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In the figure given below, the back line (upper) indicates action spectrum for photosynthesis and the lighter line (lower) indicates the absorption spectrum of chlorophyll- $a$, answer the following
(a) What does the action spectrum indicate? How can we plot an action spectrum? Explain with an example.
(b) How can we derive an absorption spectrum for any substances?
(c) If chlorophyll-a is responsible for light reaction of photosynthesis, why do the action spectrum and absorption spectrum not overlap?
(a) What does the action spectrum indicate? How can we plot an action spectrum? Explain with an example.
(b) How can we derive an absorption spectrum for any substances?
(c) If chlorophyll-a is responsible for light reaction of photosynthesis, why do the action spectrum and absorption spectrum not overlap?
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(a) Action spectrum depicts the relative rates of photosynthesis at different wavelenghths of light. Action spectrum of photosynthesis can be plotted by measurement of oxygen evolution at different wavelength. Englemann (1882) by using a green algae plotted action spectrum.
(b) Absorption spectrum of a substance can be derived by calculating amount of energy of different wavelength of light absorbed.
(c) Chlorophyll a is responsible for light reaction of photosynthesis, but the action spectrum and absorption spectrum do not overlap because, though chlorophyll $\mathrm{a}$ is the main pigment responsible for the absorption of light, other thylakoids pigment like chlorophyll b, xanthophylls, carotenoids, which are accessory pigments also absorb and transfer the energy to chlorophyll a. Indeed they not only enable a wider range of wavelength of incoming light to be utilized for photosynthesis but also protect chlorophyll from photo-oxidation.
(b) Absorption spectrum of a substance can be derived by calculating amount of energy of different wavelength of light absorbed.
(c) Chlorophyll a is responsible for light reaction of photosynthesis, but the action spectrum and absorption spectrum do not overlap because, though chlorophyll $\mathrm{a}$ is the main pigment responsible for the absorption of light, other thylakoids pigment like chlorophyll b, xanthophylls, carotenoids, which are accessory pigments also absorb and transfer the energy to chlorophyll a. Indeed they not only enable a wider range of wavelength of incoming light to be utilized for photosynthesis but also protect chlorophyll from photo-oxidation.
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