In prokaryotes and most species of unicellular eukaryotes life cycles are simple. They, as well as ontogenesis, begin with formation of new cell and

Life cycle of unicellular [single-celled, Alternation generations]

In prokaryotes and most species of unicellular eukaryotes life cycles are simple. They, as well as ontogenesis, begin with formation of new cell and end with its division. However, in some groups of parasitic unicellular, particularly in Sporozoa, or Apicomplexa (diagram 95), and in many of unicellular algae, such as Chlamydomonas, life cycle passes with alternation of generations. At a certain stage of successive mitotic divisions the cells mutate and turn into gametes that merge (copulate) and form a diploid zygote, immediately passing meiosis (meiosis at the stage of zygote is called zygotic). As a result, four haploid cells are produced that grow into new haploid organisms.

Diagram 95. The life cycle of malaria parasite Plasmodium: 1-2 — the development of Plasmodium in the first stage of the life cycle; 3 — reproduction in liver cells; 4-6 — development in red blood cells; 7- reproduction in red blood cells; 8-9 — development of gametes; 10 — maturation of gametes; 11 — copulation; 12 — zygote; 13-15 — reproduction after fertilization
Questions:
  • What eukaryote groups occurs zygotic meiosis and how it differs from gametic?

  • Why parasitic protozoa Sporozoa got its name?