Animals can respond quickly to a stimulus but cannot why

Action potentials are generated in nerves, which carry information at over 265 mph in the form of electrical impulses! This is what enables your body to almost instantly react to stimuli ( bolting out of the way of an oncoming car, or, even faster,  your hand away from a burning stove).

When compared plants and animals, the animals responds to the stimuli more faster as compared to the plants due to the presence of nerve cells. ... Whereas when talk about plants there are no nerve cells in the plant body so they cannot respond to the outer stimuli so quickly.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).