Which of the following is a provitamin -

Ans. is 'c' i.e., b-carotene o Two group of compounds have vitamin A activity -Vitamin 'A': - Vitamin 'A' refers to three biologically active Vitamers (i.e.. isomers of vitamin): - RetinolQ (an alcohol), retinalQ (an aldehyde), and retinoic acidQ (an acid). All of these are found only in animai They are polyisoprenoid compounds comprising two distinct components : (i) a cyclohexenyl ring and (ii) A side chain of several isoprene units attached to cyclohexenyl ring. The term 'Retinoids' is used to define these three compounds (retinol, retinal, and retinoic acid) and other synthetic compounds with vitamin A activity.Carotenoids : - These are provitamins of vitamin A which are present in plants. These are precursors of vitamin A which are cleaved to yield retinal (retinaldehyde) and then retinol and retinoic acid. The most important carotenoid is b-carotene, which consists of two molecules of vitamin A (retinal) joined end to end.