Genetic drift refers to the evolutionary agent that brings about the changes in the gene pool of the population by some chance event. In the given example, half of the polar bear population was wiped out of the habitat by any chance event such as natural calamity, epidemic disease or any other random events. Since no mutation or natural selection was responsible for the death of polar bears, it is an example of genetic drift.
Genetic drift is more effective in small populations. And the size of the population of the polar bear was also small to allow the genetic drift to cause the changes.
Genetic drift is defined as the random change in the allele frequency of a population is changed by chance or due to random changes in the environment. It is a random process that can lead to large changes in the overall population in a short period of time. It is a mechanism of evolution and it does produce the adaptation.
Plants respire all the time, whether it is dark or light, because their cells need energy to stay alive. But they can only photosynthesize when they have light.
