Colour. Humans have three types of cone cells, but some butterflies have at least four. Most mammals have no colour vision, for it is of no interest to their survival.
rod and cone cells
Because of the way your eyes work.Human eyes contain two types of cells that respond to light, named for their appearance: "rod cells" and "cone cells".Cone cells respond only to portions of the visible spectrum ... specifically, there are three kinds, each of which is most responsive to the band it's named after: "red", "green", and "blue". This is controlled by the specific pigment that's contained in the cell, which is very slightly different (and therefore a different color) in each.Rod cells respond to the entire visible spectrum. They may therefore seem kind of redundant ... the cone cells already cover the spectrum, so why bother keeping the rod cells around?It turns out the rod cells are a lot more sensitive to light. It takes a fair amount of light to trigger a cone cell (even if it's the right color of light to trigger that cone cell), but significantly less to trigger a rod cell.The rod cells are therefore important in low-light conditions. They give you at least minimal light-dark information, which is often enough to avoid hazards (that dark blob is probably a chair, while the lighter area surrounding it is the carpet). They don't provide any color information, though, since that comes from the cone cells.At a candlelit dinner (or any other low-light situation), the rod cells probably have enough light that you don't mistakenly stab your date's steak. However, the cone cells are only firing sporadically since they're working at the very bottom of their brightness range, so everything appears kind of grey and hopefully she won't notice the greenish tinge from the cheap meat you bought.
an opaque one
Because of the way your eyes work.Human eyes contain two types of cells that respond to light, named for their appearance: "rod cells" and "cone cells".Cone cells respond only to portions of the visible spectrum ... specifically, there are three kinds, each of which is most responsive to the band it's named after: "red", "green", and "blue". This is controlled by the specific pigment that's contained in the cell, which is very slightly different (and therefore a different color) in each.Rod cells respond to the entire visible spectrum. They may therefore seem kind of redundant ... the cone cells already cover the spectrum, so why bother keeping the rod cells around?It turns out the rod cells are a lot more sensitive to light. It takes a fair amount of light to trigger a cone cell (even if it's the right color of light to trigger that cone cell), but significantly less to trigger a rod cell.The rod cells are therefore important in low-light conditions. They give you at least minimal light-dark information, which is often enough to avoid hazards (that dark blob is probably a chair, while the lighter area surrounding it is the carpet). They don't provide any color information, though, since that comes from the cone cells.At a candlelit dinner (or any other low-light situation), the rod cells probably have enough light that you don't mistakenly stab your date's steak. However, the cone cells are only firing sporadically since they're working at the very bottom of their brightness range, so everything appears kind of grey and hopefully she won't notice the greenish tinge from the cheap meat you bought.
because each of them processes a slightly different kind of pigment
light rays
cone
it is a cone
Skin cells do not produce a hat - no matter what kind of radiation falls on them.
cinder cone volcano
it is a cc cinder cone
This kind of conic section is a circle