1. Carbon dioxide C 6 H 12 O 6 Photosynthesis H2OH2O CO 2 O2O2 Water + 66 Light energy Oxygen gas Glucose + 6  Plants use water and atmospheric carbon dioxide to produce a simple sugar and liberate oxygen –Photosynthesis: a process that converts solar energy to chemical energy

2. AN OVERVIEW OF PHOTOSYNTHESIS Copyright © 2009 Pearson Education, Inc.

3. Autotrophs Are the Producers of The Biosphere  Autotrophs make their own food without using organic molecules derived from any other living thing –Photoautotrophs : Autotrophs that use the energy of light to produce organic molecules –Most plants, algae and other protists, and some prokaryotes are photoautotrophs –The ability to photosynthesize is directly related to the structure of chloroplasts Copyright © 2009 Pearson Education, Inc.

5. Photosynthesis Occurs in Chloroplasts in Plant Cells  Chlorophyll is a light absorbing pigment in chloroplasts; responsible for green color of plants; located on thylakoid membrane  Stomata are tiny pores in the leaf; allows CO 2 to enter and O 2 to exit  Veins in the leaf: deliver water absorbed by roots Copyright © 2009 Pearson Education, Inc.

6. CO 2 O2O2 Stoma Mesophyll Cell Vein Chloroplast Mesophyll Leaf Cross Section Leaf Outer and inner membranes Intermembrane space Granum Stroma Thylakoid space Thylakoid

7. CO 2 O2O2 Stoma Vein Chloroplasts  Chlorophyll  light absorbing pigment in chloroplasts  responsible for the green color of plants  located on thylakoid membrane  Stomata  tiny pores in the leaf; allow CO 2 to enter and O 2 to exit  Veins in the leaf deliver water absorbed by roots Photosynthesis Occurs in Chloroplasts in Plant Cells

8. Chloroplast Outer and inner membranes Intermembrane space Granum Stroma Thylakoid space Thylakoid

9. Photosynthesis is a Redox Process, as is Cellular Respiration  Photosynthesis is a redox (oxidation-reduction) process  A loss of electrons = oxidation; A gain of electrons = reduction (OIL RIG)  In photosynthesis: Water is oxidized and CO 2 is reduced  The oxidation of water produces oxygen and the reduction of CO 2 produces sugar

10. 6 CO 2 + 6 H 2 O C 6 H 12 O 6 + 6 O 2 Reduction Oxidation

11. H2OH2O ADP P LIGHT REACTIONS (in thylakoids) Light Chloroplast NADPH ATP O2O2 CALVIN CYCLE (in stroma) Sugar CO 2  NADP +

12. THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY

13. Visible Radiation Drives the Light Reactions  Sunlight contains energy called electromagnetic radiation –Electromagnetic energy travels in waves –Wavelength: distance between the crests of two adjacent waves (the shorter the wavelength, the greater the energy) –Visible light: small part of the electromagnetic spectrum –Light behaves as discrete packets of energy called photons (fixed quantity of light energy)

14. Wavelength (nm) 10 –5 nm Increasing energy Visible light 650 nm 10 –3 nm 1 nm10 3 nm10 6 nm 1 m 10 3 m 380 400 500 600700 750 Radio waves Micro- waves Infrared X-rays UV Gamma rays

15.  Pigments are molecules that absorb light  Many pigments are built into the thylakoid membrane  Plant pigments absorb some wavelengths of light and transmit others –We see the color of the wavelengths that are transmitted –Ex. chlorophyll transmits green Visible Radiation Drives the Light Reactions

16.  Chloroplasts contain several different pigments and all absorb light of different wavelengths –Chlorophyll a: absorbs blue violet and red light and reflects green –Chlorophyll b: absorbs blue and orange and reflects yellow-green –The carotenoids: absorb mainly blue-green light and reflect yellow and orange Visible Radiation Drives the Light Reactions

17. Chlorophyll molecule Excited state Ground state Heat Photon (fluorescence) e–e–

18. Reaction center complex e–e– Light-harvesting complexes Photosystem Pigment molecules Pair of Chlorophyll a molecules  Solar energy could be released as heat or light but instead is conserved and passed from one molecule to another  All of the components to accomplish this are organized in thylakoid membranes in clusters called photosystems  Photosystems are light- harvesting complexes surrounding a reaction center complex Photosystems Capture Solar Power

19.  When light strikes the photosystem energy is passed from molecule to molecule within the photosystem –From the pigment molecules, energy reaches the reaction center, exciting an e- of the chl. a molecules –The excited e- are transferred to a primary electron acceptor (becomes reduced) –This solar-powered transfer of an electron from the reaction center pigment to the primary electron acceptor is the first step of the light reactions Photosystems Capture Solar Power

20.  Two types of photosystems exist: photosystem I and photosystem II –Each type of photosystem has a characteristic reaction center –Photosystem II: functions first; is called P680 (chl a best absorbs light w/ a wavelength of 680, red) –Photosystem I: functions next; is called P700 (chl a absorbs wavelength of 700, also red) Photosystems Capture Solar Power

21. Two Photosystems Connected by an Electron Transport Chain Generate ATP and NADPH  During the light reactions, light energy is transformed into the chemical energy of ATP and NADPH –Electrons removed from water pass from photosystem II to photosystem I and are accepted by NADP + –The bridge between photosystems II and I is an electron transport chain that provides energy for the synthesis of ATP –NADPH, ATP, and O 2 are the products of the light reactions

22. NADPH Photosystem II e–e– Mill makes ATP Photon Photosystem I ATP e–e– e–e– e–e– e–e– e–e– e–e– Photon

23. Stroma O2O2 H2OH2O 1212 H+H+ NADP + NADPH Photon Photosystem II Electron transport chain Provides energy for synthesis of by chemiosmosis + 2 Primary acceptor 1 Thylakoid mem- brane P680 2 4 3 Thylakoid space e–e– e–e– 5 Primary acceptor P700 6 Photon Photosystem I ATP H+H+ +

24. Chemiosmosis Powers ATP Synthesis in the Light Reactions  In Chemiosmosis, the potential energy of a H + gradient is used to synthesize ATP  The H + gradient is generated by the ETC  ATP synthase couples the flow of H + to the phosphorylation of ADP –The chemiosmotic production of ATP in photosynthesis is called photophosphorylation

25. + O2O2 H2OH2O 1212 H+H+ NADP + H+H+ NADPH + 2 H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Photosystem II Photosystem I Electron transport chain ATP synthase Light Stroma (low H + concentration) Thylakoid space (high H + concentration) ADP + P ATP

26. THE CALVIN CYCLE: CONVERTING CO 2 TO SUGARS

27. CO 2 ATP NADPH Input C ALVIN CYCLE G3P Output:  The Calvin cycle makes sugar within a chloroplast  Atmospheric CO 2, ATP, and NADPH are required to produce sugar  Using these three ingredients, an energy-rich, three-carbon sugar called glyceraldehyde-3-phosphate (G3P) is produced  A plant cell may then use G3P to make glucose and other organic molecules ATP and NADPH Power Sugar Synthesis in the Calvin Cycle

28.  The Calvin Cycle Has Three Phases:  1. Carbon Fixation-Atmospheric carbon in the form of CO2 is incorporated into a molecule of ribulose bisphosphate (RuBP) via rubisco  2. Reduction Phase – NADPH reduces 3PGA to G3P (requires 3 molec’s. of CO2 for 1 G3P)  3. Regeneration of Starting Material –RuBP is regenerated and the cycle starts again Copyright © 2009 Pearson Education, Inc. ATP and NADPH Power Sugar Synthesis in the Calvin Cycle

29. RuBP 3 P Input: CO 2 1 Rubisco 3 P Step Carbon fixation 3-PGA 6 P C ALVIN CYCLE 1

30. NADP + NADPH ATP RuBP 3 6 ADP + P G3P P Input: CO 2 1 Rubisco 3 P Step Carbon fixation 3-PGA 6 P C ALVIN CYCLE 6 6 6 6 P Step Reduction 2 2 1

31. NADPH ATP RuBP 3 P G3P P Input: CO 2 1 Rubisco 3 P Step Carbon fixation 3-PGA 6 P C ALVIN CYCLE 6 6 6 6 P Step Reduction 2 2 G3P 5 P 3 3 1 P Glucose and other compounds Output: Step Release of one molecule of G3P 1 NADP + 6 ADP +

32. NADPH ATP RuBP 3 P G3P P Input: CO 2 1 Rubisco 3 P Step Carbon fixation 3-PGA 6 P C ALVIN CYCLE 6 6 6 6 P Step Reduction 2 2 G3P 5 P 3 3 1 P Glucose and other compounds Output: Step Release of one molecule of G3P 1 Step Regeneration of RuBP 4 4 ATP 3 3 ADP NADP + 6 ADP +

33. PHOTOSYNTHESIS REVIEWED AND EXTENDED Copyright © 2009 Pearson Education, Inc.

34. NADP + NADPH ATP CO 2 + H2OH2O ADP P Electron transport chains Thylakoid membranes Light Chloroplast O2O2 C ALVIN C YCLE (in stroma) Sugars Photosystem II Photosystem I L IGHT R EACTIONS RuBP 3-PGA C ALVIN C YCLE Stroma G3P Cellular respiration Cellulose Starch Other organic compounds

35. EVOLUTION CONNECTION: Adaptations that save water in hot, dry climates evolved in C 4 and CAM plants  In hot climates, plant stomata close to reduce water loss so oxygen builds up –Rubisco adds oxygen instead of carbon dioxide to RuBP and produces a two-carbon compound, a process called photorespiration –Unlike photosynthesis, photorespiration produces no sugar, and unlike respiration, it produces no ATP Copyright © 2009 Pearson Education, Inc.

36. EVOLUTION CONNECTION: Adaptations that save water in hot, dry climates evolved in C 4 and CAM plants  Some plants have evolved a means of carbon fixation that saves water during photosynthesis –One group can shut its stomata when the weather is hot and dry to conserve water but is able to make sugar by photosynthesis –These are called the C 4 plants because they first fix carbon dioxide into a four-carbon compound Copyright © 2009 Pearson Education, Inc.

37. EVOLUTION CONNECTION: Adaptations that save water in hot, dry climates evolved in C 4 and CAM plants  Another adaptation to hot and dry environments has evolved in the CAM plants, such as pineapples and cacti –CAM plants conserve water by opening their stomata and admitting CO 2 only at night –When CO 2 enters, it is fixed into a four-carbon compound, like in C 4 plants, and in this way CO 2 is banked –It is released into the Calvin cycle during the day Copyright © 2009 Pearson Education, Inc.

38. Mesophyll cell CO 2 C ALVIN C YCLE CO 2 Bundle- sheath cell 3-C sugar C 4 plant 4-C compound CO 2 C ALVIN C YCLE CO 2 3-C sugar CAM plant 4-C compound Night Day