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Sperm Guidance
Sperm guidance is the process by which sperm cells ( spermatozoa) are directed to the oocyte (egg) for the aim of fertilization. In the case of marine invertebrates the guidance is done by chemotaxis. In the case of mammals, it appears to be done by chemotaxis, thermotaxis and rheotaxis. Background Since the discovery of sperm attraction to the female gametes in ferns over a century ago, sperm guidance in the form of sperm chemotaxis has been established in a large variety of speciesMiller, R.L. (1985) ''Sperm chemo-orientation in the metazoa''. In: ''Biology of Fertilization'' (Metz, C.B. and Monroy, A., eds.), pp. 275–337. Academic Press, New York. Although sperm chemotaxis is prevalent throughout the Metazoa kingdom, from marine species with external fertilization such as sea urchins and corals, to humans,Cosson, M.P. (1990) ''Sperm chemotaxis''. In: ''Controls of Sperm Motility: Biological and Clinical Aspects'' (Gagnon, C., ed.) pp. 103–135. CRC Press, Boca Rato ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sperm
Sperm (: sperm or sperms) is the male reproductive Cell (biology), cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, which are known as spermatozoa, while some red algae and fungi produce non-motile sperm cells, known as spermatia. Flowering plants contain non-motile sperm inside pollen, while some more basal plants like ferns and some gymnosperms have motile sperm. Sperm cells form during the process known as spermatogenesis, which in amniotes (reptiles and mammals) takes place in the seminiferous tubules of the testicles. This process involves the production of several successive sperm cell precursors, starting with spermatogonia, which Cellular differentiation, differentiate into spermatocytes. The spermatocytes then undergo meiosis, reducing their Ploidy, chromosome number by half, which produces spermatids. The sper ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fallopian Tubes
The fallopian tubes, also known as uterine tubes, oviducts or salpinges (: salpinx), are paired tubular sex organs in the human female body that stretch from the ovaries to the uterus. The fallopian tubes are part of the female reproductive system. In other vertebrates, they are only called oviducts. Each tube is a muscular hollow organ that is on average between in length, with an external diameter of . It has four described parts: the intramural part, isthmus, ampulla, and infundibulum with associated fimbriae. Each tube has two openings: a proximal opening nearest to the uterus, and a distal opening nearest to the ovary. The fallopian tubes are held in place by the mesosalpinx, a part of the broad ligament mesentery that wraps around the tubes. Another part of the broad ligament, the mesovarium suspends the ovaries in place. An egg cell is transported from an ovary to a fallopian tube where it may be fertilized in the ampulla of the tube. The fallopian tubes are line ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arbacia Punctulata
The Atlantic purple sea urchin (''Arbacia punctulata'') is a species of sea urchins from the family Arbaciidae, native to the Atlantic Ocean. Description The Atlantic purple sea urchin is a spherical, dark purple-spined sea urchin, with a nearly flat oral face. It can reach up to 8 cm in diameter, and is native to the North Atlantic Ocean. Image:Arbacia punctulata 1.jpg, Face – aboral Image:Arbacia punctulata oral face.jpg, Face – oral Habitat and range Its natural habitat is in the western Atlantic Ocean. ''A. punctulata'' can be found in shallow water from Massachusetts to Cuba and the Yucatan Peninsula, from Texas to Florida in the Gulf of Mexico, the coast from Panama to French Guiana, and in the Lesser Antilles, usually on rocky, sandy, or shelly bottoms. Ecology and behaviour ''A. punctulata'' is omnivorous, consuming a wide variety of prey although Karlson classified it as a generalized carnivore. Its galactolipids, rather than phlorotannins, act as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sepia Officinalis
The common cuttlefish or European common cuttlefish (''Sepia officinalis'') is one of the largest and best-known cuttlefish species. They are a migratory species that spend the summer and spring inshore for spawning and then move to depths of during autumn and winter. They grow to in mantle (mollusc), mantle length and in weight. Animals from subtropical seas are smaller and rarely exceed in mantle length. The common cuttlefish is native to at least the Mediterranean Sea, North Sea, and Baltic Sea, although subspecies have been proposed as far south as South Africa. It lives on sand and mud seabeds and it can tolerate brackish water conditions. Taxonomy It is unknown where the type specimen of ''S. officinalis'' was collected, as the location is given simply as "Oceano". It is deposited in the Linnean Society of London. ''Sepia officinalis jurujubai'' Oliveira, 1940, originally described as a subspecies of the common cuttlefish, is a junior synonym of ''Sepioteuthis sepioid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pteridium Aquilinum
''Pteridium aquilinum'', commonly called bracken, brake, pasture brake, common bracken, and also known as eagle fern, is a species of fern occurring in temperate and subtropical regions in both hemispheres. Originally native to Eurasia and North America, the extreme lightness of its spores has led to it achieving a cosmopolitan distribution. Description Common bracken is a herbaceous perennial plant, deciduous in winter. The large, roughly triangular fronds are produced singly, arising upwards from an underground rhizome, and grow to tall; the main stem, or stipe, is up to in diameter at the base. It dies back to ground level in autumn. The rhizome grows up to deep, about in diameter, and up to long. Because it regrows in the spring from an underground rhizome, ''P. aquilinum'' tends to be found in dense colonies of genetically identical fronds. Such colonies can be as much as 650 years of age, with individual rhizomes living up to 72 years. One colony at Raakkyla, North Ka ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Montipora
''Montipora'' is a genus of Scleractinian corals in the phylum Cnidaria. Members of the genus ''Montipora'' may exhibit many different growth morphologies. With eighty five known species, ''Montipora'' is the second most species rich coral genus after ''Acropora''. Description Growth morphologies for the genus ''Montipora'' include submassive, laminar, foliaceous, encrusting, and branching. It is not uncommon for a single ''Montipora'' colony to display more than one growth morphology. Healthy ''Montipora'' corals can be a variety of colors, including orange, brown, pink, green, blue, purple, yellow, grey, or tan. Although they are typically uniform in color, some species, such as ''Montipora spumosa'' or ''Montipora verrucosa'', may display a mottled appearance. ''Montipora'' corals have the smallest corallites of any coral family. Columellae are not present. Coenosteum and corallite walls are porous, which can result in elaborate structures. The coenosteum of each ''Montipora ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ciona
''Ciona'' is a genus of sea squirts in the family Cionidae. The body of ''Ciona'' is bag-like and covered by a tunic, which is a secretion of the epidermal cells. The body is attached at a permanent base located at the posterior part, and the opposite bears two openings, the buccal (oral) and atrial (cloacal) siphons. The water is drawn into the ascidian through the buccal siphon and leaves the atrium through the atrial siphon. Species Species in this genus include: * '' Ciona antarctica'' * ''Ciona edwardsi'' * ''Ciona fascicularis'' * '' Ciona gelatinosa'' * ''Ciona hoshinoi'' * ''Ciona imperfecta'' * '' Ciona intermedia'' * ''Ciona intestinalis'' * ''Ciona longissima'' * ''Ciona mollis'' * ''Ciona pomponiae'' * ''Ciona robusta'' * ''Ciona roulei'' * ''Ciona savignyi'' * ''Ciona sheikoi'' Genome projects As of 2008, the genomes of ''Ciona intestinalis''P. Dehal et al.: ''The draft genome of Ciona intestinalis: insights into chordate and vertebrate origins.'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Xenopus
''Xenopus'' () (Gk., ξενος, ''xenos'' = strange, πους, ''pous'' = foot, commonly known as the clawed frog) is a genus of highly aquatic frogs native to sub-Saharan Africa. Twenty species are currently described within it. The two best-known species of this genus are '' Xenopus laevis'' and '' Xenopus tropicalis'', which are commonly studied as model organisms for developmental biology, cell biology, toxicology, neuroscience and for modelling human disease and birth defects. The genus is also known for its polyploidy, with some species having up to 12 sets of chromosomes. Characteristics ''Xenopus laevis'' is a rather inactive creature. It is incredibly hardy and can live up to 15 years. At times the ponds that ''Xenopus laevis'' is found in dry up, compelling it, in the dry season, to burrow into the mud, leaving a tunnel for air. It may lie dormant for up to a year. If the pond dries up in the rainy season, ''Xenopus laevis'' may migrate long di ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chlamydomonas
''Chlamydomonas'' ( ) is a genus of green algae consisting of about 150 species of unicellular organism, unicellular flagellates, found in stagnant water and on damp soil, in freshwater, seawater, and even in snow as "snow algae". ''Chlamydomonas'' is used as a model organism for molecular biology, especially studies of flagellum, flagellar motility and chloroplast dynamics, biogenesis, and genetics. One of the many striking features of ''Chlamydomonas'' is that it contains ion channels (channelrhodopsins) that are directly activated by light. Some FLU (plant gene), regulatory systems of ''Chlamydomonas'' are more complex than their Homology (biology), homologs in Gymnosperms, with evolutionarily related Regulation of gene expression, regulatory proteins being larger and containing additional Protein domain, domains. Molecular phylogeny studies indicated that the traditional genus ''Chlamydomonas'' as defined using morphological data, was polyphyletic within Volvocales. Many s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Algae
Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, such as cyanobacteria, ''Chlorella'', and diatoms, to multicellular macroalgae such as kelp or brown algae which may grow up to in length. Most algae are aquatic organisms and lack many of the distinct cell and tissue types, such as stomata, xylem, and phloem that are found in embryophyte, land plants. The largest and most complex marine algae are called seaweeds. In contrast, the most complex freshwater forms are the Charophyta, a Division (taxonomy), division of green algae which includes, for example, ''Spirogyra'' and stoneworts. Algae that are carried passively by water are plankton, specifically phytoplankton. Algae constitute a Polyphyly, polyphyletic group because they do not include a common ancestor, and although Eu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ascidians
Ascidiacea, commonly known as the ascidians or sea squirts, is a paraphyletic class in the subphylum Tunicata of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer test or "tunic" made of the polysaccharide cellulose. Ascidians are found all over the world, usually in shallow water with salinities over 2.5%. While members of the Thaliacea (salps, doliolids and pyrosomes) and Appendicularia (larvaceans) swim freely like plankton, sea squirts are sessile animals after their larval phase: they then remain firmly attached to their substratum, such as rocks and shells. There are 2,300 species of ascidians and three main types: solitary ascidians, social ascidians that form clumped communities by attaching at their bases, and compound ascidians that consist of many small individuals (each individual is called a zooid) forming large colonies. Sea squirts feed by taking in water through a tube, the oral siphon. The water enters the mouth and ph ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proteases
A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the formation of new protein products. They do this by cleaving the peptide bonds within proteins by hydrolysis, a reaction where water breaks bonds. Proteases are involved in numerous biological pathways, including digestion of ingested proteins, protein catabolism (breakdown of old proteins), and cell signaling. In the absence of functional accelerants, proteolysis would be very slow, taking hundreds of years. Proteases can be found in all forms of life and viruses. They have independently evolved multiple times, and different classes of protease can perform the same reaction by completely different catalytic mechanisms. Classification Based on catalytic residue Proteases can be classified into seven broad groups: * Serine proteases - using a serine alcohol * Cysteine prot ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
