Final answer:
The active form of vitamin A in vision is called retinal, with the specific form related to vision being 11-cis-retinal. It undergoes photoisomerization upon being hit by light, converting to all-trans-retinal and forming rhodopsin to enable sight.
Step-by-step explanation:
Vitamin A Active in Vision
The active form of vitamin A in vision is known as retinal, specifically 11-cis-retinal. In the pathway involved in vision, 11-cis-retinal undergoes a process called photoisomerization when a photon (light) hits it. This causes the molecule to switch from a cis to a trans conformation, becoming all-trans-retinal. This molecule then combines with the protein opsin in the eye's rod cells to form rhodopsin, which, upon absorbing light, changes its configuration and sends an electrical signal to the brain. This signal translates into the images we see. In the absence of light, all-trans-retinal is converted back to 11-cis-retinal to repeat the cycle, allowing continuous vision.
Adequate levels of vitamin A are important for night vision and overall eye health, including protection against conditions such as cataracts. Plants produce carotenoids like β-carotene which are precursors to vitamin A, indicating vitamin A's essentiality in our diet.