<Tr> <Td> Have more pigment than cones, so can detect lower light levels </Td> <Td> Have less pigment than rods, require more light to detect images </Td> </Tr> <Tr> <Td> Stacks of membrane - enclosed disks are unattached to cell membrane directly </Td> <Td> Disks are attached to outer membrane </Td> </Tr> <Tr> <Td> About 120 million rods distributed around the retina </Td> <Td> About 6 million cones distributed in each retina </Td> </Tr> <Tr> <Td> One type of photosensitive pigment </Td> <Td> Three types of photosensitive pigment in humans </Td> </Tr>

Explain the basic difference between the function of rods and cones