Question

Assume you have a suspension of photosynthetic cells carrying out C3 photosynthesis in the presence of 1000 ppm carbon dioxide (0.1%) and 20% oxygen. What effect would the following changes in conditions have on the levels of G3P being produced? Explain your reasoning. a) Carbon dioxide concentration is suddenly reduced 1000-fold. b) Light is suddenly switched off.

Answer 1

a).The C3 plants have the enzyme RUBISCO that fixes CO2 in these plants and the general property of this enzyme is that the lesser the amount of carbondioxide then the enzyme fixes oxygen into the Ribulose moiety and undergo photorespiration. Hence if the level of carbondioxide was reduced suddenly then due to the high concentration of oxygen, the RUBISCO will fix oxygen molecule and hence the G3P levels being produced will decline as photorespiration is taking place.

b). The C3 plants are more resistant to light intensity fluctuations when compared with the C4 plants but as the light intensity declines in the C3 plants the CO2 fixation rate also declines and hence the ATP and NADPH being produced will be declined whereby the G3P being produced also declines.

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