Preliminary information:

Total Area:
It extends from the Arctic in the north to Antarctica in the south, bounded by Asia and Australia in the west, and the Americas in the east. At 169.2 million square kilometres (65.3 million square miles) in area, this largest division of the World Ocean – and, in turn, the hydrosphere – covers about 46% of the Earth's water surface and about 32% of its total surface area, making it larger than all of the Earth's land area combined.

Area comparative:
bout 15 times the size of the US; covers about 28% of the global surface; larger than the total land area of the world.

Coastline: 135,663 km

Geographic coordinates: 0 00 N, 160 00 W

Depth:
The lowest point on earth—the Mariana Trench—lies 10,911 metres (35,797 ft) below sea level. Its average depth is 4,280 metres (14,000 ft). Because of the depth of the Pacific Ocean, tsunamis (huge waves created by earthquakes) can reach speeds of 750 kilometers an hour, the same velocity as a jet airplane.


Prelude:

The Pacific Ocean is the largest of the Earth's oceanic divisions. Its name is derived from the Latin name Mare Pacificum, "peaceful sea", bestowed upon it by the Portuguese explorer Ferdinand Magellan. It extends from the Arctic in the north to Antarctica in the south, bounded by Asia and Australia in the west, and the Americas in the east. At 169.2 million square kilometres (65.3 million square miles) in area, this largest division of the World Ocean – and, in turn, the hydrosphere – covers about 46% of the Earth's water surface and about 32% of its total surface area, making it larger than all of the Earth's land area combined. The equator subdivides it into the North Pacific Ocean and South Pacific Ocean, with two exceptions: the Galápagos and Gilbert Islands are deemed wholly within the South Pacific. The Mariana Trench in the western North Pacific is the deepest point in the Pacific and in the world, reaching a depth of 10,911 metres (35,798 ft).
The ocean encompasses almost a third of the Earth's surface, having an area of 179.7 million square kilometres (69.4 million sq mi and 161 million cubic mi) significantly larger than Earth's entire landmass, with room for another Africa to spare. Extending approximately 15,500 kilometres (9,600 mi) from the Bering Sea in the Arctic to the icy margins of Antarctica's Ross Sea in the south (although the Antarctic regions of the Pacific are sometimes described as part of the circumpolar Southern Ocean), the Pacific reaches its greatest east-west width at about 5°N latitude, where it stretches approximately 19,800 kilometres (12,300 mi) from Indonesia to the coast of Colombia and Peru - halfway across the world, and more than five times the diameter of the Moon. The western limit of the ocean is often placed at the Strait of Malacca. The lowest point on earth—the Mariana Trench—lies 10,911 metres (35,797 ft) below sea level. Its average depth is 4,280 metres (14,000 ft).

The Pacific contains about 25,000 islands (more than the total number in the rest of the world's oceans combined), the majority of which are found south of the equator. Including partially submerged islands, the figure is substantially higher.

The Pacific Ocean is currently shrinking from plate tectonics, while the Atlantic Ocean is increasing in size, by roughly an inch per year (2-3 cm/yr) on 3 sides, roughly averaging 0.2 square miles (0.5 km2) a year.
Along the Pacific Ocean's irregular western margins lie many seas, the largest of which are the Celebes Sea, Coral Sea, East China Sea, Philippine Sea, Sea of Japan, South China Sea, Sulu Sea, Tasman Sea, and Yellow Sea. The Strait of Malacca joins the Pacific and the Indian Oceans on the west, and Drake Passage and the Straits of Magellan link the Pacific with the Atlantic Ocean on the east. To the north, the Bering Strait connects the Pacific with the Arctic Ocean.

As the Pacific straddles the ± 180° meridian, the West Pacific (or western Pacific, near Asia) is in the Eastern Hemisphere, while the East Pacific (or eastern Pacific, near the Americas) is in the Western Hemisphere.

For most of Magellan's voyage from the Strait of Magellan to the Philippines, the explorer indeed found the ocean peaceful. However, the Pacific is not always peaceful. Many tropical cyclones (typhoons, the equivalent of Atlantic hurricanes), batter the islands of the Pacific. The lands around the Pacific rim are full of volcanoes and often affected by earthquakes. Tsunamis, caused by underwater earthquakes, have devastated many islands and destroyed entire towns.

Geology:

The andesite line is the most significant regional distinction in the Pacific. It separates the deeper, mafic igneous rock of the Central Pacific Basin from the partially submerged continental areas of felsic igneous rock on its margins. The andesite line follows the western edge of the islands off California and passes south of the Aleutian arc, along the eastern edge of the Kamchatka Peninsula, the Kuril Islands, Japan, the Mariana Islands, the Solomon Islands, and New Zealand's North Island. The dissimilarity continues northeastward along the western edge of the Andes Cordillera along South America to Mexico, returning then to the islands off California. Indonesia, the Philippines, Japan, New Guinea, and New Zealand—all eastward extensions of the continental blocks of Asia, Australia and Zealandia—lie outside the Andesite Line.

Within the closed loop of the Andesite Line are most of the deep troughs, submerged volcanic mountains, and oceanic volcanic islands that characterize the Pacific basin. Here basaltic lavas gently flow out of rifts to build huge dome-shaped volcanic mountains whose eroded summits form island arcs, chains, and clusters. Outside the Andesite Line, volcanism is of the explosive type, and the Pacific Ring of Fire is the world's foremost belt of explosive volcanism. The Ring of Fire is named after the several hundred active volcanoes that sit above the various subduction zones.

The Pacific Ocean is the only ocean which is almost totally bounded by subduction zones. Only the Antarctic and Australian coasts have no nearby subduction zones.

Bottom Terrain:

The ocean floor in the eastern Pacific is dominated by the East Pacific Rise, which is a part of the worldwide Mid-Ocean Ridge system. About 3,000 km (1,800 mi) across, the rise stands about 3 km (2 mi) above the adjacent ocean floor. The western part of the Pacific Ocean floor consists of mountain arcs that rise above the sea as island groups, such as the Solomon Islands and New Zealand, and deep trenches, such as the Mariana Trench, the Philippine Trench, and the Tonga Trench. Most of the deep trenches lie adjacent to the outer margins of the wide western Pacific continental shelf.

Natural hazards:

surrounded by a zone of violent volcanic and earthquake activity sometimes referred to as the "Pacific Ring of Fire"; subject to tropical cyclones (typhoons) in southeast and east Asia from May to December (most frequent from July to October); tropical cyclones (hurricanes) may form south of Mexico and strike Central America and Mexico from June to October (most common in August and September); cyclical El Nino/La Nina phenomenon occurs in the equatorial Pacific, influencing weather in the Western Hemisphere and the western Pacific; ships subject to superstructure icing in extreme north from October to May; persistent fog in the northern Pacific can be a maritime hazard from June to December.

Seamount chains:

The Pacific Ocean contains several long seamount chains, formed by hotspot volcanism. These include the Emperor Seamounts chain and the Louisville seamount chain.


Landmasses:

The largest landmass entirely within the Pacific Ocean is the island of New Guinea— the second largest island in the world. Almost all of the smaller islands of the Pacific lie between 30°N and 30°S, extending from Southeast Asia to Easter Island; the rest of the Pacific Basin is almost entirely submerged. During the Last glacial period, New Guinea was part of Australia so the largest landmass would have been Borneo-Palawan.

The great triangle of Polynesia, connecting Hawaii, Easter Island, and New Zealand, encompasses the island arcs and clusters of the Cook Islands, Marquesas Islands, Samoa, Society, Tokelau, Tonga, Tuamotu, Tuvalu and the Wallis and Futuna islands.
North of the equator and west of the International Date Line are the numerous small islands of Micronesia, including the Caroline Islands, the Marshall Islands and the Mariana Islands.

In the southwestern corner of the Pacific lie the islands of Melanesia, dominated by New Guinea. Other important island groups of Melanesia include the Bismarck Archipelago, Fiji, New Caledonia, the Solomon Islands and Vanuatu.

Islands in the Pacific Ocean are of four basic types: continental islands, high islands, coral reefs, and uplifted coral platforms. Continental islands lie outside the Andesite line and include New Guinea, the islands of New Zealand, and the Philippines. These islands are structurally associated with nearby continents. High islands are of volcanic origin, and many contain active volcanoes. Among these are Bougainville, Hawaii, and the Solomon Islands.

The third and fourth types of islands are both the result of coralline island building. Coral reefs are low-lying structures that have built up on basaltic lava flows under the ocean's surface. One of the most dramatic is the Great Barrier Reef off northeastern Australia. A second island type formed of coral is the uplifted coral platform, which is usually slightly larger than the low coral islands. Examples include Banaba (formerly Ocean Island) and Makatea in the Tuamotu group of French Polynesia.

Climate:

planetary air pressure systems and resultant wind patterns exhibit remarkable uniformity in the south and east; trade winds and westerly winds are well-developed patterns, modified by seasonal fluctuations; tropical cyclones (hurricanes) may form south of Mexico from June to October and affect Mexico and Central America; continental influences cause climatic uniformity to be much less pronounced in the eastern and western regions at the same latitude in the North Pacific Ocean; the western Pacific is monsoonal - a rainy season occurs during the summer months, when moisture-laden winds blow from the ocean over the land, and a dry season during the winter months, when dry winds blow from the Asian landmass back to the ocean; tropical cyclones (typhoons) may strike southeast and east Asia from May to December.

The ocean and the atmosphere are closely linked — a fact that is clearly demonstrated by the global weather phenomena we know as "El Niño" and "La Niña," which arise in the Pacific Ocean.

Ages ago, Peruvian fishermen named the seasonal warming of the waters off their coast, which occurs in December, "El Nino," which is Spanish for "the Christ child." During a normal year, the waters off South America are typically cold and highly productive for fishing. Then in December (which is summer in the Southern Hemisphere), the water normally warms and fishing becomes less productive. Cold water usually returns again in June, when the fishing season begins again there. In some years, however, the water stays warm throughout the year and can cause dramatic weather around the world. The term "El Niño" is now used to refer to this climatic process.

Steady, westward-blowing trade winds cause warm water to pile up in the western Pacific. During El Niño, the trade winds weaken and cannot "contain" this huge pool of warm water. Consequently, warm water extends far eastward. In the United States, the effects of an El Niño winter include warmer than normal temperatures from the Great Lakes to Alaska, wetter than normal conditions across the southern tier of states, some dryness in the Midwest, and cooler than normal temperatures in the Southeast. It can also include a decrease in hurricanes that reach land.

In some ways, La Niña is the opposite of El Niño and is characterized by cooler than normal ocean water surface temperatures in the central tropical Pacific. In the United States, a La Niña winter includes temperatures that are cooler than normal over the Northwest, warmer than normal over the Southeast, drier than normal from Florida to Arizona, and wetter than normal over the Pacific Northwest and parts of the Midwest. La Niña may also bring an increase in hurricanes that reach land in the United States.

According to the NOAA National Weather Service's Climate Prediction Center, it's likely that El Niño conditions will persist through early 2005. Among the expected impacts around the globe are drier-than-average conditions in Indonesia (through early 2005), northern and northeastern Australia (Nov. 2004 – Feb. 2005), and southeastern Africa (Nov. 2004–March 2005). If the warming in the tropic Pacific strengthens and spreads eastward to the South American coast, then wetter-than-average conditions would be expected in coastal sections of Ecuador and northern Peru during the first few months of 2005, and drier-than-average conditions would be expected to develop in the eastern Amazon late this year and spread to northeast Brazil during Feb.–April 2005.

Terrain:

surface currents in the northern Pacific are dominated by a clockwise, warm-water gyre (broad circular system of currents) and in the southern Pacific by a counterclockwise, cool-water gyre; in the northern Pacific, sea ice forms in the Bering Sea and Sea of Okhotsk in winter; in the southern Pacific, sea ice from Antarctica reaches its northernmost extent in October; the ocean floor in the eastern Pacific is dominated by the East Pacific Rise, while the western Pacific is dissected by deep trenches, including the Mariana Trench, which is the world's deepest


Water characteristics:

Water temperatures in the Pacific vary from freezing in the poleward areas to about 30 °C (86 °F) near the equator. Salinity also varies latitudinally. The water near the equator is less salty than that found in the mid-latitudes because of abundant equatorial precipitation throughout the year. Poleward of the temperate latitudes salinity is also low, because little evaporation of seawater takes place in these frigid areas.

The motion of Pacific waters is generally clockwise in the Northern Hemisphere (the North Pacific gyre) and counter-clockwise in the Southern Hemisphere. The North Equatorial Current, driven westward along latitude 15°N by the trade winds, turns north near the Philippines to become the warm Japan or Kuroshio Current.

Turning eastward at about 45°N, the Kuroshio forks and some waters move northward as the Aleutian Current, while the rest turn southward to rejoin the North Equatorial Current. The Aleutian Current branches as it approaches North America and forms the base of a counter-clockwise circulation in the Bering Sea. Its southern arm becomes the chilled slow, south-flowing California Current.

The South Equatorial Current, flowing west along the equator, swings southward east of New Guinea, turns east at about 50°S, and joins the main westerly circulation of the Southern Pacific, which includes the Earth-circling Antarctic Circumpolar Current. As it approaches the Chilean coast, the South Equatorial Current divides; one branch flows around Cape Horn and the other turns north to form the Peru or Humboldt Current.


Natural resources:

oil and gas fields, polymetallic nodules, sand and gravel aggregates, placer deposits, fish.
One of the Pacific Ocean’s greatest assets is fish, including herring, salmon, sardines, snapper, swordfish, tuna, and shellfish. In 1996, over half (60%) of the world’s total fish catch came from the Pacific Ocean. Pearls are harvested along Australia, Japan, Papua New Guinea, Nicaragua, Panama, and the Philippines. Exploitation of offshore oil and gas reserves is playing an ever-increasing role in the energy supplies of Australia, New Zealand, China, the United States, and Peru.

Environment:

The Pacific Ocean’s endangered marine species include the dugong, sea lion, sea otter, seals, turtles, and whales. Current major environmental issues include oil pollution in the Philippine Sea and South China Sea. In terms of natural hazards, the Pacific Ocean is surrounded by a zone of violent volcanic and earthquake activity (“The Ring of Fire”). Hurricanes may form south of Mexico and strike Central America and Mexico from June to October. The greatest typhoon frequency exists within the triangle from southern Japan to the central Philippines to eastern Micronesia.
Marine pollution: Marine pollution is a generic term for the harmful entry into the ocean of chemicals or particles. The biggest culprit are rivers that empty into the Ocean, and with it the many chemicals used as fertilizers in agriculture as well as waste from livestock and humans. The excess of oxygen depleting chemicals in the water leads to hypoxia and the creation of a dead zone.

Marine debris, also known as marine litter, is a term used to describe human-created waste that has found itself floating in a lake, sea, ocean or waterway. Oceanic debris tends to accumulate at the centre of gyres and coastlines, frequently washing aground where it is known as beach litter.

History and economy:

Important human migrations occurred in the Pacific in prehistoric times, most notably those of the Polynesians from the Asian edge of the ocean to Tahiti and then to Hawaii, New Zealand, and Easter Island.

The ocean was first sighted by Europeans early in the 16th century, first by the Spanish explorer Vasco Núñez de Balboa who crossed the Isthmus of Panama in 1513, and then by Ferdinand Magellan, who sailed the Pacific during his circumnavigation from 1519 to 1522.

A native of Portugal, Magellan renounced his loyalty to that nation after King Emanuel rejected Magellan’s petition for a post within the royal navy. Magellan then left for Spain, which agreed to support Magellan’s claim of a western route to the Spice Islands through a seaway near the southern tip of South America.

On September 20, 1519, Magellan and a crew of 270 men set sail from Spain on their around-the-world voyage in five small vessels including his flagship Trinidad, Concepcion, San Antonio, Victoria, and Santiago. It took the fleet, or at least the three remaining ships in the fleet, 38 days to navigate the strait around South America that was to bear Magellan’s name. During the last week of November, the fleet emerged into what Magellan described as a “beautiful, peaceful ocean.” Thus, it was named the Pacific Ocean (“pacific” meaning “peaceful.”)

Upon entering the Pacific Ocean, Magellan mistakenly thought the Spice Islands were only a short voyage away. Nearly four months later, in March 1521, he and his crew finally reached what is known today as the Philippines. A few weeks later, he was fatally wounded after becoming involved in a dispute between warring Philippine tribes. Only one ship, Victoria, and 18 of Magellan’s original crew members returned to Spain, thereby completing the first circumnavigation of the globe. Although Magellan’s route proved impractical for the spice trade, his voyage has been called the greatest single human achievement on the seas.

In 1564, conquistadors crossed the ocean from Mexico led by Miguel López de Legazpi who sailed to the Philippines and Mariana Islands. For the remainder of the 16th century, Spanish influence was paramount, with ships sailing from Spain to the Philippines, New Guinea, and the Solomon Islands.

During the 17th century, the Dutch, sailing around southern Africa, dominated discovery and trade; Abel Janszoon Tasman discovered Tasmania and New Zealand in 1642. The 18th century marked a burst of exploration by the Russians in Alaska and the Aleutian Islands, the French in Polynesia, and the British in the three voyages of James Cook to the South Pacific and Australia, Hawaii, and the North American Pacific Northwest.

Growing imperialism during the 19th century resulted in the occupation of much of Oceania by European powers, and later, the United States and Japan. Significant contributions to oceanographic knowledge were made by the voyages of HMS Beagle in the 1830s, with Charles Darwin aboard; HMS Challenger during the 1870s; the USS Tuscarora (1873-76); and the German Gazelle (1874-76). Although the United States gained control of the Philippines from Spain in 1898, Japan controlled most of the western Pacific by 1914 and occupied many other islands during World War II. However, by the end of that war, Japan was defeated and the U.S. Pacific Fleet was the virtual master of the ocean. Since the end of World War II, many former colonies in the Pacific have become independent states.

The exploitation of the Pacific's mineral wealth is hampered by the ocean's great depths. In shallow waters of the continental shelves off the coasts of Australia and New Zealand, petroleum and natural gas are extracted, and pearls are harvested along the coasts of Australia, Japan, Papua New Guinea, Nicaragua, Panama, and the Philippines, although in sharply declining volume in some cases. The Pacific's greatest asset is its fish. The shoreline waters of the continents and the more temperate islands yield herring, salmon, sardines, snapper, swordfish, and tuna, as well as shellfish.

Economy – overview: The Pacific Ocean is a major contributor to the world economy and particularly to those nations its waters directly touch. It provides low-cost sea transportation between East and West, extensive fishing grounds, offshore oil and gas fields, minerals, and sand and gravel for the construction industry. In 1996, over 60% of the world's fish catch came from the Pacific Ocean. Exploitation of offshore oil and gas reserves is playing an ever-increasing role in the energy supplies of the US, Australia, NZ, China, and Peru. The high cost of recovering offshore oil and gas, combined with the wide swings in world prices for oil since 1985, has led to fluctuations in new drillings.


Nations & Islands:

Seventeen independent nations are located in the Pacific: Australia, Fiji, Japan, Kiribati, Marshall Islands, Micronesia, Nauru, New Zealand, Palau, Papua New Guinea, the Philippines, Samoa, Solomon Islands, Taiwan, Tonga, Tuvalu, and Vanuatu. The U.S. state of Hawaii is also located here and several island territories and possessions of Australia, Chile, France, Japan, New Zealand, United Kingdom, and the United States.

The largest land mass in this ocean is the continent of Australia, which is about equal in size to the 48 contiguous states of the United States. There are some 25,000 islands in the Pacific Ocean — which is more than the rest of the world's oceans combined. Almost all the smaller islands lie between 30°N and 30°S latitude, extending from Southeast Asia to Easter Island. The rest of the Pacific Basin is almost devoid of land.

Bordering countries and territories :
American Samoa, Australia, Brunei, Cambodia, Canada, Chile, People's Republic of China, Colombia, Cook Islands, Costa Rica, East Timor, El Salvador, Ecuador, Fiji, French Polynesia, Guam, Guatemala, Honduras, Indonesia, Japan, Kiribati, North Korea, South Korea, Malaysia, Marshall Islands, Mexico, Federated States of Micronesia, Nauru, New Caledonia, New Zealand, Nicaragua, Niue, Northern Mariana Islands, Palau, Panama, Papua New Guinea, Peru, Philippines, Pitcairn Islands, Russia, Samoa, Singapore, Solomon Islands, Taiwan, Thailand, Tokelau, Tonga, Tuvalu, United States, Vanuatu, Vietnam, Wallis and Futuna.

Major ports and harbours:
Anchorage, Alaska, United States
Antofagasta, Chile
Arica, Chile
Auckland, New Zealand
Bacolod City, Philippines
Bangkok, Thailand
Batangas, Philippines
Bluff, New Zealand
Brisbane, Queensland, Australia
Buenaventura, Colombia
Busan, South Korea
Cabo San Lucas, Baja California Sur, Mexico
Cagayan de Oro City, Philippines
Callao, Peru
Cebu City, Philippines
Chongjin, North Korea
Dalian, People's Republic of China
Danang, Vietnam
Davao City, Philippines
Ensenada, Baja California, Mexico
Esmeraldas, Ecuador
Guayaquil, Ecuador
Haiphong, Vietnam
Hong Kong, People's Republic of China
Honolulu, Hawaii, United States
Incheon, South Korea
Iloilo, Philippines
Iquique, Chile
Jayapura, Indonesia
Kaohsiung, Republic of China (Taiwan)
Kitimat, British Columbia, Canada
Keelung, Republic of China (Taiwan)
Kobe, Japan
Kuala Terengganu, Malaysia
Laem Chabang, Thailand
Lyttelton, New Zealand
Long Beach, California, United States
Los Angeles, California, United States
Manta, Ecuador
Manzanillo, Colima, Mexico
Mazatlán, Sinaloa, Mexico
Melbourne, Victoria, Australia
Manila, Philippines
Nampho, North Korea
Newcastle, New South Wales, Australia
Oakland, California, United States
Panama City, Panama
Portland, Oregon, United States
Portoviejo, Ecuador
Prince Rupert, British Columbia, Canada
Puerto Chacabuco, Chile
Puerto Montt, Chile
Puerto Vallarta, Jalisco, Mexico
Qingdao, People's Republic of China
Saigon, Vietnam
San Antonio, Chile
San Diego, California, United States
San Francisco, California, United States
Seattle, Washington, United States
Shanghai, People's Republic of China
Shenzhen, People's Republic of China
Singapore
Songkhla, Thailand
Sydney, New South Wales, Australia
Tacoma, Washington, United States
Taichung, Republic of China (Taiwan)
Talcahuano, Chile
Tauranga, New Zealand
Tianjin, People's Republic of China
Tijuana, Baja California, Mexico
Tokyo, Japan
Valparaíso, Chile
Vancouver, British Columbia, Canada
Victoria, British Columbia, Canada
Vladivostok, Russia
Xiamen, People's Republic of China
Yantai, People's Republic of China
Yokohama, Japan
Zamboanga, Philippines

Resources:

http://en.wikipedia.org/wiki/Pacific_Ocean
http://www.ceoe.udel.edu/extreme2004/mission/divelocation/pacific.html
http://geography.about.com/library/cia/blcpacific.htm

Eukaryotic animal cell

Eukaryotic cells are typically about ten times larger than prokaryotic cells. In animal cells, the plasma membrane, rather than a cell wall, forms the cell’s outer boundary. With a design similar to the plasma membrane of prokaryotic cells, it separates the cell from its surroundings and

regulates the traffic across the membrane

The eukaryotic cell cytoplasm is similar to that of the prokaryote cell except for one major difference: Eukaryotic cells house a nucleus and numerous other membrane-enclosed organelles. Like separate rooms of a house, these organelles enable specialized functions to be carried out efficiently. The building of proteins and lipids, for example, takes place in separate organelles

where specialized enzymes geared for each job are locate.

The nucleus is the largest organelle in an animal cell. It contains numerous strands of DNA, the length of each strand being many times the diameter of the cell. Unlike the circular prokaryotic DNA, long sections of eukaryotic DNA pack into the nucleus by wrapping around proteins. As a cell begins to divide, each DNA strand folds over onto itself several times, forming a rod-shaped chromosome.

The nucleus is surrounded by a double-layered membrane that protects the DNA from potentially damaging chemical reactions that occur in the cytoplasm. Messages pass between the cytoplasm and the nucleus through nuclear pores, which are holes in the membrane of the nucleus. In each nuclear pore, molecular signals flash back and forth as often as ten times per second. For example, a signal to activate a specific gene comes in to the nucleus and instructions for production of the necessary protein go out to the cytoplasm.

Attached to the nuclear membrane is an elongated membranous sac called the endoplasmic reticulum. This organelle tunnels through the cytoplasm, folding back and forth on itself to form a series of membranous stacks. Endoplasmic reticulum takes two forms: rough and smooth. Rough endoplasmic reticulum (RER) is so called because it appears bumpy under a microscope. The bumps are actually thousands of ribosomes attached to the membrane’s surface. The ribosomes in eukaryotic cells have the same function as those in prokaryotic cells—protein synthesis—but they differ slightly in structure. Eukaryote ribosomes bound to the endoplasmic reticulum help assemble proteins that typically are exported from the cell. The ribosomes work with other molecules to link amino acids to partially completed proteins. These incomplete proteins then travel to the inner chamber of the endoplasmic reticulum, where chemical modifications, such as the addition of a sugar, are carried out. Chemical modifications of lipids are also carried out in the endoplasmic reticulum.

The endoplasmic reticulum and its bound ribosomes are particularly dense in cells that produce many proteins for export, such as the white blood cells of the immune system, which produce and secrete antibodies. Some ribosomes that manufacture proteins are not attached to the endoplasmic reticulum. These so-called free ribosomes are dispersed in the cytoplasm and typically make proteins—many of them enzymes—that remain in the cell.


The second form of endoplasmic reticulum, the smooth endoplasmic reticulum (SER), lacks ribosomes and has an even surface. Within the winding channels of the smooth endoplasmic reticulum are the enzymes needed for the construction of molecules such as carbohydrates and lipids. The smooth endoplasmic reticulum is prominent in liver cells, where it also serves to detoxify substances such as alcohol, drugs, and other poisons.

Proteins are transported from free and bound ribosomes to the Golgi apparatus, an organelle that resembles a stack of deflated balloons. It is packed with enzymes that complete the processing of proteins. These enzymes add sulfur or phosphorus atoms to certain regions of the protein, for example, or chop off tiny pieces from the ends of the proteins. The completed protein then leaves the Golgi apparatus for its final destination inside or outside the cell. During its assembly on the ribosome, each protein has acquired a group of from 4 to 100 amino acids called a signal. The signal works as a molecular shipping label to direct the protein to its proper location.

Lysosomes are small, often spherical organelles that function as the cell’s recycling center and garbage disposal. Powerful digestive enzymes concentrated in the lysosome break down worn-out organelles and ship their building blocks to the cytoplasm where they are used to construct new organelles. Lysosomes also dismantle and recycle proteins, lipids, and other molecules.

The mitochondria are the powerhouses of the cell. Within these long, slender organelles, which

can appear oval or bean shaped under the electron microscope, enzymes convert the sugar glucose and other nutrients into adenosine triphosphate (ATP). This molecule, in turn, serves as an energy battery for countless cellular processes, including the shuttling of substances across the plasma membrane, the building and transport of proteins and lipids, the recycling of molecules and organelles, and the dividing of cells. Muscle and liver cells are particularly active and require dozens and sometimes up to a hundred mitochondria per cell to meet their energy needs. Mitochondria are unusual in that they contain their own DNA in the form of a prokaryote-like circular chromosome; have their own ribosomes, which resemble prokaryotic ribosomes; and divide independently of the cell.

Unlike the tiny prokaryotic cell, the relatively large eukaryotic cell requires structural support

The cytoskeleton, a dynamic network of protein tubes, filaments, and fibers, crisscrosses the cytoplasm, anchoring the organelles in place and providing shape and structure to the cell. Many components of the cytoskeleton are assembled and disassembled by the cell as needed. During cell division, for example, a special structure called a spindle is built to move chromosomes around. After cell division, the spindle, no longer needed, is dismantled. Some components of the cytoskeleton serve as microscopic tracks along which proteins and other molecules travel like miniature trains. Recent research suggests that the cytoskeleton also may be a mechanical communication structure that converses with the nucleus to help organize events in the cell.

زیست شناسی دریا

اقیانوس:

برای تعریف اقیانوسها میتوان گفت،اقیانوس پهنه وسیعی از آب است که بیش از دو سوم سطح زمین را می پوشاند.
اقيانوس ها بيشتر سطح زمین يعني حدود 70 درصد سطح زمين را مي پوشانند. اقيانوس ها 97 درصد ذخيره آب روي زمين را در خود دارند. يعني تنها حدود سه درصد آب سطح زمين شيرين است. 78 درصد بارندگي كره زمين بر روي اقيانوس ها رخ مي دهد و اقيانوس ها منبع 86 درصد بخار آب كره زمين هستند. اقيانوس هاي زمين در منظومه شمسي بي همتا هستند. هيچ سياره ديگري در منظومه شمسي آب مايع ندارد (اگرچه يافته هاي اخير نشان مي دهد كه مريخ ممكن است در گذشته هاي نزديك مقداري آب مايع داشته است).
زندگي روي سياره زمين ازدرياها منشأ گرفته و اقيانوس ها در ادامه به خانه جانوران زنده شناور تبديل شده اند.
اقیانوس یک پیکره مستغنی، ارگانیک و زنده است.نوعی سیستم بیولوژی خود متکی که برای حفظ سیستم خود تنظیم و پایدار خود که جریان انرژی را از اتمسفر و حرکت مواددر لیتوسفر را متعادل می سازد، با محیط های فیزیکی کنش متقابل دارد. به عبارت دیگر اقیانوس یک بیوسفر جهانی است که انرژی را از خورشید، بادها و امواج گرفته شده در جهان توزیع می کند.علاوه براین اقیانوس ها مواد شیمیایی را از حوزه ها و قاره های اقیانوسی به سیستم های زنده منتقل و آنها را به گردش در می آورند.

كاركرد اقيانوس ها:
اقيانوس هاي زمين كاركردهاي زيادي دارند. مخصوصاً بر روي دما و هوا تأثير مي گذارند. اگر اقيانوس وجود نداشت و همه زمين خشكي بود, اثر گلخانه اي دماي زمين را بسيار بالا مي برد. اين چرخه آب ست كه مانع مي شود تا زمين به خاطر اثر گلخانه اي خيلي گرم شود. اگر زمين جو كنوني خود را داشت ولي اقيانوس نداشت و انرژي تابشي معادل همين انرژي اي كه حالا به زمين مي رسد وجود داشت، دماي سطح زمين به 67 درجه سانتي گراد مي رسيد. اما اين اتفاق نمي افتد چون اقيانوس ها بيشتر گرمايي كه از خورشيد به زمين مي رسد را ذخيره مي كنند.
اقيانوس كه پيوسته در حال حركت است، اين انرژي گرمايي را در سراسر كره زمین پخش مي كند. اين كار باعث مي شود خشكي هاي زمين و نيز هوا در طول زمستان گرم و در طول تابستان خنك شوند. به عبارتي اقيانوس ها دماي زمين را معتدل نگه مي دارند.

چرخه آب:
چرخه آب به اين شكل است كه نور خورشيد سطح آب را گرم مي كند. درياها گرمايشان را از طريق تبخير از دست مي دهند. بادها بخار آب را از سطح درياها دور مي كنند. موقعي كه بخار آب به صورت باران ريزش مي كند، گرما را آزاد مي كند كه هوا را گرم مي كند و چرخش را درجو به راه مي اندازد. به عبارتي چرخه آب شامل بخار شدن آب از سطح اقيانوس و سطح خشكي، انتقال بخار آب به وسيله جو، بارش به اقيانوس و سطح زمين، انتقال آب از مناطق خشكي به داخل اقيانوس و بازگشت جريان آب تازه از خشكي به اقيانوس است.
شارژ الكتريكي مولكول هاي آب به آب اين توانايي را مي دهد تا اتم هاي مواد ديگر را جذب كند. اين كيفيت به آب اجازه مي دهد تا بسياري از مواد را حل شده نگه دارد. توانايي آب در نگهداري مواد حل شده به آن اين قدرت را مي دهد تا سنگ ها را تجزيه كند. آب مايع روي زمين نه تنها روي زمين تأثير مي گذارد بلكه بر داخل زمين هم اثر مي گذارد. آب در سنگ هاي طبقات پايين تر زمين, درجه حرارت ذوب سنگ را پايين تر مي آورد. آب, سنگ ها را ضعيف مي كند و فرايند ذوب شدن سنگ ها در زير سطح زمين را آسان تر مي كند.

مقدار شوري:
مقدار شوري آب اقيانوس ها متفاوت است. اقيانوس ها و درياها تقريباً 5 ضربدر 10 به توان 16 تن نمك دارند. يك فوت مكعب از آب دريا به طور متوسط 2/2 پوند نمك دارد.
از نظر وزني حدود 5/3 درصد از اقيانوس ها نمك است. به عبارتي ميزان نمك در 1000 پوند آب 35 پوند است.
شورترين آب، آب درياي سرخ و خليج فارس است كه شوري آنها حدود 40 پوند در 1000 پوند آب است. درياهايي كه كمترين شوري را دارند در مناطق قطبي هستند كه هم ذوب يخ قطبي و هم مقدار زياد باران ميزان نمك را كم مي كند.

ساختمان پوسته اقيانوسي:
اطلاعات ما از ترکیب و ساختمان قشر اقیانوسی اکثرا بر اساس مدارک ژئوفیزیکی و مطالعه نمونه‌های سنگی که از حفاریها و نمونه برداری از کف اقیانوسها بدست آمده استوار می‌باشد. اطلاعات لرزه‌ای و ثقل سنجی ، پوسته اقیانوسی ، سه لایه با ضخامت متوسط 6 کیلومتر را نشان می‌دهد:

•لایه اول : لایه اول یا بالاترین لایه شامل سنگهای رسوبی غیر متراکم به ضخامت یک کیلومتراست.
•لایه دوم : لایه دوم از سنگهای متراکم مانند آهک و شیل تشکیل شده و معمولا بین 1.5 تا 2 کیلومتر ضخامت دارد. در بعضی نواحی جریانهای گدازه بازالتی بطور بین چینه‌ای در لابلای این سنگها قرار گرفته است. از این بازالتها که پس از فوران به سرعت زیر آب سرد شده‌اند، اغلب به شکل بالشتکهای کروی در می‌آیند که پیلو (pillow) نامیده می‌شوند.
•لایه سوم : لایه سوم با ضخامتی در حدود 5 کیلومتر تا شکستگی موهورویچیک ادامه پیدا می‌کند. مرز بین پوسته جامد و گوشته با افزایش ناگهانی چگالی سنگها مشخص می‌شود. ترکیب لایه سوم به خوبی معلوم نیست، ولی از اطلاعات موجود درباره مراحل تشکیل پوسته اقیانوسی چنین استنباط می‌شود که این لایه در قسمت بالا شامل ترکیبات آذرین بازیک نفوذی و در پایین شامل سنگهای آذرین بازیک احتمالا از نوع گابرو می‌باشد.
گسترش کف دریا مکانیسمی است که در اثر آن پوسته اقیانوسی بوجود می‌آید و یا ازبین می‌رود. کف تمام اقیانوسها به علت بیرون ریختن مواد مذاب ، مخصوصا گدازه‌های بازالتی که از گوشته بیرون می‌آید دارای برجستگیهای در حال افزایش است. نسبت گسترش پوسته جدید در کف اقیانوسها در دو پهلوی برجستگی ، هر سال بین یک تا ده سانتیمتر تغییر می‌کند. نه تنها پوسته جامد در این حرکات بلکه گوشته بالایی تا عمق 70 الی 100 کیلومتر روی لایه نیمه مذاب حرکت می‌کند.
به محض رسیدن مواد مذاب جوشان بازالتی به سطح دریا ، در طول برجستگیها جامد گردیده و مغناطیسی در جهت شمال و جنوب ایجاد می‌گردد که همان میدان مغناطیسی متداول زمین است. به عبارت دیگر ، پوسته جامد مغناطیسی را بطور یکسان در دو طرف برجستگی مانند یک نوار ضبط می‌کند.
در اقیانوسهای بزرگتر و بویژه در اقیانوس کبیر ، با گسترش آخرین سطح کف اقیانوس ، پوسته اقیانوسی در اثر نیروهای کمپرسیونی یا فشاری در مانتل پایین می‌رود. این عمق پوسته اقیانوسی در محل شکافهای اقیانوسی مشاهده می‌شود. به عبارت دیگر ، یکی از پلیتها که معمولا به علت گسترش فعال کف دریا تحرک زیادی دارد، در مجاور پلیت دیگر به علت نیروهای فشاری به سمت پایین کج می‌شود. قسمتی از این فرو رفتگی که شیب تند دارد، زون فرورانش را ایجاد می‌نماید. پلیت فرو رفته ضمن پایین رفتن پوسته اقیانوسی را به سمت زیر و داخل گوشته حمل کرده و رسوبات سطحی که چگالی کمتری دارند. در طی این مراحل تغییرشکل داده و اسکارپ تشکیل می‌دهند.
تمامی بقایای پوسته اقیانوسی بین 100 تا 300 کیلومتر عمق ذوب می‌شوند، اما پلیت تا عمق 700 کیلومتر قبل از ذوب شدن کامل در مانتل پایین می‌رود. مواد مذاب پوسته اقیانوسی به علت داشتن چگالی کمتر از مانتل ، به صورت گدازه و همراه با رسوبات حاصل از اسکارپ‌ها از کف اقیانوس فوران و رشته جزایر ولکانیکی یا جزایر قوسی را در حاشیه پلیتی که در روی پلیت دیگر قرار گرفته تشکیل می‌دهند.
میانگین عمق اقیانوسها: 3795 متر است.
حوزه های جغرافیایی در سرتاسر جهان اقیانوس نامیده می شود
هنوز دقیقا مرز مشخصی برای جداسازی آب این اقیانوس ها وجود ندارد.
اقيانوس هاي زمين همه به هم متصلند

در تقسیم بندی قدیم، اقیانوسها را به 5 دسته تقسیم کرده بودند که شامل آرام، اطلس، هند، منجمد شمالی و منجمد جنوبی بود. اما در تقسیم بندی جدید 4 دسته شده اند (توسط محققی بنام Bruns در سال 1958) و اقیانوس منجمد جنوبی Anarctic ocean حذف شده است و محل تداخل، ارتباط و پیوستگی سه اقیانوس هند، کبیر و اطلس نامیده شده است. اقیانوس منجمد جنوبی چون توسط پدیده زمین شناختی مشخصی بوجود نیامده و هیچ عارضه طبیعی نظیر خشکی، برآمدگی و دماغه باعث جدایی اقیانوس منجمد جنوبی از سایر اقیانوسها نشده بود لذا بعنوان اقیانوس نامیده نمی شود. اقیانوس منجمد شمالی هم گاهی دریای منجمد شمالی نامیده میشود چون یکی از ویژگیهای مهم اقیانوسها را ندارد بدین معنی یکی از خصوصیات مهم همه اقیانوسها این است که ارتباط وسیعی در سطح و عمق با یکدیگر میباشند ولی اقیانوس منجمد شمالی فاقد چنین ویژگی است.
-قسمتهای انتهایی قاره ها را که در داخل دریاها فرو رفته اند اصطلاحا دماغه گویند مثل دماغه تازمانی و بنگال که انتهای هند است.


چه چيزي باعث ايجاد موج در اقيانوس مي شود؟
باد امواج را در سطح اقيانوس ها و درياچه ها به وجود مي آورد. باد در حين اصطكاك بين مولكول هاي هوا و مولكول هاي آب مقداري از انرژيش را به آب انتقال مي دهد. بادهاي قوي تر مثل باد هاي توفاني موج هاي بزرگ تري را به وجود مي آورند. شما مي توانيد با فوت كردن به سراسر يك كاسه آب موج هايي در ابعاد كوچك بسازيد.
امواج آب به طور افقي حركت نمي كنند. آنها فقط رو به پايين و بالا حركت مي كنند (يك موج جريان آب را ايجاد نمي كند).
تسونامي (بعضي وقت ها امواج جزر و مدي ناميده مي شود) با امواج سطحي متفاوت است. تسونامي معمولاً به وسيله زلزله هاي زير آبي، انفجارهاي آتشفشاني و ريزش كوه ايجاد مي شود.

چه چيزي باعث ايجاد جزر و مد مي شود؟
جزر و مدها , بالا رفتن و پايين افتادن دوره اي بدنه بزرگي از آب هستند. جزر و مدها به وسيله كنش و واكنش جاذبه اي بين زمين و ماه به وجود مي آيند. كشش جاذبه اي ماه باعث مي شود اقيانوس ها به سمت ماه بالا بروند و برآمده شوند. برآمدگي ديگري هم رخ مي دهدكه عكس شرايط قبلي ست. يعني زماني كه زمين به جانب ماه كشيده مي شود. از آنجايي كه موقعي كه اين اتفاق مي افتد زمين مي چرخد، هر روز دو جزر و مد در اقيانوس ها رخ مي دهد.

چرا اقيانوس آبي ست؟
نور خورشيد از همه رنگ هاي رنگين كمان تشكيل شده. اين رنگ ها عبارتند از: قرمز، نارنجي، زرد، سبز، آبي و بنفش. از قسمت سطح آب، مقداري از نور خورشيد منعكس مي شود كه اين نور رنگ آسمان را بازتاب مي دهد. بخشي از نور خورشيد هم به داخل آب نفوذ مي كند و به وسيله ريز موج ها و ذرات، در آب پخش و پراكنده مي شود. در قسمت عميق آب, بيشتر نور خورشيد به وسيله اكسيژن در آب پراكنده مي شود، و اين قسمت آب هم بيشتر نور آبي را پراكنده مي كند.
آب بيشتر نور قرمز موجود در نور خورشيد را جذب مي كند. اما توزيع و پخش نور آبي را افزايش مي دهد.
بعضي از درياهايي كه رنگشان تک است:
درياي سرخ اغلب قرمز به نظر مي رسد و اين به خاطر خزه ها و فیتوپلانکتون قرمزي ست كه در اين دريا زندگي مي كنند. درياي سياه تقريباً سياه به نظر مي رسد به خاطر اين كه در آن هيدروژن سولفيد تجمع زيادي دارد (كه به رنگ سياه ظاهر مي شود).

دریا چیست؟

آب بسیار که محوطه وسیعی را فرا گیرد و به اقیانوس راه دارد را دریا گویند(درياها شاخه هاي كوچك تري از اقيانوس هستند).
مجموع آب های شور که جزء اعظم کره زمین را می پوشاند و تقریباً سه چهارم سطح زمین را در بر گرفته و در نیمکره جنوبی بیشتر از نیمکره شمالی زمین را فرا گرفته است.

عنوان دریا معمولاً برای دریاچه های شور هم که فاقد مجرای خروجی طبیعی اند نیز استفاده می شود، مانند دریای خزر که دریاچه ای بزرگ است، و دریاچه گالیله که یک دریاچه کوچک با آب شیرین و مجرای خروجی طبیعی است.

عمق دریاها مختلف و تغییر پذیر است. بستر دریاها مانند سطح زمین ناصاف و غیر مسطح می باشد و در زیر آب دره هایی موجود است شبیه به دره هایی که در کوه های بسیار مرتفع مشاهده می کنیم و جزیره های کوچک و کم وسعت نیز قله های کوه های مرتفع زیر دریا هستند.
فهرست اسامی دریاها ( جمعاً 54 دریا ) توسط International Hydrographic Bureau جمع آوری شده است.
بزرگ ترين درياها درياي چين جنوبي، درياي كاراييب و درياي مديترانه هستند.

منابع:

http://020.ir/index.php?option=com_content&task=view&id=121&Itemid=26

http://www.ngdir.ir/GeoLab/PGeoLabExp.asp?PExpCode=5172&PID=648

http://daneshnameh.roshd.ir/mavara/mavara-index.php?page=%d8%af%d8%b1%db%8c%d8%a7&SSOReturnPage=Check&Rand=0

http://www.omba.blogfa.com/8708.aspx

Prokaryotic cell

Prokaryotic cells are among the tiniest of all cells, ranging in size from 0.0001 to 0.003 mm (0.000004 to 0.0001 in) in diameter. About a hundred typical prokaryotic cells lined up in a row would match the thickness of a book page. These cells, which can be rodlike, spherical, or spiral in shape, are surrounded by a protective cell wall. Like most cells, prokaryotic cells live in a watery environment, whether it is soil moisture, a pond, or the fluid surrounding cells in the human body. Tiny pores in the cell wall enable water and the substances dissolved in it, such as oxygen, to flow into the cell; these pores also allow wastes to flow out.

Pushed up against the inner surface of the prokaryotic cell wall is a thin membrane called the plasma membrane. The plasma membrane, composed of two layers of flexible lipid molecules and interspersed with durable proteins, is both supple and strong. Unlike the cell wall, whose open pores allow the unregulated traffic of materials in and out of the cell, the plasma membrane is selectively permeable, meaning it allows only certain substances to pass through. Thus, the plasma membrane actively separates the cell’s contents from its surrounding fluids.

While small molecules such as water, oxygen, and carbon dioxide diffuse freely across the plasma membrane, the passage of many larger molecules, including amino acids (the building blocks of proteins) and sugars, is carefully regulated. Specialized transport proteins accomplish this task. The transport proteins span the plasma membrane, forming an intricate system of pumps and channels through which traffic is conducted. Some substances swirling in the fluid around the cell can enter it only if they bind to and are escorted in by specific transport proteins. In this way the cell fine-tunes its internal environment.

The plasma membrane encloses the cytoplasm, the semifluid that fills the cell. Composed of about 65 percent water, the cytoplasm is packed with up to a billion molecules per cell, a rich storehouse that includes enzymes and dissolved nutrients, such as sugars and amino acids. The water provides a favorable environment for the thousands of biochemical reactions that take place in the cell.

Within the cytoplasm of all prokaryotes is deoxyribonucleic acid (DNA), a complex molecule in the form of a double helix, a shape similar to a spiral staircase. The DNA is about 1,000 times the length of the cell, and to fit inside, it repeatedly twists and folds to form a compact structure called a chromosome. The chromosome in prokaryotes is circular, and is located in a region of the cell called the nucleoid. Often, smaller chromosomes called plasmids are located in the cytoplasm. The DNA is divided into units called genes, just like a long train is divided into separate cars. Depending on the species, the DNA contains several hundred or even thousands of genes. Typically, one gene contains coded instructions for building all or part of a single protein. Enzymes, which are specialized proteins, determine virtually all the biochemical reactions that support and sustain the cell.

Also immersed in the cytoplasm are the only organelles in prokaryotic cells—tiny bead-like structures called ribosomes. These are the cell’s protein factories. Following the instructions encoded in the DNA, ribosomes churn out proteins by the hundreds every minute, providing needed enzymes, the replacements for worn-out transport proteins, or other proteins required by the cell.

While relatively simple in construction, prokaryotic cells display extremely complex activity. They have a greater range of biochemical reactions than those found in their larger relatives, the eukaryotic cells. The extraordinary biochemical diversity of prokaryotic cells is manifested in the wide-ranging lifestyles of the archaebacteria and the bacteria, whose habitats include polar ice, deserts, and hydrothermal vents—deep regions of the ocean under great pressure where hot water geysers erupt from cracks in the ocean floor.

زیست شناسی دریا

معرفی زیست شناسی دریا :

گرایش زیست شناسی دریا، خود يكي از 5 گرايش رشته زيست شناسي است.

زيست‌ دريا به‌ بررسي‌ و مطالعه‌ خواص‌ محيط‌ آبي‌، بيولوژي‌ آبزيان‌ و فعاليت‌هاي‌ آبزي‌پروري‌ مي‌پردازد؛ يعني‌ برخلاف‌ دو گرايش‌ علوم‌ جانوري‌ و علوم‌ گياهي‌ كه‌ در آنها بيشتر موجودات‌ خشکیزي‌ مطالعه‌ مي‌شوند اين‌ گرايش‌ جانوران‌ و گياهان‌ آبزي‌ را بررسي‌ و مطالعه‌ مي‌كند. گرايش‌ زيست‌ دريا علاوه‌ بر بررسي‌ فيزيولوژي‌ آبزيان‌ به‌ مطالعه‌ اكولوژي‌ دريا مثل بررسي‌ آلودگي‌ آب‌ درياها و تأثير آن‌ بر محيط‌ دريا مي‌پردازد.

"دنياي زير آبها دنياي بسيار اعجاب آور و شگفت انگيزي است. دنیایی که در آن مجودات میکروسکوپی از جمله اکثر فیتوپلانکتون و زئوپلانکتون وبزرگترین جانور یعنی نهنگ آبی با طول 33.5 متر ووزن 140 تن همچنين خطرناكترين، باهوشترين، زيباترين و بي آزارترين جانوران كره زمين در همين محيط پررمز و راز حضور دارند.".

گرايش زيست دريا مثل ساير گرايشهاي زيست شناسي جزو علوم پايه محسوب مي شود و در واقع هدف اين گرايش تربيت كارشناسان و محققان زيست دريا است، افرادي كه بايد عاشق كشف حقايق پديده هاي طبيعي باشند. چون شايد بتوان در رشته هايي كه جنبه فني يا اجرايي دارند بدون عشق و علاقه بسيار موفق گرديد و حتي شغلي نيز در همان زمينه پيدا كرد اما يك محقق نمي تواند بدون عشق و علاقه اي وافر با دشواري هاي كارهاي تحقيقاتي دست و پنجه نرم كند و در نهايت موفق گردد.

در زیستگاه مطالعه شده توسط زیست شناسی دریایی شامل همه مناطق دریاها و اقیانوسها بوده، از لایه های سطحی آب تا عمیقترین نقطه اقیانوسها با عمق بیش از 10.000متر مورد بررسی قرار گرفته. این مطالعات زیستگاههای مختلفی را شامل میشود از قبیل صخره های دریایی تپه های مرجانی ، جنگل های حرا، سواحل گلی، شنی و ماسه ای .

گونه های بسیاری از نظر اقتصادی برای انسان مهم هستند که در دریا وجود دارد ، از جمله مواد غذایی مثل ماهیها. زندگی دریایی تبدیل به یک منبع وسیع شده است برای فراهم کردن، غذا ، دارو ، مواد خام ومعدنی ، علاوه بر این نقش بسیار گسترده ای را در صنعت گردشگری و توریسم دارا است. در یک سطح بنیادی ، زندگی دریایی را میتوان به عنوان وجود حیات در سیاره ای دانست. موجودات دریایی کمک قابل توجهی به چرخه اکسیژن و دیگر گازهای مهم و املاح دارند ، حتی در آینده با پایان یافتن مواد معدنی در خشکی میتوان از رسوبات تجمع یافته در دریا استفاده کرد از جمله نودولهای منیزیم و آهن که وجود آنها در بخشهایی از اقیانوس اطلس گزارش شده است . همچنین نقش کسترده اقانوسها را در رابطه با آب و هوای خشکی ها نباید از یاد برد ، و حتی برخی از موجودات دریایی کمک به ایجاد سرزمینها و زیستگاههای جدید میکنند.

خیلی از گونه هایی که دراقیانوس ها زندگی می کنند هنوز به کشف نشده اند ، که این به علت به علت حجم بسیار زیاد اقیانوسها و دریا ها است. اقیانوس ها شامل حدود 71 ٪ از سطح زمین است ، به دلیل عمق خود را در حدود 300 برابر حجم قابل سکنی از زیستگاه زمینی روی زمین را در بر گرفته است.

دانشجوي‌ رشته‌ زيست‌شناسي‌ بايد عاشق‌ كشف‌ حقايق‌ پديده‌هاي‌ طبيعي‌ باشد و به‌ گردش‌ در طبيعت‌ علاقه‌مند باشد. چون‌ اطلاعاتي‌ كه‌ با حضور در محيط‌ طبيعي‌ زندگي‌ گياه‌ يا جانور مي‌توان‌ به‌ دست‌ آورد در هيچ‌ كتابي‌ پيدا نخواهد شد. در ضمن‌ دانشجو لازم‌ است‌ فردي‌ منظم‌ و مرتب‌ بوده‌ و بتواند مطالب‌ را در ذهن‌ خويش‌ به‌ خوبي‌ طبقه‌بندي‌ كند تا در همه زمينها‌ از جمله سيستماتيک موفق‌ گردد.

آشنايي با بعضي از مهارت هاي جنبي مثل غواصي و عكاسي و فيلمبرداري در زير آب مي تواند موفقيت دانشجوي اين رشته بخصوص در سطوح كارشناسي ارشد و دكترا نفش موثري داشته باشد.

البته ما در سطح ليسانس اطلاعات بسيار كمي در مورد دنياي زير آبها به دست مي آوريم. اما همين اطلاعات محدود مي تواند براي يك دانشجوي علاقه مند، راهگشا باشد و او را با نحوه مطالعه و تحقيق در زمينه اكولوژي دريا و بيولوژي آبزيان آشنا سازد .ضمناً گرايش زيست دريا در ايران تا مقطع دكترا تدريس مي شود.

دوره کارشناسی ارشد رشته زیست شناسی دریا با چهار گرایش گیاهان دریا،جانوران دریا، بوم شناسی دریا و آلودگی دریا از دوره های کارشناسی ارشد ناپیوسته است که هدف از آن تربیت کارشناسان متعهد و متخصص به نحوی است که از مفاهیم اساسی علوم زیستی دریایی آگاهی کافی و لازم داشته، جنبه های نظری و کاربردی مختلف آن را بشناسند و علاوه بر گذرانیدن دوره تخصصی در هر یک از گرایش ها بتوانند نیاز مراکز آموزشی، پژوهشی، تولیدی و خدماتی را در زمینه های مذکور برطرف نمایند.

درباره تفاوت این رشته با شیلات باید گفته شود:
دانشجوي رشته شيلات تكنيك و فن تكثير و پرورش ماهي را آموزش مي بيند و در همين زمينه فعاليت مي كند. در حالي كه دانشجوي زيست دريا بيشتر به بررسي خصوصيات موجودات دريايي به عنوان يك موجود زنده و ويژگي هاي توليد مثل آنها مي پردازد و از سوي ديگر آبزي پروري تنها بخشي از مطالعات و در نتيجه فعاليت هاي يك دانشجوي زيست دريا است و دانشجوي اين گرايش در كل به مطالعه محيط آب و جانداران آن مي پردازد.

اگر دانشجوي زيست دريا بخواهد شغلي در ارتباط با رشته تحصيلش پيدا كند، بايد توجه داشته باشد كه فرصت هاي شغلي اين گرايش بيشتر در نواحي ساحلي كشور مثل استان گيلان، مازندران و خليج فارس وجود دارد. علاوه بر كار در شيلات فارغ التحصيلان اين گرايش مي توانند در مرکز تحقیقاتی آبزیان دریایی و همچنین در مراکز تحقیقانی غذایی برای تعیین ارزش غذایی آبزیان به کار مشغول شوند.

منابع :

http://en.wikipedia.org/wiki/Marine_biology
http://www.seamuse.com
http://4tmu.ir/forum/index.php?action=thankyoupostlist;topic=1503.0;msg=8158
http://marinebiology.blogfa.com
http://www.omba.blogfa.com/8708.aspx

cell

Cell ,basic unit of life. Cells are the smallest structures capable of basic life processes, such as taking in nutrients, expelling waste, and reproducing. All living things are composed of cells. Some microscopic organisms, such as bacteria and protozoa, are unicellular, meaning they consist of a single cell. Plants, animals, and fungi are multicellular; that is, they are composed of a great many cells working in concert. But whether it makes up an entire bacterium or is just one of trillions in a human being, the cell is a marvel of design and efficiency. Cells carry out thousands of biochemical reactions each minute and reproduce new cells that perpetuate life

Cells vary considerably in size. The smallest cell, a type of bacterium known as a mycoplasma, measures 0.0001 mm (0.000004 in) in diameter; 10,000 mycoplasmas in a row are only as wide as the diameter of a human hair. Among the largest cells are the nerve cells that run down a giraffe’s neck; these cells can exceed 3 m (9.7 ft) in length. Human cells also display a variety of sizes, from small red blood cells that measure 0.00076 mm (0.00003 in) to liver cells that may be ten times larger. About 10,000 average-sized human cells can fit on the head of a pin
Along with their differences in size, cells present an array of shapes. Some, such as the bacterium Escherichia coli, resemble rods. The paramecium, a type of protozoan, is slipper shaped; and the amoeba, another protozoan, has an irregular form that changes shape as it moves around. Plant cells typically resemble boxes or cubes. In humans, the outermost layers of skin cells are flat, while muscle cells are long and thin. Some nerve cells, with their elongated, tentacle-like extensions, suggest an octopus.
In multicellular organisms, shape is typically tailored to the cell’s job. For example, flat skin cells pack tightly into a layer that protects the underlying tissues from invasion by bacteria. Long, thin muscle cells contract readily to move bones. The numerous extensions from a nerve cell enable it to connect to several other nerve cells in order to send and receive messages rapidly and efficiently.
By itself, each cell is a model of independence and self-containment. Like some miniature, walled city in perpetual rush hour, the cell constantly bustles with traffic, shuttling essential molecules from place to place to carry out the business of living. Despite their individuality, however, cells also display a remarkable ability to join, communicate, and coordinate with other cells. The human body, for example, consists of an estimated 20 to 30 trillion cells. Dozens of different kinds of cells are organized into specialized groups called tissues. Tendons and bones, for example, are composed of connective tissue, whereas skin and mucous membranes are built from epithelial tissue. Different tissue types are assembled into organs, which are structures specialized to perform particular functions. Examples of organs include the heart, stomach, and brain. Organs, in turn, are organized into systems such as the circulatory, digestive, or nervous systems. All together, these assembled organ systems form the human body.
The components of cells are molecules, nonliving structures formed by the union of atoms. Small molecules serve as building blocks for larger molecules. Proteins, nucleic acids, carbohydrates, and lipids, which include fats and oils, are the four major molecules that underlie cell structure and also participate in cell functions. For example, a tightly organized arrangement of lipids, proteins, and protein-sugar compounds forms the plasma membrane, or outer boundary, of certain cells. The organelles, membrane-bound compartments in cells, are built largely from proteins. Biochemical reactions in cells are guided by enzymes, specialized proteins that speed up chemical reactions. The nucleic acid deoxyribonucleic acid (DNA) contains the hereditary information for cells, and another nucleic acid, ribonucleic acid(RNA), works with DNA to build the thousands of proteins the cell needs.