The life cycle of organisms that reproduce sexually - is all phases of organism development of one or more sequentially occurring one after the othe

Life cycle: simple and complex [Direct indirect]

The life cycle of organisms that reproduce sexually — is all phases of organism development of one or more sequentially occurring one after the other ontogenies, from zygote occurrence (fertilization) until the stage of sexual reproduction (puberty), the result of which is a new generation of zygotes. Thus the life cycle closes.

Simple life cycle (direct)

A simple life cycle is a piece of organism life from the zygote until puberty (while ontogenesis — is the organism’s way of life from birth to death). This new generation does not differ from the old one by any structure or way of reproduction.

The life cycle of those single-celled organisms that don’t have a sexual process or it occurs without the formation of gametes, is identical to ontogenesis.

Complex life cycle (indirect)

The complex life cycle involves the alternation of generations. This means that between generations of organisms that reproduce by amphimixis (standard sexual reproduction), appears one or more generations of individuals, that reproduce asexually, or by parthenogenesis. Sexual and asexual generations differ not only by a reproduction type, but also by the structure of their body, a lifestyle, and in most organisms also by the ploidy of cells, from which their body is built. The alternation of generations occurs only in eukaryotic kingdoms of organisms; and those of them that have meiosis also have fertilization. Thus, a complex life cycle — is not one but at least two ontogeneses (and in some cases even more), since it includes two or more generations of organisms differing by reproduction method. Taken from http://worldofschool.org

Complex life cycle — is the alternation of generations of organisms with different structure and method of reproduction; they peculiar to some parasitic protozoa, fungi, most algae, many higher plants and some groups of multicellular animals. In all organisms, except representatives of the animal kingdom, there is an alternation of haploid and diploid stage in which the gamete method of reproduction is replaced by spore. In multicellular animals haploid phase is retained only on the gamete stage; they have no spores, and the alternation of generations is associated only with the features of different generations’ reproduction.

Questions:
  • What is the difference between life cycle and the ontogeny?

  • Is it correct that in some cases, the terms “life cycle” and “ontogeny” are equal?