Discoveries

Mitosis

DEFINITION Mitosis is the ordinary process of cell division resulting in the formation of two daughter cells, by which the body replaces dead cells. The daughter cells have identical diploid complements of chromosomes (46 in human somatic cells). Mitosis occurs in four main phases: prophase, metaphase, anaphase and telophase. The period between mitotic divisions is …

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Cell division

DEFINITION Cell division is the process by which a cell divides into two or more cells. Cell division is the means of reproduction in organisms that reproduce asexually, as by fission or spore formation. In organsims that reproduce sexually, cell division is the source of all tissue growth and repair. The two main types of …

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Anaphase

DEFINIITON Anaphase is the stage of mitosis or meiosis in which the chromosomes move from the equatorial plate toward the poles of the cell. In mitosis a full set of daughter chromosomes (46 in humans) moves toward each pole. In the first division of meiosis one memeber of each homologous pair (23 in humans), consisting …

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The discovery of chromatin

DEFINITION Chromatin is the genetic material of the nucleus consisting of deoxyribonucleoprotein that occurs in two forms during the phase between mitotic divisions: as heterochromatin (seen as condensed, readily stainable clumps) and as euchromatin (dispersed, lightly staining or nonstaining material). During mitotic division the chromatin condenses into chromosomes[1]. DISCOVERY The German biologist Walther Flemming discovered[2] …

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The discovery of chromosomes

DEFINITION Chromosomes are thread-like structures located within the nucleus of each cell. Chromosomes contain the genetic information necessary to direct the development and functioning of all cells and systems in the body. They pass on hereditary traits from parents to child (like eye colour) and determine whether the child will be male or female[1]. DISCOVERY …

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Tantalum

DEFINITION Tantalum is a metallic chemical element with the symbol Ta, atomic number 73 and atomic weight 180.94788. It is a hard, blue-gray metal with a body-centred cubic crystalline structure. Tantalum is majorly used in electrolytic capacitors and parts for vacuum furnaces, aircraft and missiles. As it is unaffected by body fluids and causes no …

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The discovery of the cell nucleus

DEFINITION The cell nucleus is the largest of the membrane-bounded organelles which characterise eukaryotic cells. It is thought of as the control centre since it contains the bulk of the cell’s genetic information in the form of deoxyribonucleic acid (DNA)[1]. DISCOVERY The Scottish botanist and paleobotanist Robert Brown discovered[2] the cell nucleus in 1831 while …

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Iridium

DEFINITION Iridium is a metallic chemical element with the symbol Ir, atomic number 77 and atomic weight 192.217. It is a very hard, usually brittle, extremely corrosion-resistant silver-white metal with a face-centred cubic crystalline structure. Iridium is used principally in alloys; with osmium to make fountain-pen nibs and with platinum to make heavy-duty electrical contacts[1]. …

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Hess’s law

DEFINITION Hess’s law states that the evolved or absorbed heat in a chemical reaction is the same whether the reaction takes one step or several steps. It is also known as Hess’s law of constant heat summation[1]. DISCOVERY The Swiss-Russian chemist Germain Henri Hess discovered[2] the aforementioned law while researching the quantities of heat released …

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Joule’s law

DEFINITION Joule’s law is a quantitative relationship between the quantity of heat produced in a conductor and an electric current flowing through it. The law is stated as H = RI², where “H” is the rate of evolution of heat in watts, the unit of heat being the joule; “R” is the resistance in ohms; …

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