The Archaeplastida are a major line of eukaryotes A eukaryote is an organism whose cells contain complex structures enclosed within membranes. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear envelope, within which the genetic material is carried. The presence of a nucleus gives eukaryotes their name, which comes from the, comprising the land plants The embryophytes are the most familiar group of plants. They include trees, flowers, ferns, mosses, and various other green land plants. All are complex multicellular eukaryotes with specialized reproductive organs. With very few exceptions, embryophytes obtain their energy through photosynthesis ; and they synthesize their food from carbon, green The green algae are the large group of algae from which the embryophytes (higher plants) emerged. As such, they form a paraphyletic group, although the group including both green algae and embryophytes is monophyletic (and often just known as kingdom Plantae). The green algae include unicellular and colonial flagellates, usually but not always and red algae The red algae (or Rhodophyta, pronounced /roʊˈdɒfɨtə, ˌroʊdəˈfaɪtə/, from Greek: ῥόδον = rose + φυτόν (phyton) = plant, thus red plant) are one of the oldest groups of eukaryotic algae, and also one of the largest, with about 5,000–6,000 species of mostly multicellular, marine algae, including many notable seaweeds. Other, and a small group called the glaucophytes The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of freshwater microscopic algae. Together with the red algae and Viridiplantae they form the Archaeplastida. However, the relationships between the red algae, green algae and glaucophytes are unclear, in large part due to limited study of the glaucophytes. All of these organisms have plastids Plastids are major organelles found in the cells of plants and algae. Plastids are the site of manufacture and storage of important chemical compounds used by the cell. Plastids often contain pigments used in photosynthesis, and the types of pigments present can change or determine the cell's colour surrounded by two membranes, suggesting they developed directly from endosymbiotic cyanobacteria Cyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from the color of the bacteria (Greek: κυανός = blue). They are a significant component of the marine nitrogen cycle and an important primary. In all other groups, plastids are surrounded by three or four membranes, and were acquired secondarily from green or red algae.
The cells typically lack centrioles A centriole is a barrel-shaped cell structure found in most animal eukaryotic cells, though absent in higher plants and most fungi. The walls of each centriole are usually composed of nine triplets of microtubules . Deviations from this structure include Drosophila melanogaster embryos, with nine doublets, and Caenorhabditis elegans sperm cells and have mitochondria In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 10 micrometers (μm) in diameter. Mitochondria are sometimes described as "cellular power plants" because they generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of the with flat cristae. There is usually a cell wall A cell wall is a tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to act as a pressure vessel, preventing over-expansion including cellulose Cellulose is an organic compound with the formula n, a polysaccharide consisting of a linear chain of several hundred to over ten thousand β(1→4) linked D-glucose units, and food is stored in the form of starch Starch or amylum is a polysaccharide carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. Starch is produced by all green plants as an energy store. It is the most important carbohydrate in the human diet and is contained in such staple foods as rice, wheat, maize , potatoes and cassava. However, these characters are also shared with other eukaryotes. The main evidence the Archaeplastida form a monophyletic In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it consists of an ancestor and all its descendants. The term is synonymous with the uncommon term holophyly. It is contrasted with the terms paraphyly, which is a taxon consisting of an ancestor and some of its descendants, and polyphyly, which is a taxon group comes from genetic studies, which indicate that plastids probably had a single origin. The evidence is not strong however.[1][2]
The archaeplastids fall in two main evolutionary lines. The red algae are pigmented with chlorophyll Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. Its name is derived from the Greek χλωρός and φύλλον (phyllon "leaf"). Chlorophyll absorbs light most strongly in the blue and red but poorly in the green portions of the electromagnetic spectrum, hence the green colour of chlorophyll-containing a and phycobiliproteins Phycobiliproteins are water-soluble proteins present in cyanobacteria and certain algae that capture light energy which is then passed on to chlorophylls during photosynthesis. Phycobiliproteins are formed of a complex between proteins and covalently bound phycobilins that act as chromophores (the light-capturing part). They are most important, like most cyanobacteria. The green algae and land plants (together known as Viridiplantae Viridiplantae are a clade comprising the green algae and land plants, Latin for "green plants") are pigmented with chlorophylls a and b, but lack phycobiliproteins. The positions of the glaucophytes are uncertain; they have the typical cyanobacterial pigments, and are unusual in retaining a cell wall within the plastids (called cyanelles).
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Christopher Taylor
Wed, 06 May 2009 04:03:01 GM
The monophyly of the Plantae (renamed . Archaeplastida. in the eukaryote classification of Adl et al., 2005, to avoid the confusion of the many different uses of the name "Plantae") is at a bit of a draw - Patron et al. ...
