Chlorophyll is the green colouring matter of plant leaves and absorbs the light necessary for photosynthesis.
Chlorophyll absorbs mainly red, violet, and blue light and reflects green light. The great abundance of chlorophyll in leaves and its occasional presence in other plant tissues, such as stems, causes these plant parts to appear green. In some leaves, chlorophyll is masked by other pigments.
Chlorophyll is a large molecule composed mostly of carbon and hydrogen. At the centre of the molecule is a single atom of magnesium surrounded by a nitrogen-containing group of atoms called a porphyrin ring. The structure somewhat resembles that of the active constituent of haemoglobin in the blood. A long chain of carbon and hydrogen atoms proceeds from this central core and attaches the chlorophyll molecule to the inner membrane of the chloroplast, the cell organelle in which photosynthesis takes place. As a molecule of chlorophyll absorbs a photon of light, its electrons become excited and move to higher energy levels. This initiates a complex series of chemical reactions in the chloroplast that enables the energy to be stored in chemical bonds. Research Chlorophyll
Absolute configuration is a way of denoting the absolute structure of an optical isomer. Two conventions are in use: The D-L convention relates the structure of the molecule to some reference molecule. In the case of sugars and similar compounds, the dextrorotatory form of glyceraldehyde was used. The rule is as follows. Write the structure of this molecule down with the asymmetric carbon in the centre, the -CHO group at the top, the -OH on the right, the -CH2OH at the bottom, and the -H on the left. Now imagine that the central carbonatom is at the centre of a tetrahedron with the four groups at the corners and that the -H and -OH come out of the paper and the -CHO and -CH2OH groups go into the paper. The resulting three-dimensional structure was taken to be that of d-glyceraldehyde and called D-glyceraldehyde. Any compound that contains an asymmetric carbonatom having this configuration belongs to the D-series. One having the opposite configuration belongs to the L-series. It is important to note that the prefixes D- and L- do not stand for dextrorotatory and laevorotatory (they are not the same as d- and l-).
In fact the arbitrary configuration assigned to D-glyceraldehyde is now known to be the correct one for the dextrorotatory form, although this was not known at the time. However, all D-compounds are not dextrorotatory. For instance, the acid obtained by oxidizing the -CHO group of glyceraldehyde is glyceric acid (1,2-dihydroxypropanoic acid). By convention, this belongs to the D-series, but it is in fact laevorotatory; i.e. its name can be written as D-glyceric acid or l-glyceric acid. To avoid confusion it is better to use + (for dextrorotatory) and - (for laevorotatory), as in D-(+)-glyceraldehyde and D-(-)-glyceric acid. The D-L convention can also be used with alpha amino acids. In this case the molecule is imagined as being viewed along the H-C bond between the hydrogen and the asymmetric carbonatom. If the clockwise order of the other three groups is -COOH, -R, -NH2, the amino acid belongs to the D-series; otherwise it belongs to the L-series. This is known as the CORN rule.
The R-S convention is a convention based on priority of groups attached to the chiral carbonatom. The order of priority is I, Br, Cl, SO3H, OCOCH3, OCH3, OH, NO2, NH2, COOCH3, CONH2, COCH3, CHO, CH2OH, C6H5, C2H5, CH3, H, with hydrogen being the lowest. The molecule is viewed with the group of lowest priority behind the chiral atom. If the clockwise arrangement of the other three groups is in descending priority, the compound belongs to the R-series; if the descending order is anticlockwise it is in the S-series. D-(+)-glyceraldehyde is R-(+)-glyceraldehyde. Research Absolute Configuration
Alpha Particles are the nuclei of the atom of helium, comprising two neutrons and two protons, and thus exhibiting a positive electric charge. Research Alpha Particles
In chemistry, an atomic number is a number, characteristic of an atom, that represents the number of protons in the nucleus of the atom. It indicates the location of an element in the periodic table. Research Atomic number
The BBC Microcomputer was developed in 1982 in the UK by Acorn for the BBC. The first versions were developed from Acorn's earlier microcomputers, the Electron and the Atom, and based on Rockwell's 6502 microprocessor. The computer was also the beneficiary of UK Government funding to schools, which were able to buy the BBC Micro at reduced prices. As a result, it became the dominant microcomputer in British schools. The BBC Micro was a highly advanced microcomputer for its time, with full support for disc drives and network connection. Its immediate successor, the BBC Master, also sold well to schools, but was too expensive for home use and unsuccessful in the business market. In 1998 the BBC World Service was still using a BBC Microcomputer in one of the studios for editing scripts. Research BBC Microcomputer
Abbreviations
Research Chlorophyll
