(a) The differences in the characters among the individual of a species is called variation.
(b) Human height and free ear lobe are the traits which show variation in humans.
(c) Due to the creation of variations, a species can adjust to the changing environment around it. And this promotes the survival of the species in the changing environment.
The accumulation of ‘heat resistant’ variation (or trait) in some bacteria will ensure its survival even when the temperature in its environment rises too much due to a heat wave or some other reasons. On the other hand, the bacteria which did not have this variation to withstand heat would not survive under these circumstances and die.