Prokaryotes
Prokaryotes are single celled organisms having no nucleus and differ from eukaryotes which are organisms having nucleus in their cells. It came from the Greek word “pro” means before and “karyon” means nut.
Prokaryotes contain a large DNA molecule floating in cytoplasm called nucleoid region protected by a plasma membrane. The cell contains nucleus, mitochondria, chloroplasts, Golgi apparatus, endoplasmic reticulum. The size of the Prokaryotes is roughly upto one micrometer in diameter. The shape of the cell may be rod shaped e.g. Bacilli, comma shaped e.g. Vibrio, spherical e.g.Cocci and spiral e.g. Spirochaete. Most of the bacteria are good example of single celled Prokaryotes but some organisms such as myxobacteria are having multicellular life cycle.
Prokaryotes can live in any extreme condition such as high temperature, high pH and radiation. They move by the help of flagetta. A flagellum is a rubber like device having a hook and a basal body. It can move round 3600 helping in luxuriant movement of the animal. There present a short-hair like structure called “fimbriae” which helps in adhering to the surface.
The mode of reproduction in Prokaryotes is asexual either by binary fission or budding. All the characteristics of the parents are directly transferred to the off-springs as the parent DNA divides to form new DNA cells. The Prokaryotes are anaerobic that is they don’t require oxygen for respiration. They live on organic food, thus they require molecules that contain carbon and hydrogen. According to the food habit Prokaryotes are divided into Autotrophic Prokaryotes and Heterotrophic Prokaryotes.
Prokaryotes form community called “biofilms” which is heterogeneous, composite and attached to the surface of earth. Many micro-colonies may join together and form a continuous layer above the substratum.
Prokaryotes differ strongly from eukaryote cells as they don’t have a membrane bound nucleus.
Bacteria are ubiquitous on the earth performing many major functions in decomposing and decaying, in digestive system and in many nutrient cycles.
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