Photosynthesis - Maria Regina High School
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Transcript Photosynthesis - Maria Regina High School
THE PROCESS THAT FEEDS THE BIOSPHERE
Solar energy (λ) → ___ → Glucose
Photosynthesis –the process by which green plants convert the sun’s
energy to organic compounds
light
6 CO2 + 6 H2O
→ C6H12O6 + 6 O2
chlorophyll
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
REQUIREMENTS FOR
PHOTOSYNTHESIS
REQUIREMENT
CO2
H 2O
Chlorophyll
Light
Enzymes
Chloroplasts
Minerals
USE
LEAF CROSS-SECTION
THE PROPERTIES OF LIGHT
Sir Isaac Newton
prism
prism
visible light → spectrum → white light
“light is a stream of particles or corpuscles”
James Maxwell - electromagnetic spectrum
“light travels in waves”
Fig. 10-6
10–5 nm 10–3 nm
103 nm
1 nm
Gamma
X-rays
rays
UV
106 nm
Infrared
1m
(109 nm)
Microwaves
103 m
Radio
waves
Visible light
380
450
500
Shorter wavelength
Higher energy
550
600
650
700
750 nm
Longer wavelength
Lower energy
Fig. 10-1
1900 – The Photoelectric Effect
light
zinc
Zn+ + e-
Every metal has a critical λ for effect to occur.
K, Na + Se → critical λ = visible light λ
Therefore, light → electrical energy
brightness is not a factor
Ex. Motion detectors
1905 – Albert Einstein
Light = particles of energy = photons
E of photon = 1
λ
Therefore, violet light has 2x more E
than red light.
Biological Activities
The following activities depend on the sun’s
λ of light:
1. Phototropisms
visible
2. Vision
light’s
3. Spawning of Palolo worms
λ only
4. Photosynthesis
Chlorophyll – absorbs the energy from the
sun
CHLOROPHYLL
Chlorophyll – plant pigment which absorbs
violet, blue, and red λ’s of light
* Green is reflected
PLANT PIGMENTS
Chl a C55H72O5N4Mg
Chl b C55H70O6N4Mg
made of Mg in a
porphoryn ring
Carotenoids – red, orange, yellow
Zanthophylls – red, violet
Found in thylakoid
membrane of chloroplasts.
MECHANISM OF PHOTOSYNTHESIS
1905 F.F. Blackman
Rate
Of
Photo
rate
of
photo
Light Int.
Temp (°C)
Conclusions
1. Light dependent reactions – temp
independent
2. Temp. dependent reactions – enzyme
controlled
THE SOURCE OF OXYGEN
C.B. Van Neill
Plant photosynthesis:
CO2 + H2O → Organic cmpds + O2
Bacterial Chemosynthesis
CO2 + H2S → Organic cmpds + S
Therefore,
O2 comes from ________
HOW IS THAT POSSIBLE?
6 CO2 + 6 H2O → C6H12O6 + 6 O2
IT IS NOT POSSIBLE
INSTEAD
6 CO2 + 12 H2O → C6H12O6 + 6 O2 + 6 H20
THE LIGHT REACTIONS
1.
2.
3.
4.
Light strikes chlorophyll – e are boosted to
higher energy levels
H2O is split - replaces e for chlorophyll
- O2 is released
- H atoms are attached to NADP
Energy produces ATP (by chemiosmosis) and
NADPH2
Occurs in the grana of the chloroplasts
THE DARK REACTIONS
Carbon Fixation – the attachment of H
atoms to CO2 to produce organic
compounds (glucose)
1. Enzyme controlled – temp. dependent
2. Occurs by the Calvin Cycle in the
stroma
6 CO2 + 8 ATP + 12 NADPH2 → C6H12O6
Electron Flow
Water → Photo II → Photo I → NADP
Energy production
1. ATP – produced by chemiosmosis
= photophosphoryllation
2. NADPH2 - needed for reduction of
CO2
TRAPPING THE SUN’S ENERGY
Photosystems – units of chlorophyll
molecules and other pigments
(antenna molecules) in the thylakoids
each unit = 250-400 molecules
1. Photosystem I – P700
2. Photosystem II – P680
CYCLIC ELECTRON FLOW
Process used by photosynthetic
eukaryotic cells to produce ATP
(purple-sulfer bacteria)
1. No NADPH is produced
2. No O2 is produced
3. No CO2 is reduced
e from Photo I → e acceptor → e
transport of Photo II → P 700 of Photo I
THE DARK REACTIONS
1. Carbon Fixation
RUBISCO
CO2 + RuBP
→
3-phosphoglycerate
2. Reduction of 3-phosphoglycerate to
G3P
3. Regeneration of RuBP from G3P
THE 3-CARBON PATHWAY
CH2-O-P
C=O
CHOH
CHOH
CH2-O-P
CO2 + H20
RuBisco
Ribulose Biphosphate
RuBP
2
CH2-O-P
CHOH
C=O
O¯
Phosphoglycerate
PGA
Fig. 10-18-3
Input 3
(Entering one
at a time)
CO2
Phase 1: Carbon fixation
Rubisco
3 P
Short-lived
intermediate
P
6
P
3-Phosphoglycerate
3P
P
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
Output
P
G3P
(a sugar)
Glucose and
other organic
compounds
Phase 2:
Reduction
THE CALVIN CYCLE
6 RuBP + 6 CO2 + 18 ATP + 12 NADPH + 12
H+ + 12 H2O → 6 RuBP + C6H12O6 + 18 Pi
+ 18 ADP + 12 NADP+
1 cycle → uses 1 CO2 + produces 1 RuBP
3 cycles → uses 3 CO2 + produces 1 G3P
+ 3 RuBP
6 cycles → uses 6 CO2 + produces 2 G3P →
Glucose + 6 RuBP
Photorespiration: An Evolutionary Relic?
Photorespiration – the break down of
carbohydrates, in the presence of
oxygen, without producing ATP
1. CO2 is released (for Calvin cycle)
2. Rubisco attaches to O2 instead of CO2
3. Rate of photosynthesis decreases
In photorespiration, rubisco adds O2
instead of CO2 into the Calvin cycle –
produces glycolic acid
THE 4-CARBON PATHWAY
COO
COOH
C-O-P CO2 + H20
C=O
CH2 PEP carboxylase CH2
COOH
PEP
Malic acid
or
aspartic acid
Oxaloacetic acid
Malic acid → to bundle sheath cells → decarboxylated to
ATP
CO2 +
pyruvic acid
→ PEP
to Calvin cycle in bundle sheath cells.
WHY?
Advantages of C-4 pathway
Separates the capture of CO2 from
Calvin cycle
2. Utilizes CO2 faster (due to PEP)
3. Maximizes CO2 gradient
4. Less photorespiration occurs
- PEP has a low affinity for O2
Disadvantage – more ATP is used to
produce glucose
C-4 plants = sugar cane, corn, weeds
1.
CAM PLANTS = succulents
Succulent plants – use crassulacean acid
metabolism to fix CO2
Stomates open at night
2. CO2 is converted into organic acids
3. Stomates close during the day – release CO2
for Calvin Cycle
* note: C-4 Plants and CAM Plants both produce
sugars through the Calvin cycle
1.
Fig. 10-20
Sugarcane
Pineapple
C4
CAM
CO2
Mesophyll
cell
Organic acid
Bundlesheath
cell
CO2
1 CO2 incorporated
into four-carbon Organic acid
organic acids
(carbon fixation)
CO2
Calvin
Cycle
CO2
2 Organic acids
release CO2 to
Calvin cycle
Night
Day
Calvin
Cycle
Sugar
Sugar
(a) Spatial separation of steps
(b) Temporal separation of steps
Fig. 10-3a
Leaf cross section
Vein
Mesophyll
Stomata
Chloroplast
CO2
O2
Mesophyll cell
5 µm
Fig. 10-3b
Chloroplast
Outer
membrane
Thylakoid
Stroma
Granum
Thylakoid
space
Intermembrane
space
Inner
membrane
1 µm
Fig. 10-5-4
CO2
H2O
Light
NADP+
ADP
+ P
i
Light
Reactions
Calvin
Cycle
ATP
NADPH
Chloroplast
O2
[CH2O]
(sugar)
Fig. 10-10
CH3
CHO
in chlorophyll a
in chlorophyll b
Porphyrin ring:
light-absorbing
“head” of molecule;
note magnesium
atom at center
Hydrocarbon tail:
interacts with hydrophobic
regions of proteins inside
thylakoid membranes of
chloroplasts; H atoms not
shown
Concept 10.4: Alternative mechanisms of carbon
fixation have evolved in hot, arid climates
• Dehydration is a problem for 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 a seemingly wasteful
process called photorespiration
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 10-19
The C4 pathway
C4 leaf anatomy
Mesophyll
cell
Mesophyll cell
CO2
PEP carboxylase
Photosynthetic
cells of C4
Bundleplant leaf
sheath
cell
Oxaloacetate (4C)
Vein
(vascular tissue)
PEP (3C)
ADP
Malate (4C)
Stoma
Bundlesheath
cell
ATP
Pyruvate (3C)
CO2
Calvin
Cycle
Sugar
Vascular
tissue
Fig. 10-19b
The C4
pathway
Mesophyll
cell
PEP carboxylase
Oxaloacetate (4C)
PEP (3C)
ADP
Malate (4C)
Bundlesheath
cell
CO2
ATP
Pyruvate (3C)
CO2
Calvin
Cycle
Sugar
Vascular
tissue
Fig. 10-21
H2O
CO2
Light
NADP+
ADP
+ P
i
Light
Reactions:
Photosystem II
Electron transport chain
Photosystem I
Electron transport chain
RuBP
ATP
NADPH
3-Phosphoglycerate
Calvin
Cycle
G3P
Starch
(storage)
Chloroplast
O2
Sucrose (export)
You should now be able to:
1. Describe the structure of a chloroplast
2. Describe the relationship between an action
spectrum and an absorption spectrum
3. Trace the movement of electrons in linear
electron flow
4. Trace the movement of electrons in cyclic
electron flow
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
5. Describe the similarities and differences
between oxidative phosphorylation in
mitochondria and photophosphorylation in
chloroplasts
6. Describe the role of ATP and NADPH in the
Calvin cycle
7. Describe the major consequences of
photorespiration
8. Describe two important photosynthetic
adaptations that minimize photorespiration
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
CELL ENERGY TABLE
PROCESS
RESPIRATION
GLYCOLYSIS
KREBS CYCLE
ETS
ALC FERM
LACTIC ACID FERM
PHOTOSYNTHESIS
LIGHT REACTIONS
DARK REACTIONS
SITE
INPUTS
PRODUCTS
CHEMIOSMOSIS
CHEMIOSMOSIS IN
MITOCHONDRIA
Diagram the membrane
system involved. Show
ETS pumping H and H+
moving through the ATP
ase
Where do the hydrogens
come from before they
enter the ETS
CHEMIOSMOSIS IN
CLOROPLAST