Tuesday, August 14, 2012

Dinoflagellates


    Dinoflagellates are unicellular protists which exhibit a great diversity of form. The largest, Noctiluca, may be as large as 2 mm in diameter! Though not large by human standards, these creatures often have a big impact on the environment around them. Many are photosynthetic, manufacturing their own food using the energy from sunlight, and providing a food source for other organisms. Some species are capable of producing their own light through bioluminescence, which also makes fireflies glow. There are some dinoflagellates which are parasites on fish or on other protists.
    Dinoflagellates possess a unique nuclear structure at some stage of their life cycle - a dinokaryotic nucleus (as opposed to eukaryotic or prokaryotic), in which the chromosomes are perminently condensed. The cell wall of many dinoflagellates is divided into plates of cellulose ("armor") within amphiesmal vesicles, known as a theca. These plates form a distinctive geometry/topology known as tabulation, which is the main means for classification.
   The most dramatic effect of dinoflagellates on life around them comes from the coastal marine species which "bloom" during the warm months of summer. These species reproduce in such great numbers that the water may appear golden or red, producing a "red tide". When this happens many kinds of marine life suffer, for the dinoflagellates produce a neurotoxin which affects muscle function in susceptible organisms. Humans may also be affected by eating fish or shellfish containing the toxins. The resulting diseases include ciguatera (from eating affected fish) and paralytic shellfish poisoning, or PSP (from eating affected shellfish, such as clams, mussels, and oysters); they can be serious but are not usually fatal.

    Both heterotrophic (eat other organisms) and autotrophic (photosynthetic) dinoflagellates are known. Some are both. They form a significant part of primary planktonic production in both oceans and lakes. Most dinoflagellates go through moderately complex life cycles involving several steps, both sexual and asexual, motile and non-motile. Some species form cysts composed of sporopollenin (an organic polymer), and preserve as fossils. Often the tabulation of the cell wall is somehow expressed in the shape and/or ornamentation of the cyst.
    Most zooxanthellae are dinoflagellates. The association between dinoflagellates and reef-building corals is widely known, but dinoflagellate endosymbionts inhabit a great number of other invertebrates and protists, for example many sea anemones, jellyfish, nudibranchs, the giant clam Tridacna, as well as several species of radiolarians and foraminiferans. Many extant dinoflagellates are parasites (here defined as organisms that eat their prey from the inside, i.e. endoparasites, or that remain attached to their prey for longer periods of time, i.e. ectoparasites). They can parasitize animal or protist hosts. Protoodinium, Crepidoodinium, Piscinoodinium and Blastodinium retain their plastids while feeding on their zooplanktonic or fish hosts. In most parasitic dinoflagellates the infective stage resembles a typical motile dinoflagellate cell.
     Dinoflagellates are protists which have been classified using both the International Code of Botanical Nomenclature (ICBN) and the International Code of Zoological Nomenclature (ICZN). Approximately half of living dinoflagellate species are autotrophs possessing chloroplasts and half are non-photosynthesising heterotrophs. It is now widely accepted that the ICBN should be used for their classification.


Sunday, August 12, 2012

Birds

 Birds are feathered, winged, bipedal, endothermic, egg-laying, vertebrate animals. With around 10,000 living species, they are the most speciose class of tetrapod vertebrates. 
Rank: Class
Lower classifications: Falconiformes, Owl, Bucerotiformes, Upupiformes, More...
   Birds are warm-blooded vertebrate animals that have wings, feathers, a beak, no teeth a skeleton in which many bones are fused together or are absent, and an extremely efficient,, one-way breathing system. Flying birds have strong, hollow bones and powerful flight muscles.
  Most birds can fly. Birds have a very strong heart and an efficient way of breathing - these are necessary for birds to fly. Birds also use a lot of energy while flying and need to eat a lot of food to power their flight.
Not all flying animals are birds; and not all birds can fly. The ability to fly has developed independently many times throughout the history of the Earth. Bats (flying mammals), pterosaurs (flying reptiles from the time of the dinosaurs), and flying insects are not birds.
 Modern birds are characterised by feathers, a beak with no teeth, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. All living species of birds have wings—the now extinct flightless moa of New Zealand were the only exception. Wings are evolved forelimbs, and most bird species can fly. Flightless birds include ratites, penguins, and a number of diverse endemic island species. Birds also have unique digestive and respiratory systems that are highly adapted for flight. Some birds, especially corvids and parrots, are among the most intelligent animal species; a number of bird species have been observed manufacturing and using tools, and many social species exhibit cultural transmission of knowledge across generations.
  Many species are of economic importance, mostly as sources of food acquired through hunting or farming. Some species, particularly songbirds and parrots, are popular as pets. Other uses include the harvesting of guano (droppings) for use as a fertiliser. Birds figure prominently in all aspects of human culture from religion to poetry to popular music. About 120–130 species have become extinct as a result of human activity since the 17th century, and hundreds more before then. Currently about 1,200 species of birds are threatened with extinction by human activities, though efforts are underway to protect them.
  Birds can often safely perch on a power line without being electrocuted. For the bird (or other animal) to be electrocuted, a potential difference must exist across two points of the bird's body (its feet in the case of a bird on a power line). When perching on a single power line, there is no potential difference between the bird's feet, so it is safe. If the bird (or other animal) touches two power lines at a time, or one power line and a ground (like a ground wire or the earth itself), the animal would be electrocuted and die. Many large birds (like eagles and vultures) are electrocuted when their wide wings touch a power line and a ground wire at the same time (often while flying in to land on a power line).
Amazon birds  

 More than 1500 bird species are found in the Amazon Basin, while South America as a whole is home to roughly one-third the world's birds.
  • Many birds found in the Amazon are northern or southern migrants, wintering in or passing though the rainforest at certain times of the year.
  • Macaws are famous for gathering by the hundreds, even thousands, along the clay cliffs of the Amazon river where they feed on minerals which help the birds process toxins found in the seeds they eat.
  • The world's rarest bird is Spix's macaw, a beautiful bird with a dark blue head, a blue body, and a greenish belly with a black mask and bright yellow eye. It has always been rare, limited to palm groves and river edges in small area near the center of Brazil, but recent deforestation, importation of Africaniz

    ed bees-which took their tree hollows, and over collection for the hobbyists caused this species' demise.

Thursday, August 9, 2012

ഗുരുത്വാഗര്‍ഷണ കേന്ദ്രം.....

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Tuesday, August 7, 2012

Human Resources

      Human Resources department is the department or support systems responsible for personnel sourcing and hiring, applicant tracking, skills development and tracking, benefits administration and compliance with associated government regulation.
      Human Resources evolved from personnel as the field moved beyond paying employees and managing employee benefits. The evolution made verbal the fact that people are an organization's most important resource. People are an asset that must be hired, satisfied, developed, and retained.

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 Human Resource Management