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Biology Sylvia S. Mader Michael Windelspecht
Chapter 7 Photosynthesis Lecture Outline See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1
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7.1 Photosynthetic Organisms
Biology, 9th ed,Sylvia Mader Chapter 07 7.1 Photosynthetic Organisms Photosynthesis All life on Earth depends on solar energy Photosynthetic organisms (algae, plants, and cyanobacteria) transform solar energy into the chemical energy of carbohydrates Called autotrophs because they produce their own food. Photosynthesis: A process that captures solar energy Transforms solar energy into chemical energy Energy ends up stored in a carbohydrate Photosynthesizers produce food energy Feed themselves as well as heterotrophs
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Photosynthetic Organisms
Biology, 9th ed,Sylvia Mader Chapter 07 Photosynthetic Organisms Photosynthesis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. mosses trees garden plants kelp Euglena cyanobacteria diatoms (Moss): © Steven P. Lynch; (Trees): © Digital Vision/PunchStock; (Kelp): © Chuck Davis/Stone/Getty Images; (Cyanobacteria): © Sherman Thomas/Visuals Unlimited; (Diatoms): © Ed Reschke/Peter Arnold; (Euglena): © T.E. Adams/Visuals Unlimited; (Sunflower): © Royalty-Free/Corbis
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Photosynthetic Organisms
Biology, 9th ed,Sylvia Mader Chapter 07 Photosynthetic Organisms Photosynthesis Photosynthesis takes place in the green portions of plants Leaf of flowering plant contains mesophyll tissue Cells containing chloroplasts are specialized to carry out photosynthesis The raw materials for photosynthesis are carbon dioxide and water Roots absorb water that moves up vascular tissue Carbon dioxide enters a leaf through small openings called stomata and diffuses into chloroplasts in mesophyll cells In stroma, CO2 is combined with H2O to form C6H12O6 (sugar) Energy supplied by light Chlorophyll and other pigments absorb solar energy and energize electrons prior to reduction of CO2 to a carbohydrate
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Leaves and Photosynthesis
Biology, 9th ed,Sylvia Mader Chapter 07 Leaves and Photosynthesis Photosynthesis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. cuticle upper epidermis Leaf cross section mesophyll lower epidermis CO2 O2 leaf vein stoma outer membrane inner membrane stroma stroma granum Chloroplast 37,000 thylakoid space thylakoid membrane Grana independent thylakoid in a granum overlapping thylakoid in a granum © Dr. George Chapman/Visuals Unlimited
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7.2 The Process of Photosynthesis
Biology, 9th ed,Sylvia Mader Chapter 07 7.2 The Process of Photosynthesis Photosynthesis Light Reactions – take place only in the presence of light Energy‑capturing reactions Chlorophyll absorbs solar energy This energizes electrons Electrons move down an electron transport chain Pumps H+ into thylakoids Used to make ATP out of ADP and NADPH out of NADP Calvin Cycle Reactions – take place in the stroma CO2 is reduced to a carbohydrate Use ATP and NADPH to produce carbohydrate
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Overview of Photosynthesis
Biology, 9th ed,Sylvia Mader Overview of Photosynthesis Chapter 07 Slide #7 Photosynthesis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H2O CO2 solar energy ADP + P NADP+ Calvin cycle reactions Light reactions NADPH ATP stroma thylakoid membrane CH2O O2 7
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7.3 Plants as Solar Energy Converters
Biology, 9th ed,Sylvia Mader Chapter 07 7.3 Plants as Solar Energy Converters Photosynthesis Pigments: Chemicals that absorb certain wavelengths of light Wavelengths that are not absorbed are reflected/transmitted Absorption Spectrum Pigments found in chlorophyll absorb various portions of visible light Graph showing relative absorption of the various colors of the rainbow Chlorophyll is green because it absorbs much of the reds and blues of white light
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Photosynthetic Pigments and Photosynthesis
Biology, 9th ed,Sylvia Mader Chapter 07 Photosynthetic Pigments and Photosynthesis Photosynthesis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Increasing wavelength chlorophyll a chlorophyll b carotenoids Increasing energy Gamma rays Micro- waves Radio waves X rays UV Infrared Relative Absorption visible light 500 600 750 380 500 600 750 Wavelengths (nm) Wavelengths (nm) a. The electromagnetic spectrum includes visible light. b. Absorption spectrum of photosynthetic pigments.
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Plants as Solar Energy Converters
Biology, 9th ed,Sylvia Mader Chapter 07 Plants as Solar Energy Converters Photosynthesis The light reactions consist of two alternate electron pathways: Noncyclic pathway Cyclic pathway Capture light energy with photosystems Pigment complex helps collect solar energy like an antenna Occur in the thylakoid membranes Both pathways produce ATP The noncyclic pathway also produces NADPH
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Plants as Solar Energy Converters
Biology, 9th ed,Sylvia Mader Chapter 07 Plants as Solar Energy Converters Photosynthesis Noncyclic pathway Takes place in the thylakoid membrane Uses two photosystems, PS I and PS II PS II captures light energy Causes an electron to be ejected from the reaction center (chlorophyll a) Electron travels down electron transport chain to PS I Replaced with an electron from water, which is split to form O2 and H+ This causes H+ to accumulate in thylakoid chambers The H+ gradient is used to produce ATP PS I captures light energy and ejects an electron The electron is transferred permanently to a molecule of NADP+ Causes NADPH production
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Noncyclic Electron Pathway
Biology, 9th ed,Sylvia Mader Chapter 07 Slide #12 Noncyclic Electron Pathway Photosynthesis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H2O CO2 solar energy ADP+ P NADP+ Calvin cycle sun Light reactions sun NADPH ATP electron acceptor thylakoid membrane electron acceptor O CH2O energy level e– e– e– electron transport chain (ETC) e– NADP+ H + ATP e– e– NADPH reaction center reaction center pigment complex pigment complex Photosystem I Photosystem II e– CO2 CH2O H2O Calvin cycle reactions 12 2H+ 1 – O2 2
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Plants as Solar Energy Converters
Biology, 9th ed,Sylvia Mader Chapter 07 Plants as Solar Energy Converters Photosynthesis PS II: Consists of a pigment complex and electron acceptors Receives electrons from the splitting of water Oxygen is released as a gas Electron transport chain: Consists of cytochrome complexes and plastoquinone Carries electrons between PS II and PS I Also pumps H+ from the stroma into the thylakoid space PS I: Has a pigment complex and electron acceptors Adjacent to the enzyme that reduces NADP+ to NADPH ATP synthase complex: Has a channel for H+ flow H+ flow through the channel drives ATP synthase to join ADP and Pi
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Plants as Solar Energy Converters
Biology, 9th ed,Sylvia Mader Chapter 07 Plants as Solar Energy Converters Photosynthesis The thylakoid space acts as a reservoir for hydrogen ions (H+) Each time water is oxidized, two H+ remain in the thylakoid space Transfer of electrons in the electron transport chain yields energy Used to pump H+ across the thylakoid membrane Protons move from stroma into the thylakoid space Flow of H+ back across the thylakoid membrane Energizes ATP synthase, which Enzymatically produces ATP from ADP + Pi This method of producing ATP is called chemiosmosis
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Organization of a Thylakoid
Biology, 9th ed,Sylvia Mader Organization of a Thylakoid Chapter 07 Photosynthesis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H2O CO2 solar energy ADP + P NADP + Calvin cycle reactions Light reactions NADPH ATP thylakoid membrane thylakoid membrane thylakoid thylakoid space O2 CH2O granum photosystem II electron transport chain H+ stroma photosystem I NADP reductase H+ Pq e- e- e- NADP+ NADPH e- e- H+ H+ H2O 2 1 H+ + O2 2 H+ H+ H+ H+ H+ ATP synthase H+ H+ H+ H+ H+ H+ ATP Thylakoid space H+ H+ H+ chemiosmosis P + ADP Stroma
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7.4 Plants as Carbon Dioxide Fixers
Biology, 9th ed,Sylvia Mader Chapter 07 7.4 Plants as Carbon Dioxide Fixers Photosynthesis A cyclical series of reactions Utilizes atmospheric carbon dioxide to produce carbohydrates Known as C3 photosynthesis Involves three stages: Carbon dioxide fixation Carbon dioxide reduction RuBP regeneration
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Plants as Carbon Dioxide Fixers
Biology, 9th ed,Sylvia Mader Chapter 07 Plants as Carbon Dioxide Fixers Photosynthesis CO2 is attached to 5-carbon RuBP carboxylase Results in a 6-carbon molecule This splits into two 3-carbon molecules (3PG) Reaction is accelerated by RuBP carboxylase (Rubisco) CO2 is now “fixed” because it is part of a carbohydrate
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The Calvin Cycle Reactions
Biology, 9th ed,Sylvia Mader The Calvin Cycle Reactions Chapter 07 Slide #18 Photosynthesis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H2O CO2 solar energy ADP + P NADP + Calvin cycle Light reactions NADPH ATP Metabolites of the Calvin Cycle stroma RuBP ribulose-1,5-bisphosphate O2 CH2O 3PG phosphoglycerate 3CO2 intermediate BPG ,3-bisphosphoglycerate G3P glyceraldehyde-3-phosphate 3 C6 6 3PG C3 3 RuBP C5 CO2 fixation 6 ATP CO2 reduction These ATP and NADPH molecules were produced by the light reactions. Calvin cycle 3 ADP + 3 P 6 ADP + 6 P regeneration of RuBP 6 BPG C3 These ATP molecules were produced by the light reactions. 3 ATP 5 G3P C3 6 NADPH 6 G3P C3 6 NADP+ net gain of one G3P 18 Other organic molecules Glucose
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Biology, 9th ed,Sylvia Mader
Chapter 07 Animation Photosynthesis Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at
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Plants as Carbon Dioxide Fixers
Biology, 9th ed,Sylvia Mader Chapter 07 Plants as Carbon Dioxide Fixers Photosynthesis Importance of the Calvin Cycle: G3P (glyceraldehyde-3-phosphate) can be converted to many other molecules The hydrocarbon skeleton of G3P can form Fatty acids and glycerol to make plant oils Glucose phosphate (simple sugar) Fructose (which with glucose = sucrose) Starch and cellulose Amino acids
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© Herman Eisenbeiss/Photo Researchers, Inc.
Biology, 9th ed,Sylvia Mader Fate of G3P Chapter 07 Slide #21 Photosynthesis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. G3P fatty acid synthesis amino acid synthesis glucose phosphate + fructose phosphate Sucrose (in leaves, fruits, and seeds) Starch (in roots and seeds) Cellulose (in trunks, roots, and branches) 21 © Herman Eisenbeiss/Photo Researchers, Inc.
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7.5 Other Types of Photosynthesis
Biology, 9th ed,Sylvia Mader Chapter 07 7.5 Other Types of Photosynthesis Photosynthesis In hot, dry climates Stomata must close to avoid wilting CO2 decreases and O2 increases O2 starts combining with RuBP, leading to the production of CO2 This is called photorespiration C4 plants solve the problem of photorespiration Fix CO2 to PEP (a C3 molecule) The result is oxaloacetate, a C4 molecule In hot & dry climates C4 plants avoid photorespiration Net productivity is about 2-3 times greater than C3 plants In cool, moist environments, C4 plants can’t compete with C3 plants
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Chloroplast Distribution in C4 vs. C3 Plants
Biology, 9th ed,Sylvia Mader Chapter 07 Chloroplast Distribution in C4 vs. C3 Plants Photosynthesis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. C3 Plant C4 Plant mesophyll cells bundle sheath cell vein vein bundle sheath cell stoma stoma
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CO2 Fixation in C3 and C4 Plants
Biology, 9th ed,Sylvia Mader CO2 Fixation in C3 and C4 Plants Chapter 07 Photosynthesis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CO2 RuBP Calvin cycle 3PG G3P mesophyll cell a. CO2 fixation in a C3 plant, wildflowers CO2 mesophyll cell C4 bundle sheath cell CO2 Calvin cycle G3P b. CO2 fixation in a C4 plant, corn, Zea mays a: © Brand X Pictures/PunchStock RF; b: Courtesy USDA/Doug Wilson, photographer
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Other Types of Photosynthesis
Biology, 9th ed,Sylvia Mader Chapter 07 Other Types of Photosynthesis Photosynthesis CAM Photosynthesis Crassulacean-Acid Metabolism CAM plants partition carbon fixation by time During the night CAM plants fix CO2 Form C4 molecules, which are Stored in large vacuoles During daylight NADPH and ATP are available Stomata are closed for water conservation C4 molecules release CO2 to Calvin cycle
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CO2 Fixation in a CAM Plant
Biology, 9th ed,Sylvia Mader Chapter 07 CO2 Fixation in a CAM Plant Photosynthesis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. night CO2 C4 day CO2 Calvin cycle G3P CO2 fixation in a CAM plant, pineapple, Ananas comosus © S. Alden/PhotoLink/Getty Images.
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Other Types of Photosynthesis
Biology, 9th ed,Sylvia Mader Chapter 07 Other Types of Photosynthesis Photosynthesis Each method of photosynthesis has advantages and disadvantages Depends on the climate C4 plants most adapted to: High light intensities High temperatures Limited rainfall C3 plants better adapted to Cold (below 25°C) High moisture CAM plants are better adapted to extreme aridity CAM occurs in 23 families of flowering plants Also found among nonflowering plants
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