Transcript Photosynthesis - Cathedral High School

BIOLOGY
Chapter 7: pp. 117-132
10th Edition
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CO2
H2 O
Insert figure 7.4 here
NADP+
Solar
energy
ADP + P
NADP+
Light
reactions
Calvin
Cycle
reactions
Sylvia S. Mader
Photosynthesis
NADP
ATP
thylakoid
membrane
thylakoid
membrane
O2
stroma
CH2O
PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor
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1
What is photosynthesis?
• Photosynthesis is the process by which
autotrophic organisms use light energy to make
sugar and oxygen gas from carbon dioxide and
water
Carbon
dioxide
Water
Glucose
PHOTOSYNTHESIS
Oxygen
gas
Photosynthesis Reaction
6 CO2 + 6 H2O + Light energy  C6H12O6 + 6 O2
4
Structure of the
Chloroplast
l Thylakoid – Saclike
photosynthetic
membranes
• Light-dependent
reactions occur here
l Granum – Stack of
thylakoids
l Stroma – Region
outside the
thylakoid
membrane
• Reactions of the
Calvin Cycle occur
here
5
Photosynthetic Reactions:
Two Sets of Reaction

Light Reaction – takes place only in the
presence of light




They are the energy-capturing reactions
Chlorophyll absorbs solar energy
This energizes electrons
Electrons move down electron transport chain



Pumps H+ into thylakoids
Used to make ATP out of ADP and NADPH out of NADP
Calvin Cycle Reaction takes place in stroma



CO2 is reduced to a carbohydrate
Use ATP and NADPH produced carbohydrate
They are synthetic reactions
11
Photosynthetic Pigments


Pigments:

Chemicals that absorb some colors in rainbow more
than others

Colors least absorbed reflected/transmitted most
Absorption Spectra

Pigments found in chlorophyll absorb various portions
of visible light

Graph showing relative absorption of the various colors
of the rainbow

Chlorophyll is green because it absorbs much of the
reds and blues of white light
7
The chlorophyll
absorbs the
sunlight.
Light
Chloroplast
Absorbed
light
Transmitted
light
Figure 7.6B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Reflected
light
CH3
Chlorophyll
CHO
in chlorophyll a
in chlorophyll b
Porphyrin ring:
light-absorbing
“head” of molecule;
note magnesium
atom at center
• Chlorophyll a
• Chlorophyll b
Hydrocarbon tail:
interacts with hydrophobic
regions of proteins inside
thylakoid membranes of
chloroplasts; H atoms not
shown
The Nature of Sunlight
• Light is a form of electromagnetic energy
• 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
Wavelength is the
distance between crests
of waves
Wavelength determines
the type of
electromagnetic energy
Photosynthetic Pigments
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Increasing wavelength
chlorophyll a
chlorophyll b
carotenoids
Gamma
rays
X rays
UV
Infrared
Micro- Radio
waves waves
visible light
500
600
Wavelengths (nm)
a. The electromagnetic spectrum includes visible light.
750
Relative Absorption
Increasing energy
380
500
600
750
Wavelengths (nm)
b. Absorption spectrum of photosynthetic pigments.
9
Photosynthesis Overview
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CO2
H2O
Solar
energy
ADP + P
NADP+
Light
reactions
Calvin
Cycle
reactions
NADP
ATP
stroma
thylakoid
membrane
O2
CH2O
12
Photosynthetic Reactions:
The Light Reactions


Light reactions consist of two alternate electron
pathways:

Noncyclic electron pathway

Cyclic electron pathway
Capture light energy with photosystems

Pigment complex helps collect solar energy like an
antenna

Occur in the thylakoid membranes

Both pathways produce ATP

The noncyclic pathway also produces NADPH
13
Light Reactions:
The Noncyclic Electron Pathway

Takes place in thylakoid membrane
 Uses two photosystems, PS-I and PS-II
 PS II captures light energy
 Causes an electron to be ejected from the
reaction center (chlorophyll a)





Electron travels down electron transport chain to PS-I
Replaced with an electron from water
Which causes H+ to concentrate in thylakoid chambers
Which causes ATP production
PS-I captures light energy and ejects an electron


Transferred permanently to a molecule of NADP+
Causes NADPH production
14
Light Reactions:
Noncyclic Electron Pathway
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H2O
CO2
solar
energy
ADP+
P
NADP+
sun
Light
reactions
Calvin
cycle
sun
NADPH
ATP
thylakoid
membrane
electron
acceptor
energy level
O2
CH2O
electron
acceptor
ee
e-
e
NADP+
H+
NADPH
e
e-
reaction center
reaction center
pigment
complex
pigment
complex
Photosystem I
e-
Photosystem II
CO2
H2 O
CH2O
Calvin cycle
reactions
2H+
1
2 O2
15
Light Reactions:
The Cyclic Electron Pathway

Uses only photosystem I (PS-I)

Begins when PS I complex absorbs solar energy

Electron ejected from reaction center


Travels down electron transport chain

Causes H+ to concentrate in thylakoid chambers

Which causes ATP production

Electron returns to PS-I (cyclic)
Pathway only results in ATP production
18
Organization of the Thylakoid Membrane

PS II:




Electron transport chain:




Consists of cytochrome complexes
Carries electrons between PS II and PS I
Also pump H+ from the stroma into thylakoid space
PS I:



Consists of a pigment complex and electron-acceptors
Adjacent to an enzyme that oxidizes water
Oxygen is released as a gas
Has a pigment complex and electron acceptors
Adjacent to enzyme that reduces NADP+ to NADPH
ATP synthase complex:


Has a channel for H+ flow
Which drives ATP synthase to join ADP and Pi
19
Organization of a Thylakoid
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H2O
CO2
solar
energy
P
ADP+
NADP+
Light
reactions
Calvin
cycle
NADP+ reactions
NADPH
ATP
NADP+
NADP+
thylakoid
membrane
thylakoid membrane
thylakoid space
stroma
thylakoid
CH2O
O2
granum
photosystem II
H+
electron transport
chain
stroma
photosystem I
NADP
reductase
H+
Pq
e-
NADP+
e- e
NADPH
eH+
H2O
2 H+
+
H+
1
2 O2
Thylakoid
space
ATP synthase
H+
H+
ATP
H+
H+
chemiosmosis
P +ADP
Stroma
20
ATP Production



Thylakoid space acts as a reservoir for hydrogen
ions (H+)
Each time water is oxidized, two H+ remain in the
thylakoid space
Electrons yield energy



Flow of H+ back across thylakoid membrane



Used to pump H+ across thylakoid membrane
Move from stroma into the thylakoid space
Energizes ATP synthase
Enzymatically produces ATP from ADP + Pi
This method of producing ATP is called
chemiosmosis
22
Light Dependent
Reactions
14
• The production of ATP by chemiosmosis in
photosynthesis = photophosphorylation
Thylakoid
compartment
(high H+)
Light
Light
Thylakoid
membrane
Antenna
molecules
Stroma
(low H+)
Figure 7.9
ELECTRON TRANSPORT
CHAIN
PHOTOSYSTEM II
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
PHOTOSYSTEM I
ATP SYNTHASE
BASIC DIAGRAM of LIGHT DEPENDENT REACTION
Reverse Process of Each Other
• Both create H+ gradient, allowing H+ to
diffuse through ATP synthase and ATP
production
• Oxidative phosphorylation O2 reduced to
H2O using electrons donated by NADH or
FADH2 (Respiration)
• Photophosphorylation just the reverse,
H2O oxidized to O2 with electrons
accepted (Photosynthesis)
Calvin Cycle Reactions:
Overview of C3 Photosynthesis

A cyclical series of reactions where ATP and NADPH
generated in light reactions used to fuel the
reactions which take CO2 and break it apart, then
reassemble the carbons into glucose

Utilizes atmospheric carbon dioxide to produce
carbohydrates

Known as C3 photosynthesis

Involves three stages:

Carbon dioxide fixation

Carbon dioxide reduction

RuBP regeneration
25
The Calvin Cycle
CO2
H2 O
Input
3 (Entering one
CO2 at a time)
Light
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
Phase 1: Carbon fixation
NADPH
Rubisco
O2
[CH2O] (sugar)
3 P
P
Short-lived
intermediate
3 P
P
6
P
Ribulose bisphosphate
(RuBP)
3-Phosphoglycerate
6
ATP
6 ADP
CALVIN
CYCLE
3 ADP
3
6 P
ATP
P
1,3-Bisphosphoglycerate
6 NADPH
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
6 NADP+
6 P
5
i
P
G3P
6
P
Glyceraldehyde-3-phosphate
(G3P)
1
P
G3P
(a sugar)
Output
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Glucose and
other organic
compounds
Phase 2:
Reduction
Calvin Cycle Reactions: Carbon Dioxide
Fixation


CO2 is attached to 5-carbon RuBP molecule

Result in a 6-carbon molecule

This splits into two 3-carbon molecules (3PG)

Reaction accelerated by RuBP Carboxylase (Rubisco)
CO2 now “fixed” because it is part of a
carbohydrate
26
The Calvin cycle: Carbon Fixation
H2 O
CO2
Input
3 (Entering one
CO2 at a time)
Light
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
Phase 1: Carbon fixation
NADPH
Rubisco
O2
[CH2O] (sugar)
3 P
P
Short-lived
intermediate
3 P
6
P
Ribulose bisphosphate
(RuBP)
P
3-Phosphoglycerate
6
6 ADP
CALVIN
CYCLE
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
ATP
Calvin Cycle Reactions: Carbon Dioxide
Reduction

3PG reduced to BPG

BPG then reduced to G3P

Utilizes NADPH and some ATP produced
in light reactions
28
Figure 10.18 The Calvin cycle
H2 O
CO2
Light
Input
3 (Entering one
CO2 at a time)
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
Phase 1: Carbon fixation
NADPH
O2
Rubisco
[CH2O] (sugar)
3 P
P
Short-lived
intermediate
3 P
P
Ribulose bisphosphate
(RuBP)
P
6
3-Phosphoglycerate
6
ATP
6 ADP
CALVIN
CYCLE
6 P
P
1,3-Bisphosphoglycerate
6 NADPH
6 NADP+
6 P
6
P
Glyceraldehyde-3-phosphate
(G3P)
P
1
G3P
(a sugar)
Output
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
i
Glucose and
other organic
compounds
Phase 2:
Reduction
The Calvin Cycle: Reduction of CO2
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
ATP
ADP +
3PG
P
BPG
NADPH
G3P
NADP+
As 3PG becomes G3P, ATP becomes
ADP +
P
and NADPH becomes NADP+
29
Calvin Cycle Reactions:
Regeneration of RuBP

RuBP used in CO2 fixation must be replaced

Every three turns of Calvin Cycle,

Five G3P (a 3-carbon molecule) used

To remake three RuBP (a 5-carbon molecule)

5X3=3X5
30
The Calvin Cycle: Regeneration of RuBP
CO2
H2 O
Input
3 (Entering one
CO2 at a time)
Light
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
Phase 1: Carbon fixation
NADPH
Rubisco
O2
[CH2O] (sugar)
3 P
P
Short-lived
intermediate
3 P
P
6
P
Ribulose bisphosphate
(RuBP)
3-Phosphoglycerate
6
ATP
6 ADP
CALVIN
CYCLE
3 ADP
3
6 P
ATP
P
1,3-Bisphosphoglycerate
6 NADPH
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
6 NADP+
6 P
5
i
P
G3P
6
P
Glyceraldehyde-3-phosphate
(G3P)
1
P
G3P
(a sugar)
Output
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Glucose and
other organic
compounds
Phase 2:
Reduction
The Calvin Cycle: Regeneration of RuBP
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
5 G3P
3 ATP
3 RuBP
3 ADP + P
As five molecules of G3P become three
molecules of RuBP, three molecules of ATP
become three molecules of ADP + P .
31
Importance of Calvin Cycle

G3P (glyceraldehyde-3-phosphate) can be
converted to many other molecules

The hydrocarbon skeleton of G3P can form

Fatty acids and glycerol to make plant oils

Glucose phosphate (simple sugar)

Fructose (which with glucose = sucrose)

Starch and cellulose

Amino acids
32
Fig. 10-5-1
H2O
Light
NADP+
ADP
+ P
Light
Reactions
Chloroplast
i
Fig. 10-5-2
H2O
Light
NADP+
ADP
+ P
i
Light
Reactions
ATP
NADPH
Chloroplast
O2
Fig. 10-5-3
CO2
H2O
Light
NADP+
ADP
+ P
i
Light
Reactions
ATP
NADPH
Chloroplast
O2
Calvin
Cycle
Fig. 10-5-4
CO2
H2O
Light
NADP+
ADP
+ P
i
Light
Reactions
Calvin
Cycle
ATP
NADPH
Chloroplast
O2
[CH2O]
(sugar)
The Two Stages of Photosynthesis
A Review
• Photosynthesis consists of the light reactions (the photo
part) and Calvin cycle (the synthesis part)
• The Calvin cycle (in the
• The light reactions (in the
stroma) forms sugar from
thylakoids):
CO2, using ATP and
– Split H2O
NADPH
– Release O2
– Reduce NADP+ to NADPH • The Calvin cycle begins
with carbon fixation,
– Generate ATP from ADP by
incorporating CO2 into
photophosphorylation
organic molecules
C4 Photosynthesis

In hot, dry climates





Stomata must close to avoid wilting
CO2 decreases and O2 increases
O2 starts combining with RuBP instead of CO2
Photorespiration, a problem solve in C4 plants
In C4 plants



Fix CO2 to PEP a C3 molecule
The result is oxaloacetate, a C4 molecule
In hot & dry climates



Avoid photorespiration
Net productivity about 2-3 times C3 plants
In cool, moist, can’t compete with C3
36
CO2 Fixation in C4 vs. C3 Plants
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
CO2
RuBP
Calvin
cycle
3PG
G3P
mesophyll cell
a. CO2 fixation in a C3 plant, blue columbine, Aquilegia caerulea
CO2
mesophyll
C4
cell
bundle
sheath
cell
CO2
Calvin
cycle
G3
b. CO2 fixation in a C4 plant, corn, Zea mays
b: © Nigel Cattlin/Photo Researchers, Inc.
38
• Some plants have special adaptations that
enable them to save water
– Special cells in C4
plants—corn and
sugarcane—incorporate
CO2 into a four-carbon
molecule
4-C compound
– PEP carboxylase
– This molecule can then
donate CO2 to the
Calvin cycle
CALVIN
CYCLE
Figure 7.12B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
3-C sugar
CAM Photosynthesis

Crassulacean-Acid Metabolism

CAM plants partition carbon fixation by time


During the night

CAM plants fix CO2

Forms C4 molecules,

Stored in large vacuoles
During daylight

NADPH and ATP are available

Stomata closed for water conservation

C4 molecules release CO2 to Calvin cycle
39
• The CAM plants—pineapples, most cacti, and
succulents—employ a different mechanism
– They open their stomata
at night and make a
four-carbon compound
4-C compound
Night
Day
CALVIN
CYCLE
3-C sugar
Figure 7.12C
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
CO2 Fixation in a CAM Plant
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
night
CO2
C4
day
CO2
Calvin
cycle
G3P
CO2 fixation in a CAM plant, pineapple, Ananas comosus
© S. Alden/PhotoLink/Getty Images.
40
Climatic Adaptation: Photosynthesis

Each method of photosynthesis has
 Advantages and disadvantages
 Depends on the climate
 C4 plants most adapted to:

High light intensities



C3 plants better adapted to



High temperatures
Limited rainfall
Cold (below 25°C)
High moisture
CAM plants better adapted to extreme aridity


CAM occurs in 23 families of flowering plants
Also found among nonflowering plants
42