what does excitation of chlorophyll mean..??
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Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and the chloroplasts of algae and plants.Its name is derived from the Greek words χλωρός, chloros ("green") and φύλλον, phyllon ("leaf").Chlorophyll is essential in photosynthesis, allowing plants to absorb energy from light.
Chlorophylls absorb light most strongly in the blue portion of the electromagnetic spectrum as well as the red portion.Conversely, it is a poor absorber of green and near-green portions of the spectrum, which it reflects, producing the green color of chlorophyll-containing tissues. Two types of chlorophyll exist in the photosystems of green plants: chlorophyll a and b.
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Chlorophylls absorb light most strongly in the blue portion of the electromagnetic spectrum as well as the red portion.Conversely, it is a poor absorber of green and near-green portions of the spectrum, which it reflects, producing the green color of chlorophyll-containing tissues. Two types of chlorophyll exist in the photosystems of green plants: chlorophyll a and b.
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hello where is excitation of chlorophyll...??
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If there are two molecules in close proximity, one with an absorption band at a wavelength shifted to the longer wavelengths than another, light energy absorbed by the one absorbing at the shorter wavelength is usually transferred to the one that absorbs at the longer wavelengths. That is, one molecule acts as a donor of excitation energy, and the other as an acceptor of this energy. In photosynthetic systems, the acceptor is a chlorophyll a molecule, and the donor could be chlorophyll b (in green plants), phycocyanin (in cyanobacteria), or fucoxanthin (in diatoms and brown algae), among other pigments (chromophores). This transfer probably takes place by a resonance mechanism, similar to the one familiar from acoustic experience, but properly describable only in terms of quantum mechanics. There are reasons to believe that most chlorophyll a molecules also do not participate directly in the primary photochemical process in photosynthesis, but transfer their excitation energy to the few chlorophyll a molecules directly associated with the reaction centers that lead to the primary charge separation. Excitation energy is in the form of a couple, an electron that is in the excited state of the molecule with the "hole" it has left behind in the ground state. What is transferred is the "excited electron and the hole". We shall call this entity an "exciton". Thus, we can talk about exciton transfer.
We shall deal here with energy transfer between different pigments ("heterogeneous" transfer), as well as with transfer between identical molecules ("homogeneous" transfer). The latter can be repeated many times, giving rise to energy migration. Direct evidence of energy transfer between different pigments is provided by sensitized fluorescence. Light quanta absorbed by molecules of one pigment (for example, chlorophyll b) are transferred to molecules of another pigment (for example, chlorophyll a). When the first pigment is excited, only fluorescence of the second is observed. This phenomenon, of sensitized fluorescence, is well known from studies on gases and solutions. The occurrence of heterogeneous energy transfer from various pigments to chlorophyll a is inferred from the action spectra (or "excitation spectra") of chlorophyll a fluorescence in vivo.
We shall deal here with energy transfer between different pigments ("heterogeneous" transfer), as well as with transfer between identical molecules ("homogeneous" transfer). The latter can be repeated many times, giving rise to energy migration. Direct evidence of energy transfer between different pigments is provided by sensitized fluorescence. Light quanta absorbed by molecules of one pigment (for example, chlorophyll b) are transferred to molecules of another pigment (for example, chlorophyll a). When the first pigment is excited, only fluorescence of the second is observed. This phenomenon, of sensitized fluorescence, is well known from studies on gases and solutions. The occurrence of heterogeneous energy transfer from various pigments to chlorophyll a is inferred from the action spectra (or "excitation spectra") of chlorophyll a fluorescence in vivo.
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