1. Photosynthesis Photosynthesis = Capturing Solar Energy
Interconnection of photosynthesis & cellular respiration
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2. Photosynthesis Occurs in Chloroplasts of Some Leaf Cells cuticle upper
Leaves
Photosynthesis
Internal leaf structure
cuticle
upper
epidermis
mesophyll
cells
stoma
lower epidermis
chloroplasts
Figure :7-2
Title:
An overview of photosynthetic structures
Caption:
(a) Photosynthesis occurs primarily in the leaves of land plants. (b) A section of a leaf, showing mesophyll cells where chloroplasts are concentrated and the waterproof cuticle that coats the leaf's upper epidermis. (c) A single chloroplast, showing the stroma and thylakoids where photosynthesis occurs.
Chloroplast in mesophyll cell
bundle sheath
outer membrane
vascular bundle
(vein)
inner membrane
thylakoid
stroma
Occurs in Chloroplasts
of Some Leaf Cells
granum
(stack of
thylakoids)
channel interconnecting thylakoids

3. Photosynthesis? Photosynthesis Consists of: Light-Dependent Reactions
Light-Independent Reactions
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4. LIGHT-DEPENDENT REACTIONS (thylakoids) H2O O2 depleted carriers
(ADP, NADP+)
energized
carriers
(ATP, NADPH)
Figure: 7-UN1
Title:
Overview of Photosynthesis
Caption:
In light-dependent reactions, chlorophyll and other molecules embedded in the membranes of the thylakoids capture sunlight energy and convert some of it into the chemical energy stored in energy-carrier molecules (ATP and NADPH). Oxygen gas is released as a by-product. In light-independent reactions, enzymes in the stroma use the chemical energy of the carrier molecules to drive the synthesis of glucose or other organic molecules.
LIGHT-INDEPENDENT
REACTIONS
(stroma)
CO2 + H2O
glucose

5. Light Captured by Chloroplast Pigments in Thylakoid Membrane
Light-Dependent Reactions Convert Light Energy to Chemical Energy I. Light Capture
Light Captured by Chloroplast Pigments in Thylakoid Membrane
Thylakoid Membrane, Thylakoid Space
Light, chloroplast pigments, and photosynthesis (F7.3 p. 118)
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6. within thylakoid membrane
thylakoids
chloroplast
within thylakoid membrane
Figure: 7-UN2
Title:
Electron Transport Chain
ETC
PS II
ETC
PS I r
eaction centers

7. chlorophyll b carotenoids chlorophyll Visible light ("rainbow colors")
Micro-
waves
Radio
waves
Gamma rays
X-rays UV
Infrared
Visible light
400
450
500
550
600
650
700
750
Wavelength (nanometers)
Absorbance of photosynthetic pigments
100
chlorophyll b 80
Figure :7-3
Title:
Light, chloroplast pigments, and photosynthesis
Caption:
(a) Visible light, a small part of the electromagnetic spectrum (top line), consists of wavelengths that correspond to the colors of the rainbow. (b) Chlorophyll (blue and green curves) strongly absorbs violet, blue, and red light. Carotenoids (orange curve) absorb blue and green wavelengths. Question Based on the information in this graph, what color are carotenoids? What color is phycocyanin? 60
carotenoids
light absorption (percent) 40
chlorophyll a 20
400
500
600
700
wavelength (nanometers)

8. Light-Dependent Reactions Convert Light Energy to Chemical Energy II
Light-Dependent Reactions Convert Light Energy to Chemical Energy II. Production of ATP & NADPH
Photosystem II Generates ATP
Photosystem I Generates NADPH
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9. energy level of electrons 2e– NADPH
sunlight
energy level of electrons
2e–
NADPH
within thylakoid membrane
+ H+
NADP+
electron transport chain
2e–
synthesis
energy to drive
ATP
photosystem I
2e–
Figure :7-4
Title:
The light-dependent reactions of photosynthesis
Caption:
1 Light is absorbed by photosystem II, and the energy is passed to electrons in the reaction-center chlorophyll molecules. 2 Energized electrons leave the reaction center. 3 The electrons move into the adjacent electron transport chain. 4 The chain passes the electrons along, and some of their energy is used to drive ATP synthesis by chemiosmosis. Energy-depleted electrons replace those lost by photosystem I. 5 Light strikes photosystem I, and the energy is passed to electrons in the reaction-center chlorophyll molecules. 6 Energized electrons leave the reaction center. 7 The electrons move into the electron transport chain. 8 The energetic electrons from photosystem I are captured in molecules of NADPH. 9 The electrons lost from the reaction center of photosystem II are replaced by electrons obtained from splitting water, a reaction that also releases oxygen, and H+ used to form NADPH. Question If these reactions produce ATP and NADPH, then why do plant cells need mitochondria?
photosystem II
reaction
center 1
/2 O2 + 2 H+
H2O
2e–

10. Light-Dependent Reactions Convert Light Energy to Chemical Energy III
Light-Dependent Reactions Convert Light Energy to Chemical Energy III. Electrons, Protons & Oxygen Production
Splitting Water: Source of Electrons for the Photosystems
Chemiosmosis: produces a proton gradient (FE7.1 p121)
Chemiosmosis: ATP Synthesis (F E7.2 p. 121)
Oxygen: a by-product of photosynthesis (F7.5 p. 122)
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11. photosystem II thylakoid membrane H+ H+ 2e– H+ H+ (thylakoid interior)
Figure: E7-1
Title:
Chemiosmosis: creating the hydrogen ion gradient
Caption:
The energy released from the exergonic reaction of these electron transfers in Photosystem II is used to power active transport of hydrogen ions across the thylakoid membrane from the stroma into the thylakoid interior.
(stroma)

12. (high H+ concentration in thylakoid) H+ H+
(low H+ concentration
in stroma) H+ H+ H+ H+
(high H+ concentration
in thylakoid) H+ H+
Figure: E7-2
Title:
Chemiosmosis: ATP Synthesis
Caption:
The thylakoid membrane does not allow hydrogen ions to leak out, except at specific protein channels that are coupled to ATP-synthesizing enzymes. When hydrogen ions flow through these channels, down their gradients of charge and concentration, the energy released drives the synthesis of ATP. H+
ADP
ATP P

13. Figure :7-5
Title:
Oxygen is a by-product of photosynthesis
Caption:
The bubbles released by the leaves of this aquatic plant (Elodea) are composed of oxygen, a by-product of photosynthesis.

14. 6 CO2 6 H2O 6 12 RuBP PGA C3 cycle 12 6 12 G3P glucose
Figure :7-6
Title:
The C3 cycle of carbon fixation
Caption:
1 Six molecules of RuBP react with 6 molecules of CO2 and 6 molecules of H2O to form 12 molecules of PGA. This reaction is carbon fixation, the capture of carbon from CO2 into organic molecules. 2 The energy of 12 ATPs and the electrons and hydrogens of 12 NADPHs are used to convert the 12 PGA molecules to 12 G3Ps. 3 Two G3P molecules are available to synthesize glucose or other organic molecules. This occurs outside the chloroplast and is not part of the C3 cycle. 4 Energy from 6 ATPs is used to rearrange 10 G3Ps into 6 RuBPs, completing one turn of the C3 cycle.
G3P 12
glucose
(or other organic
compounds)

15. 7.3 Light-Independent Reactions: How Is Chemical Energy Stored in Glucose Molecules?
7.3.2
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16. Light-Independent Reactions: Store Chemical Energy in Glucose
C3 Cycle Captures Carbon Dioxide (F7.6 p122)
Carbon Captured in C3 Cycle Used to Synthesize Glucose
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17. Interconnection Between Light-Dependent & Light-Independent Reactions
Photosynthesis Summary Diagram (F7.7 p. 123)
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18. Interconnection Between Light-Dependent & Light-Independent Reactions
energy from
sunlight O2
CO2
H2O
ATP
NADPH
Light-dependent
reactions occur
in thylakoids.
Light-
independent
reactions
(C3 cycle) occur
in stroma.
Figure :7-7
Title:
A summary diagram of photosynthesis
Caption:
The light-dependent reactions in the thylakoids convert the energy of sunlight into the chemical energy of ATP and NADPH. Part of the sunlight energy is also used to split H2O, forming O2. In the stroma, the light-independent reactions use the energy of ATP and NADPH to convert CO2 and H2O to glucose. The depleted carriers, ADP and NADP+, return to the thylakoids to be recharged by the light-dependent reactions. Question Could a plant survive in an oxygen-free atmosphere?
ADP
NADP+
H20
Photosynthesis Summary Diagram (F7.7 p. 123)
chloroplast
glucose