1. AP Biology Ms. Haut

2. Light energy enzymes  Photosynthesis is the process that converts solar energy into chemical energy  Directly or indirectly, photosynthesis nourishes almost the entire living world  Photosynthesis—process in which some of the solar energy is captured by plants (producers) and transformed into glucose molecules used by other organisms (consumers). 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2

3.  Glucose is the main source of energy for all life. The energy is stored in the chemical bonds.  Cellular Respiration— process in which a cell breaks down the glucose so that energy can be released. This energy will enable a cell to carry out its activities. C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + energy enzymes

4.  Autotroph —organisms that synthesize organic molecules from inorganic materials (a.k.a. producers) –Photoautotrophs —use light as an energy source (plants, algae, some prokaryotes) –Chemoautotrophs —use the oxidation of inorganic substances (some bacteria) Heterotroph —organisms that acquire organic molecules from compounds produced by other organisms (a.k.a. consumers)

6. Sunlight = electromagnetic energy Wavelike properties Particlelike properties (photon) Thylakoids trap sunlight Light may be reflected, transmitted, or absorbed when it contacts matter

7.  Pigments are substances that absorb visible light  Different pigments absorb different wavelengths  Wavelengths that are not absorbed are reflected or transmitted  Leaves appear green because chlorophyll reflects and transmits green light

8.  Absorb light of varying wavelengths and transfer the energy to chlorophyll a  Chlorophyll b -yellow-green pigment  Carotenoids -yellow and orange pigments

9.  An absorption spectrum is a graph plotting a pigment’s light absorption versus wavelength  The absorption spectrum of chlorophyll a suggests that violet-blue and red light work best for photosynthesis  An action spectrum profiles the relative effectiveness of different wavelengths of radiation in driving a process

10.  Endergonic redox process; energy is required to reduce CO 2  Light is the energy source that boosts potential energy of electrons (e-) as they are moved from water to CO 2  When water is split, e- are transformed from the water to CO 2, reducing it to sugar

11. 6CO 2 + 6H 2 O reduction oxidation C 6 H 12 O 6 + 6O 2

12.  Photosynthesis consists of the light reactions (the photo part) and Calvin cycle (the synthesis part)  Light reactions (in the thylakoids) split water, release O 2, produce ATP, and form NADPH  Calvin cycle (in the stroma) forms sugar from CO 2, using ATP and NADPH  The Calvin cycle begins with carbon fixation, incorporating CO 2 into organic molecules

13.  Light reactions —convert light energy to chemical bond energy in ATP and NADPH  Occurs in thylakoids in chloroplasts  NADP+ reduced to NADPH—temporary energy storage (transferred from water)  Give off O 2 as a by-product  Generates ATP by phosphorylating ADP

14.  Calvin Cycle —carbon fixation reactions assimilate CO2 and then reduce it to a carbohydrate  Occur in the stroma of the chloroplast  Do not require light directly, but requires products of the light reactions  Incorporates into existing organic molecules and then reduces fixed carbon into carbohydrate  NADPH provides the reducing power  ATP provides chemical energy

15. Light reactions produce: ATP and NADPH that are used by the Calvin cycle; O 2 released Calvin Cycle produces: ADP and NADP+ that are used by the light reactions; glucose produced Interdependent Reactions

16.  Photosystem: assemblies of several hundred chlorophyll a, chlorophyll b, and carotenoid molecules in the thylakoid membrane  form a light gathering antennae that absorb photons and pass energy from molecule to molecule  Photosystem I —specialized chlorophyll a molecule, P700  Photosystem II —specialized chlorophyll a molecule, P680

18. Light drives the light reactions to synthesize NADPH and ATP Includes cooperation of both photosystems, in which e- pass continuously from water to NADP+

19. 1.When photosystem II absorbs light an e- is excited in the reaction center chlorophyll (P680) and gets captured by the primary e- acceptor. This leaves a hole in the P680

20. 2.To fill the hole left in P680, an enzyme extracts e- from water and supplies them to the reaction center A water molecule is split into 2 H+ ions and an oxygen atom, which immediately combines with another oxygen to form O2

21. 3.Each photoexcited e- passes from primary e- acceptor to photosystem I via an electron transport chain. e- are transferred to plastoquinone (Pq) and plastocyanin (Pc) (e- carriers)

22. 4.As e- cascade down the e- transport chain, energy is released and harnessed by the thylakoid membrane to produce ATP (PHOTOPHOSPHORYLATION) This ATP is used to make glucose during Calvin cycle

23. 5.When e- reach the bottom of e- transport chain, it fills the hole in the reaction center P700 of photosystem I. Pre-existing hole was left by former e- that was excited

24. 6.When photosystem I absorbs light an e- is excited in the reaction center chlorophyll (P700) and gets captured by the primary e- acceptor. e- are transferred to ferredoxin (Fd) (e- carrier) NADP+ reductase transfers e- from Fd to NADP+, storing energy in NADPH (reduction reaction) NADPH provides reducing power for making glucose in Calvin cycle

25.  Only photosystem I is used  Only ATP is produced

26. Chemiosmosis  Energy released from e- transport chain is used to pump H+ ions (from the split water) from the stroma across the thylakoid membrane to the interior of the thylakoid.  Creates concentration gradient across thylakoid membrane  Process provides energy for chemisomostic production of ATP

27. LIGHT REACTOR NADP + ADP ATP NADPH CALVIN CYCLE [CH 2 O] (sugar) STROMA (Low H + concentration) Photosystem II LIGHT H2OH2O CO 2 Cytochrome complex O2O2 H2OH2O O2O2 1 1⁄21⁄2 2 Photosystem I Light THYLAKOID SPACE (High H + concentration) STROMA (Low H + concentration) Thylakoid membrane ATP synthase Pq Pc Fd NADP + reductase NADPH + H + NADP + + 2H + To Calvin cycle ADP P ATP 3 H+H+ 2 H + +2 H + 2 H + Figure 10.17  The light reactions and chemiosmosis: the organization of the thylakoid membrane

28.  Carbon enters the cycle in the form of CO 2 and leaves in the form of sugar (glucose)  The cycle spends ATP as an energy source and consumes NADPH as a reducing agent for adding high energy e- to make sugar  For the net synthesis of this sugar, the cycle must take place 2 times

30. Calvin Cycle

32. 1.Carbon Fixation: 3 CO 2 molecules bind to 3 5- Carbon sugars, ribulose bisphosphate (RuBP) using enzyme called RuBP carboxylase (rubisco) Produces 6 molecules of a 3-carbon sugar, 3-phosphoglycerate

33. 1.Carbon Fixation 2.Reduction: 6 ATP molecules transfer phosphate group to each molecule of 3-phos. to make 1,3- diphosphoglycerate 6 molecules of NADPH reduce each molecule of 1,3-diphosph. to make glyceraldehyde 3- phosphate (G3P) 3.One of the G3P exits the cycle to be used by the plant; the other 5 molecules are used to regenerate the CO 2 acceptor, RuBP: 3 molecules of ATP are used to convert 5 molecules of G3P into RuBP

34. 3 more CO 2 molecules enter the cycle, following the same chemical pathway to release another G3P from the cycle. 2 G3P molecules can be used to make glucose

36. Interdependent

37.  Dehydration is a problem for plants, sometimes requiring tradeoffs with other metabolic processes, especially photosynthesis  On hot, dry days, plants close stomata, which conserves water but also limits photosynthesis  The closing of stomata reduces access to CO 2 and causes O 2 to build up  These conditions favor a seemingly wasteful process called photorespiration

38. In most plants (C 3 plants), initial fixation of CO 2, via rubisco, forms a three-carbon compound In photorespiration, rubisco adds O 2 to the Calvin cycle instead of CO 2  Photorespiration consumes O 2 and organic fuel and releases CO 2 without producing ATP or sugar

39. Photorespiration may be an evolutionary relic because rubisco first evolved at a time when the atmosphere had far less O 2 and more CO 2  In many plants, photorespiration is a problem because on a hot, dry day it can drain as much as 50% of the carbon fixed by the Calvin cycle

40.  C 4 plants minimize the cost of photorespiration by incorporating CO 2 into four-carbon compounds in mesophyll cells  These four-carbon compounds are exported to bundle- sheath cells, where they release CO 2 that is then used in the Calvin cycle Corn Crab Grass

41.  PEP carboxylase-high affinity to CO 2 and no affinity for O 2, thus no photorespiration possible C 4 Plants

42.  CAM plants open their stomata at night, incorporating CO 2 into organic acids  Organic acids stored in vacuoles of mesophyll cells until morning, when stomata close  Stomata close during the day, and CO 2 is released from organic acids and used in the Calvin cycle http://ecology.botany.ufl.edu/ecologyf02/graphics/saguaro.GIF

43. Bundle- sheath cell Mesophyll cell Organic acid C4C4 CO 2 CALVIN CYCLE SugarcanePineapple Organic acids release CO 2 to Calvin cycle CO 2 incorporated into four-carbon organic acids (carbon fixation) Organic acid CAM CO 2 CALVIN CYCLE Sugar Spatial separation of stepsTemporal separation of steps Sugar Day Night

44.  Are similar in that CO 2 is first incorporated into organic intermediates before it enters the Calvin cycle  Differ in that the initial steps of carbon fixation in C4 plants are structurally separate from the Calvin cycle; in CAM plants, the two steps occur at separate times  Regardless of whether the plant uses C3, C4, or CAM pathway, all plants use the Calvin Cycle to produce sugar from CO 2 The CAM and C4 pathways: