Download AP Biology Photosynthesis Guided Notes

LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 10
Photosynthesis
Lectures by
Erin Barley
Kathleen Fitzpatrick
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Overview: The Process That Feeds the
Biosphere
• _______________is the process that converts
solar energy into chemical energy
• Directly or indirectly, photosynthesis __________
almost the entire living world
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• ______________ sustain themselves without
eating anything derived from other organisms
• Autotrophs are the producers of the biosphere,
producing ____________________ from CO2
and other inorganic molecules
• Almost all plants are ____________________,
using the energy of sunlight to make organic
molecules
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• Photosynthesis occurs in __________________,
certain other __________, and some __________
• These organisms feed not only themselves but
also most of the living world
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Figure 10.2
(b) Multicellular
alga
(a) Plants
(d) Cyanobacteria
(c) Unicellular
protists
10 m
(e) Purple sulfur
1 m
bacteria
40 m
• ________________ obtain their organic
material from other organisms
• Heterotrophs are the _________________ of
the biosphere
• Almost all heterotrophs, including humans,
depend on photoautotrophs for _____________
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• The Earth’s supply of ________________ was
formed from the remains of organisms that died
hundreds of millions of years ago
• In a sense, fossil fuels represent stores of
__________________ from the distant past
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Concept 10.1: Photosynthesis converts
light energy to the chemical energy of food
• ____________________ are structurally
similar to and likely evolved from
photosynthetic bacteria
• The ___________________________ of these
cells allows for the chemical reactions of
photosynthesis
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Chloroplasts: The Sites of Photosynthesis
in Plants
• __________________ are the major locations
of photosynthesis
• Their green color is from _________________,
the green pigment within chloroplasts
• Chloroplasts are found mainly in cells of the
_______________, the interior tissue of the leaf
• Each mesophyll cell contains ____________
chloroplasts
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• CO2 enters and O2 exits the leaf through
microscopic pores called _________________
• The chlorophyll is in the membranes of
_______________ (connected sacs in the
chloroplast); thylakoids may be stacked in
columns called grana
• Chloroplasts also contain ____________, a
dense interior fluid
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Figure 10.4a
Leaf cross section
Chloroplasts Vein
Mesophyll
Stomata
Chloroplast
CO2
O2
Mesophyll
cell
20 m
Figure 10.4b
Chloroplast
Thylakoid
Stroma Granum Thylakoid
space
1 m
Outer
membrane
Intermembrane
space
Inner
membrane
Tracking Atoms Through Photosynthesis:
Scientific Inquiry
• Photosynthesis is a complex series of reactions
that can be summarized as the following
equation:
___________________________________________
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The Splitting of Water
• Chloroplasts split ________ into hydrogen and
oxygen, incorporating the electrons of hydrogen
into ______________ molecules and releasing
______________ as a by-product
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Figure 10.5
Reactants:
Products:
6 CO2
C6H12O6
12 H2O
6 H2O
6 O2
Photosynthesis as a Redox Process
• Photosynthesis ________________ the
direction of electron flow compared to respiration
• Photosynthesis is a redox process in which
______ is oxidized and __________ is reduced
• Photosynthesis is an ______________ process;
the energy boost is provided by light
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Figure 10.UN01
becomes reduced
Energy  6 CO2  6 H2O
C6 H12 O6  6 O2
becomes oxidized
The Two Stages of Photosynthesis:
A Preview
• Photosynthesis consists of the
______________ (the photo part) and
________________ (the synthesis part)
• The light reactions (in the thylakoids)
–
–
–
–
____________________
Release __________
Reduce ___________ to NADPH
Generate ATP from ADP by
_______________________________
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• The ____________________ (in the stroma)
forms sugar from CO2, using ATP and NADPH
• The Calvin cycle begins with
__________________________, incorporating
CO2 into organic molecules
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Figure 10.6-4
CO2
H2O
Light
NADP
ADP
+ Pi
Light
Reactions
Calvin
Cycle
ATP
NADPH
Chloroplast
O2
[CH2O]
(sugar)
Concept 10.2: The light reactions convert
solar energy to the chemical energy of
ATP and NADPH
• ______________ are solar-powered chemical
factories
• Their thylakoids transform light energy into the
chemical energy of _________ and __________
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The Nature of Sunlight
• Light is a form of electromagnetic energy, also
called _________________________________
• Like other electromagnetic energy, light travels in
rhythmic _______________
• ________________ is the distance between
crests of waves
• _________________ determines the type of
electromagnetic energy
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• The _____________________ is the entire
range of electromagnetic energy, or radiation
• ________________________ 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 ___________________
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Figure 10.7
105
nm 103 nm
103
1 nm
Gamma
X-rays
rays
UV
nm
1m
(109 nm)
106 nm
Infrared
Microwaves
103 m
Radio
waves
Visible light
380
450
500
Shorter wavelength
Higher energy
550
600
650
700
750 nm
Longer wavelength
Lower energy
Photosynthetic Pigments: The Light
Receptors
• ________________are substances that absorb
visible light
• Different pigments absorb different __________
• Wavelengths that are not absorbed are
_____________ or _________________
• Leaves appear green because chlorophyll
______________ and ______________ green
light
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Figure 10.8
Light
Reflected
light
Chloroplast
Absorbed
light
Granum
Transmitted
light
• A _____________________ measures a
pigment’s ability to absorb various wavelengths
• This machine sends light through pigments and
measures the fraction of light _____________ at
each wavelength
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Figure 10.9
TECHNIQUE
Refracting Chlorophyll Photoelectric
solution
tube
White prism
Galvanometer
light
Slit moves to
pass light
of selected
wavelength.
Green
light
High transmittance
(low absorption):
Chlorophyll absorbs
very little green light.
Blue
light
Low transmittance
(high absorption):
Chlorophyll absorbs
most blue light.
• An _____________________ is a graph plotting
a pigment’s light absorption versus wavelength
• The absorption spectrum of _______________
suggests that violet-blue and red light work best
for photosynthesis
• An ____________________ profiles the relative
effectiveness of different wavelengths of
radiation in driving a process
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(a) Absorption
spectra
(b) Action spectrum
Absorption of light by
chloroplast pigments
RESULTS
Rate of photosynthesis
(measured by O2 release)
Figure 10.10
Chlorophyll a
Chlorophyll b
Carotenoids
400
500
600
Wavelength of light (nm)
400
500
600
700
700
Aerobic bacteria
Filament
of alga
(c) Engelmann’s
experiment
400
500
600
700
• The action spectrum of photosynthesis was first
demonstrated in 1883 by Theodor W.
_______________
• In his experiment, he exposed different segments
of a filamentous alga to different wavelengths
• Areas receiving wavelengths favorable to
photosynthesis produced excess _______
• He used the growth of aerobic bacteria clustered
along the alga as a measure of O2 production
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• _________________ is the main photosynthetic
pigment
• Accessory pigments, such as ______________,
broaden the spectrum used for photosynthesis
• Accessory pigments called _______________
absorb excessive light that would damage
chlorophyll
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Figure 10.11
CH3
CH3 in chlorophyll a
CHO in chlorophyll b
Porphyrin ring
Hydrocarbon tail
(H atoms not shown)
Excitation of Chlorophyll by Light
• When a pigment absorbs light, it goes from a
____________ state to an _____________
state, which is unstable
• When excited electrons fall back to the ground
state, photons are given off, an afterglow called
____________________
• If illuminated, an isolated solution of chlorophyll
will fluoresce, giving off _________________
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Figure 10.12
Energy of electron
e
Excited
state
Heat
Photon
(fluorescence)
Photon
Chlorophyll
molecule
Ground
state
(a) Excitation of isolated chlorophyll molecule
(b) Fluorescence
A Photosystem: A Reaction-Center Complex
Associated with Light-Harvesting
Complexes
• A ________________ consists of a
______________ _______________ (a type of
protein complex) surrounded by light-harvesting
complexes
• The ___________________________ (pigment
molecules bound to proteins) transfer the energy
of photons to the reaction center
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Figure 10.13a
Photosystem
Lightharvesting
complexes
Thylakoid membrane
Photon
Reactioncenter
complex
STROMA
Primary
electron
acceptor
e
Transfer
of energy
Pigment
Special pair of
molecules
chlorophyll a
molecules
THYLAKOID SPACE
(INTERIOR OF THYLAKOID)
(a) How a photosystem harvests light
Thylakoid membrane
Figure 10.13b
Chlorophyll
Protein
subunits
(b) Structure of photosystem II
STROMA
THYLAKOID
SPACE
• A _____________________________ in the
reaction center accepts excited electrons and is
reduced as a result
• Solar-powered transfer of an electron from a
_____________________ molecule to the
_________________________ is the first step
of the light reactions
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• There are _______ types of photosystems in the
thylakoid membrane
• _____________________ functions first (the
numbers reflect order of discovery) and is best at
absorbing a wavelength of ______________
• The reaction-center chlorophyll a of PS II is
called ____________
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• ____________________ is best at absorbing a
wavelength of ________________
• The reaction-center chlorophyll a of PS I is
called _______________
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Linear Electron Flow
• During the light reactions, there are two possible
routes for electron flow: ________ and _______
• ________________________, the primary
pathway, involves both photosystems and
produces ATP and NADPH using light energy
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• A photon hits a pigment and its energy is passed
among pigment molecules until it excites ______
• An excited electron from P680 is transferred to
the _________________________________
(we now call it ___________)
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• P680+ is a very strong ______________ agent
• __________ is split by enzymes, and the electrons
are transferred from the hydrogen atoms to P680+,
thus reducing it to P680
• ____________ is released as a by-product of this
reaction
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• Each electron “__________” down an electron
transport chain from the primary electron
acceptor of PS II to PS I
• Energy released by the fall drives the creation of
a _______________ across the thylakoid
membrane
• Diffusion of H+ (protons) across the membrane
drives __________________
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• In _________ (like PS II), transferred light
energy excites P700, which loses an electron to
an electron acceptor
• ____________ (P700 that is missing an
electron) accepts an electron passed down from
PS II via the electron transport chain
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• Each electron “falls” down an electron transport
chain from the primary electron acceptor of PS I
to the protein _____________
• The electrons are then transferred to
_____________ and reduce it to __________
• The electrons of NADPH are available for the
reactions of the ______________ cycle
• This process also removes an _____ from the
stroma
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Figure 10.14-5
4
Primary
acceptor
2
H
+
1/ O
2
2
H2O
e
2
Primary
acceptor
e
Pq
7
Fd
e 
e
Cytochrome
complex
8
NADP
reductase
3
Pc
e
e
P700
5
P680
Light
1 Light
6
ATP
Pigment
molecules
Photosystem II
(PS II)
Photosystem I
(PS I)
NADP
+ H
NADPH
Figure 10.15
e
e
e
e
Mill
makes
ATP
e
NADPH
e
e
ATP
Photosystem II
Photosystem I
Cyclic Electron Flow
• ___________________ uses only photosystem
I and produces ATP, but not NADPH
• No _______________ is released
• Cyclic electron flow generates surplus _______,
satisfying the higher demand in the Calvin cycle
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Figure 10.16
Primary
acceptor
Primary
acceptor
Fd
Fd
Pq
NADP
reductase
Cytochrome
complex
NADPH
Pc
Photosystem I
Photosystem II
ATP
NADP
+ H
• Some organisms such as
____________________ have PS I but not PS II
• ____________________ is thought to have
evolved before linear electron flow
• Cyclic electron flow may protect cells from
______________________
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A Comparison of Chemiosmosis in
Chloroplasts and Mitochondria
• Chloroplasts and mitochondria generate ATP
by ________________, but use different
sources of energy
• Mitochondria transfer _________________
from food to ATP; chloroplasts transform
____________ into the chemical energy of ATP
• __________________ of chemiosmosis differs
between chloroplasts and mitochondria but also
shows similarities
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• In mitochondria, protons are pumped to the
_________________ and drive ATP synthesis
as they diffuse back into the mitochondrial matrix
• In chloroplasts, protons are pumped into the
________________ and drive ATP synthesis as
they diffuse back into the stroma
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Figure 10.17
Chloroplast
Mitochondrion
CHLOROPLAST
STRUCTURE
MITOCHONDRION
STRUCTURE
H
Intermembrane
space
Inner
membrane
Diffusion
Electron
transport
chain
Thylakoid
space
Thylakoid
membrane
ATP
synthase
Matrix
Stroma
ADP  P i
Key
[H ]
Higher
Lower [H ]
H
ATP
• _______________________ are produced on
the side facing the stroma, where the
______________________ takes place
• In summary, light reactions ________________
and increase the potential energy of electrons
by moving them from ____________________
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Figure 10.18
STROMA
(low H concentration)
Photosystem II
4 H+
Light
Cytochrome
complex
Photosystem I
Light
NADP
reductase
3
NADP + H
Fd
Pq
H2O
NADPH
Pc
2
1
THYLAKOID SPACE
(high H concentration)
1/
2
O2
+2 H+
4 H+
To
Calvin
Cycle
Thylakoid
membrane
STROMA
(low H concentration)
ATP
synthase
ADP
+
Pi
ATP
H+
Concept 10.3: The Calvin cycle uses the
chemical energy of ATP and NADPH to
reduce CO2 to sugar
• The _________________, like the citric acid
cycle, regenerates its starting material after
molecules enter and leave the cycle
• The cycle builds ___________ from smaller
molecules by using __________ and the
reducing power of electrons carried by
______________
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• Carbon enters the cycle as CO2 and leaves as
a sugar named ________________________
• For net synthesis of 1 G3P, the cycle must take
place ___________, fixing ___ molecules of
CO2
• The Calvin cycle has three phases
– _______________ (catalyzed by _________)
– _______________
– ____________________________________
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Figure 10.19-3
Input
(Entering one
CO2 at a time)
3
Phase 1: Carbon fixation
Rubisco
3 P
Short-lived
intermediate
P
6
P
3-Phosphoglycerate
P
3P
Ribulose bisphosphate
(RuBP)
6
ATP
6 ADP
3 ADP
3
Calvin
Cycle
6 P
P
1,3-Bisphosphoglycerate
ATP
6 NADPH
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
6 NADP
6 Pi
P
5
G3P
6
P
Glyceraldehyde 3-phosphate
(G3P)
1
P
G3P
(a sugar)
Output
Glucose and
other organic
compounds
Phase 2:
Reduction
Concept 10.4: Alternative mechanisms of
carbon fixation have evolved in hot, arid
climates
• _________________ is a problem for plants,
sometimes requiring trade-offs with other
metabolic processes, especially photosynthesis
• On hot, dry days, plants close ________, which
conserves _____ but also limits _____________
• The closing of stomata reduces access to
______ and causes __________ to build up
• These conditions favor an apparently wasteful
process called __________________________
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Photorespiration: An Evolutionary Relic?
• In most plants (_____________), initial fixation
of CO2, via ____________, forms a
___________ compound (3-phosphoglycerate)
• In photorespiration, rubisco adds ____ instead
of _____ in the Calvin cycle, producing a
______________ compound
• Photorespiration consumes ____ and
______________ and releases ______ without
producing ATP or sugar
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• 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
• In many plants, photorespiration is a problem
because on a hot, dry day it can drain as much
as ______ of the carbon fixed by the Calvin cycle
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C4 Plants
• ______________ minimize the cost of
photorespiration by incorporating CO2 into
______________ compounds in mesophyll cells
• This step requires the enzyme _____________
• PEP carboxylase has a higher affinity for _____
than rubisco does; it can __________ even
when CO2 concentrations are low
• These four-carbon compounds are exported to
______________, where they release ______
that is then used in the Calvin cycle
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Figure 10.20
The C4 pathway
C4 leaf anatomy
Mesophyll
cell
PEP carboxylase
Mesophyll cell
Photosynthetic
cells of C4
Bundleplant leaf
sheath
cell
Oxaloacetate (4C)
Vein
(vascular tissue)
PEP (3C)
ADP
Malate (4C)
Stoma
Bundlesheath
cell
CO2
ATP
Pyruvate (3C)
CO2
Calvin
Cycle
Sugar
Vascular
tissue
• In the last 150 years since the Industrial
Revolution, _________ levels have risen greatly
• Increasing levels of CO2 may affect C3 and C4
plants differently, perhaps changing the
______________________ of these species
• The effects of such changes are unpredictable
and a cause for concern
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CAM Plants
• Some plants, including ________________, use
_______________________________ to fix
carbon
• ________________ open their stomata at night,
incorporating CO2 into organic acids
• ________________ close during the _______,
and CO2 is released from organic acids and
used in the Calvin cycle
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Figure 10.21
Sugarcane
Pineapple
C4
Mesophyll Organic acid
cell
CAM
CO2
1 CO2 incorporated
(carbon fixation) Organic acid
Calvin
Cycle
Night
CO2
CO2
Bundlesheath
cell
CO2
2 CO2 released
to the Calvin
cycle
Sugar
(a) Spatial separation of steps
Calvin
Cycle
Day
Sugar
(b) Temporal separation of steps
The Importance of Photosynthesis: A Review
• The energy entering chloroplasts as sunlight gets
stored as _____________________________
• Sugar made in the chloroplasts supplies chemical
energy and carbon skeletons to synthesize the
organic molecules of cells
• Plants store excess sugar as _________ in
structures such as ________________________
• In addition to food production, photosynthesis
produces the _____ in our atmosphere
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