner segment into the outer segment to maintain its structure and function. Since each region has its own role that fits together to keep the photoreceptor working, all of the statements describing them are true.