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Overview of the Calvin Cycle
In plants, carbon dioxide enters the interior of a leaf via pores called stomata and diffuses into the stroma of the chloroplast—the site of the Calvin cycle reactions, where sugar is synthesized. These reactions are also called the light-independent reactions because they are not directly driven by light.
In the Calvin cycle, carbon atoms are fixed (incorporated into organic molecules) and used to build three-carbon sugars. This process is fueled by, and dependent on, ATP and NADPH from the light reactions. Unlike the light reactions, which take place in the thylakoid membrane, the reactions of the Calvin cycle take place in the stroma (the inner space of chloroplasts).
What is the primary function of the Calvin cycle?
A) use ATP to release carbon dioxide
B) use NADPH to release carbon dioxide
C) split water and release oxygen
D) transport RuBP out of the chloroplast
E) synthesize simple sugars from carbon dioxide
A) use ATP to release carbon dioxide
B) use NADPH to release carbon dioxide
C) split water and release oxygen
D) transport RuBP out of the chloroplast
E) synthesize simple sugars from carbon dioxide
synthesize simple sugars from carbon dioxide
In C₃ photosynthesis, the reactions that require ATP take place in
A) the light reactions alone.
B) the Calvin cycle alone.
C) both the light reactions and the Calvin cycle.
D) neither the light reactions nor the Calvin cycle.
E) the chloroplast, but is not part of photosynthesis.
A) the light reactions alone.
B) the Calvin cycle alone.
C) both the light reactions and the Calvin cycle.
D) neither the light reactions nor the Calvin cycle.
E) the chloroplast, but is not part of photosynthesis.
the Calvin cycle alone.
In a plant leaf, the reactions that produce NADH occur in
A) the light reactions alone.
B) the Calvin cycle alone.
C) both the light reactions and the Calvin cycle.
D) neither the light reactions nor the Calvin cycle.
E) the chloroplast, but is not part of photosynthesis.
A) the light reactions alone.
B) the Calvin cycle alone.
C) both the light reactions and the Calvin cycle.
D) neither the light reactions nor the Calvin cycle.
E) the chloroplast, but is not part of photosynthesis.
neither the light reactions nor the Calvin cycle.
The NADPH required for the Calvin cycle comes from
A) reactions initiated in photosystem I.
B) reactions initiated in photosystem II.
C) the citric acid cycle.
D) glycolysis.
E) oxidative phosphorylation.
A) reactions initiated in photosystem I.
B) reactions initiated in photosystem II.
C) the citric acid cycle.
D) glycolysis.
E) oxidative phosphorylation.
reactions initiated in photosystem I.
Reactions that require CO₂ take place in
A) the light reactions alone.
B) the Calvin cycle alone.
C) both the light reactions and the Calvin cycle.
D) neither the light reactions nor the Calvin cycle.
E) the chloroplast, but is not part of photosynthesis.
A) the light reactions alone.
B) the Calvin cycle alone.
C) both the light reactions and the Calvin cycle.
D) neither the light reactions nor the Calvin cycle.
E) the chloroplast, but is not part of photosynthesis.
the Calvin cycle alone.
Which of the following statements best represents the relationships between the light reactions and the Calvin cycle?
A) The light reactions provide ATP and NADPH to the Calvin cycle, and the cycle returns ADP, Pi, and NADP⁺ to the light reactions.
B) The light reactions provide ATP and NADPH to the carbon fixation step of the Calvin cycle, and the cycle provides water and electrons to the light reactions.
C) The light reactions supply the Calvin cycle with CO₂ to produce sugars, and the Calvin cycle supplies the light reactions with sugars to produce ATP.
D) The light reactions provide the Calvin cycle with oxygen for electron flow, and the Calvin cycle provides the light reactions with water to split.
E) There is no relationship between the light reactions and the Calvin cycle.
A) The light reactions provide ATP and NADPH to the Calvin cycle, and the cycle returns ADP, Pi, and NADP⁺ to the light reactions.
B) The light reactions provide ATP and NADPH to the carbon fixation step of the Calvin cycle, and the cycle provides water and electrons to the light reactions.
C) The light reactions supply the Calvin cycle with CO₂ to produce sugars, and the Calvin cycle supplies the light reactions with sugars to produce ATP.
D) The light reactions provide the Calvin cycle with oxygen for electron flow, and the Calvin cycle provides the light reactions with water to split.
E) There is no relationship between the light reactions and the Calvin cycle.
The light reactions provide ATP and NADPH to the Calvin cycle, and the cycle returns ADP, Pi, and NADP⁺ to the light reactions.
Three “turns” of the Calvin cycle generate a “surplus” molecule of glyceraldehyde 3-phosphate (G3P). Which of the following is a consequence of this?
A) Formation of a molecule of glucose would require nine “turns.”
B) G3P more readily forms sucrose and other disaccharides than it does monosaccharides.
C) Some plants would not taste sweet to us.
D) The formation of sucrose and starch in plants involves assembling G3P molecules, with or without further rearrangements.
E) Plants accumulate and store G3P.
A) Formation of a molecule of glucose would require nine “turns.”
B) G3P more readily forms sucrose and other disaccharides than it does monosaccharides.
C) Some plants would not taste sweet to us.
D) The formation of sucrose and starch in plants involves assembling G3P molecules, with or without further rearrangements.
E) Plants accumulate and store G3P.
The formation of sucrose and starch in plants involves assembling G3P molecules, with or without further rearrangements.
In the process of carbon fixation, RuBP attaches a CO₂ to produce a six-carbon molecule, which is then split to produce two molecules of 3-phosphoglycerate. After phosphorylation and reduction produces glyceraldehyde 3-phosphate (G3P), what more needs to happen to complete the Calvin cycle?
A) addition of a pair of electrons from NADPH
B) inactivation of RuBP carboxylase enzyme
C) regeneration of ATP from ADP
D) regeneration of RuBP
E) regeneration of NADP⁺
A) addition of a pair of electrons from NADPH
B) inactivation of RuBP carboxylase enzyme
C) regeneration of ATP from ADP
D) regeneration of RuBP
E) regeneration of NADP⁺
regeneration of RuBP
The pH of the inner thylakoid space has been measured, as have the pH of the stroma and of the cytosol of a particular plant cell. Which, if any, relationship would you expect to find?
A) The pH within the thylakoid is less than that of the stroma.
B) The pH of the stroma is lower than that of the other two measurements.
C) The pH of the stroma is higher than that of the thylakoid space but lower than that of the cytosol.
D) The pH of the thylakoid space is higher than that anywhere else in the cell.
E) There is no consistent relationship.
A) The pH within the thylakoid is less than that of the stroma.
B) The pH of the stroma is lower than that of the other two measurements.
C) The pH of the stroma is higher than that of the thylakoid space but lower than that of the cytosol.
D) The pH of the thylakoid space is higher than that anywhere else in the cell.
E) There is no consistent relationship.
The pH within the thylakoid is less than that of the stroma.
The phylogenetic distribution of the enzyme rubisco is limited to
A) C₃ plants only.
B) C₃ and C₄ plants.
C) all photosynthetic eukaryotes.
D) all known photoautotrophs, both bacterial and eukaryotic.
E) all living cells.
A) C₃ plants only.
B) C₃ and C₄ plants.
C) all photosynthetic eukaryotes.
D) all known photoautotrophs, both bacterial and eukaryotic.
E) all living cells.
all known photoautotrophs, both bacterial and eukaryotic.
Photorespiration occurs when rubisco reacts RuBP with
A) CO₂.
B) O₂.
C) glyceraldehyde 3-phosphate.
D) 3-phosphoglycerate.
E) NADPH.
A) CO₂.
B) O₂.
C) glyceraldehyde 3-phosphate.
D) 3-phosphoglycerate.
E) NADPH.
O₂.
In an experiment studying photosynthesis performed during the day, you provide a plant with radioactive carbon (¹⁴C) dioxide as a metabolic tracer. The ¹⁴C is incorporated first into oxaloacetate. The plant is best characterized as a
A) C₄ plant.
B) C₃ plant.
C) CAM plant.
D) heterotroph.
E) chemoautotroph.
A) C₄ plant.
B) C₃ plant.
C) CAM plant.
D) heterotroph.
E) chemoautotroph.
C₄ plant.
Why are C₄ plants able to photosynthesize with no apparent photorespiration?
A) They do not participate in the Calvin cycle.
B) They use PEP carboxylase to initially fix CO₂.
C) They are adapted to cold, wet climates.
D) They conserve water more efficiently.
E) They exclude oxygen from their tissues.
A) They do not participate in the Calvin cycle.
B) They use PEP carboxylase to initially fix CO₂.
C) They are adapted to cold, wet climates.
D) They conserve water more efficiently.
E) They exclude oxygen from their tissues.
They use PEP carboxylase to initially fix CO₂.
CAM plants keep stomata closed in daytime, thus reducing loss of water. They can do this because they
A) fix CO₂ into organic acids during the night.
B) fix CO₂ into sugars in the bundle-sheath cells.
C) fix CO₂ into pyruvate in the mesophyll cells.
D) use the enzyme phosphofructokinase, which outcompetes rubisco for CO₂.
E) use photosystem I and photosystem II at night.
A) fix CO₂ into organic acids during the night.
B) fix CO₂ into sugars in the bundle-sheath cells.
C) fix CO₂ into pyruvate in the mesophyll cells.
D) use the enzyme phosphofructokinase, which outcompetes rubisco for CO₂.
E) use photosystem I and photosystem II at night.
fix CO₂ into organic acids during the night.
Photorespiration lowers the efficiency of photosynthesis by
A) carbon dioxide molecules.
B) 3-phosphoglycerate molecules.
C) ATP molecules.
D) ribulose bisphosphate molecules.
E) RuBP carboxylase molecules.
A) carbon dioxide molecules.
B) 3-phosphoglycerate molecules.
C) ATP molecules.
D) ribulose bisphosphate molecules.
E) RuBP carboxylase molecules.
3-phosphoglycerate molecules.
The alternative pathways of photosynthesis using the C₄ or CAM systems are said to be compromises. Why?
A) Each one minimizes both water loss and rate of photosynthesis.
B) C₄ compromises on water loss and CAM compromises on photorespiration.
C) Both minimize photorespiration but expend more ATP during carbon fixation.
D) CAM plants allow more water loss, while C₄ plants allow less CO₂ into the plant.
E) C₄ plants allow less water loss but CAM plants allow more water loss.
A) Each one minimizes both water loss and rate of photosynthesis.
B) C₄ compromises on water loss and CAM compromises on photorespiration.
C) Both minimize photorespiration but expend more ATP during carbon fixation.
D) CAM plants allow more water loss, while C₄ plants allow less CO₂ into the plant.
E) C₄ plants allow less water loss but CAM plants allow more water loss.
Both minimize photorespiration but expend more ATP during carbon fixation.
If plant gene alterations cause the plants to be deficient in photorespiration, what would most probably occur?
A) Photosynthetic efficiency would be reduced at low light intensities.
B) Cells would carry on the Calvin cycle at a much slower rate.
C) Less ATP would be generated.
D) There would be more light-induced damage to the cells.
E) Less oxygen would be produced.
A) Photosynthetic efficiency would be reduced at low light intensities.
B) Cells would carry on the Calvin cycle at a much slower rate.
C) Less ATP would be generated.
D) There would be more light-induced damage to the cells.
E) Less oxygen would be produced.
There would be more light-induced damage to the cells.
Compared to C₃ plants, C₄ plants
A) can continue to fix CO₂ even at relatively low CO2 concentrations and high oxygen concentrations.
B) have higher rates of photorespiration.
C) do not use rubisco for carbon fixation.
D) grow better under cool, moist conditions.
E) make a four-carbon compound, oxaloacetate, which is then delivered to the citric acid cycle in mitochondria.
A) can continue to fix CO₂ even at relatively low CO2 concentrations and high oxygen concentrations.
B) have higher rates of photorespiration.
C) do not use rubisco for carbon fixation.
D) grow better under cool, moist conditions.
E) make a four-carbon compound, oxaloacetate, which is then delivered to the citric acid cycle in mitochondria.
can continue to fix CO₂ even at relatively low CO2 concentrations and high oxygen concentrations.
If atmospheric CO₂ concentrations increase twofold or more, how will plants be affected, disregarding any changes in climate?
A) All plants will experience increased rates of photosynthesis.
B) C₃ plants will have faster growth; C₄ plants will be minimally affected.
C) C₄ plants will have faster growth; C₃ plants will be minimally affected.
D) C₃ plants will have faster growth; C₄ plants will have slower growth.
E) Plant growth will not be affected because atmospheric CO₂ concentrations are never limiting for plant growth.
A) All plants will experience increased rates of photosynthesis.
B) C₃ plants will have faster growth; C₄ plants will be minimally affected.
C) C₄ plants will have faster growth; C₃ plants will be minimally affected.
D) C₃ plants will have faster growth; C₄ plants will have slower growth.
E) Plant growth will not be affected because atmospheric CO₂ concentrations are never limiting for plant growth.
C₃ plants will have faster growth; C₄ plants will be minimally affected.
Plants photosynthesize only in the light. Plants respire
A) in the dark only.
B) in the light only.
C) both in light and dark.
D) never-they get their ATP from photophosphorylation.
E) only when excessive light energy induces photorespiration.
A) in the dark only.
B) in the light only.
C) both in light and dark.
D) never-they get their ATP from photophosphorylation.
E) only when excessive light energy induces photorespiration.
both in light and dark.
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