A cell is the smallest biological unit of life with most having a nucleus in its center. However, there are cells without a nucleus, which are called prokaryotes. They are a group of organisms which lack a cell nucleus. The organisms with this type of cell are called prokaryotic organisms or prokaryotes. These organisms were the first to be found in the planet Earth.
A prokaryotic cell is mostly composed of a plasma membrane, cell wall, cytoplasm, genetic material in the nucleoid and ribosome. They are single-celled and are much smaller compared to eukaryotic cells. They exist in different shapes including spherical, rod, flat, coccus, spirochete, and some are also shapeless, not having a consistent shape.
Only a few of them can move, swim, spin, or rotate with the help of a helical shaped membrane called flagella. The ways prokaryotes receive nutrients include synthesizing their own food by using light energy from the atmosphere, prepare its own food by the process of chemosynthesis, or depend on other substances for nutrition when they cannot synthesize their own food.
1. Escherichia Coli Bacterium (E. coli)
It is a rod-shaped bacterium commonly found in the lower intestine of warm-blooded organisms. Most E. coli strains are harmless, but some can cause food poisoning, and are occasionally responsible for food recalls. Harmless E. coli can be beneficial by producing vitamin K2 and preventing the intestine in becoming colonized with pathogenic bacteria.
2. Streptococcus Bacterium
This prokaryote is responsible for strep throat. It is an infection of the back of the throat which includes the tonsils. Symptoms include fever, red tonsils, sore throat and enlarged lymph nodes in the neck. Cell division in this bacterium occurs along a single axis and they grow in chains or pairs.
3. Streptomyces Soil Bacteria
Over 500 of this type of bacteria have been described. They are predominantly found in soil and in decaying vegetation, with most producing spores. They have a distinct earthy odor resulting from the production of a volatile metabolite, geosmin.
The subclass of archaea are prokaryotes and are able to survive in very harsh environments. An example of archaea can be found in geothermally active areas and live in extremely acidic mud pots, which is called sulfolobus acidocaldarius archeobacterium.
Prokaryotes vs. Eukaryotes
Microscopic World Quiz
Function of Ribosomes
Function of the Nucleus
Eukaryotic Cells Examples