biology stuff

ciliophora

Ciliophora , phylum in the kingdom Protista consisting of the ciliates, or ciliophores, complex freshwater or saltwater protozoans that swim by the coordinated beating of their cilia—short, hairlike structures that cover the cell surface. Like other protozoans, ciliates are unicellular heterotrophs. Some feed on bacteria and other particles as well as algae by means of cilia-created currents; many are carnivorous. In some species the cilia are organized into rows or clumps that the organisms use to walk or jump. Ciliates contain a variety of organelles plus two kinds of nuclei. The larger type of nucleus, the macronucleus, contains a great deal more DNA than the smaller nucleus, the micronucleus. Although the ciliates typically reproduce asexually, they also exchange genetic information with other ciliate cells by the process of conjugation. During this process two cells unite, the micronuclei undergo meiosis, then pair up and fuse with similar haploid micronuclei from the other organism, mixing the DNA from the two organisms.

There are approximately 8,000 species of ciliates. The phylum includes the slipper-shaped paramecium and the trumpet-shaped stentor. The suctorians are sessile ciliates that suck out the protoplasm of their prey through tentacles.


euglenophyta

Euglenophyta , small phylum (division) of the kingdom Protista, consisting of mostly unicellular aquatic algae. Most live in freshwater; many have flagella and are motile. The outer part of the cell consists of a firm but flexible layer called a pellicle, or periplast, which cannot properly be considered a cell wall. Some euglenoids contain chloroplasts that contain the photosynthetic pigments chlorophyll a and b, as in the phylum Chlorophyta; others are heterotrophic and can ingest or absorb their food. Food is stored as a polysaccharide, paramylon. Reproduction occurs by longitudinal cell division. The most characteristic genus is Euglena, common in ponds and pools, especially when the water has been polluted by runoff from fields or lawns on which fertilizers have been used. There are approximately 1,000 species of euglenoids.


chlorophyta

Chlorophyta , phylum (division) of the kingdom Protista consisting of the photosynthetic organisms commonly known as green algae. The organisms are largely aquatic or marine. The various species can be unicellular, multicellular, coenocytic (having more than one nucleus in a cell), or colonial. Those that are motile have two apical or subapical flagella. A few types are terrestrial, occurring on moist soil, on the trunks of trees, on moist rocks, and even in snowbanks. Various species are highly specialized, some living exclusively on turtles, sloths, or within the gill mantles of marine mollusks.

It is generally accepted that early chlorophytes gave rise to the plants. Cells of the Chlorophyta contain organelles called chloroplasts in which photosynthesis occurs; the photosynthetic pigments chlorophyll a and chlorophyll b, and various carotenoids, are the same as those found in plants and are found in similar proportions. Chlorophytes store their food in the form of starch in plastids and, in many, the cell walls consist of cellulose. Unlike in plants, there is no differentiation into specialized tissues among members of the division, even though the body, or thallus, may consist of several different kinds of cells. There are four evolutionary lineages of green algae. Most living species are grouped in classes that are coextensive with three of these lineages.


phaeophyta

Phaeophyta , phylum (division) of the kingdom Protista consisting of those organisms commonly called brown algae. Many of the world's familiar seaweeds are members of Phaeophyta. There are approximately 1,500 species. Like the chrysophytes (see Chrysophyta), brown algae derive their color from the presence, in the cell chloroplasts, of several brownish carotenoid pigments, including fucoxanthin, in addition to the photosynthetic pigments chlorophyll a and c. With only a few exceptions, brown algae are marine, growing in the colder oceans of the world, many in the tidal zone, where they are subjected to great stress from wave action; others grow in deep water. Among the brown algae are the largest of all algae, the giant kelps, which may reach a length of over 100 ft (30 m). Fucus (rockweed), Sargassum (gulfweed), and the simple filamentous Ectocarpus are other examples of brown algae.

The cell wall of the brown algae consists of a cellulose differing chemically from that of plants. The outside is covered with a series of gelatinous pectic compounds, generically called algin; this substance, for which the large brown algae, or kelps, of the Pacific coast are harvested commercially, is used industrially as a stabilizer in emulsions and for other purposes. The normal food reserve of the brown algal cell is a soluble polysaccharide called laminarin; mannitol and oil also occur as storage products. The body, or thallus, of the larger brown algae may contain tissues differentiated for different functions, with stemlike, rootlike, and leaflike organs, the most complex structures of all algae.

Some groups of brown algae have evolved an interesting type of alternation of generations, in which physiologically independent haploid gametophyte plants produce gametes, the fusion of which initiates the diploid sporophyte generation. The mature sporophyte plant produces, through meiosis, haploid spores, which develop into new gametophytes. The two generations, or phases, may be indistinguishable in size and form, or they may differ greatly. The genus Ectocarpus, for example, is found growing attached to larger algae. It has similar-looking gametophyte and sporophyte plants. In the kelps, however, the gametophyte is only a microscopic filament, in contrast to the occasionally tree-sized sporophyte.


rhodophyta

Rhodophyta , phylum (division) of the kingdom Protista consisting of the photosynthetic organisms commonly known as red algae. Most of the world's seaweeds belong to this group. Members of the division have a characteristic clear red or purplish color imparted by accessory pigments called phycobilins, unique to the red algae and the cyanobacteria. The chloroplasts of red algae are believed to be derived from cyanobacteria that formed an ancient symbiotic relationship with the algae.

Of the approximately 4,000 known species of red algae, nearly all are marine; a few species occur in freshwater. Although red algae are found in all oceans, they are most common in warm-temperate and tropical climates, where they may occur at greater depths than any other photosynthetic organisms. The red algae are multicellular and are characterized by a great deal of branching, but without differentiation into complex tissues. The red algal cell wall has a firm inner layer containing cellulose and a mucilaginous or gelatinous outer layer. Cells may have one or more nuclei, depending on the species. Cell division is by mitosis. The red algae are remarkable in that they are not flagellated; none has motile cells of any kind.

Cells of the Rhodophyta possess chloroplasts that, in addition to the phycobilins, contain chlorophyll a, carotenes, and xanthophylls. At great ocean depths, where the wavelength of light available for photosynthesis is very different from that in shallow water, the phycobilins become more active than the chlorophylls in absorbing light; this fact may explain the ability of red algae to exist at depths of up to 879 ft (268 m). The carbohydrate reserves of red algae are in the form of floridean starch, a specialized glucose polymer of different structure than the starch of plants.

The life cycle of the red algae is extremely complex, involving one haploid phase and two diploid phases. Most marine red algae have soft and delicate bodies, or thalli; however, the coralline algae have thalli that become strongly calcified and contribute significantly to the growth of coral reefs in tropical seas. Because of the permanent nature of the structures that they produce, coralline algae have a rich fossil record that extends back as far as 700 million years. Commercial agar, used as a culture medium for bacteria and other organisms as well as for other purposes, is produced from several genera of red algae. The so-called Irish moss is the source of carrageenin, a substance widely used as a stabilizing agent in emulsions and in ice cream.

chrysophyta

Chrysophyta , phylum (division) of unicellular marine or freshwater organisms of the kingdom Protista consisting of the diatoms (class Bacillariophyceae), the golden, or golden-brown, algae (class Chrysophyceae), and the yellow-green algae (class Xanthophyceae). In many chrysophytes the cell walls are composed of cellulose with large quantities of silica. Some have one or two flagella, which can be similar or dissimilar. A few species are ameboid forms with no cell walls. The food storage products of chrysophytes are oils or the polysaccharide laminarin. Formerly classified as plants, the chrysophytes contain the photosynthetic pigments chlorophyll a and c; all but the yellow-green algae also contain the carotenoid pigment fucoxanthin. Under some circumstances diatoms will reproduce sexually, but the usual form of reproduction is cell division. The diatoms and golden-brown algae are of great importance as components of the plankton and nanoplankton that form the foundation of the marine food chain.