Photosynthesis

1. Photosynthesis • Capturing and using solar energy

2. W O R K T O G E T H E R Quick, think! • Does photosynthesis: • create energy? • use energy? • “store” energy? • release energy? No Yes Yes No

3. W O R K T O G E T H E R True or False? • Plants do photosynthesis but not cellular respiration. • Photosynthesis is a plant’s way of creating ATP for its cells. • Plants make sugar and other carbon compounds so that animals can eat. False False False

4. Photosynthesis • What photosynthesis does: • Converts sunlight into stored chemical energy. • Makes carbon compounds that can be broken down for energy or used to build tissue.

5. Photosynthesis is an ___ process. • Endergonic • Exergonic

6. Photosynthesis is endergonic because: • Energy is consumed by the process. • Energy is given off by the process. • Energy is made by the process.

7. Remember this? energy input C6H12O6 (glucose) + O2 (oxygen) 6 CO2 (carbon dioxide) + 6 H2O (water) Photosynthesis is an endergonic process. Photosynthesis takes in energy and uses it to build carbon compounds.

8. This diagram shows that photosynthesis is an endergonic reaction because it takes in energy. Energy is captured from sunlight. Oxygen is released. Sugar is synthesized and used in plant tissues. Carbon dioxide is absorbed from the air. plant tissues, growth photosynthesis Carbon for making carbon compounds (such as sugar) comes from the atmosphere. Water is absorbed from soil, used in photosynthesis, and stored in cells. Inorganic mineral nutrients (nitrate, phosphate) are absorbed from soil and used in plant tissues. Oxygen, hydrogen, and minerals are needed also. Oxygen and hydrogen come from water. Minerals comes from the soil

9. Plants make carbon-based molecules from raw inorganic compounds. (chloroplast) photosynthesis H2O CO2 ATP sugar O2 cellular respiration (mitochondrion) Plants use the organic carbon compounds as “food” and to build cell parts.

10. Organic molecules are: • Natural, not man-made. • Molecules that contain carbon. • Molecules that contain carbon AND hydrogen. • Any molecule from a living organism.

11. Internal leaf structure cuticle upper epidermis mesophyll cells lower epidermis chloroplasts stoma bundle sheath vascular bundle (vein)

12. Chloroplast outer membrane inner membrane thylakoid stroma channel interconnecting thylakoids

13. The function of the chloroplast is to: • Produce energy. • Gather light energy and convert it to chemical energy. • Break sugars down for energy.

14. Light energy is “captured” by chlorophyl, which is embedded in the thylakoid membranes. energy from sunlight O2 CO2 ATP NADPH Light-dependent reactions are associated with thylakoids. Light- independent reactions (C3 cycle) occur in stroma. Energy from the light-dependent reactions drives the reactions where carbon compounds are produced. ADP NADP+ H2O chloroplast G3P

15. ATP and NADPH are used to move energy from one part of the chloroplast to another. LIGHT-DEPENDENT REACTIONS (in thylakoids) H2O O2 DEPLETED CARRIERS (ADP, NADP+) ENERGIZED CARRIERS (ATP, NADPH) ATP made in the chloroplast is ONLY used to power production of carbon compounds. It is not available to the rest of the cell. LIGHT-INDEPENDENT REACTIONS (in stroma) CO2 G3P

16. Overall, the light-dependent reactions do what? • Make energy. • Capture energy. • Make carbon compounds. • Break down carbon compounds.

17. Overall, the light-independent reactions do what? • Make energy. • Capture energy. • Make carbon compounds. • Break down carbon compounds.

18. W O R K T O G E T H E R • Suppose for a moment that the ATP made in the chloroplast was available to the cell, and was the ONLY source of ATP for the cell. Could the plant survive? (Remember that ATP is an unstable molecule that cannot be stored longer than a few minutes.)

19. Light-dependent reactions convert light energy into temporary chemical energy. electron transport chain sunlight NADPH 2e– 2e– electron transport chain NADP+ H+ 2e– energy level of electrons 2e– energy to drive ATP synthesis photosystem I reaction center 9 H2O 2e– 2H+ photosystem II 1/2 O2 The electron transport chain produces NADPH and drives ATP synthesis.

20. ATP synthase uses energy from the diffusion of H+ to drive ATP synthesis. Energy from energized electrons powers active transport of H+ by ETC. Energy-carrier molecules power the C3 cycle. ETC PSII PSI stroma ETC C3 cycle Energy from energized electrons powers NADPH synthesis. thylakoid space High H+ concentration generated by active transport. H+ channel coupled to ATP-synthesizing enzyme. Flow of H+ down concentration gradient powers ATP synthesis.

21. What’s important in the light-dependent (“photo”) reactions: • The ETC uses light energy to produce NADPH. • Energy from the ETC concentrates H+ ions. The energy released as they diffuse through ATP synthase makes ATP. • ATP and NADPH are used to power the light-independent reactions.

22. In photosynthesis, water is split in order to: • Release oxygen. • Get protons and electrons. • Make energy. • Make chlorophyll.

23. In photosynthesis, light energy is captured by: • Protons • Oxygen • Chlorophyll • ATP

24. The membrane protein that makes ATP is: • ATP synthase • Chlorophyll • ADP • Oxygen

25. Light-independent reactions. Notice where ATP and NADPH are used up. 1 Carbon fixation combines CO2 with RuBP. 6 CO2 2 G3P synthesis uses energy. 6 12 6 RuBP PGA C3 cycle (Calvin-Benson cycle) 3 RuBP synthesis uses energy and 10 G3P. 12 ATP 12 ADP 12 NADPH 6 ADP 12 6 ATP 12 NADP+ G3P 4 G3P availablefor synthesis of carbon compounds such as glucose. glucose (or other molecules)

26. What’s important in the light-independent (“synthesis”) reactions: • Energy carried by ATP and NADPH is used to power synthesis of G3P. • G3P can be used to make glucose as well as other monomers. • These monomers can be used to build polymers, or may be broken down to make ATP for the cell.

27. The source of carbon to make carbon compounds in photosynthesis is: • Glucose • G3P • Carbon dioxide • Water

28. Which of these happens in the C3 cycle? • ATP is made from ADP and P. • ATP is broken down to power molecule synthesis. • ATP becomes the monomer of other compounds.

29. Plant cells need ATP to run cell processes. Where does that ATP come from? • Sunlight. • The light-dependent reactions of photosynthesis. • The light-independent reactions of photosynthesis. • Cellular respiration

30. IMPORTANT!!! • Photosynthesis does NOT supply energy to the cell. Photosynthesis USES light energy to make organic compounds. • To get energy for the cell, plant cells must use cellular respiration to break down glucose and make ATP.

31. An analogy: • Photosynthesis is like going to the grocery store and buying food to store in your cupboard. The food and the energy in it is stored. • Cellular respiration is like eating the food when you are hungry and need energy. The energy in food is released only by eating the food.

32. While animals can only do cellular respiration, plants make “food” using photosynthesis and break the “food” down for energy in cellular respiration. (chloroplast) photosynthesis H2O CO2 ATP sugar O2 cellular respiration (mitochondrion)

33. Cellular Respiration Cellular Respiration Cellular Respiration Cellular Respiration Animals Plants Photosynthesis Day Day Night Night Photosynthesis supplies the “food” that plants need to carry out cellular respiration.

34. C3 plants use the C3 pathway Much photorespiration occurs under hot, dry conditions. CO2 O2 PGA CO2 rubisco C3 Cycle RuBP G3P glucose stoma within mesophyll chloropast bundle- sheath cells Little glucose is synthesized. In a C3 plant, mesophyll cells contain chloroplasts; bundle- sheath cells do not. C3 plants are at a disadvantage in hot, dry climates.

35. CO2 is captured with a highly specific enzyme. C4 plants use the C4 pathway CO2 PEP C4 Pathway 4-carbon molecule AMP ATP within mesophyll chloropast pyruvate CO2 O2 PGA rubisco CO2 stoma C3 Cycle RuBP bundle- sheath cells G3P Almost no photorespiration occurs in hot, dry conditions. glucose In a C4 plant, both mesophyll and bundle-sheath cells contain chloroplasts. within bundle-sheath chloropast Lots of glucose is synthesized. C4 plants essentially store carbon for hot times of the day. Guess what pathway many weeds use?

36. Fill in the blanks in this generalized diagram showing what goes into and what comes out of the chloroplast. W O R K T O G E T H E R Chloroplast

37. Recap • Think of photosynthesis as an energy “storing” process, not an energy-making or energy-releasing process. • The products of photosynthesis can be: • used to build cell parts. • broken down to make ATP for the cell.

38. Photosynthesis animations • Electron transport chains • Light-dependent and light-independent reactions