Ontogenesis (from Greek ldquo;ontosrdquo; - ldquo;a creaturerdquo; and ldquo;genesisrdquo; - ldquo;the birthrdquo;), or morphogenesis

Ontogeny [Ontogenesis, Morphogenesis, Organism development]

Ontogenesis (from Greek “ontos” — “a creature” and “genesis” — “the birth”), or morphogenesis — is a period of life of the organism from the zygote (primary cell) until death.

Every organism, whether it’s unicellular or multicellular, and whatever kingdom it belongs, undergoes for all its life an ontogeny development. The area of biology that studies ontogenesis is called the developmental biology.

During ontogenesis, the organism goes through a number of phases — states in which it differs in structure, functionality and lifestyle. There are two stages of ontogeny: embryogenesis — embryonic development, and post-embryonic development — the period of the organism life from birth (hatching) until death.

In multicellular

In multicellular organisms, the ontogenesis usually starts with the formation of the zygote, and ends with death. Upon morphogenesis process occurs not only the organism growth, by increasing its size, but it also undergo a series of different life phases, during each of which it has a special structure, different functions, and, in some cases, has fundamentally different lifestyle.

In single-cell

In single-cell, the beginning of ontogeny is the moment of separation from the mother or the sister cell. It goes until next division or death. While ontogeny of unicellular organisms externally looks like only as a slight increase in cell size, in fact this masks very different periods of its life.

Ontogeny program

Each species has its own program of ontogenesis. This is not just a set and the sequence of stages which it passes, but also the duration of each of them. At the same time, any individual has its own features of ontogeny, which, however, do not go beyond the species, and they, in turn, obey the laws of ontogeny on generic, family, even ordinal and class levels.

Ontogeny program — is nothing more than the realization of the genetic information stored in genes. Therefore, the specificity of ontogeny on the individual level is determined by individual combinations of genes, and on the levels of species, genera, and families — by special genes that are unique to each taxonomic group of organisms.

The mechanism of hereditary information realization lies primarily in differential gene activity. This means that, in the different periods of development and in different tissues of multicellular organisms are active genes, on the nucleotide sequences of which occurs the synthesis of certain mRNA. As a result, specific structural proteins and enzymes are synthesized, which ultimately determine the features of functioning and behavior of cells at certain stages of an organism development, the characteristics of its metabolism. Taken from http://worldofschool.org

Stages of ontogeny

In animals and in flowers the ontogenesis is divided into two periods (stages). The embryonic development or embryogenesis (from Greek “embryo” and “genesis”) lasts from the formation of the zygote before birth or hatching and post-embryonic (from Greek “post” — “after” and “embryo”) development continues from birth or hatching and ends with the body's death.

Phases of embryogenesis

General embryogenesis scheme includes the following phases:

  1. sequential division of the zygote, ending with the formation of a multicellular embryo, consisting of hundreds or even thousands of identical cells;
  2. differentiation of cells, leading to the formation of tissues;
  3. generation of organs and fetal growth.
Questions:
  • What is ontogeny?

  • Why ontogeny of each species is strictly specific?

  • What steps ontogeny has?

  • Why aging time is also considered one of the periods of the organism individual development?

  • Why do they say that the organism is in the process of individual development manifests itself as an integral structure, not as a set of dividing cells?