Concerning their biological function what is the difference between mitosis and meiosis?
The major biological function of mitosis is cellular multiplication, a fundamental process for the growth and development of multicellular organisms, tissue renewing, asexual reproduction, etc. The biological function of meiosis is gamete formation (in gametic meiosis) or spore formation (in sporic meiosis), i.e., the production of cells qualified for sexual reproduction with half the quantity of chromosomes compared to the original cell.
There is a special type of meiosis that occurs in zygotes of some algae, protozoans and fungi. This meiosis, known as zygotic meiosis, has the function of decreasing to a half the number of chromosomes of adult individuals that will be formed from the zygote. In species with zygotic meiosis the adult individuals are haploid and they form gametes by mitosis. These gametes fuse in pairs with others and generate a diploid zygote that, then, undergoes meiosis to restitute the normal ploidy of adult individuals.