Transcript Document

Photosynthesis
Converting Light Energy to
Chemical Energy
Photosynthesis Is an Endergonic Reaction
Energy
Supplied
O
+
O O
H
+
O C O
O
OH
6 CO2
+ 6 H2O
H
CH2OH
O
glucose
(C6H12O6)
+ energy =
+ 6 O2
Photosynthesis Occurs in Chloroplasts
of Leaf Mesophyll Cells
Leaf Structure
Upper Epidermis
Mesophyll
Cells
Vein
Stoma
Lower
Epidermis
Chloroplast
Structure
Thylakoids
(contain pigments)
Stroma
(interior matrix)
Granum
(stack of thylakoids)
Inner & Outer
Membranes
Light, Chloroplast Pigments, &
Photosynthesis
Gamma Rays
X-Rays UV
Infrared Microwaves
Radio
Waves
Visible Light
400
450
500
550
600
650
7000
Wavelength (nanometers)
750
Visible Light
450
500
550
600
Chlorophyll
650
700
Collectively
750
100
80
60
Carotenoids
20
Phycocyanin
400
450
500
550
600
650
Wavelength (nanometers)
40
700
0
750
% Light Absorption
400
Photosynthetic Pigments
• Chlorophyll
– major photosynthetic pigment
– absorbs violet, blue, red wavelengths,
reflects green
• Accessory Pigments
– Carotenoids
• absorb blue and green,
reflect yellow
– Phycocyanins
• absorb green and yellow,
reflect blue
Photosynthesis Involves
Two Sets of Reactions
Light-Dependent
Reactions
O2
H2O
(in thylakoids)
Depleted
Carriers
Energized
Carriers
(ADP, NADP+)
Glucose
(ATP, NADPH)
Light-Independent
Reactions
(in stroma)
CO2+H2O
Light-Dependent Reactions
• Energy from light is used to form
– ATP: energy carrier
– NADPH: electron carrier
• Occur in photosystems located in
thylakoid membranes
– organized array of pigment molecules
– each photosystem contains
• light-harvesting complex, with reaction center
• electron transport system
Photosystems
II and I
Reach electron
carriers
Electrons
absorb energy
Absorbs light energy and transfers it to
Electron Flow in
Light-dependent
Reactions
Summary of
Light-Dependent
Reactions
Reactants
Water
+ energy + PO4
Products
½ O2
Protons (2H+)
Electrons (2e- )
ATP
+ 2e- + H+ 
NADPH
electron supplier
ADP
energy carrier
NADP+
electron carrier
Applying Your Knowledge
1.
2.
3.
4.
Photosystem I
Photosystem II
Both PS I and PS II
Neither PS I nor PS II
A. Where is ATP produced?
B. Which one contains an electron
transport system?
C. Where is NADPH produced?
Chemiosmosis Produces ATP
Chemiosmosis
Produces ATP
ATP is Produced by
Chemiosmosis
• Diffusion of hydrogen ions (H+ ) through
a differentially permeable membrane,
resulting in ATP production
– energy from electron transport pumps H+
to interior of thylakoid
– H+ diffuses to exterior through pores of
ATP-synthesizing enzyme
– movement of H+ provides energy for ATP
synthesis
Light-Independent Reactions
(C3 Photosynthesis Cycle)
• Produce Glucose (C6 H12O6) using CO2
as a carbon source
• Occur in stroma of chloroplast
• Use ATP and NADPH from LightDependent Reactions
• Six turns of the cycle produce one
glucose molecule
6-Carbon Compounds
form briefly
Cycle is named for
3-Carbon Compounds
The C3
Cycle of
Carbon
Fixation
C3 Photosynthesis Cycle
Carbon Dioxide C
X6
C
C
C
C
C
5-Carbon Reactants X 6
6 ADP
RUBISCO
6 ATP
Rearrangements
to reform 5C reactants
3-Carbon X 10
C
C
C
C
C
Glucose
6-Carbon Product
C
C
C
C
C
C
6-Carbon Intermediates X 6
C
C
C
C
C
C
3-Carbon Intermediates X 12
12 ADP
12 NADP+
C
3-Carbon X 2
C
C
C
12 ATP
12 NADPH
C
C
Modified 3-Carbon
Intermediates X 12
C
Summary of
Light-Independent
Reactions
CH2OH
O
O
OH
Reactants
Products
6 CO2
Glucose (C6 H12O6)
ATP
energy carrier
NADPH
ADP + PO4
+ energy (in bonds of glucose)
NADP+
+ 2e- + H+ (used in C3 reactions)
electron carrier
A Summary of Photosynthesis
Light-dependent
reactions occur
in thylakoids
Lightindependent
reactions (c3
cycle) occur in
stroma
Applying Your Knowledge
1.
2.
3.
4.
A.
B.
C.
D.
Light-Dependent Reactions
Light-Independent Reactions
Neither choice 1 nor 2
Both choices 1 and 2
Which reactions produce glucose? 2
Which reactions use water? 4
Which reactions release oxygen? 1
Which reactions use energy from ATP? 2
Adaptations to
Hot and Dry
Conditions
• Plants close leaf pores (stoma) to avoid losing
water at high temperatures
• Closed stoma prevent diffusion of CO2 into
leaf and diffusion of O2 out of leaf
• Excess O2 leads to photorespiration,
interferes with photosynthesis
• C4 Pathway is used to continue CO2
collection
C3 Plants & the C3 Pathway
C3 plants use the C3
pathway
In a C3 plant, most
chloroplasts are in
mesophyll cells.
C3 Plants & the C3 Pathway
RUBISCO
RUBISCO combines
with O2 instead of CO2
Much photorespiration
occurs under hot, dry
conditions
C4 Plants & the C4 Pathway
C4 plants use the C4
pathway
In a C4 plant, both
mesophyll & bundlesheath cells contain
chloroplasts.
Mesophyll cell in a C4 plant
CO2 is captured
with a highly
specific enzyme.
3C
4C
C4 Plants
& the C4
Pathway
RUBISCO
Much glucose
synthesis occurs.
Almost no
photorespiration
occurs under hot,
dry conditions.
Bundle-sheath cell in a C4 plant
Interconnections:
Photosynthesis & Respiration