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Chapter 10 Photosynthesis
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Products of photosynthesis create ecosystems.
Organic compounds produced by photosynthesis Provide the energy and building material for ecosystems. Energy for other organisms Make photoautotrophs the biological infrastructure of ecosystems. Ecosystems are defined by their PLANTS!
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6 CO2 + 12 H2O + Light energy C6H12O6 + 6 O2 + 6 H2 O
Photosynthesis Photosynthesis is summarized as 6 CO H2O + Light energy C6H12O6 + 6 O2 + 6 H2 O
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An overview of photosynthesis
CO2 Light LIGHT REACTIONS CALVIN CYCLE Chloroplast [CH2O] (sugar) NADPH NADP ADP + P O2 Figure 10.5 ATP
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Quiz What is the summary equation for photosynthesis? Where does the light energy go? What role does Oxygen play in Cellular Respiration?
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6 CO2 + 12 H2O + Light energy C6H12O6 + 6 O2 + 6 H2 O
Quiz What is the summary equation for photosynthesis? 3 points Where does the light energy go? 3 Points Bonds in glucose What role does Oxygen play in Cellular Respiration? (2 points) accepts H+ to form H2O 6 CO H2O + Light energy C6H12O6 + 6 O2 + 6 H2 O
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10.2 Light reactions The light reactions convert solar energy to the chemical energy of ATP and NADPH. Harness energy in light
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The electromagnetic spectrum
Gamma rays X-rays UV Infrared Micro- waves Radio 10–5 nm 10–3 nm 1 nm 103 nm 106 nm 1 m 103 m 380 450 500 550 600 650 700 750 nm Visible light Shorter wavelength Higher energy Longer wavelength Lower energy Figure 10.6
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Photosynthetic Pigments: The Light Receptors
Absorb light of certain wavelengths (energy) and transmit or reflect unused light.
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Chlorophyll b, Carotenoids
Chlorophyll a Is the main photosynthetic pigment Chlorophyll b, Carotenoids Are accessory pigments
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Excitation of Chlorophyll by Light
When a pigment absorbs light It goes from a ground state to an excited state, which is unstable Excited state Energy of election Heat Photon (fluorescence) Chlorophyll molecule Ground e– Figure A
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(INTERIOR OF THYLAKOID)
Primary election acceptor Photon Thylakoid Light-harvesting complexes Reaction center Photosystem STROMA Thylakoid membrane Transfer of energy Special chlorophyll a molecules Pigment THYLAKOID SPACE (INTERIOR OF THYLAKOID) Figure 10.12 e– A photosystem Is composed of a reaction center surrounded by a number of light-harvesting complexes
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The light-harvesting complexes
Consist of pigment molecules bound to particular proteins Funnel the energy of photons of light to the reaction center
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When a reaction-center chlorophyll molecule absorbs energy
One of its electrons gets bumped up to a primary electron acceptor The thylakoid membrane Is populated by two types of photosystems, I (P700) and II (P680)
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Noncyclic Electron Flow
Is the primary pathway of energy transformation in the light reactions. Produces NADPH, ATP and O2.
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O2 e Energy of electrons Light P680 Photosystem II (PS II) H2O CO2
NADP+ ADP CALVIN CYCLE LIGHT REACTIONS ATP NADPH O2 [CH2O] (sugar) e Energy of electrons Light P680 1 Photosystem II (PS II)
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O2 Primary acceptor e 2 H+ + 1⁄2 Energy of electrons P680
H2O CO2 Light LIGHT REACTIONS CALVIN CYCLE O2 NADP+ NADPH [CH2O] (sugar) Photosystem II (PS II) e Primary acceptor ADP ATP 2 H+ + 1⁄2 1 3 2 Energy of electrons P680
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Electron transport chain
+ H2O CO2 Light LIGHT REACTIONS CALVIN CYCLE NADP+ NADPH [CH2O] (sugar) Photosystem II (PS II) e Primary acceptor ATP 2 H+ 1⁄2 2 Energy of electrons ADP Pq Cytochrome complex Pc Electron transport chain 4 3 e 5 e P680 1
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Electron transport chain
H2O CO2 Light LIGHT REACTIONS CALVIN CYCLE NADPH [CH2O] (sugar) Photosystem II (PS II) e Primary acceptor 2 H+ 1⁄2 2 Energy of electrons ADP Pq Cytochrome complex Pc ATP Electron transport chain 5 NADP+ Photosystem I (PS I) 6 1 3 4 + e e P700 P680
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Electron transport chain
+ CO2 Photosystem II (PS II) H2O Light LIGHT REACTIONS CALVIN CYCLE O2 NADPH [CH2O] (sugar) e Primary acceptor 2 H+ 1⁄2 1 Energy of electrons Pq Cytochrome complex Pc ATP Electron transport chain NADP+ Photosystem I (PS I) 6 2 ADP 5 Fd Electron Transport chain 7 reductase + 2 H+ 8 + H+ 3 4 P680
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Under certain conditions
Cyclic Electron Flow Under certain conditions Photoexcited electrons take an alternative path. This involves only PSI and short circuits the system. But, does produce one ATP
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The light reactions and chemiosmosis: the organization of the thylakoid membrane
REACTOR NADP+ ADP ATP NADPH CALVIN CYCLE [CH2O] (sugar) STROMA (Low H+ concentration) Photosystem II H2O CO2 Cytochrome complex O2 1 1⁄2 2 Photosystem I Light THYLAKOID SPACE (High H+ concentration) Thylakoid membrane synthase Pq Pc Fd reductase + H+ NADP+ + 2H+ To Calvin cycle P 3 H+ 2 H+ +2 H+ Figure 10.17
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Homework Read and outline C 10. Pp ( )
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An elegant experiment by Engelmann
Illuminated a filament of green algae on a microscope slide using a prism to break up the light. Included an aerobic bacterium. Observed where the bacteria congregated. They need O2 and will move towards it.
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Englemann’s results. Where are the bacteria congregating? Why?
What does that tell us.
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Quiz What carbohydrate is produced directly from the Calvin Cycle? What are the three phases of the Calvin cycle? Where does O2 come from? What molecule?
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Quiz What carbohydrate is produced directly from the Calvin Cycle? (2 Points) Glyceraldehyde 3-phosphate (or G3P) What are the three phases of the Calvin cycle? (3 points) Carbon Fixation, Reduction, Regeneration of RuBP What part of Photosynthsis generates O2 from? What molecule? (2 Points) Light Reactions, H2O
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10.3 The Calvin Cycle The Calvin cycle
Is similar to the citric acid cycle (but in reverse) Occurs in the stroma Uses the products from the light reactions Is light independent.
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Calvin Cycle Three phases Carbon fixation Reduction
Regeneration of the CO2 acceptor
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Overview of the Calvin Cycle
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6 simultaneous turns of the Calvin cycle
Think of it this way… 6 simultaneous turns of the Calvin cycle 6 CO2‘s are fixed by 6 molecules of RuBP 2 G3P’s pop out (2 x 3C’s = 6 C’s) 1 molecule of Glucose (6C ÷ 6C = 1) 10 G3P’s go to reform RuBP (10x3C’s = 30C’s) 6 molecules (30C’s ÷ 5C’s = 6) of RuBP.
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Figure 10.18 The Calvin cycle
Light H2O CO2 LIGHT REACTIONS ATP NADPH NADP+ [CH2O] (sugar) CALVIN CYCLE ADP (Entering one at a time) CO2 3 Phase 1: Carbon fixation Rubisco Short-lived intermediate 3 P P Ribulose bisphosphate (RuBP) 3-Phosphoglycerate 6 ATP 6 ADP Input O2 6 CALVIN CYCLE
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Figure 10.18 The Calvin cycle
(Entering one at a time) CO2 3 Phase 1: Carbon fixation Rubisco Short-lived intermediate 3 P P Ribulose bisphosphate (RuBP) 3-Phosphoglycerate 6 P 1,3-Bisphosphoglycerate 6 NADPH 6 NADP+ 6 P i 6 Glyceraldehyde-3-phosphate (G3P) Phase 2: Reduction 6 ATP CALVIN CYCLE 1 G3P (a sugar) Output Glucose and other organic compounds 6 ADP Input Light H2O LIGHT REACTIONS ATP NADP+ [CH2O] (sugar) CALVIN CYCLE NADPH ADP O2 6
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Figure 10.18 The Calvin cycle
(Entering one at a time) CO2 3 Phase 1: Carbon fixation Rubisco Short-lived intermediate 3 P P Ribulose bisphosphate (RuBP) 3-Phosphoglycerate 6 P 1,3-Bisphosphoglycerate 6 NADPH 6 NADP+ 6 P i 6 Glyceraldehyde-3-phosphate (G3P) Phase 2: Reduction 6 ATP 3 ATP 3 ADP CALVIN CYCLE 5 Phase 3: Regeneration of the CO2 acceptor (RuBP) 1 G3P (a sugar) Output Glucose and other organic compounds G3P 6 ADP Light H2O LIGHT REACTIONS NADPH NADP+ [CH2O] (sugar) CALVIN CYCLE Input ATP ADP O2 6
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Alternative mechanisms of Carbon fixation
On hot, dry days, plants close their stomata Conserving water Limits CO2 Light reactions continue Causing oxygen to build up Rubisco preferentially binds O2. Uses ATP w/out replacement. Decreases photosynthetic output.
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Leaf Anatomy (See p 725 for more details)
Upper Epidermis Cuticle Mesophyll Vein Stomate Lower Epidermis
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C4 plants minimize the cost of photorespiration
By incorporating CO2 into four carbon compounds in mesophyll cells. PEP Carboxylase to fix CO2. Forms Oxaloacetate Moved to Bundle sheath cells Calvin cycle occurs. Spatial separation of light and dark reactions.
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C4 leaf anatomy and the C4 pathway
CO2 Mesophyll cell Bundle- sheath cell Vein (vascular tissue) Photosynthetic cells of C4 plant leaf Stoma Mesophyll C4 leaf anatomy PEP carboxylase Oxaloacetate (4 C) PEP (3 C) Malate (4 C) ADP ATP Sheath Pyruate (3 C) CALVIN CYCLE Sugar Vascular tissue Figure 10.19
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During the day, the stomata close
CAM Plants CAM plants Open their stomata at night, incorporating CO2 into organic acids. During the day, the stomata close And the CO2 is released from the organic acids for use in the Calvin cycle. Temporal separation of Light and Dark reactions.
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The CAM pathway is similar to the C4 pathway
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The Importance of Photosynthesis: A Review
A review of photosynthesis Light reactions: • Are carried out by molecules in the thylakoid membranes • Convert light energy to the chemical energy of ATP and NADPH • Split H2O and release O2 to the atmosphere Calvin cycle reactions: • Take place in the stroma • Use ATP and NADPH to convert CO2 to the sugar G3P • Return ADP, inorganic phosphate, and NADP+ to the light reactions O2 CO2 H2O Light Light reaction Calvin cycle NADP+ ADP ATP NADPH + P 1 RuBP 3-Phosphoglycerate Amino acids Fatty acids Starch (storage) Sucrose (export) G3P Photosystem II Electron transport chain Photosystem I Chloroplast Figure 10.21
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Read Enzyme lab (#2) In your lab book.
Homework Read Enzyme lab (#2) In your lab book. Pre-lab tomorrow. Exam on Monday C-7-10 Finish review given out last week, do self quizzes and review quizzes on CD, think of potential essay questions!
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