Understanding Photosynthesis: Energy Transformation and Chemical Reactions

2. PHOTOSYNTHESIS

3. KEY CONCEPTPhotosynthesis is a series of chemical reactions that transform light energy into chemical energy stored in food.

4. Chemical Equation of Photosynthesis 6CO2 + 6H2O C6H12O6 + 6O2 Carbon dioxide + Water Glucose + Oxygen REACTANTS PRODUCTS Carbon dioxideGlucose (sugar) Water Oxygen Sunlight Energy Sunlight Energy

5. CO2 enters a leaf through guard cell/stomata by diffusion

6. H2O enters roots through osmosis.

7. Chloroplasts • In plants, Photosynthesis occurs in chloroplasts

8. chloroplast grana (thylakoids) stroma Structure of the Chloroplast Organelle Thylakoids- coin shaped compartments surrounded by a membrane filled with chlorophyll Grana – Stacks of thylakoids Chlorophyll – green colored molecule in thylakoid membrane Stroma – Fluid filled space between grana

9. chloroplast leaf cell leaf . Chloroplast vs. Chlorophyll • Chloroplast = Organelle where photosynthesis occurs • Chlorophyll = Green colored molecule that “fills” the chloroplast

10. 2 Stages of Photosynthesis Reactions 1. Light Dependent Reactions *Require light energy 2.Light Independent Reactions *Do NOT require light energy

11. Light-Dependent Reactions . Requires Light energy and Water as reactants *Occur in the thylakoid *Produces high energy molecules that will transfer their energy to the Light Independent Rxns. *Waste product is Oxygen

12. Stage 1: LIGHT DEPENDENT REACTIONS

13. Steps of the Light Dependent Reactions 1. Light energy “excites” electrons in a chlorophyll molecule. 2. The “excited”, high energy electrons are passed from one protein molecule to another along the electron transport chain in the thylakoid membrane and are used to make 2 energy carrier molecules 3. Enzymes split the water molecule: H2O 2H+ + 2e- + O- * The 2e- replace the electrons the chlorophyll molecule lost * Oxygen gas is released

14. Light-Independent Reactions (Calvin Cycle) • Do NOT require light energy – can happen in the dark • Source of Energy: the energy stored in high E molecules made in the light rxns • Occurs in the stroma fluid

15. *CO2 is needed – it diffuses across the chloroplast membrane into the stroma. *CO2 is rearranged using H+ from the breakdown of water and Energyfrom energy carrying molecules made in the light dependent reactions to make GLUCOSE.

16. Making the Energy Storing GLUCOSE Is the #1 Job of PHOTOSYNTHESIS

17. Big Picture of Energy Transformation in Photosynthesis • Light Dependent Reactions – • Chlorophyll molecule captures and transforms Light Energy into Chemical energy temporarily stored in energy carrier molecules. • Light Independent Reactions – • Chemical E from the energy carrier molecules made in Light Dependent reactions is transformed and stored as chemical energy in glucose

18. Photosynthesis plays a role in carbon cycling • Inorganic Carbon in CO2 gas from the atmosphere gets “fixed” into organic compounds like carbohydrates, lipids and proteins.

19. The Big Picture • Write the chemical equation for Photosynthesis using logic or memory – No Notes Allowed!!

20. The Big Picture Write the chemical equation for Photosynthesis using logic or memory – No Notes Allowed!! 6CO2 + 6H2O C6H12O6 + 6O2

21. Sample Exam Question • Using a microscope, a student observes a small, green organelle in a plant cell. • What is the name of this organelle? • Which energy transformation occurs first within the organelle? A. ATP to light B. Light to Chemical C. Heat to Electrical D. Chemical to Chemical

22. Sample Exam Question • Using a microscope, a student observes a small, green organelle in a plant cell. • What is the name of this organelle? Chloroplast • Which energy transformation occurs first within the organelle? A. ATP to light B. Light to Chemical C. Heat to Electrical D. Chemical to Chemical

23. Photosynthesis is series of chemical reactions that involve the transformation of energy from one form to another. The many reactions of photosynthesis are grouped into two set of reactions. Name each reaction set. Explain the energy transformation that occurs in each.

24. Photosynthesis is series of chemical reactions that involve the transformation of energy from one form to another. The many reactions of photosynthesis are grouped into two set of reactions. Name each reaction set. Explain the energy transformation that occurs in each. • Light Dependent Rxns Light Energy .> Chemical E stored in energy carrying molecules • Light Dependent Rxns Chemical E in energy carriers > Chemical E stored in glucose

25. Overall Energy Transformation in Photosynthesis • Light Energy > Chemical Energy stored in Glucose

26. Sample Exam Question • Photosynthesis and cellular respiration are two major processes in which carbon atoms are cycled through the bodies of living things.

27. granum (stack of thylakoids) 1 chloroplast sunlight 6H2O 6O2 2 energy thylakoid stroma (fluid outside the thylakoids) 6CO2 1 six-carbon sugar C6H12O6 3 4 • The equation for the overall process is: 6CO2 + 6H2O  C6H12O6 + 6O2

28. Water is absorbed by osmosis through the roots