Members of a species can recognize mates using

Members of a species can recognize mates using combination of smell, behavior, call and appearance. Recognizing and mating with a member within species is necessary because inter-species mating would result in sterile offspring.

Example: in case of peacocks, males have large colorful feathers, so it is appearance which attracts mating in them.

a polymer is a chainlike molecule made up of small molecular units. these small molecular units are called monomers. monomers of polymer can be joined together either naturally or synthetically.