Assertion (A): Bacteria that can withstand heat have better chances of survival in a heat wave.

Reason (R): Accumulation of variations in a species increases the chances of its survival in changing environment.

The assertion states that bacteria that can withstand heat have better chances of survival in a heat wave. This is true because such bacteria have a variation that allows them to survive in high temperatures. The reason states that accumulation of variations in a species increases the chances of its survival in changing environment. This is also true because variations provide different traits that can help individuals survive in different environments. The reason explains the assertion because it provides the underlying principle for why bacteria that can withstand heat have better chances of survival.