Final answer:
Retinal, also known as vitamin A1, is the form of vitamin A that enables the eye to react to changes in light by participating in the rhodopsin cycle and photoisomerization in the retina's rod cells.
Step-by-step explanation:
The form of vitamin A that enables the eye to react to changes in light is retinal. This aldehydic form of vitamin A, also known as vitamin A1, plays a crucial role in vision by participating in the rhodopsin cycle within the rod cells of the retina.
When light strikes the retina, retinal undergoes a chemical change known as photoisomerization, switching from a cis to a trans conformation.
This change triggers a series of events that result in an electrical signal being sent to the brain, which is interpreted as visual information. Moreover, retinal is crucial for producing the photopigment molecule rhodopsin, essential for dim light vision.
Retinal is also important for the synthesis of opsin proteins which contain this retinal cofactor. Upon absorbing light, the 11-cis-retinal isomerizes to all-trans-retinal, thereby altering the opsin's conformation and sending signals to the brain. Retinal, therefore, is indispensable for the conversion of light into electrical signals for the nervous tissue of the eye.