Q.
Statement (S): Species are groups of potentially inter breeding natural populations that are isolated from other such groups. Reason (R): Reproductive isolation brings about distinctive morphological characters.
A species is a group of individuals which resemble with each other in morphological physiological, biochemical and behavoural characters. These individuals are capable are breeding, feeding in between themse under natural conditions, but are incapable of breeding with members of other species. Reproductive isolation is mainly responsible for formation of new species.