This explains why colors cannot be seen at low light levels: only one type of photoreceptor cell is active.

The photoreceptor cells involved in vision are the rods and cones.

Thus defined, they need not consist of more than one photoreceptor cell.

The simplest photoreceptor cells in conscious vision connect light to movement.

The retina, at the back of the eye, contains photoreceptor cells.

Once photoreceptor cells die, however, they cannot be restored.

They help integrate and regulate the input from multiple photoreceptor cells.

The eyes are simple in structure, sometimes with just a single photoreceptor cell.

Therefore the tips must contain the photoreceptor cells although the bending takes place lower down on the shoot.

Without proper function of the photoreceptor cells, vision is not possible.