Biochemistry Study Set 13

Biology

Quiz 10 :

Photosynthesis

Quiz 10 :

Photosynthesis

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The two absorption maxima of light were given as 400 and 700 nm. What is the maximum amount of energy that can be incorporated to drive electron flow?
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The two wavelengths at which light is absorbed are 600 nm and 700 nm. The light is absorbed in the form of photons. The amount of light that is required to use one mole of carbon dioxide is 114 kcal.
The amount of light that is absorbed by 600 nm of light is 381 kcal approximately. Thus, the maximum amount of light that can be absorbed at 700 nm would be 445 kcal approximately.

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While all plants would benefit from the use of the C₄ route, most do not use it. What steps of the C₄ pathway require extra energy formation by the plant? What is one possible effect of global warming?
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There are two types of plants which are C₃ and C₄ plants. C₃ plants are those which utilize CO ₂ (carbon dioxide) to produce a three carbon compound PGA (3-phosphoglyceric acid) of GAP (glyceraldehydes-3-phosphate). The C₄ plants are those which produce a four carbon compound OAA (oxalo-acetic acid).
All the plants mostly benefits and use C₄ pathway while some use C₃ because they might be deficient of or might have inefficient RuBisCo (Ribulose Bisphosphate Carboxylase). The pathways of C₄ cycle is as follows:
img Thus, it gets clear that at two steps there is formation of NADPH (Nicotinamide adenine dinucleotide phosphate) which produces extra energy. The carbon dioxide formation in this cycle may be responsible for the global warming. This is because most of the plants prefer undergoing C₄ pathway.

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Other accessory pigments in plants account for the autumnal colors, mainly orange and reds. One of these was identified in this chapter as carotene. What are some others? Why should those molecules persist in leaves while chlorophyll, which is typically far more abundant, does not?
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The plants consist of chloroplasts in their leaves which contain chlorophyll that is responsible for the green colored in the leaves. The plants also consist of other pigments like xanthophylls (impart yellow color), carotenoids (impart orange color) and anthocyanins (impart red and purple color to the leaves).
During autumn season, the temperature lowers down and the sun light time shortens. This causes the veins in the leaves to tighten and cork cells block the supply of minerals and water to the leaves. This blockage slowly causes shortage of chlorophyll in the leaves. Such leaves then develop the pigments mentioned above and start appearing red or yellow in color.

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What is the principal advantage of energy transfer by exciton transfer in the antenna complex versus direct absorption at the reaction center?
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In terms of overall pathway consequence, distinguish CO ₂ incorporation by RuBisCo from CO ₂ incorporation by PEP carboxylase in C₄ plants.
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