Final answer:
Retinol is synthesized in the body from ß-carotene, with the conversion occurring mainly in the liver. ß-carotene is split by an enzyme to produce retinal, which is then reduced to retinol.
Step-by-step explanation:
In the context of vitamin A, retinol can be synthesized in the body from ß-carotene. Plants synthesize provitamins known as carotenoids, among which ß-carotene is the most effective precursor for vitamin A in animals and humans. Within the body, specifically the liver, an enzyme known as ß-carotene 15, 15'-oxygenase catalyzes the conversion of ß-carotene into two molecules of vitamin A aldehyde (retinal), which is then further reduced to form retinol. This process is essential for obtaining vitamin A, since animals cannot synthesize it directly but must convert it from plant-derived carotenoids.