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From Wikipedia

Brown algae

The Phaeophyceae or brown algae (singular: alga), is a large group of mostly marine multicellular algae, including many seaweeds of colder Northern Hemisphere waters. They play an important role in marine environments both as food, and for the habitats they form. For instance Macrocystis, a member of theLaminariales or kelps, may reach 60 m in length, and forms prominent underwater forests. Another example is Sargassum, which creates unique habitats in the tropical waters of theSargasso Sea. Many brown algae such as members of the order Fucales are commonly found along rocky seashores. Some members of the class are used as food for humans.

Worldwide there are about 1500-2000 species of brown algae. Some species are of sufficient commercial importance, such as Ascophyllum nodosum, that they have become subjects of extensive research in their own right.

Brown algae belong to a very large group, the Heterokontophyta, a eukaryotic group of organisms distinguished most prominently by having chloroplasts surrounded by four membranes, suggesting an origin from a symbiotic relationship between a basal eukaryote and another eukaryotic organism. Most brown algae contain the pigment fucoxanthin, which is responsible for the distinctive greenish-brown color that gives them their name. Brown algae are unique among heterokonts in developing into multicellular forms with differentiatedtissues, but they reproduce by means of flagellatespores and gametes, which closely resemble other heterokont cells. Genetic studies show their closest relatives to be the yellow-green algae.

Morphology

Brown algae exist in a wide range of sizes and forms. The smallest members of the group grow as tiny, feathery tufts of threadlike cells no more than a few centimeters long. Some species even have a stage in their life cycle that consists of only a few cells, making the entire alga microscopic. Other groups of brown algae grow to much larger sizes. The leathery kelps and rockweeds are often the most conspicuous algae in their habitats. Kelps can range in size from the two-foot-tall sea palm (Postelsia) to the giant kelpMacrocystis pyrifera, which grows to over 45 m (150 ft) long and is the largest of all the algae. In form, the brown algae range from small crusts or cushions to leafy free-floating mats formed by species ofSargassum. They may consist of delicate felt-like strands of cells, as inEctocarpus, or of foot-long flattened branches resembling a fan, as inPadina.

Reagrdless of size or form, two visible features set the Phaeophyceae apart from all other algae. First, members of the group possess a characteristic color that ranges from an olive green to various shades of brown. The particular shade depends on the amount of fucoxanthin present in the alga. Second, all brown algae are multicellular. There are no known species that exist as single cells or as colonies of cells, and the brown algae are the only major group of seaweeds that does not include such forms. However, this may be the result of classification rather than evolutionary, as all the groups hypothesized to be the closest relatives of the browns include single-celled or colonial forms.

Visible structures

Whatever their form, the body of all brown algae is termed a thallus, indicating that it lacks the complexxylem and phloem of vascular plants. This does not mean that brown algae completely lack specialized structures. But, because some botanists define "true" stems, leaves, and roots by the presence of these tissues, their absence in the brown algae means that the stem-like and leaf-like structures found in some groups of brown algae must be described using different terminology. Although not all brown algae are structurally complex, those that are typically possess one or more characteristic parts.

A holdfastis a rootlike structure present at the base of the alga. Like a root system in plants, a holdfast serves to anchor the alga in place on the substrate where it grows, and thus prevents the alga from being carried away by the current. Unlike a root system, the holdfast generally does not serve as the primary organ for water uptake, nor does it take in nutrients from the substrate. The overall physical appearance of the holdfast differs among various brown algae and among various substrates. It may be heavily branched, or it may be cup-like in appearance. A single alga typically has just one holdfast, although some species have more than one stipe growing from their holdfast.

A stipeis a stalk or stemlike structure present in an alga. It may grow as a short structure near the base of the alga (as inLaminaria), or it may develop into a large, complex structure running throughout the algal body (as inSargassumor


From Yahoo Answers

Question:hi!can you help me with my problem,my teacher is asking for the multicellular green algae and it's examples..please and thankyou!

Answers:The very widespread blue-green algae may or may not qualify as green algae. Your typical pond scum would be a true green algae. But you likely need a botanical name.

Question:Im not sure which three divisions contain Multicellular Algae. What two character distinguish them from each other. Could you guys help me out?

Answers:Seaweeds are macroscopic, multicellular, marine algae. Types of seaweed Seaweeds are classified into brown algae (Phaeophyta), red algae (Rhodophyta), and green algae (Chlorophyta). Note that in reality the term algae is mainly used for convenience, rather than taxonomic purposes, as there appears little relationship between the various phyla. Seaweeds are often confused with other photosynthetic organisms. Seaweeds are popularly described as plants, but biologists typically do not consider them true Plantae. They also should not be confused with seagrasses, which are vascular plants. In addition, a few species of cyanobacteria bear a resemblance to seaweed algae. Some biologists prefer the term "marine macroalgae" over "seaweeds." Brown algae The Phaeophyta, or brown algae (Class Phaeophyceae, Division Heterokontophyta or Phaeophyta, Kingdom Protista or Plantae or Chromalveolata), are a large group of multicellular, mostly marine algae, and include many seaweeds of colder Northern Hemisphere waters. One example of brown algae seaweed is Sargassum, which creates unique habitats in the tropical waters of the Sargasso Sea. This is one of the few areas where a large biomass of brown algae may be found in tropical waters. Kelp are large seaweeds belonging to the brown algae and are classified in the order Laminariales. There are about 30 different genera. Kelp grows in underwater forests (kelp forests) in clear, shallow oceans. They require nutrient rich water below about 20 C. Kelp is known for its high growth rate and is the largest seaweed. Macrocystis, a member of the Laminariales, may reach 60 meters in length and grows up to 30 centimeters per day. Red algae The red algae (Phylum Rhodophyta, from Greek rhodon = rose + phyton = plant, thus red plant) are a large group of mostly multicellular, marine algae, including many notable seaweeds. Red algae are a traditional part of European and Asian cuisine and are used to make other products like agar, carrageenans, and other food additives. Green algae The Chlorophyta, or green algae (Division Chlorophyta), include about eight thousand species of mostly aquatic organisms. Like the land plants (Bryophyta and Tracheophyta), green algae contain chlorophylls a and b, and store food as starch in their plastids. They contain both unicellular and multicellular species. While most species live in freshwater habitats, and a large number in marine habitats, other species are adapted to a wide range of environments. Few are actually seaweeds, however, either because they are freshwater or microscopic. The sea lettuces (genus genus) are a notable exception.

Question:

Answers:Algae plants Animals Humans Fungi

Question::) thankyou.

Answers:When you have multiple cells you can have specialization of different cells, or in other words you can form tissues. These tissues can serve different functions. Since these tissues are specialized they don't have to perform as many tasks, so they get really good at performing one main task. For example muscle cells are grouped into muscle tissue that allows movement to be possible. The main reason is multicellular species also have the ability to communicate between cells which allows it to function as a whole. This allows increases the survival of the organism.

From Youtube

Calcareous Algae :Calcareous algae are important producers of calcium carbonate and organic matter in both tropical and subtropical marine environment (Millman 1980). Calcareous green algae, such as members of the genus Halimeda, are one of the key players in the production of reef substrate by laying precipitated calcium carbonate, ie limestone. For example, Halimeda spp. were found to be the primary contributor to the carbonate budget in a Tahitian reef system (Payri 1988). Growth rates suggest that Halimeda spp. can renew their biomass approximately once every month during their growing season (Wefer 1980). The calcareous sand is deposited as a result of the natural die-off of the algae leaving the skeletal remains and the consumption by some herbivores such as parrotfish. The high rate of productivity from calcareous algae is critical in the maintenance and balance of a healthy reef from bio-erosion processes. Credits Cinematography: Dr. Stuart Sandin Edited by: Neilan Kuntz Written by: Dr. Olga Pantos Location: Palmyra Island, Line Islands, Central Pacific (2004) Milliman JD. (1974) Marine Carbonates. Springer, Berlin Heidelberg New York, p 375. Payri, CE (1988) Halimeda contribution to organic and inorganic production in a Tahitian reef system. Coral Reefs 6:251-262. Wefer G (1980) Carbonate production by algae Halimeda, Penicillus and Padina. Nature 285:323-324.