are single-celled organisms lacking a membrane-bounded nucleus (karyon), mitochondria, or any other membranous organelle.
Prokaryotes are so many that the number of prokaryotic cells in the world is absolutely larger than that of eukaryotic cells!
Even in each of us, human beings, there are much more prokaryotic than eukaryotic cells!
Very likely you are thinking now:
“but prokaryotes are bacteria, the microorganisms causing so many diseases. So they are dangerous and we have to fight them and possibly eliminate them!!!!
Yes, you are right: among prokaryotes there are many pathogenic bacteria. However these “bad” prokaryotes are only a part of the prokaryotes at present we know.
A great many of them are not dangerous and, in many cases, are even essential for our life:
they are “good” prokaryotes!!!
They work for us!!!!!!!
1) Prokaryotes were the first living beings and the life on our earth, in the present form and biodiversity, would have not arisen and would not exist without them (see the post “the first atmospheric pollution).
2) Biogeochemical cycles and nutrient recycling would be unfinished or even impossible without prokaryotes. Remember that production in the open sea is only performed by microorganisms, a great part of them Prokaryotes. Thus they play an important role in supporting the life of all marine organisms. (See the post “Nature big recycler”)
3) Prokaryotes are able to use as energetic source elements and substances that cannot be utilized by other living beings and render them accessible. In some environments, where the sun light cannot arrive (i.e. deep sea or underground) and where obviously photosynthesis is not possible, prokaryotes sustain the life trough different chemiosynthetic processes.
4) Prokaryotes can survive in extreme environments where eukaryotes would succumb: they can be found in hot water up to 121°C and in cold lakes under kilometers of ice in
Antarctica. They are able to live in extremely acid or basic environments. In addition all natural products and, thankfully, many man productions can be degraded and recycled by bacteria.
5) Many so called superior organisms, man included, would not survive for a long time without their endosymbiotic bacteria, for example the so called intestinal flora.
These few considerations are less than crumbs of knowledge about the wide Prokaryotic world!!!
and….consider that, according to the scientists, prokaryotes we know represent only a little part of those existing in the earth!!!!!!