Topic 20 Photosynthesis Part 1 Light reactions Topic 20 Photosynthesis • Part 1, Light and Light Reactions • 20.1 Light reactions structures and functions • 20.2 Photosystems, chlorophyll and light • 20.3 Light reactions in five steps • Part 2, Calvin Cycle and more • 20.4 Calvin cycle structures and functions • 20.5 Calvin cycle in three steps • 20.6 Alternative photosynthetic pathways: CAM and C4 Review 19.2 Leaf Anatomy and Photosynthesis 20.1 Light reaction structures and functions Image shows one chloroplast Part 2: Calvin cycle reaction – Part 1: Light reactions – Water Oxygen Carbon Photons Carbon-based molecules Temporary chemical energy 20.1 Light reaction structures and functions Follow-along Activity: Learning the thylakoid membrane structures. Zoomed in on a section of the thylakoid membrane Photosystem II Photosystem I NADP+ Reductase Chloroplast stroma ATP synthase Hydrolase Thylakoid lumen Cytochrome complex 20.2 Photosystems, Chlorophyll, and Light Structure • Photosystems are clusters of pigments embedded in the thylakoid membranes. • Each photosystem has two parts: a broad antenna region (purple) and a smaller reaction center (blue). 20.2 Photosystems, Chlorophyll, and Light Structure-function: Each photosystem has two parts: a broad antenna region (light green) and a smaller reaction center (dark green and purple). Pigment defined: Broad antennae structure: Broad antennae function: Reaction center structure: Reaction center function: 20.2 Photosystems, Chlorophyll, and Light What is light energy? Light is made up of packets of kinetic (in motion) energy, or electromagnetic radiation, called photons, that move in waves. We can tell what type of light it is by measuring the wavelength(s) of the light. Wavelength defined: 20.2 Photosystems, Chlorophyll, and Light Photosystem pigments absorb light energy by “attaching” it to electrons. Chlorophyll a Q. Which wavelengths of light are best absorbed by the photosystem pigments? A. 400-600 nm (not so much 500-600) Chlorophyll b Carotenoids B. 350-500 nm and 625-700 nm (both ranges have higher absorption activity) C. 500-600 nm and longer than 700 nm D. All wavelengths shown, 400-700 nm Poll question 20.2 Photosystems, Chlorophyll, and Light • Electrons associated with the pigments enter a higher energy state when the correct wavelengths of light are absorbed. Topic 20.2 Photosystems, Chlorophyll, and Light Chloroplast absorb red and blue wavelengths of light. Q. Which model correctly shows how chloroplasts utilize light energy? Note: 20.3 Light Reactions in Five Steps Step 1 Step 1: Step 2 Step 2: Step 3 Step 3: Step 4 Step 4: Step 5: Step 5 20.3 Light Reactions in Five Steps Step 1 • Structure: • Event: Step 2 • Structure: • Event: 20.3 Light Reactions in Five Steps Step 3 • Structure: • Event: Step 4 • Structure: • Event: 20.3 Light Reactions in Five Steps Step 5 • Structure: • Event: Balance sheet: Topic 20.3 Light reactions Chloroplasts contain thousands of cytochrome complexes in the thylakoid membrane. They are used in much the same way as the ETC observed in the mitochondria. Q. What do the cytochrome complexes do in the chloroplast? A. B. C. D. Produce high energy electrons Produce a proton gradient Produce water Absorb light energy Poll question. Topic 20.3 Light reactions Q. What structure energizes (or re-energizes) electrons? A. B. C. D. A photosystem (structures A or C in image) An electron transport chain An ATP synthase A thylakoid membrane Poll question. 24.3 Light Reactions Q. The light reactions depend on a steady supply of electrons. What supplies the electrons to the light reactions? A. Conversion of oxygen and protons into water B. Catabolism of glucose C. ATP synthase D. Splitting of water Clicker participation question. Topic 20 continues with Part 2 (Calvin Cycle, CAM and C4 photosynthesis) slide set next time… Student Learning Objectives Topic 20: Photosynthesis (full set) 1. Define: Photosynthesis, pigment, lumen, wavelength, carboxylation, reduction, and photorespiration. 2. Identify the two main parts of photosynthesis and the function of each part. Identify the roles that ATP and NADPH play in connecting parts 1 and 2 of photosynthesis. 3. Identify what light energy is, and how plant pigments help absorb the light energy. 4. Describe the anatomical parts used by plants to light energy, including chlorophyll pigments, chloroplasts, thylakoid membranes, granum, stroma, and thylakoid lumen. Understand the locational relationships among these different anatomical structures. 5. Describe the five steps of the light reaction (part 1 of photosynthesis) in detail and identify the structures-functions of each step. 6. Describe the three steps of the Calvin cycle (part 2 of photosynthesis) in detail and identify the structures-functions of each step. 7. Understand the role of water and its relation to the production of oxygen gas during the light reactions. 8. Describe how the ATP synthase works, how it makes ATP. 9. Describe why the regeneration step is needed to keep the Calvin cycle going. 10. Identify two conditions when normal (C3) photosynthesis would jeopardize the survival of a plant. 11. Describe the changes to photosynthesis that occur in CAM plants (to the extent discussed in lecture). 12. Describe the changes to photosynthesis that occur in C4 plants (to the extent discussed in lecture). Include in your description the problem that arises with RUBISCO. 13. Compare and contrast the C3, CAM and C4 pathways. Identify which pathways are most ideal for wet vs. dry environments, or hot vs. cooler environments. Review Topic 20.3 Light reactions Thylakoid Photosystem I ATP Synthase Activity: Match each structure to its correct letter and description. Letter Structure Photosystem II Cytochrome complex Function A Absorbs red and blue wavelengths of lights. Absorbed energy excites electrons into higher energy state (increase energy levels). B Uses extra energy from electrons to create proton gradient across the membrane. Electrons return to lower energy state. C Absorbs red and blue wavelengths of light. Absorbed energy re-excites (increase energy levels) electrons to higher energy state. Electrons donated to NADP+ reductase or back to cytochrome complex (50:50) D Membrane-bound compartment contains elevated proton concentration (source of gradient). E Produces ATP using oxidative phosphorylation driven by the proton gradient.
