In plasma, retinol is transported primarily bound to which molecule?

• A. Retinol
• B. Transferrin
• C. Albumin
• D. Ceruloplasmin

Answer: (A)

The main concept is how retinol travels in the bloodstream. In plasma, retinol is carried by a specific carrier protein called retinol-binding protein. It typically forms a complex with transthyretin to stay stable in circulation and to prevent loss of retinol in the kidneys. This binding keeps retinol soluble and ensures it can be delivered to target tissues where vitamin A is needed. Transferrin transports iron, ceruloplasmin carries copper, and albumin binds many substances but is not the primary carrier for retinol. So, the proper transporter for retinol in plasma is retinol-binding protein (often in a complex with transthyretin). The option that names retinol itself does not describe this transport mechanism.