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单选题 In many plants that grow in the tropics (and in temperate-zone crop plants native to the tropics, such as maize, sugarcane, and sorghum) a mechanism has evolved to circumvent the problem of wasteful photorespiration. The step in which CO2 is fixed into a three-carbon product, 3-phosphoglycerate, is preceded by several steps, one of which is temporary fixation of CO2 into a four-carbon compound. Plants that use this process are referred to as __________, and the assimilation process as C4 metabolism or the C4 pathway
学科：Biochemistry 《生物化学》一 专业基础课（全英教学）
时间：2025-04-28 10:15:25
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题目1单选题
The cost of fixing three CO2 into one triose phosphate in plants is ____________________ moleculesA. 6 ATP and 4 NADPHB. 7 ATP and 5 NADPHC. 8 ATP and 6 NADPHD. 9 ATP and 6 NADPH
题目2单选题
Carbon dioxide is assimilated via a cyclic pathway, its key intermediates constantly regenerated. The pathway was elucidated in the early 1950s by Melvin Calvin, Andrew Benson, and James A. Bassham, and is often called the _____________ or, perhaps more descriptively, the photosynthetic carbon-reduction cycleA. Benson cycleB. Bassham cycleC. Calvin cycleD. Cori cycle
题目3单选题
NADPH and ATP are produced in the light-dependent reactions of photosynthesis in about the same ratio (___) as they are consumed in the Calvin cycle. Nine ATP molecules are converted to ADP and phosphate in the generation of a molecule of triose phosphate; eight of the phosphates are released as Pi and combined with eight ADP to regenerate ATP. The ninth phosphate is incorporated into the triose phosphate itselfA. 1:3B. 1:2C. 2:3D. 3:4
题目4单选题
Sucrose synthesis in the ________ and starch synthesis in the chloroplast are the major pathways by which the excess triose phosphate from photosynthesis is "harvested."A. cytosolB. mitochondriaC. ribosomeD. lysosome
题目5单选题
Rubisco is activated by covalent modification (carbamoylation of _____) catalyzed by rubisco activase and is inhibited by a natural transition-state analog, the concentration of which rises in the dark and falls during daylightA. Lys101B. Lys151C. Lys201D. Lys251
题目6单选题
Rubisco is not absolutely specific for CO2 as a substrate. Molecular oxygen (O2) competes with CO2 at the active site, and about once in every ______ turnovers, rubisco catalyzes the condensation of O2 with ribulose 1,5-bisphosphate to form 3-phosphoglycerate and 2-phosphoglycolate, a metabolically useless productA. 1 or 2B. 2 or 3C. 3 or 4D. 4 or 5
题目7单选题
In many plants that grow in the tropics (and in temperate-zone crop plants native to the tropics, such as maize, sugarcane, and sorghum) a mechanism has evolved to circumvent the problem of wasteful photorespiration. The step in which CO2 is fixed into a three-carbon product, 3-phosphoglycerate, is preceded by several steps, one of which is temporary fixation of CO2 into a four-carbon compound. Plants that use this process are referred to as __________, and the assimilation process as C4 metabolism or the C4 pathwayA. C2 plantsB. C3 plantsC. C4 plantsD. C5 plants
题目8单选题
The pathway of CO2 assimilation has a greater energy cost in C4 plants than in C3 plants. For each molecule of CO2 assimilated in the C4 pathway, a molecule of phosphoenolpyruvate (PEP) must be regenerated at the expense of two phosphoanhydride bonds in ATP. Thus C4 plants need ___ ATP molecules to assimilate one molecule of CO2, whereas C3 plants need only three (nine per triose phosphate)A. 4B. 5C. 6D. 7
题目9单选题
During active photosynthesis in bright light, a plant leaf produces more carbohydrate (as triose phosphates) than it needs for generating energy or synthesizing precursors. The excess is converted to sucrose and transported to other parts of the plant, to be used as fuel or stored. In most plants, _______ is the main storage formA. glycogenB. sucroseC. starchD. cellulose
题目10单选题
The structure of cellulose in the plant cell wall is simple: linear polymers of thousands of (β1→4)-linked D-glucose units, assembled into bundles of at least ___ chains, which co-crystallize to form microfibrils, which may in turn be assembled into larger macrofibrils, 5 to 12 nm in diameterA. 14B. 16C. 18D. 20
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