What unit of light stimulates photoreceptor cells in the retina?

Photons

Explanation:

The retina is a thin layer (membrane) in the eye that receives light through photoreceptor cells that convert this light into chemical and nervous signals transported to the brain's visual center.

The photoreceptors in the retina are known as rods and cones. Rods detect motion and sare responsible for black and white vision, they are present in the macula. Cones on the other and, are responsible for central and color vision. These photoreceptors absorb photons that trigger the membrane's potential of the cells.

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explanation:

the fossil record extends back to a dog-like ancestor some 55 million years ago, which gave rise to the first horse-like species 55 to 42 million years ago in the genus eohippus.