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All life ultimately depends on photosynthesis.

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 C3, C4, and CAM plants

5.1 Life Depends on 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 (C6H12O6) from carbon dioxide (CO2) Uses water and releases oxygen gas (O2) Light energy 6CO2 + 6H2O → C6H12O6 + 6O2

5.1 Life Depends on Photosynthesis Oxidation- reduction (redox) process Electrons moved from H2O to CO2 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 Feeds plants Provides energy and raw materials for other organisms Waste product oxygen essential to life

Figure 5.1 Cycle of 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

Figure 5.2 Oxygen Gas Changed the World.

Why is photosynthesis essential to life on Earth? 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

Figure 5.3 The Electromagnetic Spectrum.

Clicker question Which below has the MOST energy? Visible violet light Visible red light Ultraviolet radiation 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 CO2 and O2 enter/exit through stomata Leaf mesophyll contains chloroplasts

Clicker question Oxygen is a _____ of photosynthesis. waste product substrate

Figure 5.5 Leaf and Chloroplast Anatomy.

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

Figure 5.5 Leaf and Chloroplast Anatomy.

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

Figure 5.6 Thylakoid membrane.

5.2 Mastering Concepts How does it benefit a photosynthetic organism to have more than one type of pigment?

5.3 Photosynthesis Occurs in Two Stages Light reactions Convert solar energy to chemical energy Produce ATP and NADPH Carbon Reactions Reduce CO2 to glucose CO2 from atmosphere

Figure 5.7 Overview of Photosynthesis.

Clicker Question The high energy molecule is? ADP AMP ATP 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 2nd electron transport chain Electrons replaced from 1st electron transport chain Electrons reduce NADP+ to NADPH

Clicker Question Photosystem II replaces its electrons from water. oxygen. the electron transport system. NADPH.

5.5 The Carbon Reactions Produce Carbohydrates Also called Calvin cycle Occur in stroma Uses NADPH and ATP to reduce CO2

5.5 The Carbon Reactions Produce Carbohydrates Carbon fixation Ribulose bisphosphate (RuBP) RUBP carboxylase/oxygenase (rubisco) PGAL synthesis PGAL combined to form glucose RuBP regeneration ATP and NADPH from light reactions

Clicker Question Which below does NOT come out of the light reactions? Glucose Water NADPH ATP

5.6 C3 Plants Use Only the Calvin Cycle to Fix Carbon C3 pathway 3-carbon PGA is first stable molecule 95% of plants are C3 Photorespiration reduces efficiency Rubisco uses O2 instead of CO2 Open stomata minimizes problem Water loss problem

5.7 The C4 and CAM Pathways Save Carbon and Water C4 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 C4 and CAM Pathways Save Carbon and Water Crassulacean acid metabolism Open their stomata to fix CO2 only at night Fix it again in the Calvin cycle during the day Both fixation reactions occur in the same cell

Describe how a C4 plant minimizes photorespiration. 5.7 Mastering Concepts Describe how a C4 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?