Chapter 7 Photosynthesis Using Light to Make Food

Chapter 7 Photosynthesis: Using Light to Make Food Power. Point Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko

Introduction § Plants, algae, and certain prokaryotes – convert light energy to chemical energy and – store the chemical energy in sugar, made from – carbon dioxide and – water. © 2012 Pearson Education, Inc.

Introduction § Algae farms can be used to produce – oils for biodiesel or – carbohydrates to generate ethanol. © 2012 Pearson Education, Inc.

Figure 7. 0_1 Chapter 7: Big Ideas An Overview of Photosynthesis The Calvin Cycle: Reducing CO 2 to Sugar The Light Reactions: Converting Solar Energy to Chemical Energy Photosynthesis Reviewed and Extended

Figure 7. 0_2

AN OVERVIEW OF PHOTOSYNTHESIS © 2012 Pearson Education, Inc.

7. 1 Autotrophs are the producers of the biosphere § Autotrophs – make their own food through the process of photosynthesis, – sustain themselves, and – do not usually consume organic molecules derived from other organisms. © 2012 Pearson Education, Inc.

7. 1 Autotrophs are the producers of the biosphere § Photoautotrophs use the energy of light to produce organic molecules. § Chemoautotrophs are prokaryotes that use inorganic chemicals as their energy source. § Heterotrophs are consumers that feed on – plants or – animals, or – decompose organic material. © 2012 Pearson Education, Inc.

7. 1 Autotrophs are the producers of the biosphere § Photosynthesis in plants – takes place in chloroplasts, – converts carbon dioxide and water into organic molecules, and – releases oxygen. © 2012 Pearson Education, Inc.

Figure 7. 1 A-D

Figure 7. 1 A

Figure 7. 1 B

Figure 7. 1 C

Figure 7. 1 D

7. 2 Photosynthesis occurs in chloroplasts in plant cells § Chloroplasts are the major sites of photosynthesis in green plants. § Chlorophyll – is an important light-absorbing pigment in chloroplasts, – is responsible for the green color of plants, and – plays a central role in converting solar energy to chemical energy. © 2012 Pearson Education, Inc.

7. 2 Photosynthesis occurs in chloroplasts in plant cells § Chloroplasts are concentrated in the cells of the mesophyll, the green tissue in the interior of the leaf. § Stomata are tiny pores in the leaf that allow – carbon dioxide to enter and – oxygen to exit. § Veins in the leaf deliver water absorbed by roots. © 2012 Pearson Education, Inc.

Figure 7. 2 Leaf Cross Section Mesophyll Vein CO 2 Stoma Mesophyll Cell Chloroplast Inner and outer membranes Granum Thylakoid space Stroma

Figure 7. 2_1 Leaf Cross Section Leaf Mesophyll Vein Mesophyll Cell CO 2 Stoma Chloroplast

7. 2 Photosynthesis occurs in chloroplasts in plant cells § Chloroplasts consist of an envelope of two membranes, which – enclose an inner compartment filled with a thick fluid called stroma and – contain a system of interconnected membranous sacs called thylakoids. © 2012 Pearson Education, Inc.

7. 2 Photosynthesis occurs in chloroplasts in plant cells § Thylakoids – are often concentrated in stacks called grana and – have an internal compartment called the thylakoid space, which has functions analogous to the intermembrane space of a mitochondrion. – Thylakoid membranes also house much of the machinery that converts light energy to chemical energy. § Chlorophyll molecules – are built into the thylakoid membrane and – capture light energy. © 2012 Pearson Education, Inc.

Figure 7. 2_2 Chloroplast Inner and outer membranes Granum Thylakoid space Stroma

Figure 7. 2_3 Mesophyll Cell Chloroplast

Figure 7. 2_4 Granum Stroma

7. 3 SCIENTIFIC DISCOVERY: Scientists traced the process of photosynthesis using isotopes § Scientists have known since the 1800 s that plants produce O 2. But does this oxygen come from carbon dioxide or water? – For many years, it was assumed that oxygen was extracted from CO 2 taken into the plant. – However, later research using a heavy isotope of oxygen, 18 O, confirmed that oxygen produced by photosynthesis comes from H 2 O. © 2012 Pearson Education, Inc.

Figure 7. 3 A

7. 3 SCIENTIFIC DISCOVERY: Scientists traced the process of photosynthesis using isotopes § Experiment 1: 6 CO 2 12 H 2 O → C 6 H 12 O 6 6 H 2 O 6 O 2 § Experiment 2: 6 CO 2 12 H 2 O → C 6 H 12 O 6 6 H 2 O 6 O 2 © 2012 Pearson Education, Inc.

Figure 7. 3 B Reactants: Products:

7. 4 Photosynthesis is a redox process, as is cellular respiration § Photosynthesis, like respiration, is a redox (oxidation-reduction) process. – CO 2 becomes reduced to sugar as electrons along with hydrogen ions from water are added to it. – Water molecules are oxidized when they lose electrons along with hydrogen ions. © 2012 Pearson Education, Inc.

Figure 7. 4 A Becomes reduced Becomes oxidized

7. 4 Photosynthesis is a redox process, as is cellular respiration § Cellular respiration uses redox reactions to harvest the chemical energy stored in a glucose molecule. – This is accomplished by oxidizing the sugar and reducing O 2 to H 2 O. – The electrons lose potential as they travel down the electron transport chain to O 2. – In contrast, the food-producing redox reactions of photosynthesis require energy. © 2012 Pearson Education, Inc.

7. 4 Photosynthesis is a redox process, as is cellular respiration § In photosynthesis, – light energy is captured by chlorophyll molecules to boost the energy of electrons, – light energy is converted to chemical energy, and – chemical energy is stored in the chemical bonds of sugars. © 2012 Pearson Education, Inc.

Figure 7. 4 B Becomes oxidized Becomes reduced

7. 5 Overview: The two stages of photosynthesis are linked by ATP and NADPH § Photosynthesis occurs in two metabolic stages. 1. The light reactions occur in the thylakoid membranes. In these reactions – water is split, providing a source of electrons and giving off oxygen as a by-product, – ATP is generated from ADP and a phosphate group, and – light energy is absorbed by the chlorophyll molecules to drive the transfer of electrons and H+ from water to the electron acceptor NADP+ reducing it to NADPH. – NADPH produced by the light reactions provides the electrons for reducing carbon in the Calvin cycle. © 2012 Pearson Education, Inc.

7. 5 Overview: The two stages of photosynthesis are linked by ATP and NADPH 2. The second stage is the Calvin cycle, which occurs in the stroma of the chloroplast. – The Calvin cycle is a cyclic series of reactions that assembles sugar molecules using CO 2 and the energy-rich products of the light reactions. – During the Calvin cycle, CO 2 is incorporated into organic compounds in a process called carbon fixation. – After carbon fixation, enzymes of the cycle make sugars by further reducing the carbon compounds. – The Calvin cycle is often called the dark reactions or lightindependent reactions, because none of the steps requires light directly. © 2012 Pearson Education, Inc.

Figure 7. 5_s 1 H 2 O Light NADP+ ADP P Light Reactions (in thylakoids) Chloroplast

Figure 7. 5_s 2 H 2 O Light NADP+ ADP P Light Reactions (in thylakoids) ATP NADPH Chloroplast O 2

Figure 7. 5_s 3 H 2 O CO 2 Light NADP+ ADP P Calvin Cycle (in stroma) Light Reactions (in thylakoids) ATP NADPH Chloroplast O 2 Sugar

THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY © 2012 Pearson Education, Inc.

7. 6 Visible radiation absorbed by pigments drives the light reactions § Sunlight contains energy called electromagnetic energy or electromagnetic radiation. – Visible light is only a small part of the electromagnetic spectrum, the full range of electromagnetic wavelengths. – Electromagnetic energy travels in waves, and the wavelength is the distance between the crests of two adjacent waves. © 2012 Pearson Education, Inc.

7. 6 Visible radiation absorbed by pigments drives the light reactions § Light behaves as discrete packets of energy called photons. – A photon is a fixed quantity of light energy. – The shorter the wavelength, the greater the energy. © 2012 Pearson Education, Inc.

Figure 7. 6 A Increasing energy 10 5 nm 10 3 nm Gamma rays X-rays 103 nm 1 nm UV 106 nm Infrared 103 m 1 m Microwaves Radio waves Visible light 380 400 500 600 Wavelength (nm) 700 650 nm 750

7. 6 Visible radiation absorbed by pigments drives the light reactions § Pigments – absorb light and – are built into the thylakoid membrane. § Plant pigments – absorb some wavelengths of light and – reflect or transmit other wavelengths. § We see the color of the wavelengths that are transmitted. For example, chlorophyll transmits green wavelengths. © 2012 Pearson Education, Inc.

Animation: Light and Pigments Right click on animation / Click play © 2012 Pearson Education, Inc.

Figure 7. 6 B Light Reflected light Chloroplast Thylakoid Absorbed light Transmitted light

Figure 7. 6 B_1

7. 6 Visible radiation absorbed by pigments drives the light reactions § Chloroplasts contain several different pigments, which absorb light of different wavelengths. – Chlorophyll a absorbs blue-violet and red light and reflects green. – Chlorophyll b absorbs blue and orange and reflects yellow-green. – Carotenoids – broaden the spectrum of colors that can drive photosynthesis and – provide photoprotection, absorbing and dissipating excessive light energy that would otherwise damage chlorophyll or interact with oxygen to form reactive oxidative molecules. © 2012 Pearson Education, Inc.

7. 7 Photosystems capture solar energy § Pigments in chloroplasts absorb photons (capturing solar power), which – increases the potential energy of the pigment’s electrons and – sends the electrons into an unstable state. – These unstable electrons – drop back down to their “ground state, ” and as they do, – release their excess energy as heat. © 2012 Pearson Education, Inc.

Figure 7. 7 A Excited state Photon of light Heat Photon (fluorescence) Ground state Chlorophyll molecule

Figure 7. 7 A_1

Figure 7. 7 A_2 Excited state Photon of light Heat Photon (fluorescence) Ground state Chlorophyll molecule

7. 7 Photosystems capture solar energy § Within a thylakoid membrane, chlorophyll and other pigment molecules – absorb photons and – transfer the energy to other pigment molecules. § In the thylakoid membrane, chlorophyll molecules are organized along with other pigments and proteins into photosystems. © 2012 Pearson Education, Inc.

7. 7 Photosystems capture solar energy § A photosystem consists of a number of lightharvesting complexes surrounding a reactioncenter complex. § A light-harvesting complex contains various pigment molecules bound to proteins. § Collectively, the light-harvesting complexes function as a light-gathering antenna. © 2012 Pearson Education, Inc.

Figure 7. 7 B Photosystem Light-harvesting Reaction-center complexes complex Thylakoid membrane Primary electron acceptor Transfer of energy Pair of chlorophyll a molecules Pigment molecules

7. 7 Photosystems capture solar energy § The light energy is passed from molecule to molecule within the photosystem. – Finally it reaches the reaction center where a primary electron acceptor accepts these electrons and consequently becomes reduced. – This solar-powered transfer of an electron from the reaction-center pigment to the primary electron acceptor is the first step in the transformation of light energy to chemical energy in the light reactions. © 2012 Pearson Education, Inc.

7. 7 Photosystems capture solar energy § Two types of photosystems (photosystem I and photosystem II) cooperate in the light reactions. § Each type of photosystem has a characteristic reaction center. – Photosystem II, which functions first, is called P 680 because its pigment absorbs light with a wavelength of 680 nm. – Photosystem I, which functions second, is called P 700 because it absorbs light with a wavelength of 700 nm. © 2012 Pearson Education, Inc.

7. 8 Two photosystems connected by an electron transport chain generate ATP and NADPH § In the light reactions, light energy is transformed into the chemical energy of ATP and NADPH. § To accomplish this, electrons are – removed from water, – passed from photosystem II to photosystem I, and – accepted by NADP+, reducing it to NADPH. § Between the two photosystems, the electrons – move down an electron transport chain and – provide energy for the synthesis of ATP. © 2012 Pearson Education, Inc.

Figure 7. 8 A Light Photosystem II Stroma Electron transport chain Provides energy for synthesis of ATP by chemiosmosis NADP H Light Photosystem I 1 Primary acceptor Thylakoid membrane Primary acceptor 2 4 P 700 P 680 Thylakoid space 3 H 2 O 1 2 5 O 2 2 H 6 NADPH

Figure 7. 8 A_1 Light Photosystem II Stroma Electron transport chain Provides energy for synthesis of ATP by chemiosmosis 1 Thylakoid membrane Primary acceptor 2 4 P 680 Thylakoid space 3 H 2 O 1 2 O 2 2 H

Figure 7. 8 A_2 Electron transport chain Provides energy for synthesis of ATP by chemiosmosis NADP H+ Light Photosystem I Primary acceptor 4 5 P 700 6 NADPH

Figure 7. 8 B ATP Photon Photosystem II Phot Mill makes ATP on NADPH Photosystem I

7. 8 Two photosystems connected by an electron transport chain generate ATP and NADPH § The products of the light reactions are – NADPH, – ATP, and – oxygen. © 2012 Pearson Education, Inc.

7. 9 Chemiosmosis powers ATP synthesis in the light reactions § Interestingly, chemiosmosis is the mechanism that – is involved in oxidative phosphorylation in mitochondria and – generates ATP in chloroplasts. § ATP is generated because the electron transport chain produces a concentration gradient of hydrogen ions across a membrane. © 2012 Pearson Education, Inc.

7. 9 Chemiosmosis powers ATP synthesis in the light reactions § In photophosphorylation, using the initial energy input from light, – the electron transport chain pumps H+ into the thylakoid space, and – the resulting concentration gradient drives H+ back through ATP synthase, producing ATP. © 2012 Pearson Education, Inc.

Figure 7. 9 Chloroplast To Calvin Cycle Light Stroma (low H+ concentration) ADP H+ NADP+ H+ P NADPH H+ H+ H+ Thylakoid membrane H 2 O Thylakoid space (high H+ concentration) 1 O + 2 + H 2 2 Photosystem II H+ H + H+ Electron transport chain H+ H+ Photosystem I H+ H+ H+ ATP synthase ATP

Figure 7. 9_1 To Calvin Cycle ADP Light H+ NADPH H+ H+ H 2 O 1 2 O 2 2 H+ Photosystem II H+ Electron transport chain P H+ H+ + H H+ H+ H+ Photosystem I H+ H+ H+ ATP synthase ATP

7. 9 Chemiosmosis powers ATP synthesis in the light reactions § How does photophosphorylation compare with oxidative phosphorylation? – Mitochondria use oxidative phosphorylation to transfer chemical energy from food into the chemical energy of ATP. – Chloroplasts use photophosphorylation to transfer light energy into the chemical energy of ATP. © 2012 Pearson Education, Inc.

THE CALVIN CYCLE: REDUCING CO 2 TO SUGAR © 2012 Pearson Education, Inc.

7. 10 ATP and NADPH power sugar synthesis in the Calvin cycle § The Calvin cycle makes sugar within a chloroplast. § To produce sugar, the necessary ingredients are – atmospheric CO 2 and – ATP and NADPH generated by the light reactions. § The Calvin cycle uses these three ingredients to produce an energy-rich, three-carbon sugar called glyceraldehyde-3 -phosphate (G 3 P). § A plant cell may then use G 3 P to make glucose and other organic molecules. © 2012 Pearson Education, Inc.

Figure 7. 10 A Input CO 2 ATP NADPH Calvin Cycle Output: G 3 P

7. 10 ATP and NADPH power sugar synthesis in the Calvin cycle § The steps of the Calvin cycle include – carbon fixation, – reduction, – release of G 3 P, and – regeneration of the starting molecule ribulose bisphosphate (Ru. BP). © 2012 Pearson Education, Inc.

Figure 7. 10 B_s 1 Step 1 Carbon fixation Input: 3 CO 2 Rubisco 1 3 P 6 P Ru. BP 3 -PGA Calvin Cycle P

Figure 7. 10 B_s 2 Step 1 Carbon fixation Input: 3 CO 2 Rubisco 1 3 P Step 2 Reduction 6 P Ru. BP 3 -PGA P 6 ATP 6 ADP Calvin Cycle 2 6 NADPH 6 P G 3 P 6 NADP P

Figure 7. 10 B_s 3 Step 1 Carbon fixation Input: 3 CO 2 Rubisco 1 3 P Step 2 6 P Ru. BP Reduction 3 -PGA P 6 ATP 6 ADP Calvin Cycle Step 3 Release of one molecule of G 3 P 5 G 3 P 2 6 NADPH 6 P P 6 NADP G 3 P 3 Output: 1 P G 3 P Glucose and other compounds P

Figure 7. 10 B_s 4 Step 1 Carbon fixation Input: 3 CO 2 Rubisco 1 3 P Step 2 6 P Ru. BP Reduction 3 -PGA P 3 ADP Calvin Cycle 4 5 G 3 P Step 4 Regeneration of Ru. BP ATP 6 ADP 3 ATP Step 3 Release of one molecule of G 3 P 6 2 6 NADPH 6 P P 6 NADP G 3 P 3 Output: 1 P G 3 P Glucose and other compounds P

7. 11 EVOLUTION CONNECTION: Other methods of carbon fixation have evolved in hot, dry climates § Most plants use CO 2 directly from the air, and carbon fixation occurs when the enzyme rubisco adds CO 2 to Ru. BP. § Such plants are called C 3 plants because the first product of carbon fixation is a three-carbon compound, 3 -PGA. © 2012 Pearson Education, Inc.

7. 11 EVOLUTION CONNECTION: Other methods of carbon fixation have evolved in hot, dry climates § In hot and dry weather, C 3 plants – close their stomata to reduce water loss but – prevent CO 2 from entering the leaf and O 2 from leaving. – As O 2 builds up in a leaf, rubisco adds O 2 instead of CO 2 to Ru. BP, and a two-carbon product of this reaction is then broken down in the cell. – This process is called photorespiration because it occurs in the light, consumes O 2, and releases CO 2. – But unlike cellular respiration, it uses ATP instead of producing it. © 2012 Pearson Education, Inc.

7. 11 EVOLUTION CONNECTION: Other methods of carbon fixation have evolved in hot, dry climates § C 4 plants have evolved a means of – carbon fixation that saves water during photosynthesis while – optimizing the Calvin cycle. § C 4 plants are so named because they first fix CO 2 into a four-carbon compound. § When the weather is hot and dry, C 4 plants keep their stomata mostly closed, thus conserving water. © 2012 Pearson Education, Inc.

7. 11 EVOLUTION CONNECTION: Other methods of carbon fixation have evolved in hot, dry climates § Another adaptation to hot and dry environments has evolved in the CAM plants, such as pineapples and cacti. § CAM plants conserve water by opening their stomata and admitting CO 2 only at night. § CO 2 is fixed into a four-carbon compound, – which banks CO 2 at night and – releases it to the Calvin cycle during the day. © 2012 Pearson Education, Inc.

Figure 7. 11 Mesophyll cell Bundlesheath cell CO 2 4 -C compound CO 2 Calvin Cycle 3 -C sugar C 4 plant Sugarcane CO 2 Night 3 -C sugar Day CAM plant Pineapple

Figure 7. 11_1 Mesophyll cell Bundlesheath cell CO 2 Night 4 -C compound CO 2 Calvin Cycle 3 -C sugar C 4 plant 3 -C sugar Day CAM plant

Figure 7. 11_2 Sugarcane

Figure 7. 11_3 Pineapple

PHOTOSYNTHESIS REVIEWED AND EXTENDED © 2012 Pearson Education, Inc.

7. 12 Review: Photosynthesis uses light energy, carbon dioxide, and water to make organic molecules § Most of the living world depends on the foodmaking machinery of photosynthesis. § The chloroplast – integrates the two stages of photosynthesis and – makes sugar from CO 2. © 2012 Pearson Education, Inc.

7. 12 Review: Photosynthesis uses light energy, carbon dioxide, and water to make organic molecules § About half of the carbohydrates made by photosynthesis are consumed as fuel for cellular respiration in the mitochondria of plant cells. § Sugars also serve as the starting material for making other organic molecules, such as proteins, lipids, and cellulose. § Excess food made by plants is stockpiled as starch in roots, tubers, seeds, and fruits. © 2012 Pearson Education, Inc.

Figure 7. 12 H 2 O Light CO 2 Chloroplast NADP Light Reactions ADP P Ru. BP Calvin Cycle 3 -PGA (in stroma) Photosystem II Electron transport chain Thylakoids Photosystem I ATP NADPH O 2 Stroma G 3 P Sugars Cellular respiration Cellulose Starch Other organic compounds

7. 13 CONNECTION: Photosynthesis may moderate global climate change § The greenhouse effect operates on a global scale. – Solar radiation includes visible light that penetrates the Earth’s atmosphere and warms the planet’s surface. – Heat radiating from the warmed planet is absorbed by gases in the atmosphere, which then reflects some of the heat back to Earth. – Without the warming of the greenhouse effect, the Earth would be much colder and most life as we know it could not exist. © 2012 Pearson Education, Inc.

Figure 7. 13 A

Figure 7. 13 B Some heat energy escapes into space Sunlight Atmosphere Radiant heat trapped by CO 2 and other gases

7. 13 CONNECTION: Photosynthesis may moderate global climate change § The gases in the atmosphere that absorb heat radiation are called greenhouse gases. These include – water vapor, – carbon dioxide, and – methane. © 2012 Pearson Education, Inc.

7. 13 CONNECTION: Photosynthesis may moderate global climate change § Increasing concentrations of greenhouse gases have been linked to global climate change (also called global warming), a slow but steady rise in Earth’s surface temperature. § Since 1850, the atmospheric concentration of CO 2 has increased by about 40%, mostly due to the combustion of fossil fuels including – coal, – oil, and – gasoline. © 2012 Pearson Education, Inc.

7. 13 CONNECTION: Photosynthesis may moderate global climate change § The predicted consequences of continued warming include – melting of polar ice, – rising sea levels, – extreme weather patterns, – droughts, – increased extinction rates, and – the spread of tropical diseases. © 2012 Pearson Education, Inc.

7. 13 CONNECTION: Photosynthesis may moderate global climate change § Widespread deforestation has aggravated the global warming problem by reducing an effective CO 2 sink. § Global warming caused by increasing CO 2 levels may be reduced by – limiting deforestation, – reducing fossil fuel consumption, and – growing biofuel crops that remove CO 2 from the atmosphere. © 2012 Pearson Education, Inc.

7. 14 SCIENTIFIC DISCOVERY: Scientific study of Earth’s ozone layer has global significance § Solar radiation converts O 2 high in the atmosphere to ozone (O 3), which shields organisms from damaging UV radiation. § Industrial chemicals called CFCs have caused dangerous thinning of the ozone layer, but international restrictions on CFC use are allowing a slow recovery. © 2012 Pearson Education, Inc.

Figure 7. 14 A Southern tip of South America Antarctica

Figure 7. 14 B

You should now be able to 1. Define autotrophs, heterotrophs, producers, and photoautotrophs. 2. Describe the structure of chloroplasts and their location in a leaf. 3. Explain how plants produce oxygen. 4. Describe the role of redox reactions in photosynthesis and cellular respiration. 5. Compare the reactants and products of the light reactions and the Calvin cycle. © 2012 Pearson Education, Inc.

You should now be able to 6. Describe the properties and functions of the different photosynthetic pigments. 7. Explain how photosystems capture solar energy. 8. Explain how the electron transport chain and chemiosmosis generate ATP, NADPH, and oxygen in the light reactions. 9. Compare photophosphorylation and oxidative phosphorylation. 10. Describe the reactants and products of the Calvin cycle. © 2012 Pearson Education, Inc.

You should now be able to 11. Compare the mechanisms that C 3, C 4, and CAM plants use to obtain and use carbon dioxide. 12. Review the overall process of the light reactions and the Calvin cycle, noting the products, reactants, and locations of every major step. 13. Describe the greenhouse effect. 14. Explain how the ozone layer forms, how human activities have damaged it, and the consequences of the destruction of the ozone layer. © 2012 Pearson Education, Inc.

Figure 7. UN 01 Light energy 6 CO 2 Carbon dioxide 6 H 2 O Water C 6 H 12 O 6 Photosynthesis Glucose 6 O 2 Oxygen gas

Figure 7. UN 02 Light CO 2 H 2 O NADP Stroma ADP Thylakoids P Light Reactions Calvin Cycle ATP NADPH Chloroplast O 2 Sugar

Figure 7. UN 03 Mitochondrion Chloroplast Intermembrane space H c. Membrane Matrix d. a. b. e.

Figure 7. UN 04 Photosynthesis converts includes both (a) (c) (b) to in which chemical energy light-excited electrons of chlorophyll H 2 O is split in which CO 2 is fixed to Ru. BP and then and are passed down (d) reduce NADP to (h) using (f) (e) to produce producing (g) by chemiosmosis sugar (G 3 P)