Eukaryote
From EvoWiki
A eukaryote is an organism consisting of one or more eukaryotic cell. Eukarya or Eucarya is one of the three domains classifying life on earth. The group is divided up into these kingdoms:
However, a more representative tree can be found on the Tree Of Life Web [1].
Eukaryotic cells are characterized by a membrane-bound nucleus and membrane-bound organelles, which include:
- Nucleus
- Mitochondria
- Chloroplasts
- Endoplasmic reticulum
- Golgi complex
- Lysosomes
- Peroxisomes
- Secretory vesicles
- Vacuoles
In addition to the cell as a whole, mitochondria and chloroplasts have their own genomes and transcription and translation apparatus -- but most other organelles do not. This circumstance has led Lynn Margulis and others to propose that eukaryotic cells are chimeric or collages of organisms. This endosymbiotic theory is now well-established for mitochondria and chloroplasts, with the rest of the cell having at least one additional source. Among them was an archaebacterium, which became the cell nucleus, the cell's central repository of genetic information.
Eukaryotic cells also have a cytoskeleton, an internal framework of protein strands that assists cell division and that can enable the cells to change their shape and to engulf small objects (phagocytosis).
Amoebas and similar organisms have no well-defined shape; they move and catch their prey by changing their shape. Vertebrate phagocytes (certain white blood cells) and similar invertebrate blood cells consume unwanted organisms in amoeba fashion.
Many other eukaryotic cells, however, have well-defined shapes, with some having cell walls, usually of either cellulose (plants, many algae) or chitin (fungi).
