1. Capturing Solar Energy: Photosynthesis
chapter 7
Capturing Solar Energy: Photosynthesis 1

2. Chapter 7 At a Glance 7.1 What Is Photosynthesis?
7.2 The Light Reactions: How Is Light Energy Converted to Chemical Energy?
7.3 The Calvin Cycle: How Is Chemical Energy Stored in Sugar Molecules?
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3. 7.1 What Is Photosynthesis?
For most organisms, energy is derived from sunlight, either directly or indirectly
Organisms that can directly trap sunlight do so by photosynthesis
Process of trapping and storing solar energy as chemical energy
Leaves and chloroplasts are adaptations for photosynthesis
Solar energy is trapped and stored as chemical energy in the bonds of a sugar.
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4. energy from sunlight carbon sugar + photosynthesis + water oxygen
Figure 7-1
energy from
sunlight
carbon
sugar +
photosynthesis +
Figure 7-1 An overview of photosynthesis
water
oxygen
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5. Animation: Photosynthesis
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6. 7.1 What Is Photosynthesis?
Both upper and lower leaf surfaces consist of epidermis
Protective layer of transparent cells
Photosynthesis in plants takes place in chlorophyll-containing organelles called chloroplasts
Mostly contained within leaf cells
Contain chemical reactions able to convert energy in sunlight into stored energy in sugars
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7. (a) Leaves Figure 7-3a Figure 7-3a Photosynthetic structures
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8. (b) Internal leaf structure
Figure 7-3b
vascular bundle
(vein)
cuticle
upper
epidermis
mesophyll
cells
lower
epidermis
stoma
Figure 7-3b Photosynthetic structures
stoma
chloroplasts
bundle sheath
cells
(b) Internal leaf structure
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9. (c) Mesophyll cell containing chloroplasts
Figure 7-3c
Figure 7-3c Photosynthetic structures
(c) Mesophyll cell containing
chloroplasts
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10. 7.1 What Is Photosynthesis?
Outer surface of both epidermal layers is covered by cuticle
Transparent, waxy, waterproof covering that reduces evaporation of water
Leaves obtain CO2 for photosynthesis from air through stomata (singular, stoma)
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11. (a) Leaves Figure 7-3a Figure 7-3a Photosynthetic structures
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12. (b) Internal leaf structure
Figure 7-3b
vascular bundle
(vein)
cuticle
upper
epidermis
mesophyll
cells
lower
epidermis
stoma
Figure 7-3b Photosynthetic structures
stoma
chloroplasts
bundle sheath
cells
(b) Internal leaf structure
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13. (a) Stomata open (b) Stomata closed Figure 7-2 Figure 7-2 Stomata
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14. 7.1 What Is Photosynthesis?
Mesophyll
Loosely packed layers of internal leaf cells where chloroplasts are located
Photosynthesis
Gas exchange
Features vascular bundles
Veins transporting water, minerals, and sugars throughout the plant
Surrounded by bundle sheath cells
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15. (a) Leaves Figure 7-3a Figure 7-3a Photosynthetic structures
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16. (b) Internal leaf structure
Figure 7-3b
vascular bundle
(vein)
cuticle
upper
epidermis
mesophyll
cells
lower
epidermis
stoma
Figure 7-3b Photosynthetic structures
stoma
chloroplasts
bundle sheath
cells
(b) Internal leaf structure
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17. 7.1 What Is Photosynthesis?
Chloroplasts are organelles with a double membrane enclosing fluid called stroma
Embedded with thylakoids
Disk-shaped membranous sacs, stacked into grana
Light-dependent reactions of photosynthesis occur in and adjacent to the membranes of the thylakoids
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18. (a) Leaves Figure 7-3a Figure 7-3a Photosynthetic structures
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19. (b) Internal leaf structure
Figure 7-3b
vascular bundle
(vein)
cuticle
upper
epidermis
mesophyll
cells
lower
epidermis
stoma
Figure 7-3b Photosynthetic structures
stoma
chloroplasts
bundle sheath
cells
(b) Internal leaf structure
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20. (c) Mesophyll cell containing chloroplasts
Figure 7-3c
Figure 7-3c Photosynthetic structures
(c) Mesophyll cell containing
chloroplasts
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21. (d) Electron micrograph of a chloroplast
Figure 7-3d
grana (stacks
of thylakoids)
stroma
thylakoids
Figure 7-3d Photosynthetic structures
(d) Electron micrograph of
a chloroplast
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22. inner membrane outer membrane grana (stacks of thylakoids) stroma
Figure 7-3e
inner
membrane
outer
membrane
grana (stacks
of thylakoids)
stroma
Figure 7-3e Photosynthetic structures
thylakoids
(e) Chloroplast
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23. energy from sunlight carbon sugar + photosynthesis + water oxygen
Figure 7-1
energy from
sunlight
carbon
sugar +
photosynthesis +
Figure 7-1 An overview of photosynthesis
Starting with carbon dioxide (CO2) and water (H2O), photosynthesis converts sunlight energy into chemical energy stored in bonds of glucose and releases oxygen (O2) as a product.
water
oxygen
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24. 7.1 What Is Photosynthesis?
6 CO2  6 H2O  light energy → C6H12O6  6 O2
carbon water sunlight glucose oxygen
dioxide (sugar)
Starting with carbon dioxide (CO2) and water (H2O), photosynthesis converts sunlight energy into chemical energy stored in bonds of glucose and releases oxygen (O2) as a product.
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25. 7.1 What Is Photosynthesis?
“Photo” refers to light reactions
Chlorophyll and other pigment molecules embedded in thylakoid membranes capture sunlight energy and convert some into chemical energy stored in the energy-carrier molecules ATP and NADPH
“Synthesis” refers to Calvin cycle
Enzymes in stroma use CO2 and chemical energy (from ATP and NADPH) to synthesize a three-carbon sugar (will be used to make glucose)
NADPH (NADP+; nicotinamide adenine dinucleotide phosphate)
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26. Calvin cycle light reactions
Figure 7-4 6
H2O 6
CO2
energy from
sunlight
ATP
Calvin
cycle
light
reactions
NADPH
Figure 7-4 The relationship between the light reactions and the Calvin cycle
Light reactions are made possible by molecules—pigments—anchored within membranes of the thylakoid.
Reactions of the Calvin cycle occur in the stroma.
ADP
NADP+
thylakoid
3-C sugar
(stroma)
chloroplast 6 O2
C6H12O6
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27. Living things consistently use energy to survive
Living things consistently use energy to survive. For nearly all forms of life, this energy comes from ___________. O2
C6H12O6 (glucose)
fossil fuels
sunlight
Question: 7-1
Answer: d
Diff: Easy
Text Ref: Section 7.1
Skill: Factual
Also relates to: Chapter 6
Notes:
As mentioned in Chapter 6 in the discussion of entropy, sunlight allows all organisms to exist. This concept highlights the reliance of cellular respiration on photosynthesis.
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28. Living things consistently use energy to survive
Living things consistently use energy to survive. For nearly all forms of life, this energy comes from ___________. O2
C6H12O6 (glucose)
fossil fuels
sunlight
Question: 7-1
Answer: d
Diff: Easy
Text Ref: Section 7.1
Skill: Factual
Also relates to: Chapter 6
Notes:
As mentioned in Chapter 6 in the discussion of entropy, sunlight allows all organisms to exist. This concept highlights the reliance of cellular respiration on photosynthesis.
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29. Where in the plant does the majority of photosynthesis occur?
Roots
Leaves
Stem
Branches
Question: 7-4
Answer: b
Diff: Easy
Text Ref: Section 7.1
Skill: Factual
Also relates to: Chapter 21
Notes:
If you go over the anatomy of the leaf, it will show students the importance of the flatness of leaves for generating a large surface area for the absorption of sunlight. Also, if you show a leaf cross-section, students can see that the mesophyll cells within the middle of the leaf are packed with chloroplasts.
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30. Where in the plant does the majority of photosynthesis occur?
Roots
Leaves
Stem
Branches
Question: 7-4
Answer: b
Diff: Easy
Text Ref: Section 7.1
Skill: Factual
Also relates to: Chapter 21
Notes:
If you go over the anatomy of the leaf, it will show students the importance of the flatness of leaves for generating a large surface area for the absorption of sunlight. Also, if you show a leaf cross-section, students can see that the mesophyll cells within the middle of the leaf are packed with chloroplasts.
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31. In the Calvin cycle, where do the carbon atoms used to synthesize glucose originate?
RuBP
NADPH
ATP
CO2
Question: 7-9
Answer: d
Diff: Moderate
Text Ref: Section 7.3
Skill: Conceptual
Notes:
Typically, students do not understand where the carbons come from, even after the whole Calvin cycle has been explained. This question reinforces the importance of CO2 and emphasizes that important events occur even during this last stage of photosynthesis.
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32. In the Calvin cycle, where do the carbon atoms used to synthesize glucose originate?
RuBP
NADPH
ATP
CO2
Question: 7-9
Answer: d
Diff: Moderate
Text Ref: Section 7.3
Skill: Conceptual
Notes:
Typically, students do not understand where the carbons come from, even after the whole Calvin cycle has been explained. This question reinforces the importance of CO2 and emphasizes that important events occur even during this last stage of photosynthesis.
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33. How are the light-dependent reactions and the Calvin cycle related?
The energy-carrier molecules of the light- dependent reactions fuel the Calvin cycle.
The energy-carrier molecules of the light- independent reactions fuel the Calvin cycle.
They produce the same products.
They occur in the same place within the thylakoid membrane.
Question: 7-10
Answer: a
Diff: Easy
Text Ref: Section 7.4
Skill: Conceptual
Also relates to: Chapter 6
Notes:
Going back to Chapter 6, this question relates the buildup and breakdown of energy-carrier molecules to the coupled metabolic reactions in photosynthesis.
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34. How are the light-dependent reactions and the Calvin cycle related?
The energy-carrier molecules of the light- dependent reactions fuel the Calvin cycle.
The energy-carrier molecules of the light- independent reactions fuel the Calvin cycle.
They produce the same products.
They occur in the same place within the thylakoid membrane.
Question: 7-10
Answer: a
Diff: Easy
Text Ref: Section 7.4
Skill: Conceptual
Also relates to: Chapter 6
Notes:
Going back to Chapter 6, this question relates the buildup and breakdown of energy-carrier molecules to the coupled metabolic reactions in photosynthesis.
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35. 7.2 The Light Reactions: How Is Light Energy Converted to Chemical Energy?
The sun emits energy within a broad spectrum of electromagnetic radiation
Electromagnetic spectrum
Ranges from short-wavelength gamma rays through ultraviolet, visible, and infrared light to long-wavelength radio waves
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36. 7.2 The Light Reactions: How Is Light Energy Converted to Chemical Energy?
Light is composed of individual packets of energy called photons
Visible light has wavelengths with energies strong enough to alter biological pigment molecules such as chlorophyll a
Key light-capturing pigment molecule in chloroplasts, absorbing violet, blue, and red light
Green light, however, is reflected, which is why leaves appear green
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37. 7.2 The Light Reactions: How Is Light Energy Converted to Chemical Energy?
Chloroplasts also contain accessory pigments
Absorb additional wavelengths of light energy and transfer them to chlorophyll a
Chlorophyll b absorbs blue and red-orange wavelengths of light missed by chlorophyll a
Carotenoids absorb blue and green light, and appear yellow or orange to our eyes because they reflect these colors
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38. light absorption (percent) 80
Figure 7-5
100
chlorophyll b
light absorption (percent) 80
carotenoids 60
chlorophyll a 40 20
wavelength (nanometers)
Figure 7-5 Light and chloroplast pigments
400
450
500
550
600
650
700
750
visible light
micro-
waves
radio
waves
gamma rays
X-rays UV
infrared
higher energy
lower energy
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39. 7.2 The Light Reactions: How Is Light Energy Converted to Chemical Energy?
In autumn, more-abundant green chlorophyll breaks down before carotenoids do, revealing their yellow color, which in summer is masked
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40. Figure 7-6 Loss of chlorophyll reveals carotenoid pigments
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41. 7.2 The Light Reactions: How Is Light Energy Converted to Chemical Energy?
Light reactions occur in association with thylakoid membranes, which contain many photosystems
Clusters of chlorophyll and accessory pigment molecules (surrounded by various proteins)
Photosystem II (PS II) and photosystem I (PS I) work together during the light reactions
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42. 7.2 The Light Reactions: How Is Light Energy Converted to Chemical Energy?
Each PS has a unique electron transport chain (ETC) located adjacent to it
Series of electron-carrier molecules
Reaction center
Pair of specialized chlorophyll a molecules and primary electron acceptor molecule embedded in a complex of proteins
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43. PS II → ETC II → PS I → ETC I → NADP+
7.2 The Light Reactions: How Is Light Energy Converted to Chemical Energy?
Within the thylakoid membrane, the overall path of electrons is as follows:
PS II → ETC II → PS I → ETC I → NADP+
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44. Steps in the Light Reactions
Photons of light are absorbed by pigment molecules clustered in PS II
An energized electron is ejected from the reaction center
The primary electron acceptor captures the electron
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45. Figure 7-7 Energy transfer and the light reactions of photosynthesis
CO2
ATP
Calvin
cycle
light
reactions
NADPH
ADP
NADP+
3-C sugar O2
C6H12O6
high e
electron
transport
chain e
primary
electron
acceptor
of reaction
center
energy level of electrons
NADPH e e e
light
energy
NADP+ H+
electron
transport
chain
Figure 7-7 Energy transfer and the light reactions of photosynthesis
ATP
pigment
molecules e
reaction center
chlorophyll a molecules
Photosystem I
Photosystem II e
low
in thylakoid membrane
H2O 2 H+ O2
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46. Steps in the Light Reactions
The primary electron acceptor passes the electron to the first molecule of ETC II, then it is passed from one electron-carrier molecule to the next, releasing energy as it goes
Some of the energy released is used to pump H+ across the thylakoid membrane into the thylakoid space, leading to ATP synthesis
The low-energy electron leaves ETC II and enters the reaction the center of PS I, replacing the electron ejected when light strikes PS I
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47. Figure 7-7 Energy transfer and the light reactions of photosynthesis
CO2
ATP
Calvin
cycle
light
reactions
NADPH
ADP
NADP+
3-C sugar O2
C6H12O6
high e
electron
transport
chain e
primary
electron
acceptor
of reaction
center
energy level of electrons
NADPH e e e
light
energy
NADP+ H+
electron
transport
chain
Figure 7-7 Energy transfer and the light reactions of photosynthesis
ATP
pigment
molecules e
reaction center
chlorophyll a molecules
Photosystem I
Photosystem II e
low
in thylakoid membrane
H2O 2 H+ O2
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48. Steps in the Light Reactions
The primary electron acceptor of PS I captures the electron
The primary electron acceptor passes the electron to the first molecule of ETC I, passed along until it reaches NADP+
NADPH is formed when the NADP+ molecule picks up two energetic electrons, along with H+
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49. Figure 7-7 Energy transfer and the light reactions of photosynthesis
CO2
ATP
Calvin
cycle
light
reactions
NADPH
ADP
NADP+
3-C sugar O2
C6H12O6
high e
electron
transport
chain e
primary
electron
acceptor
of reaction
center
energy level of electrons
NADPH e e e
light
energy
NADP+ H+
electron
transport
chain
Figure 7-7 Energy transfer and the light reactions of photosynthesis
ATP
pigment
molecules e
reaction center
chlorophyll a molecules
Photosystem I
Photosystem II e
low
in thylakoid membrane
H2O 2 H+ O2
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50. 7.2 The Light Reactions: How Is Light Energy Converted to Chemical Energy?
Energy of electron movement through the thylakoid membrane creates an H+ gradient that drives ATP synthesis in a process called chemiosmosis
As the energized electron travels along ETC II, some of the energy it liberates is used to pump H+ into thylakoid space
Pumping creates a high concentration of H+ inside space relative to surrounding stroma
H+ flows down its concentration gradient through thylakoid channel protein called ATP synthase, generating ATP from ADP
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51. Figure 7-8
thylakoid
membrane
thylakoid
thylakoid
space
chloroplast
(stroma)
CO2
light
energy
H+ is pumped into
the thylakoid space. H+
electron
transport
chain
Calvin
cycle
electron transport chain
NADP+ e H+
NADPH
3-C sugar e e e
ATP
synthase
C6H12O6
Figure 7-8 Events of the light reactions occur in and near the thylakoid membrane e
ADP e
photosystem II
photosystem I Pi H+ H+ H+
ATP 2 H+ H+
H2O H+ O2 H+ H+ H+
The flow of H+ down
its concentration gradient
powers ATP synthesis.
A high H+ concentration is
created in the thylakoid space.
thylakoid
membrane
(thylakoid space)
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52. When less water is available during a drought, why is the rate of photosynthesis in plants reduced?
The turgor pressure of the plant drops and the plant falls over.
Fewer electrons are available to fuel the ETC.
Electrons are not supplied to fuel the Calvin cycle.
Oxygen is not available to fuel the metabolic pathway of photosynthesis.
Question: 7-5
Answer: b
Diff: Moderate
Text Ref: Section 7.2
Skill: Application
Notes:
This question stresses the importance of water to the process of photosynthesis.
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53. When less water is available during a drought, why is the rate of photosynthesis in plants reduced?
The turgor pressure of the plant drops and the plant falls over.
Fewer electrons are available to fuel the ETC.
Electrons are not supplied to fuel the Calvin cycle.
Oxygen is not available to fuel the metabolic pathway of photosynthesis.
Question: 7-5
Answer: b
Diff: Moderate
Text Ref: Section 7.2
Skill: Application
Notes:
This question stresses the importance of water to the process of photosynthesis.
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54. What is responsible for the beautiful shades of red, orange, and gold in autumn leaves?
Accessory pigments become visible after chlorophyll breaks down.
Chlorophyll becomes visible after accessory pigments break down.
Carotenoids function only during autumn.
Chlorophyll functions only during autumn.
Question: 7-6
Answer: a
Diff: Moderate
Text Ref: Section 7.2
Skill: Conceptual
Also relates to: Chapter 21
Notes:
Students should know that chlorophyll is not the only pigment utilized in photosynthesis and that other pigments are present but are normally masked by chlorophyll.
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55. What is responsible for the beautiful shades of red, orange, and gold in autumn leaves?
Accessory pigments become visible after chlorophyll breaks down.
Chlorophyll becomes visible after accessory pigments break down.
Carotenoids function only during autumn.
Chlorophyll functions only during autumn.
Question: 7-6
Answer: a
Diff: Moderate
Text Ref: Section 7.2
Skill: Conceptual
Also relates to: Chapter 21
Notes:
Students should know that chlorophyll is not the only pigment utilized in photosynthesis and that other pigments are present but are normally masked by chlorophyll.
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56. What is the purpose of having two photosystems in the light-dependent reactions?
One photosystem fuels the light-dependent reactions; the other fuels the Calvin cycle reactions.
The two generate different energy carriers.
The two function in different places in the plant.
One photosystem functions in C3 plants; the other functions in C4 plants.
Question: 7-7
Answer: b
Diff: Moderate
Text Ref: Section 7.2
Skill: Conceptual
Also relates to: Chapter 21
Notes:
Students seem to forget that photosystem II produces ATP and photosystem I produces NADPH.
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57. What is the purpose of having two photosystems in the light-dependent reactions?
One photosystem fuels the light-dependent reactions; the other fuels the Calvin cycle reactions.
The two generate different energy carriers.
The two function in different places in the plant.
One photosystem functions in C3 plants; the other functions in C4 plants.
Question: 7-7
Answer: b
Diff: Moderate
Text Ref: Section 7.2
Skill: Conceptual
Also relates to: Chapter 21
Notes:
Students seem to forget that photosystem II produces ATP and photosystem I produces NADPH.
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58. How are energy-carrier molecules generated in the light-dependent reactions?
Energy-carrier molecules give off energy, pushing electrons through the light-dependent reactions.
CO2 is split and releases energy, forming energy-carrier molecules.
Water is split and releases energy, forming energy-carrier molecules.
The energy given off as electrons jump from carrier to carrier and are captured in coupled reactions, making ATP and NADPH.
Question: 7-8
Answer: d
Diff: Moderate
Text Ref: Section 7.2
Skill: Conceptual
Also relates to: Chapter 21
Notes:
This question summarizes the electron transport system, emphasizing the importance of the transfer of electrons and the release of energy at each step.
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59. How are energy-carrier molecules generated in the light-dependent reactions?
Energy-carrier molecules give off energy, pushing electrons through the light-dependent reactions.
CO2 is split and releases energy, forming energy-carrier molecules.
Water is split and releases energy, forming energy-carrier molecules.
The energy given off as electrons jump from carrier to carrier and are captured in coupled reactions, making ATP and NADPH.
Question: 7-8
Answer: d
Diff: Moderate
Text Ref: Section 7.2
Skill: Conceptual
Also relates to: Chapter 21
Notes:
This question summarizes the electron transport system, emphasizing the importance of the transfer of electrons and the release of energy at each step.
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60. In the figure, what wavelength would most likely be used for photosynthesis by fall plants?
440 nanometers
480 nanometers
500 nanometers
675 nanometers
Question: 7-12
Answer: c
Diff: Moderate
Text Ref: Section 7.5
Skill: Conceptual
Also relates to: Chapter 21
Notes:
Carotenoids are present in leaves throughout the year, but in fall the chlorophyll breaks down before the carotenoids do; thus, at this time only the carotenoids are present to photosynthesize, at an optimum light absorption wavelength of 500 nanometers.
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61. In the figure, what wavelength would most likely be used for photosynthesis by fall plants?
440 nanometers
480 nanometers
500 nanometers
675 nanometers
Question: 7-12
Answer: c
Diff: Moderate
Text Ref: Section 7.5
Skill: Conceptual
Also relates to: Chapter 21
Notes:
Carotenoids are present in leaves throughout the year, but in fall the chlorophyll breaks down before the carotenoids do; thus, at this time only the carotenoids are present to photosynthesize, at an optimum light absorption wavelength of 500 nanometers.
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62. 7.3 The Calvin Cycle: How Is Chemical Energy Stored in Sugar Molecules?
The Calvin cycle captures carbon dioxide
ATP and NADPH synthesized from light reactions are used to power the synthesis of a simple sugar (gyceraldehyde-3-phosphate, or G3P)
Accomplished through a series of reactions occurring in the stroma called the Calvin cycle
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63. 7.3 The Calvin Cycle: How Is Chemical Energy Stored in Sugar Molecules?
Carbon fixation
Carbon from CO2 is incorporated, or “fixed,” into a larger organic molecule
Enzyme rubisco combines three CO2 molecules with three RuBP molecules, forming three unstable six-carbon molecules that each quickly split in half, forming six molecules of phosphoglyceric acid (PGA)
Because of generation of this three-carbon PGA molecule, the Calvin cycle is often referred to as C3 pathway
Because of the generation of this three-carbon PGA molecule, the Calvin cycle is often called the C3 pathway.
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64. 7.3 The Calvin Cycle: How Is Chemical Energy Stored in Sugar Molecules?
Synthesis of G3P
Energy donated by ATP and NADPH (generated by light reactions) is used to convert six PGA molecules into six three-carbon G3P molecules
Regeneration of ribulose bisphosphate (RuBP)
ATP from light reactions is used with five of the six G3P molecules formed to regenerate five-carbon RuBP (three molecules) necessary to repeat cycle
Remaining G3P molecule exits cycle
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65. Figure 7-9
H2O
CO2
ATP
Carbon fixation
combines three CO2
with three RuBP using
the enzyme rubisco.
Calvin
cycle
light
reactions
NADPH
ADP
NADP+
3-C sugar O2
C6H12O6
RuBP
PGA 6
ATP
Calvin
cycle 6
ADP 3
ADP 6
NADPH 3
ATP 6
NADP+
G3P
G3P
Energy from ATP
and NADPH is used
to convert the six
molecules of PGA to
six molecules of G3P.
Figure 7-9 The Calvin cycle fixes carbon from CO2 and produces the simple sugar G3P
Using the energy
from ATP, the five
remaining molecules
of G3P are converted
to three molecules
of RuBP.
G3P
One molecule of
G3P leaves the cycle.
G3P
G3P
glucose
Two molecules of G3P combine
to form glucose.
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66. 7.3 The Calvin Cycle: How Is Chemical Energy Stored in Sugar Molecules?
Photorespiration
Photosynthesis is not always 100% efficient
Rubisco will allow O2 to bind rather than CO2, especially when O2 > CO2
About 33% less carbon fixed
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67. 7.3 The Calvin Cycle: How Is Chemical Energy Stored in Sugar Molecules?
Some species of flowering plants have evolved alternate pathways to circumvent wasteful photorespiration
C4 pathway
Crassulacean acid metabolism (CAM)
When plant stomata are closed in hot environments to prevent water loss, oxygen builds up in the plant cells and RuBP combines with it, rather than CO2, in a wasteful process called photorespiration.
This process prevents the Calvin cycle from synthesizing sugar, and plants may die under these circumstances.
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68. Figure E7-2 The CAM pathway
Figure E7-1 & Figure E7-2
crabgrass
corn
daisies
pineapples
succulents
cacti
mesophyll cell
bundle sheath cell
mesophyll cell
pyruvate
(3C)
pyruvate
(3C)
PEP
(3C)
pyruvate
(3C)
PEP
(3C)
CO2
(1C)
CO2
(1C)
CO2
(1C)
CO2
(1C)
*(rubisco)
*(rubisco)
(PEP carboxylase)
Calvin
cycle
(PEP carboxylase)
Calvin
Figure E7-1 The C4 pathway
Figure E7-2 The CAM pathway
Closed stomata in hot/dry weather minimize water loss, but O2 accumulates.
C4: Calvin cycle (rubisco) is in separate cell; rubisco is not exposed to accumulated O2.
CAM (crassulacean acid metabolism): CO2 is harvested at night but stored to be fixed during the day, when stomata are closed and O2 is accumulating (same place, different time).
malic acid
in central
vacuole
cycle
oxaloacetate
(4C)
oxaloacetate
(4C)
sugar
sugar
malate
(4C)
malate
(4C)
malate
(4C)
malate
(4C)
night
day
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69. 7.3 The Calvin Cycle: How Is Chemical Energy Stored in Sugar Molecules?
What do plants do with glucose?
Broken down during cellular respiration so the plant’s cells get energy
Linked to form starch (a storage molecule)
Linked to form cellulose (a major component of plant cell walls)
Components may be used in amino acids, nucleic acids, nectar, fruit
© 2017 Pearson Education, Inc.

70. What is the significance of the C4 pathway?
It gives individual plants the option of undergoing the C3 or C4 pathway for more efficient photosynthesis.
It minimizes photorespiration in plants that live in dry environments.
It maximizes photorespiration in plants that live in dry environments.
It minimizes photorespiration in plants that live in humid environments.
Question: 7-11
Answer: b
Diff: Hard
Text Ref: Section 7.5
Skill: Conceptual
Also relates to: Chapter 21
Notes:
Students will need to apply what they know about photorespiration to understand the significance of plants that have evolved the two methods of carbon fixation. This is a good question to lead into a discussion of how environment influences function.
© 2017 Pearson Education, Inc.

71. What is the significance of the C4 pathway?
It gives individual plants the option of undergoing the C3 or C4 pathway for more efficient photosynthesis.
It minimizes photorespiration in plants that live in dry environments.
It maximizes photorespiration in plants that live in dry environments.
It minimizes photorespiration in plants that live in humid environments.
Question: 7-11
Answer: b
Diff: Hard
Text Ref: Section 7.5
Skill: Conceptual
Also relates to: Chapter 21
Notes:
Students will need to apply what they know about photorespiration to understand the significance of plants that have evolved the two methods of carbon fixation. This is a good question to lead into a discussion of how environment influences function.
© 2017 Pearson Education, Inc.