<span>Eukaryotic cells contain membrane-bound organelles, including a nucleus. Eukaryotes can be single-celled or multi-celled, such as you, me, plants, fungi, and insects.</span>
<em>They are exothermic as they take temperature from the surrounding and then maintain their internal body temperature according to the amount of heat absorbed :)</em>
Genetic variation is essential for natural selection because natural selection can only increase or decrease frequency of alleles that already exist in the population. Genetic variation is caused by: mutation. random mating between organisms.
