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week-06b-photo-resp-tx-gene - BIOL 101 Fall 2007 Week 6...

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Week 6 - Page - 1- BIOL 101 - Fall 2007- Week 6 - Photosynthesis - Energy - Respiration Gene Structure - Transcription Please note - all lecture notes are© Timothy C. Hall, Biology Dept., Texas A&M University PHOTOSYNTHESIS HISTORICAL 1577 - 1644 Jan-Baptista Van Helmont Showed that soil contributed only a little to the increase in weight of a potted willow plant. 1733-1804 2 Joseph Priestley Showed (1772) rejuvenation of air by (O ) from mint sprig. 1742-1809 2 Jean Senebier Showed (1782) that plants need CO . 1730-1799 Jan Ingen-Housz Showed (1778) that light and green parts of plants are needed for 2 O generation and (1796) that C goes into the plant. 1767-1845 2 2 Nicholas de Saussure Showed (1804) that equal volumes of CO and O are exchanged 2 and also showed that H O was needed. 1843 - 1909 T.W. Engelmann Action spectrum experiment (1883) showing red and blue light efficacy for photosynthesis. 1843 - 1909 Julius Sachs Showed that photosynthesis occurs only in light 2 2 2 1934 C.B. van Niel Theorized that O is evolved from H O, not CO in photosynthesis. 2 2 2 2 Sulphur bacteria: CO + 2H S + light 6 CH O + H O + 2S 2 2 2 2 General equation: CO + 2H X + light 6 CH O + H O + 2X 2 2 2 2 Green plants: CO + 2H O + light 6 CH O + H O + 2O 1930s Robin Hill Showed that light drives the splitting of water. Hill showed that 2 2 isolated chloroplasts can release O in the absence of CO if given 2 a suitable electron acceptor for electrons removed from H O. Samuel Ruben; 2 Martin Kamen Proved (1941) above in experiment using O , a non-radioactive 18 2 isotope of O . The nature of light 1660 Sir Isaac Newton Separated light into the spectrum. 1905 Albert Einstein Proposed that light consists of photons , packets of energy. Light intensity depends on the number of photons absorbed per unit of time. The amount of energy carried by each photon is determined by its vibration. The distance moved during a complete vibration is
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Week 6 - Page - 2- the wavelength . The energy of a photon is called a quantum and is inversely proportional to the wavelength: the longer the wavelength, the less energy per photon. Ultraviolet radiation Has too much energy for most organisms. Its ionizing radiation breaks weak bonds. Infrared radiation Has too little energy for living systems but does warm them up. Visible light Contains just the right amount of energy. But it must be absorbed by pigments . PIGMENTS Pigments absorb visible light and changes the configuration of electrons in the photons, resulting in transfer of energy to heat , fluorescence or chemical forms. chlorophyll a absorbs red, violet and blue; reflects green. Accessory pigments broaden the action spectrum by passing energy to chlorophyll a. Are typically embedded in the thylakoid membrane . chlorophyll b 25% of chlorophyll in leaves. chlorophyll C found in brown and other algae. bacteriochlorophyll purple photosynthetic bacteria.
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