One of the main results of the postembryonic development is the increase in the linear dimensions and weight of the body, which is achieved in the pr

Growth in animals and plants [Organism]

One of the main results of the postembryonic development is the increase in the linear dimensions and weight of the body, which is achieved in the process of growth. It is based on two mechanisms: an increase in the number of cells by cell division; the growth of the cells themselves that occurs due to volume increase of the cytoplasm.

Differences of growth in plants and animals

Tissue structure of higher plants and animals are different: their bodies form in different ways, different organ systems develop. When plants’ body is branchy, and it seeks to capture a larger space and light, which is achieved by the development of external organs (they do not have visceral at all), the body of the animal, on the contrary, is compact, and primarily internal body system develops. Not casually plants and animals grow differently.

Growth in plants

The growth of higher plants is called apical, since it is carried out due to cell division in the special tissues (meristems). Apical meristems provide growth of roots and shoot tips in length; intercalary — lengthening of internodes, and the side — thickening of the stems and roots. Plants grow all their life. Taken from http://worldofschool.org

Diagram 91. Changes in growth rates in men and women in different periods of development

Growth in animals

In animals, the growth is also carried out due to cell division and the growth of the cells themselves. However, the process goes differently in different tissues. For example, cell division in the nervous and muscular human tissues occurs only during embryonic development and in epithelial and connective — during lifetime. Unlike plants that grow certain parts of their body, the animals grow all over, although at certain stages of post-embryonic development the growth of individual organs can go with the acceleration, or, conversely, slow down. In some species the growth does not stop for the whole life (fish), in others — goes to a certain age limit (birds and mammals), and in some — occurs only during molting (crustaceans and nematodes), while in insects — only in the larval stage.

Vertebrate

Growth of vertebrate is controlled by special growth hormones that are secreted by the pituitary gland and are synthesized in the liver. It’s interestingly, that the growth of human is also affected by sex hormones. That is why the sharp acceleration of growth occurs in girls during active puberty in 12-13 years, and the boys — 15-16 years and by 18-20 years the growth stops completely (diagram 91).

Questions:
  • What is the difference between growth in plants and in animals?

  • Why growth in fish is unrestricted, and in mammals — limited?