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Semelhante a Biology in Focus - Chapter 8 (20)
Biology in Focus - Chapter 8
- 1. CAMPBELL BIOLOGY IN FOCUS
© 2014 Pearson Education, Inc.
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
Lecture Presentations by
Kathleen Fitzpatrick and Nicole Tunbridge
8
Photosynthesis
- 2. Overview: The Process That Feeds the Biosphere
Photosynthesis is the process that converts solar
energy into chemical energy
Directly or indirectly, photosynthesis nourishes
almost the entire living world
© 2014 Pearson Education, Inc.
- 3. Autotrophs sustain themselves without eating
anything derived from other organisms
Autotrophs are the producers of the biosphere,
producing organic molecules from CO2 and other
inorganic molecules
Almost all plants are photoautotrophs, using the
energy of sunlight to make organic molecules
© 2014 Pearson Education, Inc.
- 5. Heterotrophs obtain their organic material from
other organisms
Heterotrophs are the consumers of the biosphere
Almost all heterotrophs, including humans, depend
on photoautotrophs for food and O2
© 2014 Pearson Education, Inc.
- 6. Photosynthesis occurs in plants, algae, certain other
protists, and some prokaryotes
These organisms feed not only themselves but also
most of the living world
© 2014 Pearson Education, Inc.
- 7. © 2014 Pearson Education, Inc.
Figure 8.2
(a) Plants
(d) Cyanobacteria
(e) Purple sulfur
bacteria
(b) Multicellular
alga
(c) Unicellular eukaryotes
10µm
1µm40µm
- 10. © 2014 Pearson Education, Inc.
Figure 8.2c
(c) Unicellular eukaryotes
10µm
- 12. © 2014 Pearson Education, Inc.
Figure 8.2e
(e) Purple sulfur
bacteria
1µm
- 13. Concept 8.1: Photosynthesis converts light
energy to the chemical energy of food
The structural organization of photosynthetic cells
includes enzymes and other molecules grouped
together in a membrane
This organization allows for the chemical reactions
of photosynthesis to proceed efficiently
Chloroplasts are structurally similar to and likely
evolved from photosynthetic bacteria
© 2014 Pearson Education, Inc.
- 14. Chloroplasts: The Sites of Photosynthesis in
Plants
Leaves are the major locations of photosynthesis
Their green color is from chlorophyll, the green
pigment within chloroplasts
Chloroplasts are found mainly in cells of the
mesophyll, the interior tissue of the leaf
Each mesophyll cell contains 30–40 chloroplasts
© 2014 Pearson Education, Inc.
- 15. CO2 enters and O2 exits the leaf through microscopic
pores called stomata
The chlorophyll is in the membranes of thylakoids
(connected sacs in the chloroplast); thylakoids may
be stacked in columns called grana
Chloroplasts also contain stroma, a dense interior
fluid
© 2014 Pearson Education, Inc.
- 16. © 2014 Pearson Education, Inc.
Figure 8.3
Leaf cross section
20 µm
Mesophyll
Stomata
Chloroplasts Vein
CO2 O2
Mesophyll cell
Chloroplast
Stroma
Thylakoid
Thylakoid
space
Outer
membrane
Intermembrane
space
Inner membrane
Granum
1 µm
- 17. © 2014 Pearson Education, Inc.
Figure 8.3a
Leaf cross section
Mesophyll
Stomata
Chloroplasts Vein
CO2 O2
- 18. © 2014 Pearson Education, Inc.
Figure 8.3b
20 µm
Mesophyll cell
Chloroplast
Stroma
Thylakoid
Thylakoid
space
Outer
membrane
Intermembrane
space
Inner membrane
Granum
1 µm
- 21. Tracking Atoms Through Photosynthesis:
Scientific Inquiry
Photosynthesis is a complex series of reactions that
can be summarized as the following equation
6 CO2 + 12 H2O + Light energy → C6H12O6 + 6 O2 + 6 H2O
© 2014 Pearson Education, Inc.
- 22. The Splitting of Water
Chloroplasts split H2O into hydrogen and oxygen,
incorporating the electrons of hydrogen into sugar
molecules and releasing oxygen as a by-product
© 2014 Pearson Education, Inc.
- 23. © 2014 Pearson Education, Inc.
Figure 8.4
Products:
Reactants: 6 CO2
6 O2C6H12O6 6 H2O
12 H2O
- 24. Photosynthesis as a Redox Process
Photosynthesis reverses the direction of electron
flow compared to respiration
Photosynthesis is a redox process in which H2O is
oxidized and CO2 is reduced
Photosynthesis is an endergonic process; the energy
boost is provided by light
© 2014 Pearson Education, Inc.
- 25. © 2014 Pearson Education, Inc.
Figure 8.UN01
becomes reduced
becomes oxidized
- 26. The Two Stages of Photosynthesis: A Preview
Photosynthesis consists of the light reactions (the
photo part) and Calvin cycle (the synthesis part)
The light reactions (in the thylakoids)
Split H2O
Release O2
Reduce the electron acceptor, NADP+
, to NADPH
Generate ATP from ADP by adding a phosphate
group, photophosphorylation
© 2014 Pearson Education, Inc.
- 27. The Calvin cycle (in the stroma) forms sugar from
CO2, using ATP and NADPH
The Calvin cycle begins with carbon fixation,
incorporating CO2 into organic molecules
© 2014 Pearson Education, Inc.
Animation: Photosynthesis
- 28. © 2014 Pearson Education, Inc.
Figure 8.5
Light
CO2H2O
P i
Chloroplast
Light
Reactions
Calvin
Cycle
[CH2O]
(sugar)
O2
ADP
ATP
NADP+
+
NADPH
- 29. © 2014 Pearson Education, Inc.
Figure 8.5-1
Light
H2O
Chloroplast
Light
Reactions
P i
ADP
NADP+
+
- 30. © 2014 Pearson Education, Inc.
Figure 8.5-2
Light
H2O
P i
Chloroplast
Light
Reactions
O2
ADP
ATP
NADP+
+
NADPH
- 31. © 2014 Pearson Education, Inc.
Figure 8.5-3
Light
CO2H2O
P i
Chloroplast
Light
Reactions
Calvin
Cycle
O2
ADP
ATP
NADP+
+
NADPH
- 32. © 2014 Pearson Education, Inc.
Figure 8.5-4
Light
CO2H2O
P i
Chloroplast
Light
Reactions
Calvin
Cycle
[CH2O]
(sugar)
O2
ADP
ATP
NADP+
+
NADPH
- 33. Concept 8.2: The light reactions convert solar
energy to the chemical energy of ATP and NADPH
Chloroplasts are solar-powered chemical factories
Their thylakoids transform light energy into the
chemical energy of ATP and NADPH
© 2014 Pearson Education, Inc.
- 34. The Nature of Sunlight
Light is a form of electromagnetic energy, also called
electromagnetic radiation
Like other electromagnetic energy, light travels in
rhythmic waves
Wavelength is the distance between crests of waves
Wavelength determines the type of electromagnetic
energy
© 2014 Pearson Education, Inc.
- 35. The electromagnetic spectrum is the entire range
of electromagnetic energy, or radiation
Visible light consists of wavelengths (including
those that drive photosynthesis) that produce colors
we can see
Light also behaves as though it consists of discrete
particles, called photons
© 2014 Pearson Education, Inc.
- 36. © 2014 Pearson Education, Inc.
Figure 8.6
Gamma
rays
10−5
nm 10−3
nm 1 nm 103
nm 106
nm
1 m
(109
nm) 103
m
Radio
waves
Micro-
wavesX-rays InfraredUV
Visible light
Shorter wavelength Longer wavelength
Lower energyHigher energy
380 450 500 550 650600 700 750 nm
- 37. Photosynthetic Pigments: The Light Receptors
Pigments are substances that absorb visible light
Different pigments absorb different wavelengths
Wavelengths that are not absorbed are reflected or
transmitted
Leaves appear green because chlorophyll reflects
and transmits green light
© 2014 Pearson Education, Inc.
Animation: Light and Pigments
- 38. © 2014 Pearson Education, Inc.
Figure 8.7
Reflected
light
Light
Absorbed
light
Chloroplast
Granum
Transmitted
light
- 39. A spectrophotometer measures a pigment’s ability
to absorb various wavelengths
This machine sends light through pigments and
measures the fraction of light transmitted at each
wavelength
© 2014 Pearson Education, Inc.
- 40. © 2014 Pearson Education, Inc.
Figure 8.8
Refracting
prism
White
light
Green
light
Blue
light
Chlorophyll
solution
Photoelectric
tube
Galvanometer
Slit moves to pass
light of selected
wavelength.
The low transmittance (high
absorption) reading indicates
that chlorophyll absorbs most
blue light.
The high transmittance (low
absorption) reading indicates
that chlorophyll absorbs very
little green light.
Technique
1
2
4
3
- 41. An absorption spectrum is a graph plotting a
pigment’s light absorption versus wavelength
The absorption spectrum of chlorophyll a suggests
that violet-blue and red light work best for
photosynthesis
Accessory pigments include chlorophyll b and a
group of pigments called carotenoids
An action spectrum profiles the relative
effectiveness of different wavelengths of radiation in
driving a process
© 2014 Pearson Education, Inc.
- 42. © 2014 Pearson Education, Inc.
Figure 8.9
Chloro-
phyll a
Rateof
photosynthesis
(measuredbyO2
release)
Results
Absorptionoflight
bychloroplast
pigments
Chlorophyll b
Carotenoids
Filament
of alga
Aerobic bacteria
(a) Absorption spectra
(b) Action spectrum
(c) Engelmann’s experiment
400 700600500
400 700600500
400 700600500
Wavelength of light (nm)
- 43. © 2014 Pearson Education, Inc.
Figure 8.9a
Chloro-
phyll a
Absorptionoflight
bychloroplast
pigments
Chlorophyll b
Carotenoids
(a) Absorption spectra
400 700600500
Wavelength of light (nm)
- 44. © 2014 Pearson Education, Inc.
Figure 8.9b
(b) Action spectrum
400 700600500
Rateof
photosynthesis
(measuredbyO2
release)
- 45. © 2014 Pearson Education, Inc.
Figure 8.9c
Filament
of alga
Aerobic bacteria
(c) Engelmann’s experiment
400 700600500
- 46. The action spectrum of photosynthesis was first
demonstrated in 1883 by Theodor W. Engelmann
In his experiment, he exposed different segments of
a filamentous alga to different wavelengths
Areas receiving wavelengths favorable to
photosynthesis produced excess O2
He used the growth of aerobic bacteria clustered
along the alga as a measure of O2 production
© 2014 Pearson Education, Inc.
- 47. Chlorophyll a is the main photosynthetic pigment
Accessory pigments, such as chlorophyll b, broaden
the spectrum used for photosynthesis
A slight structural difference between chlorophyll a
and chlorophyll b causes them to absorb slightly
different wavelengths
Accessory pigments called carotenoids absorb
excessive light that would damage chlorophyll
© 2014 Pearson Education, Inc.
Video: Chlorophyll Model
- 48. © 2014 Pearson Education, Inc.
Figure 8.10
Hydrocarbon tail:
interacts with hydrophobic
regions of proteins inside
thylakoid membranes of
chloroplasts; H atoms not
shown
Porphyrin ring:
light-absorbing
“head” of molecule;
note magnesium
atom at center
CH3 in chlorophyll a
CHO in chlorophyll b
CH3
- 49. Excitation of Chlorophyll by Light
When a pigment absorbs light, it goes from a ground
state to an excited state, which is unstable
When excited electrons fall back to the ground state,
photons are given off, an afterglow called
fluorescence
If illuminated, an isolated solution of chlorophyll will
fluoresce, giving off light and heat
© 2014 Pearson Education, Inc.
- 50. © 2014 Pearson Education, Inc.
Figure 8.11
Photon
(fluorescence)
Ground
state
(b) Fluorescence
Excited
state
Chlorophyll
molecule
Photon
Heat
e−
(a) Excitation of isolated chlorophyll molecule
Energyofelectron
- 52. A Photosystem: A Reaction-Center Complex
Associated with Light-Harvesting Complexes
A photosystem consists of a reaction-center
complex (a type of protein complex) surrounded by
light-harvesting complexes
The light-harvesting complexes (pigment
molecules bound to proteins) transfer the energy of
photons to the reaction center
© 2014 Pearson Education, Inc.
- 53. © 2014 Pearson Education, Inc.
Figure 8.12
(b) Structure of a photosystem(a) How a photosystem harvests light
Chlorophyll STROMA
THYLAKOID
SPACE
Protein
subunits
STROMA
THYLAKOID SPACE
(INTERIOR OF THYLAKOID)
Photosystem
Photon
Light-
harvesting
complexes
Reaction-
center
complex
Primary
electron
acceptor
Special pair of
chlorophyll a
molecules
Transfer
of energy
Pigment
molecules
Thylakoidmembrane
Thylakoidmembrane
e−
- 54. © 2014 Pearson Education, Inc.
Figure 8.12a
(a) How a photosystem harvests light
STROMA
THYLAKOID SPACE
(INTERIOR OF THYLAKOID)
Photosystem
Photon
Light-
harvesting
complexes
Reaction-
center
complex
Primary
electron
acceptor
Special pair of
chlorophyll a
molecules
Transfer
of energy
Pigment
molecules
Thylakoidmembrane
e−
- 55. © 2014 Pearson Education, Inc.
Figure 8.12b
(b) Structure of a photosystem
Chlorophyll STROMA
THYLAKOID
SPACE
Protein
subunits
Thylakoidmembrane
- 56. A primary electron acceptor in the reaction center
accepts excited electrons and is reduced as a result
Solar-powered transfer of an electron from a
chlorophyll a molecule to the primary electron
acceptor is the first step of the light reactions
© 2014 Pearson Education, Inc.
- 57. There are two types of photosystems in the thylakoid
membrane
Photosystem II (PS II) functions first (the numbers
reflect order of discovery) and is best at absorbing a
wavelength of 680 nm
The reaction-center chlorophyll a of PS II is called
P680
© 2014 Pearson Education, Inc.
- 58. Photosystem I (PS I) is best at absorbing a
wavelength of 700 nm
The reaction-center chlorophyll a of PS I is called
P700
© 2014 Pearson Education, Inc.
- 59. Linear Electron Flow
Linear electron flow involves the flow of electrons
through both photosystems to produce ATP and
NADPH using light energy
© 2014 Pearson Education, Inc.
- 60. Linear electron flow can be broken down into a series
of steps
1. A photon hits a pigment and its energy is passed
among pigment molecules until it excites P680
2. An excited electron from P680 is transferred to the
primary electron acceptor (we now call it P680+
)
3. H2O is split by enzymes, and the electrons are
transferred from the hydrogen atoms to P680+
, thus
reducing it to P680; O2 is released as a by-product
© 2014 Pearson Education, Inc.
- 61. © 2014 Pearson Education, Inc.
Figure 8.UN02
Calvin
Cycle
NADPH
NADP+
ATP
ADP
Light
CO2
[CH2O] (sugar)
Light
Reactions
O2
H2O
- 62. © 2014 Pearson Education, Inc.
Figure 8.13-1
Primary
acceptor
Photosystem II
(PS II)
Light
P680
Pigment
molecules
1
2e−
- 63. © 2014 Pearson Education, Inc.
Figure 8.13-2
Primary
acceptor
2 H+
O2
+
Photosystem II
(PS II)
H2O
Light
/2
1
P680
Pigment
molecules
1
2
3
e−
e−
e−
- 64. © 2014 Pearson Education, Inc.
Figure 8.13-3
Primary
acceptor
2 H+
O2
+
ATP
Photosystem II
(PS II)
H2O
Light
/2
1
P680
Pq
Electron
transport
chain
Cytochrome
complex
Pc
Pigment
molecules
1
2
3
4
5
e−
e−
e−
- 65. © 2014 Pearson Education, Inc.
Figure 8.13-4
Primary
acceptor
2 H+
O2
+
ATP
Photosystem II
(PS II)
H2O
Light
/2
1
P680
Pq
Electron
transport
chain
Cytochrome
complex
Pc
Pigment
molecules
Primary
acceptor
Photosystem I
(PS I)
P700
Light
1
2
3
4
5
6
e−
e−
e−
e−
- 66. © 2014 Pearson Education, Inc.
Figure 8.13-5
Primary
acceptor
2 H+
O2
+
ATP
NADPH
Photosystem II
(PS II)
H2O e−
e−
e−
Light
/2
1
P680
Pq
Electron
transport
chain
Cytochrome
complex
Pc
Pigment
molecules
Primary
acceptor
Photosystem I
(PS I)
e−
P700
e−
e−
Fd
Light
Electron
transport
chain
H+
+
NADP+
NADP+
reductase
1
2
3
4
5
6
7
8
- 67. 4. Each electron “falls” down an electron transport
chain from the primary electron acceptor of PS II
to PS I
5. Energy released by the fall drives the creation of a
proton gradient across the thylakoid membrane;
diffusion of H+
(protons) across the membrane drives
ATP synthesis
© 2014 Pearson Education, Inc.
- 68. 6. In PS I (like PS II), transferred light energy excites
P700, causing it to lose an electron to an electron
acceptor (we now call it P700+
)
P700+
accepts an electron passed down from PS II
via the electron transport chain
© 2014 Pearson Education, Inc.
- 69. 7. Excited electrons “fall” down an electron transport
chain from the primary electron acceptor of PS I to
the protein ferredoxin (Fd)
8. The electrons are transferred to NADP+
, reducing it
to NADPH, and become available for the reactions
of the Calvin cycle
This process also removes an H+
from the stroma
© 2014 Pearson Education, Inc.
- 70. The energy changes of electrons during linear
flow can be represented in a mechanical analogy
© 2014 Pearson Education, Inc.
- 71. © 2014 Pearson Education, Inc.
Figure 8.14
Photosystem II Photosystem I
NADPH
Mill
makes
ATP
Photon
Photon
- 72. A Comparison of Chemiosmosis in
Chloroplasts and Mitochondria
Chloroplasts and mitochondria generate ATP by
chemiosmosis but use different sources of energy
Mitochondria transfer chemical energy from food to
ATP; chloroplasts transform light energy into the
chemical energy of ATP
Spatial organization of chemiosmosis differs
between chloroplasts and mitochondria but also
shows similarities
© 2014 Pearson Education, Inc.
- 73. In mitochondria, protons are pumped to the
intermembrane space and drive ATP synthesis
as they diffuse back into the mitochondrial matrix
In chloroplasts, protons are pumped into the
thylakoid space and drive ATP synthesis as they
diffuse back into the stroma
© 2014 Pearson Education, Inc.
- 74. © 2014 Pearson Education, Inc.
Figure 8.15
Electron
transport
chain
Higher [H+
]
P i
H+
CHLOROPLAST
STRUCTURE
Inter-
membrane
space
MITOCHONDRION
STRUCTURE
Thylakoid
space
Inner
membrane
Matrix
Key
Lower [H+
]
Thylakoid
membrane
Stroma
ATP
ATP
synthase
ADP +
H+
Diffusion
- 75. © 2014 Pearson Education, Inc.
Figure 8.15a
Electron
transport
chain
Higher [H+
] H+
CHLOROPLAST
STRUCTURE
Inter-
membrane
space
MITOCHONDRION
STRUCTURE
Thylakoid
space
Inner
membrane
Matrix
Key
Lower [H+
]
Thylakoid
membrane
Stroma
ATP
ATP
synthase
ADP +
H+
Diffusion
P
i
- 76. ATP and NADPH are produced on the side facing
the stroma, where the Calvin cycle takes place
In summary, light reactions generate ATP and
increase the potential energy of electrons by moving
them from H2O to NADPH
© 2014 Pearson Education, Inc.
- 77. © 2014 Pearson Education, Inc.
Figure 8.UN02
Calvin
Cycle
NADPH
NADP+
ATP
ADP
Light
CO2
[CH2O] (sugar)
Light
Reactions
O2
H2O
- 78. © 2014 Pearson Education, Inc.
Figure 8.16
Photosystem II Photosystem I
To
Calvin
Cycle
H+
THYLAKOID SPACE
(high H+
concentration)
Thylakoid
membrane
STROMA
(low H+
concentration)
ATP
synthase
NADPH
e−
Light
NADP+
ATP
ADP
+
NADP+
reductase
Fd
H+
+
Pq
Pc
Cytochrome
complex
4 H+
Light
+2 H+
O2
H2O
/21
4 H+
e−
1
2
3
P
i
- 79. © 2014 Pearson Education, Inc.
Figure 8.16a
Photosystem II Photosystem I
H+
THYLAKOID SPACE
(high H+
concentration)
Thylakoid
membrane
STROMA
(low H+
concentration)
ATP
synthase
e−
Light
ATP
ADP
+
Fd
Pq
Pc
Cytochrome
complex
4 H+
Light
+2 H+
O2
H2O
/2
1
4 H+
e−
1
2
P
i
- 80. © 2014 Pearson Education, Inc.
Figure 8.16b
2
3
Photosystem I
To
Calvin
Cycle
H+
ATP
synthase
NADPH
Light
NADP+
ATP
ADP
+
NADP+
reductase
Fd
H+
+
Pc
Cytochrome
complex
4 H+
THYLAKOID SPACE
(high H+
concentration)
STROMA
(low H+
concentration)
P
i
- 81. Concept 8.3: The Calvin cycle uses the chemical
energy of ATP and NADPH to reduce CO2 to
sugar
The Calvin cycle, like the citric acid cycle,
regenerates its starting material after molecules
enter and leave the cycle
Unlike the citric acid cycle, the Calvin cycle is
anabolic
It builds sugar from smaller molecules by using ATP
and the reducing power of electrons carried by
NADPH
© 2014 Pearson Education, Inc.
- 82. Carbon enters the cycle as CO2 and leaves as a
sugar named glyceraldehyde 3-phospate (G3P)
For net synthesis of one G3P, the cycle must take
place three times, fixing three molecules of CO2
The Calvin cycle has three phases
Carbon fixation
Reduction
Regeneration of the CO2 acceptor
© 2014 Pearson Education, Inc.
- 83. Phase 1, carbon fixation, involves the incorporation
of the CO2 molecules into ribulose bisphosphate
(RuBP) using the enzyme rubisco
© 2014 Pearson Education, Inc.
- 84. © 2014 Pearson Education, Inc.
Figure 8.UN03
Calvin
Cycle
NADPH
NADP+
ATP
ADP
Light
CO2
[CH2O] (sugar)
Light
Reactions
O2
H2O
- 85. © 2014 Pearson Education, Inc.
Figure 8.17-1
Input 3
Calvin
Cycle
as 3 CO2
Rubisco Phase 1: Carbon fixation
RuBP 3-Phosphoglycerate
6
3
3 P
P
P P
P
- 86. © 2014 Pearson Education, Inc.
Figure 8.17-2
6 P i
NADPH
Input 3
ATP
Calvin
Cycle
as 3 CO2
Rubisco Phase 1: Carbon fixation
Phase 2:
Reduction
G3P
Output
Glucose and
other organic
compounds
G3P
RuBP 3-Phosphoglycerate
1,3-Bisphosphoglycerate
6 ADP
6
6
6
6
3
6 NADP+
6
3
1
P
P P
P
P
P P
P
P
- 87. © 2014 Pearson Education, Inc.
Figure 8.17-3
6 P i
NADPH
Input 3
ATP
Calvin
Cycle
as 3 CO2
Rubisco Phase 1: Carbon fixation
Phase 2:
Reduction
Phase 3:
Regeneration
of RuBP
G3P
Output
Glucose and
other organic
compounds
G3P
RuBP 3-Phosphoglycerate
1,3-Bisphosphoglycerate
6 ADP
6
6
6
6 P
3
P P
P
6 NADP+
6 P
5 P
G3P
ATP
3 ADP
3
3 P P
1 P
P
- 88. Phase 2, reduction, involves the reduction and
phosphorylation of 3-phosphoglycerate to G3P
© 2014 Pearson Education, Inc.
- 89. Phase 3, regeneration, involves the rearrangement
of G3P to regenerate the initial CO2 receptor, RuBP
© 2014 Pearson Education, Inc.
- 90. Evolution of Alternative Mechanisms of
Carbon Fixation in Hot, Arid Climates
Adaptation to dehydration is a problem for land
plants, sometimes requiring trade-offs with other
metabolic processes, especially photosynthesis
On hot, dry days, plants close stomata, which
conserves H2O but also limits photosynthesis
The closing of stomata reduces access to CO2 and
causes O2 to build up
These conditions favor an apparently wasteful
process called photorespiration
© 2014 Pearson Education, Inc.
- 91. In most plants (C3 plants), initial fixation of CO2,
via rubisco, forms a three-carbon compound (3-
phosphoglycerate)
In photorespiration, rubisco adds O2 instead of
CO2 in the Calvin cycle, producing a two-carbon
compound
Photorespiration decreases photosynthetic output by
consuming ATP, O2, and organic fuel and releasing
CO2 without producing any ATP or sugar
© 2014 Pearson Education, Inc.
- 92. Photorespiration may be an evolutionary relic
because rubisco first evolved at a time when the
atmosphere had far less O2 and more CO2
Photorespiration limits damaging products of light
reactions that build up in the absence of the Calvin
cycle
© 2014 Pearson Education, Inc.
- 93. C4 plants minimize the cost of photorespiration by
incorporating CO2 into a four-carbon compound
An enzyme in the mesophyll cells has a high affinity
for CO2 and can fix carbon even when CO2
concentrations are low
These four-carbon compounds are exported to
bundle-sheath cells, where they release CO2 that is
then used in the Calvin cycle
C4 Plants
© 2014 Pearson Education, Inc.
- 94. © 2014 Pearson Education, Inc.
Figure 8.18
Bundle-
sheath
cell
Sugarcane
CO2
Pineapple
CO2
(a) Spatial separation of steps
C4
CO2
CO2
CAM
Day
Night
Sugar
Calvin
Cycle
Calvin
Cycle
Sugar
Organic
acid
Organic
acid
Mesophyll
cell
(b) Temporal separation of steps
1
2
1
2
- 97. © 2014 Pearson Education, Inc.
Figure 8.18c
Bundle-
sheath
cell
CO2
CO2
(a) Spatial separation of steps
C4
CO2
CO2
CAM
Day
Night
Sugar
Calvin
Cycle
Calvin
Cycle
Sugar
Organic
acid
Organic
acid
Mesophyll
cell
(b) Temporal separation of steps
1
2
1
2
- 98. CAM Plants
Some plants, including succulents, use crassulacean
acid metabolism (CAM) to fix carbon
CAM plants open their stomata at night,
incorporating CO2 into organic acids
Stomata close during the day, and CO2 is released
from organic acids and used in the Calvin cycle
© 2014 Pearson Education, Inc.
- 99. The Importance of Photosynthesis: A Review
The energy entering chloroplasts as sunlight gets
stored as chemical energy in organic compounds
Sugar made in the chloroplasts supplies chemical
energy and carbon skeletons to synthesize the
organic molecules of cells
Plants store excess sugar as starch in the
chloroplasts and in structures such as roots, tubers,
seeds, and fruits
In addition to food production, photosynthesis
produces the O2 in our atmosphere
© 2014 Pearson Education, Inc.
- 100. © 2014 Pearson Education, Inc.
Figure 8.19
Photosystem II
Electron transport chain
Calvin
Cycle
NADPH
Light
NADP+
ATP
CO2
H2O
ADP
+
3-Phosphpglycerate
G3P
RuBP
Sucrose (export)
Starch
(storage)
Chloroplast
O2
Light
Reactions:
Photosystem I
Electron transport chain
P
i
- 102. © 2014 Pearson Education, Inc.
Figure 8.UN05
Photosystem II
Photosystem I
NADP+
ATP
Fd
H+
+Pq
Cytochrome
complex
O2
H2O
Pc
NADP+
reductase
NADPH
Primary
acceptor
Electron
transport
chain
Primary
acceptor
Electron
transport
chain
- 103. © 2014 Pearson Education, Inc.
Figure 8.UN06
Calvin
Cycle
Regeneration of
CO2 acceptor
Carbon fixation
Reduction
1 G3P (3C)
3 CO2
3 × 5C 6 × 3C
5 × 3C
Notas do Editor
- Figure 8.1 How can sunlight, seen here as a spectrum of colors in a rainbow, power the synthesis of organic substances?
- Figure 8.2 Photoautotrophs
- Figure 8.2a Photoautotrophs (part 1: plants)
- Figure 8.2b Photoautotrophs (part 2: multicellular alga)
- Figure 8.2c Photoautotrophs (part 3: unicellular eukaryotes)
- Figure 8.2d Photoautotrophs (part 4: cyanobacteria)
- Figure 8.2e Photoautotrophs (part 5: purple sulfur bacteria)
- Figure 8.3 Zooming in on the location of photosynthesis in a plant
- Figure 8.3a Zooming in on the location of photosynthesis in a plant (part 1: leaf cross section)
- Figure 8.3b Zooming in on the location of photosynthesis in a plant (part 2: chloroplast)
- Figure 8.3c Zooming in on the location of photosynthesis in a plant (part 3: mesophyll cell, LM)
- Figure 8.3d Zooming in on the location of photosynthesis in a plant (part 4: chloroplast, TEM)
- Figure 8.4 Tracking atoms through photosynthesis
- Figure 8.UN01 In-text figure, photosynthesis equation, p. 158
- Figure 8.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle
- Figure 8.5-1 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (step 1)
- Figure 8.5-2 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (step 2)
- Figure 8.5-3 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (step 3)
- Figure 8.5-4 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (step 4)
- Figure 8.6 The electromagnetic spectrum
- Figure 8.7 Why leaves are green: interaction of light with chloroplasts
- Figure 8.8 Research method: determining an absorption spectrum
- For the Cell Biology Video Space-Filling Model of Chlorophyll a, go to Animation and Video Files.
- Figure 8.9 Inquiry: which wavelengths of light are most effective in driving photosynthesis?
- Figure 8.9a Inquiry: which wavelengths of light are most effective in driving photosynthesis? (part 1: absorption spectra)
- Figure 8.9b Inquiry: which wavelengths of light are most effective in driving photosynthesis? (part 2: action spectrum)
- Figure 8.9c Inquiry: which wavelengths of light are most effective in driving photosynthesis? (part 3: Engelmann’s experiment)
- Figure 8.10 Structure of chlorophyll molecules in chloroplasts of plants
- Figure 8.11 Excitation of isolated chlorophyll by light
- Figure 8.11a Excitation of isolated chlorophyll by light (photo: fluorescence)
- Figure 8.12 The structure and function of a photosystem
- Figure 8.12a The structure and function of a photosystem (part 1)
- Figure 8.12b The structure and function of a photosystem (part 2)
- Figure 8.UN02 In-text figure, light reaction schematic, p. 164
- Figure 8.13-1 How linear electron flow during the light reactions generates ATP and NADPH (steps 1-2)
- Figure 8.13-2 How linear electron flow during the light reactions generates ATP and NADPH (step 3)
- Figure 8.13-3 How linear electron flow during the light reactions generates ATP and NADPH (steps 4-5)
- Figure 8.13-4 How linear electron flow during the light reactions generates ATP and NADPH (step 6)
- Figure 8.13-5 How linear electron flow during the light reactions generates ATP and NADPH (steps 7-8)
- Figure 8.14 A mechanical analogy for linear electron flow during the light reactions
- Figure 8.15 Comparison of chemiosmosis in mitochondria and chloroplasts
- Figure 8.15a Comparison of chemiosmosis in mitochondria and chloroplasts (detail)
- Figure 8.UN02 In-text figure, light reaction schematic, p. 164
- Figure 8.16 The light reactions and chemiosmosis: the organization of the thylakoid membrane
- Figure 8.16a The light reactions and chemiosmosis: the organization of the thylakoid membrane (part 1)
- Figure 8.16b The light reactions and chemiosmosis: the organization of the thylakoid membrane (part 2)
- Figure 8.UN03 In-text figure, Calvin cycle schematic, p. 168
- Figure 8.17-1 The Calvin cycle (step 1)
- Figure 8.17-2 The Calvin cycle (step 2)
- Figure 8.17-3 The Calvin cycle (step 3)
- Figure 8.18 C4 and CAM photosynthesis compared
- Figure 8.18a C4 and CAM photosynthesis compared (part 1: C4, sugarcane)
- Figure 8.18b C4 and CAM photosynthesis compared (part 2: CAM, pineapple)
- Figure 8.18c C4 and CAM photosynthesis compared (part 3: detail)
- Figure 8.19 A review of photosynthesis
- Figure 8.UN04 Skills exercise: making scatter plots with regression lines
- Figure 8.UN05 Summary of key concepts: the light reactions
- Figure 8.UN06 Summary of key concepts: the Calvin cycle
- Figure 8.UN07 Test your understanding, question 9 (thylakoid experiment)