A colleague from Asia brings you two plants that seem to have potential as food
ID: 41720 • Letter: A
Question
A colleague from Asia brings you two plants that seem to have potential as food crops. You conduct a series of experiments on the two plants, named Blue, Ribbon (BR) and Underdog (UD). The data in THE FIGURE TO THE LEFT are from one experiment in which you measured the rate of photosynthesis (PHS; in percent CO2 fixed per hour) in both plants under experimental conditions of increasing levels of oxygen in air. From these data, what is the best conclusion about the mechanism of photosynthesis in the two plants? Explain your answer to the above question. For questions #25-27, use the FIGURE ON THE RIGHT. Each step is lettered. Use the letters to indicate the correct reaction to answer the questions. The figure below illustrates some of the steps (reactions) of glycolysis in their proper sequence. NOTE: Questions can have more than one answer and tetters can be used multiple times. In which step does an intermediate in the pathway become dephophorylated? In which step is an inorganic phosphate added to the reactant? Identify the enzyme that catalyzes reactionExplanation / Answer
23. D. UD is C4 plant and BR is a C3 plant.
24. In C3 plants the first stable compound formed is a three- carbon molecule (3-phosphoglycerate) whose formation is catalysed by the presence of enzyme ribulose bisphosphate carboxylase (Rubisco). Whereas in case of C4 plants the first stable compound formed is a four- carbon acid (malate)whose formation is catalysed by the presence of enzyme phosphoenolpyruvate carboxylase (PEP carboxylase).
Extensive research have revealed that the enzyme Rubisco involved in C3 pathway is highly inefficient in action when exposed to higher and increasing levels of oxygen. Therefore increasing oxygen levels inhibits only C3 pathway (decrease rate of photosynthesis) but not C4 pathway.
From the graph we can interpret that the rate of photosynthesis is constant for plant UD and it is unaffected by the increasing levels of oxygen. Hence we can conclude that UD is a C4 plant. But the rate of photosynthesis gradually decreases for plant BR with increasing levels of oxygen. Hence we can conclude that BR is a C plant.
25. Answer is Option D, D
Dephosphorylation refers to removal of phosphate group from a compound. 1,3- Bisphosphoglycerate contains two phosphate groups. When 1,3- Bisphosphoglycerate is converted to 2-phosphoglycerate (2-PGA) one of the phosphate group from 1,3- Bisphosphoglycerate is removed and transferred to ADP to form ATP.
26. Answer is Option A, A
When glucose is converted to Fructose 1, 6-bisphosphate two phosphate groups are transferred from two ATP to glucose resulting in formation of Fructose 1, 6-bisphosphate and two ADP molecules.
27. Answer is Option D, Dehydrogense
Dehydrogenation refers to removal of hydrogen from a compound. Glyceraldehyde-3-phospate is dehydrogented to form 1,3-Bisphosphoglycerate. The hydrogen removed from Glyceraldehyde-3-phospate is used to convert NAD to NADH.
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