1. Capturing Solar Energy: Photosynthesis

2. Photosynthesis  Light energy captured and stored as chemical potential energy in the covalent bonds of carbohydrate molecules  6 CO 2 + 6 H 2 O + light  C 6 H 12 O 6 + 6 O 2  Light energy captured and stored as chemical potential energy in the covalent bonds of carbohydrate molecules  6 CO 2 + 6 H 2 O + light  C 6 H 12 O 6 + 6 O 2

3. Photosynthesis  Less Than 1% of the Sun's Energy Is Captured in Photosynthesis  Sun energy drives reduction of carrier molecules  Electrons in respiration loose energy going from sugar to oxygen  Mitochondria use released energy to make ATP  Electrons in photosynthesis must gain energy going from water to sugar  Energy provided by the sun  Occurs in 1 million billionths of a second  Less Than 1% of the Sun's Energy Is Captured in Photosynthesis  Sun energy drives reduction of carrier molecules  Electrons in respiration loose energy going from sugar to oxygen  Mitochondria use released energy to make ATP  Electrons in photosynthesis must gain energy going from water to sugar  Energy provided by the sun  Occurs in 1 million billionths of a second

6. Photosynthesis  Light  A. Light consists of units of energy called photons  B. Photons possess differing amounts of energy  C. Energy in visible light  1.Violet has short wavelength and high energy photons  2.Red has long wavelength and low energy photons  D. Absorbed vs reflected  E. Specific atoms can absorb only certain photons of light  Light  A. Light consists of units of energy called photons  B. Photons possess differing amounts of energy  C. Energy in visible light  1.Violet has short wavelength and high energy photons  2.Red has long wavelength and low energy photons  D. Absorbed vs reflected  E. Specific atoms can absorb only certain photons of light

8. Pigments-molecules that absorb light  A. Molecules that absorb light  B. Types  1. Carotenoids-absorbs some green  a. Absorb photons over a broad range, not highly efficient  b. Include beta-carotene, vitamin A and retinal   2. Chlorophylls  a. Absorb photons by excitation like the photoelectric effect  1. Complex ring structure called a porphyrin ring  2. Metal ion within a network of alternating single and double bonds(Fe)  b. Absorb photons over a narrow range  1. Chlorophyll a absorbs in violet-blue range  2. Chlorophyll b absorbs in the red range  3. Wavelength not absorbed by chlorophylls reflected as green  4. Chlorophyll absorbs in a narrow range, but with great efficiency  c. xanthrophyll  A. Molecules that absorb light  B. Types  1. Carotenoids-absorbs some green  a. Absorb photons over a broad range, not highly efficient  b. Include beta-carotene, vitamin A and retinal   2. Chlorophylls  a. Absorb photons by excitation like the photoelectric effect  1. Complex ring structure called a porphyrin ring  2. Metal ion within a network of alternating single and double bonds(Fe)  b. Absorb photons over a narrow range  1. Chlorophyll a absorbs in violet-blue range  2. Chlorophyll b absorbs in the red range  3. Wavelength not absorbed by chlorophylls reflected as green  4. Chlorophyll absorbs in a narrow range, but with great efficiency  c. xanthrophyll

15. Life depends on photosynthesis  A. Foundation of energy for most ecosystems  B. Source of oxygen  C. Key component of the carbon cycle  A. Foundation of energy for most ecosystems  B. Source of oxygen  C. Key component of the carbon cycle

16. The mechanism of photosynthesis  Chloroplasts are the sites of photosynthesis  Have a membrane system within internal space (stroma)  Arranged in disk-shaped sacks (thylakoids)  The thylakoids contain light-harvesting photosynthetic pigments & enzymes  Internal membranes define space (lumen) that is separate from the rest of the stroma  Chloroplasts are the sites of photosynthesis  Have a membrane system within internal space (stroma)  Arranged in disk-shaped sacks (thylakoids)  The thylakoids contain light-harvesting photosynthetic pigments & enzymes  Internal membranes define space (lumen) that is separate from the rest of the stroma

17. The mechanism of photosynthesis  Photosynthesis occurs in two steps  1. Light-dependent reactions  a. Provides the energy necessary to fix carbon  b. Occurs in the thylakoid membranes  c. Generates ATP  Photosynthesis occurs in two steps  1. Light-dependent reactions  a. Provides the energy necessary to fix carbon  b. Occurs in the thylakoid membranes  c. Generates ATP

18. LIMITATIONS  1. Geared only towards energy production(ATP)  2. Does not provide for biosynthesis(glucose synthesis)  1. Geared only towards energy production(ATP)  2. Does not provide for biosynthesis(glucose synthesis)

20. CYCLIC PHOTOSYNTHESIS  PRIMATIVE FORM  COMES IN TO PLAY ON ITS OWN IN FALL IN HIGHER PLANTS.  PRIMATIVE FORM  COMES IN TO PLAY ON ITS OWN IN FALL IN HIGHER PLANTS.

25. Light-Dependent Reactions  What happens during light reactions?  During transport of electrons from PS II to PS I  Some energy is harnessed to produce ATP  Eventually, chlorophyll from PS II is oxidized  Gets replacement electrons from water- photolysis  What happens during light reactions?  During transport of electrons from PS II to PS I  Some energy is harnessed to produce ATP  Eventually, chlorophyll from PS II is oxidized  Gets replacement electrons from water- photolysis

26. Light-Dependent Reactions  Energy of light has thus been captured in two forms:  The synthesis of NADPH from NADP+  Proton gradient across the thylakoid membrane  Cannot be used directly to make food  Must first be converted to ATP by chloroplast ATP synthase  Energy of light has thus been captured in two forms:  The synthesis of NADPH from NADP+  Proton gradient across the thylakoid membrane  Cannot be used directly to make food  Must first be converted to ATP by chloroplast ATP synthase

27. The mechanism of photosynthesis  Energy carriers ATP and NADPH transport energy from the light- dependent reactions to the light- independent reactions

30. The mechanism of photosynthesis  2. Light-independent reactions  a. Uses energy of the light-dependent reaction to make sugar from CO 2  b. Occurs in the stroma  2. Light-independent reactions  a. Uses energy of the light-dependent reaction to make sugar from CO 2  b. Occurs in the stroma

32. Light-Independent Reactions  Steps in Light-Independent Reactions:  CO 2 joins with RuBP forming an unstable 6- C molecule  Breaks into two 3-C PGA molecules  This first step in Calvin-Benson/C 3 cycle is catalyzed by enzyme  Called ribulose biphosphate carboxylase (Rubisco)  Steps in Light-Independent Reactions:  CO 2 joins with RuBP forming an unstable 6- C molecule  Breaks into two 3-C PGA molecules  This first step in Calvin-Benson/C 3 cycle is catalyzed by enzyme  Called ribulose biphosphate carboxylase (Rubisco)

33. 2 G3P available for synthesis of organic molecules. 3 RuBP regeneration uses energy and 10 G3P. 2 G3P synthesis uses energy. 1 Carbon fixation combines CO 2 with RuBP.

34. PHOTORESPIRATION Many land plants take up oxygen and release CO 2 in the light. There is a superficial resemblance to true respiration, but the process is much faster. However, it is normally masked by photosynthesis, which is even faster. Photorespiration differs from true respiration. Although plants do respire normally (with mitochondria, etc.) this is useful (produces ATP and NADH), and occurs mostly in the dark. In contrast, photorespiration is wasteful and occurs mostly in the light. Photorespiration appears to serve no useful purpose. Its main effect is to reduce the apparent rate of photosynthesis. Most of our important crops photorespire about half of their potential yield away!

37. PHOTORESPIRATION  A.O 2 competes for CO 2 with RuBP oxidizes it-high oxygen low carbon dioxide  B.CO 2 released without ATP or NADPH  C.C3 lose 1/4 to 1/2 of carbon fixed-40%  D. C4 And CAM plants adapted to counter act this problem  E.Rubisco takes oxygen makes phosphoglycerate and glycolate  F.Goes to perioxisome-takes oxygen and makes a compound that goes to mitochondria to make carbon dioxide like respiration.  A.O 2 competes for CO 2 with RuBP oxidizes it-high oxygen low carbon dioxide  B.CO 2 released without ATP or NADPH  C.C3 lose 1/4 to 1/2 of carbon fixed-40%  D. C4 And CAM plants adapted to counter act this problem  E.Rubisco takes oxygen makes phosphoglycerate and glycolate  F.Goes to perioxisome-takes oxygen and makes a compound that goes to mitochondria to make carbon dioxide like respiration.

40. Much photorespiration occurs under hot, dry conditions. CO 2 is captured with a highly specific enzyme. Almost no photorespiration occurs in hot, dry conditions. Much glucose synthesis occurs. mesophyll cell in C 4 plant mesophyll cell in C 3 plant bundle-sheath cell in C 4 plant bundle- sheath cells C 3 plants use the C 3 pathway C 4 plants use the C 4 pathway In a C 3 plant, most chloroplasts are in mesophyll cells. In a C 4 plant, both mesophyll and bundle-sheath cells contain chloroplasts. (a) (b)

41. ADAPTATIONS  C4 plants-Hatch Slack plants  a. Different leaf structure  b. Bundle sheath surrounded by palisade mesophyll  c. Grasses-Found in hot climates, lots of sun,above 300 C  d. Uses about 2x ATP but stores CO 2 at night or anytime stomates are open. Saves CO 2 when plant can  e. Cycle  1. CO 2 is picked up by PEP in mesophyll-no rubisco  2. Converted to oxaloacetic acid then malic acid  3. Stored in this stable form  4. Malic converted to Pyruvic acid + CO 2  5. Pumped into bundle sheath thru plasmodesmata  6. Deeper than surface because there is less oxygen to cause photorespiration to occur  C4 plants-Hatch Slack plants  a. Different leaf structure  b. Bundle sheath surrounded by palisade mesophyll  c. Grasses-Found in hot climates, lots of sun,above 300 C  d. Uses about 2x ATP but stores CO 2 at night or anytime stomates are open. Saves CO 2 when plant can  e. Cycle  1. CO 2 is picked up by PEP in mesophyll-no rubisco  2. Converted to oxaloacetic acid then malic acid  3. Stored in this stable form  4. Malic converted to Pyruvic acid + CO 2  5. Pumped into bundle sheath thru plasmodesmata  6. Deeper than surface because there is less oxygen to cause photorespiration to occur

42. C4 plants/Hatch Slack  Utilize an alternate pathway to make sugars in dry environments  Closing stomata to conserve water results in photorespiration in C3 plants  Utilize an alternate pathway to make sugars in dry environments  Closing stomata to conserve water results in photorespiration in C3 plants

43. CAM PLANTS  a. Hot(desert) climates-high daytime temps, low soil moisture,intense light  b. Stomates only open at night  c. Central Vacuole stores malic acid  d. Leaves vacuole and and releases CO 2  Diatoms  1. Have both C3 and C4 cycles  2. C3 in chloroplasts  3. C4 in cytosol  4. Uses because of low CO 2 in the ocean  a. Hot(desert) climates-high daytime temps, low soil moisture,intense light  b. Stomates only open at night  c. Central Vacuole stores malic acid  d. Leaves vacuole and and releases CO 2  Diatoms  1. Have both C3 and C4 cycles  2. C3 in chloroplasts  3. C4 in cytosol  4. Uses because of low CO 2 in the ocean