Package 16 Photosynthesis
What was the purpose of the experiment in which Calvin and his colleagues injected algae with 14C-labeled CO2, incubated the cells for various time periods, and then separated the radiolabeled molecules with paper chromatography?
To determine the order of reactions in the Calvin cycle
In C4 plants, the first product of carbon fixation is:
a four-carbon molecule
What chemical reaction is catalyzed by the enzyme rubisco?
carbon fixation
True or false: In the reduction phase of the Calvin cycle, ATP is the source of electrons used to reduce a C-O bond to a C-H bond.
f
True or false: The term "C3" was derived from the 3-carbon sugar that represents the end product of photosynthesis.
f
The end product of phase 2 of the Calvin cycle is G3P. This molecule is used to synthesize ---- and to regenerate the starting material ----bisphosphate.
glucose RU
Photorespiration is favored when plants are exposed to a(n) --- and --- environment.
hot dry
In a cool climate, a C3 plant uses ______ a C4 plant to fix CO2.
less energy than
PEP carboxylase can attach CO2 to phosphoenolpyruvate, resulting in the synthesis of a four-carbon molecule called
oxaloacetate
In the Calvin cycle, CO2 is:
reduced
The Calvin cycle is affected by certain environmental conditions, including light intensity, ----availability, and ----
water temperature
What advantages do C4 plants have over C3 plants in warm, dry climates?
-They can keep their stomata partially closed during the day to conserve water. -They can minimize photorespiration.
The G3P produced at the end of the second phase of the Calvin cycle is directly used for which of the following?
-regenerate ribulose bisphosphate -make glucose or other carbohydrates
What are the three phases of the Calvin cycle?
1.Carbon Fixation 2.Reduction and carbohydrate production 3.Regeneration of ribulose bisphosphate
In the Calvin cycle, for every SIX carbon dioxide molecules that are incorporated into a carbohydrate such as glucose, ----molecules of ATP are hydrolyzed and ----molecules of NADPH are oxidized.
18 12
The Calvin cycle can be very energy-expensive. How many molecules of ATP and NADPH respectively are required to incorporate one carbon dioxide molecule into the six-carbon sugar being formed?
3 ATP, 2 NADPH
The Calvin cycle uses energy from ---, and high-energy ----supplied by NADPH
ATP Electrons
Which of the following are products of the light reactions that are used by the Calvin cycle to make carbohydrates?
ATP NADPH
Which of the following summarizes the events of the first phase of the Calvin cycle?
Atmospheric carbon dioxide is fixed into a five carbon sugar.
Why are C3 plants so-named?
Because 3PG is a three-carbon molecule
What molecule is reduced in the Calvin cycle?
CO2
The end product of phase 2 of the Calvin cycle is G3P. This molecule is used to synthesize ----and to regenerate the starting material---- bisphosphate.
Carbohydrates RuBP
In plants, which of the following is polymerized to form starch?
Glucose
Which of the following is the primary output of the Calvin cycle?
Glyceraldehyde-3-phosphate
What is carbon fixation?
Incorporation of carbon into an organic molecule that is not a gas
Which of the following happens to the molecule formed by the addition of carbon dioxide to ribulose bisphosphate?
It is immediately split into two more stable three carbon molecules.
What is the source of electrons used to reduce the C-O bond of 3-phosphoglycerate during the Calvin cycle?
NADPH
What two molecules can be attached to RuBP by the enzyme rubisco?
O2 CO2
Which of the following differentiates PEP carboxylase from rubisco?
PEP carboxylase does not bind oxygen
What chemical reaction is catalyzed by the enzyme PEP carboxylase?
Phosphoenolpyruvate + CO2 → oxaloacetate
In the last phase of the Calvin cycle, what molecule is regenerated so that the next cycle can occur?
Ribulose bisphosphate
What two chemical reactions are catalyzed by rubisco?
RuBP + O2 → 3PG + phosphoglycolate RuBP + CO2 → 2 3PG
What happens during photorespiration?
Rubisco attaches O2 to RuBP, and CO2 is produced.
Which of the following is the purpose of phase 3 of the Calvin cycle?
To create a new 5-carbon sugar for the "next" Calvin cycle