Learning Outcomes Explain how plants convert light into chemical energy Draw and describe the net reaction in photosynthesis Explain how photosynthesis has influenced the evolution of life Explain how light interacts with pigments Describe the structures in a leaf that are involved in photosynthesis
Learning Outcomes Compare and contrast the light and carbon reactions of photosynthesis Describe how light energy is converted to ATP and NADPH in the light reaction. Identify the products and reactants in the carbon reaction Explain how the products and reactants of the light and carbon reactions are linked Compare and contrast C 3, C 4, and CAM plants
5.1 Life Depends on Photosynthesis Photosynthesis –Solar energy harnessed –Converted into chemical energy All life ultimately depends on photosynthesis
5.1 Life Depends on Photosynthesis A. Photosynthesis Builds Carbohydrates Out of Carbon Dioxide and Water –Pigment molecules capture the sun’s energy –Energy to build glucose (C 6 H 12 O 6 ) from carbon dioxide (CO 2 ) –Uses water and releases oxygen gas (O 2 ) 6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2 Light energy
5.1 Life Depends on Photosynthesis Oxidation- reduction (redox) process –Electrons moved from H 2 O to CO 2 –Energy from sunlight Uses for glucose –Half for plant’s own fuel –Manufacture other compounds –Cellulose for cell walls –Store as starch or sucrose
5.1 Life Depends on Photosynthesis Photosynthesis –Feeds plants –Provides energy and raw materials for other organisms –Waste product oxygen essential to life
5.1 Life Depends on Photosynthesis B. The Evolution of Photosynthesis Changed Planet Earth –Most organisms rely directly or indirectly on photosynthesis –First organisms all heterotrophs –Autotrophs evolved later –Photosynthesis release oxygen gas –Aerobic organisms outcompeted anaerobic organisms
5.1 Mastering Concepts Why is photosynthesis essential to life on Earth?
5.2 Sunlight Is the Energy Source for Photosynthesis A. What is Light? –Visible light part of electromagnetic spectrum –Photons Shorter wavelength = more energy –Sunlight Ultraviolet radiation, visible light, infrared radiation
Clicker question Which below has the MOST energy? A.Visible violet light B.Visible red light C.Ultraviolet radiation D.Infrared radiation
5.2 Sunlight Is the Energy Source for Photosynthesis B. Photosynthetic Pigments Capture Light Energy –Pigments capture light energy Chlorophyll a Accessory pigments –Absorb only some wavelengths Transmit or reflect others
Figure 5.4 Everything but Green. If you could expose plants to just one wavelength of light at a time, would a wavelength of 300 nm, 450 nm, or 600 nm produce the highest photosynthetic rate?
5.2 Sunlight Is the Energy Source for Photosynthesis C. Chloroplasts Are the Sites of Photosynthesis –Leaves are the main organ of photosynthesis –CO 2 and O 2 enter/exit through stomata –Leaf mesophyll contains chloroplasts
Clicker question Oxygen is a _____ of photosynthesis. A.waste product B.substrate
5.2 Sunlight Is the Energy Source for Photosynthesis Chloroplast structure –2 membranes enclose stroma –Grana composed of stack of thylakoids –Thylakoid membrane studded with photosynthetic pigments –Thylakoid membrane encloses thylakoid space
5.2 Sunlight Is the Energy Source for Photosynthesis Chloroplast structure –Photosystem Chlorophyll a aggregated with other pigment molecules Proteins anchor complex in membrane Reaction center Antenna pigments – funnel energy to reaction center
Clicker Question The high energy molecule is? A.ADP B.AMP C.ATP D.APP
5.4 The Light Reactions Begin Photosynthesis 2 types of photosystems –Photosystem I Reaction center P700 – 700nm –Photosystem II Reaction center P680 – 680nm Connected by electron transport chain
5.4 The Light Reactions Begin Photosynthesis A. Photosystem II Produces ATP –Light energy transferred to reaction center –Boosts 2 electrons from chlorophyll a –Passed down electron transport system –Chlorophyll a replaces electrons Split water Oxygen waste product
5.4 The Light Reactions Begin Photosynthesis A. Photosystem II Produces ATP –Electron transport chain Energy drives proton active transport From stroma into thylakoid space ATP synthase uses potential energy ATP produced Chemiosmotic phosphorylation
5.4 The Light Reactions Begin Photosynthesis B. Photosystem I Produces NADPH –Energy passed to reaction center –2 nd electron transport chain –Electrons replaced from 1 st electron transport chain –Electrons reduce NADP + to NADPH
Clicker Question Photosystem II replaces its electrons from A.water. B.oxygen. C.the electron transport system. D.NADPH.
5.5 The Carbon Reactions Produce Carbohydrates Also called Calvin cycle Occur in stroma Uses NADPH and ATP to reduce CO 2
5.5 The Carbon Reactions Produce Carbohydrates 1.Carbon fixation –Ribulose bisphosphate (RuBP) –RUBP carboxylase/oxygenase (rubisco) 2.PGAL synthesis –PGAL combined to form glucose 3.RuBP regeneration ATP and NADPH from light reactions
Clicker Question Which below does NOT come out of the light reactions? A.Glucose B.Water C.NADPH D.ATP
5.6 C 3 Plants Use Only the Calvin Cycle to Fix Carbon C 3 pathway –3-carbon PGA is first stable molecule –95% of plants are C 3 Photorespiration reduces efficiency –Rubisco uses O 2 instead of CO 2 –Open stomata minimizes problem Water loss problem
5.7 The C 4 and CAM Pathways Save Carbon and Water C 4 pathway –Physically separate light reactions and carbon reactions –Light reactions in mesophyll cells –Calvin cycle in bundle-sheath cells –Unique arrangement of cells in leaves
5.7 The C 4 and CAM Pathways Save Carbon and Water CAM pathway –Crassulacean acid metabolism –Open their stomata to fix CO 2 only at night –Fix it again in the Calvin cycle during the day –Both fixation reactions occur in the same cell
5.7 Mastering Concepts Describe how a C 4 plant minimizes photorespiration.
5.8 Investigating Life: Solar- Powered Sea Slugs Sea slug Elysia chlorotica Acquire the chloroplasts by eating algae Cells lining the slug’s gut absorb the chloroplasts 2 hypotheses –Chloroplasts autonomous – no –Slug’s cells support chloroplasts psbO gene
5.8 Mastering Concepts The researchers also looked for the psbO gene in pufferfish (a vertebrate animal) and slime molds (a nonphotosynthetic protist). The gene was absent in both species. How was this finding important to the interpretation of the results of this study?