Prokaryotes are group of organisms lacking with cell nucleus or any membrane-bound organelles. Most of the prokaryotic organisms are unicellular (singled cell), but few of them are multicellular such as mycobacterium. Their body size ranges between 1 m and 10 m. In some cases, they can vary in size from 0.2 m to 750 m (i.e. E. coli). One of the distinct features of prokaryotic organisms is flagellum.  Flagellum contains homologues of actin and tubulin, i.e. MreB and FtsZ. The helically arranged building blocks of the flagellum, i.e. flagellin, provides structural backgrounds of chemotaxis. Chemotaxis is the basic cell physiological response of bacteria. Membrane systems such as vacuoles are also found in cytoplasm of prokaryotes. It may function to serve as a reservoir for food and waste products. It also functions to special metabolic properties in prokaryotes such as photosynthesis or chemolithotrophy.

Eukaryotes are membrane-bounded organisms with true nucleus. The genetic material is contained inside its nucleus or nuclear envelope. The nucleus of a typical plant cell is described with a large spherical and oval shaped organelle containing its genetic material and the site of DNA and RNA biosynthesis. Most eukaryotic cells also contain other membrane bound organelles such as ribosomes, Golgi apparatus, chloroplast and endoplasmic reticulum. The structure of endoplasmic reticulum contains a network of membrane enclosed channels continuous with the nuclear pore. It functions to process and transport proteins from one site in the cell to another. In addition, endoplasmic reticulum in a plant cell contains enzymes responsible for detoxifying substances that gain entry to the cell.    


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