Plant cell the major classes of cells and tissues of roots, stems, leaves, flowers, and reproductive structures, each of which may be composed of several cell types. Parenchyma cells are living cells that have functions ranging from storage and support to photosynthesis (mesophyll cells) and phloem loading (transfer cells). Apart from the xylem and phloem in their vascular bundles, leaves are composed mainly of parenchyma cells. Some parenchyma cells, as in the epidermis, are specialized for light penetration and focusing or regulation of gas exchange, but others are among the least specialized cells in plant tissue, and may remain totipotent, capable of
Photoreceptor cell across different cone types. The process of phototransduction occurs in the retina. The retina has many layers of various cell types. The best-known photoreceptor cells ("rods" and "cones") form the outermost layer. They are the photoreceptors responsible for sight. The middle layer contains bipolar cells, which collect neural signals from the rods and the cones and then transmit them to the innermost layer of the retina, where the neurons called retinal ganglion cells (RGCs), a small percentage of which are themselves photosensitive, organize the signals and send them to the brain. Activation of rods and cones is actually hyperpolarization; when