ISBN
978-3-00-064888-5
Monograph of Dr. rer. nat. Andreas Heinrich Malczan
"The Earth is populated by a multitude of single-cell organisms. Most of them are prokaryota, but the unicellular eukaryota also exist in an enormous number of species and individuals that can hardly be estimated." [120]
This quotation from the textbook Special Zoology, Part 1, Protozoa and Invertebrates, by Wilfried Westheide and Reinhard Rieger (eds.) is at the beginning of the first chapter "Single-celled Eukaryota", Protozoa. The 25 authors of this extremely readable textbook are all proven experts in this field. The reader is warmly recommended to read this book, because the vertebrates ultimately evolved from the unicellular organisms.
Anyone who wants to establish a theory about the formation of the vertebrate brain in the course of evolution must go back further and also deal with the formation and development of life itself. Apart from special forms such as viruses, the simplest living beings are those that consist of only one cell. From them, multicellular organisms could have developed, which can be divided into plants and animals. The multicellular animals are called metazoa, the vertebrates belong to them.
The unicellular organisms are divided into prokaryota and unicellular eukaryota depending on the presence of a cell nucleus. Prokaryota do not have a cell nucleus. Bacteria and archaeae belong to the prokaryota. Eukaryotic cells have a cell nucleus. Eukaryota can be both unicellular and multicellular organisms.
Whereas in multicellular animals the division of labour is realised by the formation of organs, each of which is responsible for specific tasks, the division of labour in unicellular organisms is realised by special structures, many of which are also called organelles.
Examples of such structures are given in [120]:
- At least one nucleus (control centre with genetic information)
Mitochondria (supply the necessary energy)
- Plastids (for plants, including for photosynthesis)
- Endoplastic reticulum (branched membrane network with many functions)
- Dictyosomes (form the Golgi apparatus)
- Lyosomes (cell organelles that serve the intracellular digestion)
- Peroxisomes (used for the detoxification of reactive oxygen compounds)
- Acanthosomes (specialized plasma membrane region for the endocytotic cell cycle)
- Ribosomes (protein factories of the cell)
- Microfilaments (filamentous protein structures, serve, among other things, for movements and transport processes in the cell)
- Microtubules (form the cytoskeleton, serve among other things for mitosis and other tasks)
According to [120], the following are among the organelles that occur:
- Contractile vacuoles (water excretion)
- Extrusomes (can fling their contents outwards like an arrow when irritated)
- Axostyle (support movements of the cell)
- Parabasal apparatuses (special Golgi apparatus)
- Chromosomes (memory for genetic information)
- A mitotic distribution apparatus for vegetative propagation.
According to [120], both the ability of vegetative reproduction by mitosis and the formation of haploid cells by meiosis and their fusion are original characteristics of unicellular eukaryota.
In the unicellular organism, the cell must have all the abilities necessary for survival, in addition it must be able to multiply so that such cells are also available in the future. The unicellular organisms already have two possibilities, they can reproduce vegetatively (asexually) and sexually. We give the unicellular eukaryota a new name, which makes it easier for us to differentiate them later.
In this monograph we refer to the unicellular Eukaryota as living beings of replication stage 1.
It is astonishing that the transition from a single-celled organism to a multi-celled organism took place very early. A sensational find of multicellular fossils in Gabon made it possible to date them chronologically, according to which the multicellular organisms whose fossils were found there lived about 2.1 billion years ago.
Monograph of Dr. rer. nat. Andreas Heinrich Malczan