FROM SINGLE CELLS TO MULTICELULAR ORGANISMS.
CLONING
CHAPTER 4
The cell theory postulates the general principle of biology, that all plant
and animal organisms are built up of cells. As it was already mentioned in
Chapter 2 (Section 2. 2), immediately after its appearance a lot of
questions arise. One of them, deserving greatest attention, is the
following: are the multicellular organisms a mechanical sum of
autonomous cells or they represent a specific community?
Different opinions are expressed on this question. Some authors
defend the idea that multicellular organisms are a sum of cells with
completely independent functions. Ardent adherents of this view are:
R. Virchow — in his book “Cellular Pathology”, M. Verworn — “General
Physiology”, E. Haeckel — with his formulation “state of cells, in which
they are independent citizens”, etc. In their opinion the general
biological problems have their roots in the individual cells. The concept
that multicellular organisms are a sum of constituents (cells) is also
included in the formulation of Th. Schwann substantiating the cell
theory. Other authors, like W. Ritter, E. Russell and Z. Katznelson
resolutely oppose to that concept and consider it a mechanistic
approach.
The above-mentioned gives some notion about the two extreme
concepts on the question posed. As early as in 1864 in his book
“Principles of Biology” the English philosopher H. Spencer expresses the
idea, that “in the course of emerging the multicellularity not only a simple
summing but integration of cells occurs” (cited by Katznelson, 1963).
By now nobody chalenge that multicellular organisms are built of cells.
As most logical, it is accepted that they have been formed through
integration of individual cells in multicellular systems. Diagrammaticaly this
process is presented with Volvox green algae in Fig. 4–1.
Volvocaceae family includes coenobial and colonial forms, more
typical are the representatives of Gonium and Eudorina genera. The
cells included in them form 16- or 32-cell coenobia and are located in a
single loose layer in the form of a packet with a common mucous
membrane. In contrast to them, in Pandorina genus the cells are more
compact. The motions of outer flagella are coordinate which enables the
cell formation to move in the same direction. They reproduce asexually
by forming a new coenobia from each cell, but toward the end of
vegetation, i.e. when conditions become adverse, sexual process is
realized.