'he cells of all organisms can be divided into two cells. Prokaryotic cells are cells with a relatively broad categories: prokaryotic cells and eukaryotic simple structure, having no internal, membrane-
Eukaryotic cells constitute all but the simplest life-forms: protists, fungi, plants, and animals. Based on an electron microscope image of a leaf cell from a corn plant, this depiction shows the basic parts of the cell. Eukaryotic cells are distinguished from more primitive prokaryotic (mainly bacterial) cells by the presence of a nucleus that contains the genetic materials as well as membrane-bound organelles such as mitochondria and, in algae and plants, plastids such as chloroplasts.
from a single ancestral archaean cell.
Eukarya includes the traditional kingdoms Plantae, Ani-malia, Fungi, and Protista. Protists include a diverse assemblage of single-celled eukaryotic organisms including algae, amoebas, and paramecia. Because algae are photosynthetic, they have often been included in the study of plants, although they are not members of the plant kingdom.
Fungi include such organisms as smuts, rusts, molds, and mushrooms. Fungal cells have external cell walls and because of this have often been included in the study of plants. However, fungal cell walls have a completely different structure and composition from those of plant cell walls, and fungi lack plastids and photosynthetic pigments. Fungi represent a unique evolutionary line. They too, however, tend to be studied in botany courses, even though they are not plants.
bound organelles. The most striking feature of pro-karyotic cells is that they lack a distinct nucleus, hence the name prokaryotic, literally translated from its Greek roots as "before nucleus." The prokary-otic organisms comprise two domains of the three domains of life: the ancient bacteria, Archaea; and the modern bacteria, Bacteria or Eubacteria. The Archaea are single-celled organisms that often inhabit extreme environments, such as hot springs. The remainder of bacteria are classified as Eubac-teria.
All other organisms, including fungi, plants, and animals, are composed of eukaryotic cells and belong to the domain Eukarya. Eukaryotic cells are more structurally complex than prokaryotic cells, having internal, membrane-bound organelles and a distinct nucleus that physically separates the genetic material of the cell from the all of the other parts of the cell. Based on genetic analysis, the Archaea and Eukarya are more closely related to each other than they are to the Bacteria, suggesting that eukaryotic cells may have arisen
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