DNA

Deoxyribonucleic acid (ⁱ/diˈɒksiˌraɪboʊnjʊˌkliːɪk, -ˌkleɪɪk/;DNA) is a molecule that carries most of the genetic instructions used in the development, functioning and reproduction of all known living organisms and many viruses. DNA is a nucleic acid; alongside proteins and carbohydrates, nucleic acids compose the three major macromolecules essential for all known forms of life. Most DNA molecules consist of two biopolymer strands coiled around each other to form a double helix. The two DNA strands are known as polynucleotides since they are composed of simpler units called nucleotides. Each nucleotide is composed of a nitrogen-containing nucleobase—either cytosine (C), guanine (G), adenine (A), or thymine (T)—as well as a monosaccharide sugar called deoxyribose and a phosphate group. The nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. According to base pairing rules (A with T, and C with G), hydrogen bonds bind the nitrogenous bases of the two separate polynucleotide strands to make double-stranded DNA. The total amount of related DNA base pairs on Earth is estimated at 5.0 x 10³⁷, and weighs 50 billion tonnes. In comparison, the total mass of the biosphere has been estimated to be as much as 4 TtC (trillion tons of carbon).

Sea

A sea is a large body of salt water that is surrounded in whole or in part by land. More broadly, "the sea" is the interconnected system of Earth's salty, oceanic waters—considered as one global ocean or as several principal oceanic divisions. The sea moderates Earth's climate and has important roles in the water cycle, carbon cycle, and nitrogen cycle. Although the sea has been travelled and explored since prehistory, the modern scientific study of the sea—oceanography—dates broadly to the British Challenger expedition of the 1870s. The sea is conventionally divided into up to five large oceanic sections—including the IHO's four named oceans (the Atlantic, Pacific, Indian, and Arctic) and the Southern Ocean; smaller, second-order sections, such as the Mediterranean, are known as seas.

Owing to the present state of continental drift, the Northern Hemisphere is now fairly equally divided between land and sea (a ratio of about 2:3) but the South is overwhelmingly oceanic (1:4.7).Salinity in the open ocean is generally in a narrow band around 3.5% by mass, although this can vary in more landlocked waters, near the mouths of large rivers, or at great depths. About 85% of the solids in the open sea are sodium chloride. Deep-sea currents are produced by differences in salinity and temperature. Surface currents are formed by the friction of waves produced by the wind and by tides, the changes in local sea level produced by the gravity of the Moon and Sun. The direction of all of these is governed by surface and submarine land masses and by the rotation of the Earth (the Coriolis effect).

Desert

A desert is a barren area of land where little precipitation occurs and consequently living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to the processes of denudation. About one third of the land surface of the world is arid or semi-arid. This includes much of the polar regions where little precipitation occurs and which are sometimes called polar deserts or "cold deserts". Deserts can be classified by the amount of precipitation that falls, by the temperature that prevails, by the causes of desertification or by their geographical location.

Deserts are formed by weathering processes as large variations in temperature between day and night put strains on the rocks which consequently break in pieces. Although rain seldom occurs in deserts, there are occasional downpours that can result in flash floods. Rain falling on hot rocks can cause them to shatter and the resulting fragments and rubble strewn over the desert floor is further eroded by the wind. This picks up particles of sand and dust and wafts them aloft in sand or dust storms. Wind-blown sand grains striking any solid object in their path can abrade the surface. Rocks are smoothed down, and the wind sorts sand into uniform deposits. The grains end up as level sheets of sand or are piled high in billowing sand dunes. Other deserts are flat, stony plains where all the fine material has been blown away and the surface consists of a mosaic of smooth stones. These areas are known as desert pavements and little further erosion takes place. Other desert features include rock outcrops, exposed bedrock and clays once deposited by flowing water. Temporary lakes may form and salt pans may be left when waters evaporate. There may be underground sources of water in the form of springs and seepages from aquifers. Where these are found, oases can occur.

Hebrew University of Jerusalem

The Hebrew University of Jerusalem (Hebrew: האוניברסיטה העברית בירושלים‎, ha-Universita ha-Ivrit B'irushalayim; Arabic: الجامعة العبرية في القدس‎, al-Ǧāmiʻah al-ʻIbriyyah fil-Quds; abbreviated HUJI) is Israel's second oldest university established in 1918, 30 years before the State of Israel. The Hebrew University has three campuses in Jerusalem and one in Rehovot. The world's largest Jewish studies library is located on its Edmond J. Safra Givat Ram campus.

The first Board of Governors included Albert Einstein, Sigmund Freud, Martin Buber, and Chaim Weizmann. Four of Israel's prime ministers are alumni of the Hebrew University. In the last decade, seven researchers and alumni of the University received the Nobel Prize and one was awarded the Fields Medal.

History

One of the visions of the Zionist movement was the establishment of a Jewish university in the Land of Israel. Founding a university was proposed as far back as 1884 in the Kattowitz (Katowice) conference of the Hovevei Zion society.

BTS

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