Chapter 23 The Calvin Cycle
Matching Questions
Use the following to answer questions 1-10:
Choose the correct answer from the list below. Not all of the answers will be used.
a) rubisco
b) transketolase
c) Crassulacean acid metabolism
d) autotrophs
e) C6
f) pyruvate-Pi dikinase
g) hexose monophosphate pool
h) heterotrophs
i) glycolysis
j) C4
k) sucrose
l) 3-phosphoglycerate
1.
____________ These organisms can synthesize glucose from carbon dioxide and water.
2.
____________ This is the product of CO2 fixation with ribulose-1,6-bisphosphate.
Ans: l
Section: 23.1
3.
____________ This is another name for ribulose 1,5-bisphosphate carboxylase/oxygenase.
Ans: a
Section: 23.1
4.
____________ This is the pathway that ensures that sufficient amounts of CO2 are available to
minimize wasteful photorespiration.
Ans: j
5.
Glucose 1-phosphate, glucose 6-phosphate, and fructose 1-phosphate belong to the
____________.
Ans: g
Section: 23.1
Ans: d
Section: Introduction
Chapter 23 The Calvin Cycle
2
6.
____________ This enzyme is involved in both the Calvin cycle and the pentose phosphate
pathway.
7.
____________ This metabolic adaptation is employed by plants living in hot, dry climates.
Ans: c
Section: 23.2
8.
____________ This sugar found in plants is readily transported and easily mobilized.
Ans: k
Section: 23.1
9.
____________ These organisms obtain energy from chemical fuels.
Ans: h
Section: Introduction
10.
____________ is the final enzyme in the C4 pathway.
Ans: f
Section: 23.2
Fill–in-the-Blank Questions
11.
The biochemist who first described the pathway for fixing CO2 is _____.
Ans: Melvin Calvin Section: Introduction
12.
The enzymes that catalyze the dark reactions of photosynthesis are located in the _____of the
chloroplasts.
Ans: stroma Section: 23.1
13.
The first step of the Calvin cycle involves the addition of CO2 to _____ to produce two
molecules of 3-phosphoglycerate.
Ans: ribulose-1,5-bisphosphate Section: 23.1
14.
and CO2.
Ans: carbamate Section: 23.1
The binding site of Mg2+ to rubisco involves the formation of a _____ group between lysine 221
15.
In photorespiration oxygen is consumed and _____ is released.
Ans: carbon dioxide Section: 23.1
Ans: b
Section: 23.1
Chapter 23 The Calvin Cycle
3
16.
The three stages of the Calvin cycle are _____.
17.
In C4 plants, carbon dioxide is added to _____ to form oxaloacetate, which is reduced to malate,
which carries CO2 to the bundle-sheath cells.
Ans: phosphoenolpyruvate Section: 23.2
18.
Volcanoes, which spew millions of tons of gasses and particles into the atmosphere, cause a(an)
(decrease/increase) _____ in photosynthesis specifically during the daytime.
Ans: increase Section: 23.1
19.
_____is an example of a mechanism of accelerating photosynthesis by increasing carbon
dioxide concentration.
Ans: C4 or hack-slack pathway Section: 23.2
20.
Plants adapt to arid ecosystems using _____.
Ans: crassuacean acid metabolism Section: 23.2
Multiple-Choice Questions
21.
ATP is called the energy currency. The currency of biosynthetic reducing power is
A) NADPH. B) CoA. C) AMP. D) ADP. E) None of the above.
Ans: A Section: Introduction
22.
What is the source of carbons for the Calvin cycle?
A)
glucose
D)
glyoxylate
B)
carbon dioxide
E)
None of the above.
C)
glycogen
Ans: B Section: 23.1
23.
Plants store glucose as ___________ and ____________.
A)
starch; sucrose
B)
fructose; sucrose
C)
starch; fructose
D)
All of the above.
E)
None of the above.
Ans: A Section: 23.1
24.
The most abundant protein on Earth is:
A)
ribulose 1.5-bisphosphate.
B)
aldolase.
C)
rubisco.
D)
phosphopentose epimerase.
E)
transketolase.
Ans: C Section: 23.1
Ans: carbon fixation, reduction of fixed carbon, and regeneration of ribulose 1.5 bisphosphate
Section: 23.1
Chapter 23 The Calvin Cycle
4
25.
In the Calvin cycle, 3-phosphoglycerate is converted into which hexose phosphate?
A)
glucose 1-phosphate
D)
All of the above.
B)
glucose 6-phosphate
E)
None of the above.
C)
fructose 6-phosphate
26.
Which form of thioredoxin activates certain Calvin cycle enzymes?
A) reduced B) oxidized C) dimeric D) A and C E) B and C
Ans: A Section: 23.2
27.
Which coenzyme is required by glyceraldehyde 3-phosphate dehydrogenase in chloroplasts to
convert 3-phosphoglycerate into glyceraldehyde-3-phosphate?
A)
NADH
D)
NADP+
B)
NADPH
E)
thiamine pyrophosphate
C)
NAD+
Ans: B Section: 23.1
28.
The C4 pathway is necessary in tropical plants because:
A)
at high temperatures, the plants cannot maintain sufficient water levels within the cells.
B)
tropical plants do not have proper day/light cycles to maintain the balance of CO2
necessary for carbohydrate storage.
C)
at high temperatures, the oxygenase activity of rubisco is high.
D)
All of the above.
E)
None of the above.
Ans: C Section: 23.2
29.
What is the energy cost of the C4 pathway?
A)
Thirty molecules of ATP are used per hexose molecule made.
B)
Eighteen molecules of ATP are used per hexose molecule made.
C)
Thirty molecules of NADPH are used per hexose molecule made.
D)
Eighteen molecules of ATP and 12 of NADPH are used per hexose molecule made.
E)
None of the above.
Ans: A Section: 23.2
30.
Rubisco is found:
A)
in the meso sheath bundles.
B)
in the stroma of the chloroplasts.
C)
embedded in the plant cell wall.
D)
in the lumen of the thylakoid disc.
E)
None of the above.
Ans: B Section: 23.1
31.
The enzyme that catalyzes the rate-limiting step in hexose synthesis is:
A)
aldolase.
B)
transketolase.
C)
rubisco.
D)
phosphosepentose isomerase.
E)
None of the above.
Ans: C Section: 23.1
Ans: D Section: 23.1
Chapter 23 The Calvin Cycle
5
32.
________ rounds of the Calvin cycled are required for the production of hexose.
A)
One
B)
Three
C)
Six
D)
Twelve
E)
Nine
33.
The immediate unwanted side reaction of rubisco is:
A)
phosphoglycolate .
B)
ribulose 1,5-bisphosphate.
C)
glycerol.
D)
amylose.
E)
phosphofuctose.
Ans: A Section: 23.2
34.
The energetic equivalent of ______ ATP molecules is(are) consumed in transporting CO2 to the
chloroplasts of the bundle-sheath cells.
A)
1
B)
2
C)
3
D)
4
E)
6
Ans: B Section: 23.2
35.
The protein that regulates the Calvin cycle is:
A)
protein kinase C.
B)
rubisco .
C)
thioredoxin.
D)
ferredoxin-thioredoxin reductase.
E)
None of the above.
Ans: C Section: 23.2
36.
On a molecular level, how might global warming affect carbon dioxide fixation?
A)
B)
C)
D)
E)
Ans: D Section: 23.2
Ans: C Section: 23.1
Chapter 23 The Calvin Cycle
6
37.
Desert plants prevent loss of water vapor by closing stomata during the heat of the day and
opening them at night. How does this affect the movement of CO2 and what are the implications
for CO2 fixation?
A)
Stomata, like cellular transporters can be selective and bent water molecules enter
through different stomata than linear CO2 and O2; thus, desert plant CO2 fixation is not
affected.
B)
CO2, being a non-polar molecule moves easily thought cell membranes, thus, the opening
and closing of stomata does not affect CO2 fixation.
C)
Under normal conditions, the light reactions don’t work at maximum saturation,
therefore, a diurnal pattern of H2O decreases CO2+ fixation only minimally.
D)
CO2 entry into the plant is also inhibited by the closing of the stomata; however, the
impact on CO2 fixation is minimal.
E)
CO2 entry into the plant is also inhibited by the closing of the stomata; however, CO2 is
sequestered in vacuoles in the form of malate.
38.
Knowing what you do about the distribution of the light reaction enzymes, where would you
expect to find Calvin cycle enzymes and why?
A)
lumen of the thylakoid membrane, as this is the location of the splitting of water
B)
lumen of the thylakoid membrane, as this is the location of NADPH and ATP synthesis
C)
thylakoid integral membrane proteins that derive energy from proton pumping
D)
stromal side of thylakoid membrane, as this is the location of NADPH and ATP
formation
E)
stromal side of the thylakoid membrane, as this is the location of the splitting of water
Ans: D Section: 23.1
39.
The mechanics of CO2 binding involves Mg2+ and Lys 201. What would you expect to be the pH
optimum and [Mg2+] for this to occur?
A)
high pH, high [Mg2+]
B)
high pH, low [Mg2+]
C)
low pH, high [Mg2+]
D)
low pH, low [Mg2+]
neutral pH, low [Mg2+]
Ans: A Section: 23.2
Short-Answer Questions
40.
Why are reactions of the Calvin cycle called the “dark reactions”?
Ans:
Unlike photosynthetic reactions, the reactions of the Calvin cycle do not depend on light
in order to proceed.
Section: Introduction
41.
Describe the stages of the Calvin cycle.
Ans: E Section: 23.1
Chapter 23 The Calvin Cycle
7
42.
Which enzyme is cited as the most abundant enzyme in the biosphere? Why is this so?
43.
What is photorespiration? Why is it wasteful?
molecule produced that can serve as an energy source.
Section: 23.2
44.
Give the sequence of reactions involved in the synthesis of sucrose from two glucose 6-
phosphate.
Section: 23.1
45.
Why is the chemistry of the “dark reactions” referred to as a cycle and not a pathway?
last step of the process produces ribulose-1,5-bisphosphate. The starting compound is
regenerated and acts catalytically. Thus, it is considered a cycle and not a pathway.
Section: 23.1
46.
Explain/describe the stoichiometry of the Calvin cycle to convert three molecules of CO2 into
one molecule of dihydroxyacetone phosphate.
triosephosphate isomerase, glyceraldehyde-3-phosphate is converted to dihydroxyacetone
phosphate.
Section: 23.1
due to the slow catalytic activity of the enzyme, which means larger numbers of rubisco
are necessary to carry out the reaction at sufficient levels.
Section: 23.1
Chapter 23 The Calvin Cycle
8
47.
What is the energy requirement for the formation of hexose from CO2 in terms of ATP
equivalents and NADPH?
48.
How is rubisco activity controlled?
stimulates formation of the carbamate.
Section: 23.1
49.
Describe the role of thioredoxin in regulating the Calvin cycle.
bonds. The enzymes are converted to the inactive form by spontaneous oxidation by
oxygen, a product of photosynthesis.
Section: 23.2
50.
Write the balanced reaction for the Calvin cycle.
Ans:
6 CO2 + 18 ATP + 12 NADPH + 12 H2O → C6H12O6 + 18 ADP + 18 Pi + 12 NADP+ +
Section: 23.1
51.
Describe, in biochemical terms, how bread becomes stale.
amorphous starch structure evaporates leaving crystalline amylose and amylopectin.
Section: 23.1
52.
Explain how the relationship of the mesophyll cell and the bundle-sheath cell help to regulate
the Calvin cycle.
occur. C4 plants produce Malate in mesophyll cells to be used as CO2 by the Calvin cycle
in the bundle-sheath cells, thus building up the concentration of CO2 for fixation.
Section: 23.2
additional six molecules of ATP. Thus a total of 18 equivalents of ATP and 12 NADPH
are required to convert six CO2 into a hexose.
Section: 23.1
Chapter 23 The Calvin Cycle
9
53.
How does light alter the fixation of CO2?
54.
What is the basic difference between C4 and C3 plants?
pathway (PEP carboxylate) to fix CO2.
Section: 23.1 and 23.2
55.
Rubisco’s Km for CO2 is 50 times higher than for O2 but kcat values are similar. This
suggests that at the level of oxygenase activity would be negligible. Why then is it not?
[O2] vs. [CO2].
hand, is 21% in air by volume.
Section: 23.
ions are not available in the stroma for the carbamation of lysine 201 of rubisco.