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The Energy Conversion Process of Photosynthesis. Chloroplasts: The Sites of Photosynthesis in Plants  Leaves are the major locations of photosynthesis.

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Presentation on theme: "The Energy Conversion Process of Photosynthesis. Chloroplasts: The Sites of Photosynthesis in Plants  Leaves are the major locations of photosynthesis."— Presentation transcript:

1 The Energy Conversion Process of Photosynthesis

2 Chloroplasts: The Sites of Photosynthesis in Plants  Leaves are the major locations of photosynthesis  Their green color is from chlorophyll, the green pigment within chloroplasts  Light energy absorbed by chlorophyll drives the synthesis of organic molecules in the chloroplast  CO 2 enters and O 2 exits the leaf through microscopic pores called stomata Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

3  Chloroplasts are found mainly in cells of the mesophyll, the interior tissue of the leaf  A typical mesophyll cell has 30–40 chloroplasts  The chlorophyll is in the membranes of thylakoids (connected sacs in the chloroplast); thylakoids may be stacked in columns called grana  Chloroplasts also contain stroma, a dense fluid Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

4 Fig Leaf cross section Vein Mesophyll Stomata CO 2 O2O2 Chloroplast Mesophyll cell Outer membrane Intermembrane space 5 µm Inner membrane Thylakoid space Thylakoid Granum Stroma 1 µm

5 Fig. 10-3a 5 µm Mesophyll cell Stomata CO 2 O2O2 Chloroplast Mesophyll Vein Leaf cross section

6 Fig. 10-3b 1 µm Thylakoid space Chloroplast Granum Intermembrane space Inner membrane Outer membrane Stroma Thylakoid

7 Photosynthesis  Photosynthesis-  Converting solar energy into the usable energy of carbohydrates.  Photosynthesis requires:  Light Energy  Carbon Dioxide  Water  Chlorophyll Putting together with light

8  Chloroplasts split H 2 O into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules.  Photosynthesis consists of the light reactions (the photo part) and Calvin cycle (the synthesis part)  The light reactions (in the thylakoids):  Split H 2 O  Release O 2  Reduce NADP + to NADPH  Generate ATP from ADP by photophosphorylation

9 Light Energy  Photon- packets of Energy  Light travels in waves and is a type of radiation  Short wave length radiation has high energy photons  Long wave length radiation has lower energy photons

10 Light Energy  Photons of visible light have enough energy to raise electrons to higher levels of energy which is needed for photosynthesis.  Visible light energy is absorbed by plants to produce sugar. (C 6 H 12 O 6 )  Chlorophyll is the substance that absorbs light energy.

11 Pop Quiz  1. In your own words, define photosynthesis  2. In your own words, define cellular respiration.  3. What is ATP  4. How is ATP generated or made?  5. Which bond in ATP is loaded with energy?

12 Chlorophyll (borophyll)  Two Types of Chlorophyll  Chlorophyll A  Chlorophyll B  Carotenoids  Other pigments that are yellow-orange in plants which absorb violets, blues, and greens. As chlorophyll A and B breakdown they become more noticeable, especially during the fall. Both absorb violet, blue, and red light. Because green is only minimally absorbed, the leaf appears green. The green light is reflected off of the leaf. }

13 Photosynthesis- the formula  6 CO H 2 O  C 6 H 12 O O 2 LIGHT CHLOROPHYLL

14 Light Fig H2OH2O Chloroplast Light Reactions NADP + P ADP i +

15 Light Fig H2OH2O Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2

16 Light Fig H2OH2O Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2 Calvin Cycle CO 2

17 Chloroplasts – contain chlorophyll  Chloroplasts are double membrane organelles. (See figure in book)  Note the granum, stroma, thylakoid, and thylakoid space  Chlorophyll is found within the membranes of the thylakoids

18 Photosynthesis has two reactions  Light dependent Reactions (light RXN)  Light capturing reaction  absorbs solar energy  Occurs in the thylakoid membrane  Light independent Reactions (dark RXN) Now called the Calvin Cycle  Synthesis reaction  Produces glucose  Occurs in the stroma

19 Light Dependent Reactions  Takes place in the thylakoid membrane  Requires two light gathering systems  Photosystems- systems used to gather solar energy which contain chlorophyll A,B, and carotenoids.  The photosystems were named in the order that they were discovered, not the order in which they occur.  Photosystem I (PSI) The molecules of Chlorophyll a & b which make up the photosystems Photosystem II (PSII)act like antennas gathering solar energy and focus it to a particular spot. }

20 Light Fig H2OH2O Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2 Calvin Cycle CO 2 [CH 2 O] (sugar)

21 PSI and PSII  Basically, the function of the photosystems is to convert energy so that glucose can be produced. This is accomplished by generating electron flow.  Sometimes PSI occurs exclusively called the cyclic electron pathway.  When both PSI and PSII occur PSII occurs first and then PSI. This process is the non-cyclic electron pathway.

22 Generating electron flow  Energy is directed onto a particular molecule of chlorophyll A. The electrons of this molecule are so excited that they escape their orbitals and move through a series of electron acceptors.  Reaction center- The molecule of chlorophyll A that loses an electron.

23 Fig THYLAKOID SPACE (INTERIOR OF THYLAKOID) STROMA e–e– Pigment molecules Photon Transfer of energy Special pair of chlorophyll a molecules Thylakoid membrane Photosystem Primary electron acceptor Reaction-center complex Light-harvesting complexes

24 Cyclic Electron Pathway (PS1) ( not play station 1 )  An electron leaves the RXN center but eventually returns to it.  As the electron is passed from acceptor to acceptor Energy for ATP is released.  Occurs when:  CO 2 levels are extremely low  by photosynthetic bacteria

25 Cyclic pathway – PS1 ( cont. )  Does not produce NADPH  Produces ONLY ATP  Probably first to evolve,  Because CO 2 levels are low no glucose is produced and the organism must survive on the small amount of ATP that is generated

26 Non-cyclic Pathway (PS 2) (not play station 2)  Water is split and an electron enters PSII  Causes the reaction center to lose an electron and travel through a series of electron acceptors.  As the electron is passed along ATP is generated. This ATP will be used in the Light independent reactions  The electron then enters PSI which during the non-cyclic pathway produces the molecule NADPH instead of ATP.

27 Non-cyclic (cont.)  The products of the non-cyclic pathway, NADPH and ATP, enter the Stroma  NADP is one of several biological molecules that act as an electron carrier.  In the stroma, the light independent reactions occur.  The splitting of water results in a H ion (which is basically an electron) and O which is released from the leaf as a waste product.

28 Pigment molecules Light P680 e–e– Primary acceptor 2 1 e–e– e–e– 2 H + O2O2 + 3 H2OH2O 1/21/2 4 Pq Pc Cytochrome complex Electron transport chain 5 ATP Photosystem I (PS I) Light Primary acceptor e–e– P700 6 Fd Electron transport chain NADP + reductase NADP + + H + NADPH 8 7 e–e– e–e– 6 Fig Photosystem II (PS II)

29 Fig Light Reactions: Photosystem II Electron transport chain Photosystem I Electron transport chain CO 2 NADP + ADP P i + RuBP 3-Phosphoglycerate Calvin Cycle G3P ATP NADPH Starch (storage) Sucrose (export) Chloroplast Light H2OH2O O2O2

30 Photophosphorylation  Occurs when ATP is generated using photosynthesis.  Photophosphorylation occurs because of severe differences in the concentration of H+ ions inside the thylakoid space compared to the stroma.  The movement of ions allows for a phosphate to be added to ADP.

31 Diagram of the Light Dependent Reactions and ATP Synthase

32 Quiz 1. How is the cyclic pathway different than the non-cyclic pathway? 2. In the non-cyclic pathway, what produces ATP? 3. In the non-cyclic pathway, what produces NADPH? 4. What is the role of NADPH?

33 Light Independent Reactions AKA- Calvin Cycle (The Dark RXN)  The products of the light dependent reactions are NADPH and ATP.  Both are used in the light independent reactions.  The actual process of producing glucose during the light independent RXN is called the Calvin Cycle.

34 A Comparison of Chemiosmosis in Chloroplasts and Mitochondria  Chloroplasts and mitochondria generate ATP by chemiosmosis, but use different sources of energy  Mitochondria transfer chemical energy from food to ATP; chloroplasts transform light energy into the chemical energy of ATP  Spatial organization of chemiosmosis differs between chloroplasts and mitochondria but also shows similarities

35  In mitochondria, protons are pumped to the intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix  In chloroplasts, protons are pumped into the thylakoid space and drive ATP synthesis as they diffuse back into the stroma

36 Fig Key Mitochondrion Chloroplast CHLOROPLAST STRUCTURE MITOCHONDRION STRUCTURE Intermembrane space Inner membrane Electron transport chain H+H+ Diffusion Matrix Higher [H + ] Lower [H + ] Stroma ATP synthase ADP + P i H+H+ ATP Thylakoid space Thylakoid membrane

37  In summary, light reactions generate ATP and increase the potential energy of electrons by moving them from H 2 O to NADPH Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

38 The Calvin Cycle (light independent reactions)  Has three steps/parts (see fig) 1. CO 2 fixation 2. CO 2 reduction 3. Regeneration of RuBP  RuBP is a 5 carbon compound that will combine with CO 2 to form a 6 Carbon Compound. Remember, glucose is a 6 C compound

39 Step 1- CO 2 Fixation  Refers to the attachment of CO 2 to an organic compound.  3 CO 2 bind with 3 RuBP molecules.  Results in 3 six Carbon compounds  which change to 6 three carbon compounds  The three Carbon compound is called PGA  The Calvin Cycle is sometimes called the C-3 cycle because of PGA.

40 Fig Ribulose bisphosphate (RuBP) 3-Phosphoglycerate Short-lived intermediate Phase 1: Carbon fixation (Entering one at a time) Rubisco Input CO 2 P P P P P

41 Step 2 - CO 2 Reduction  Requires ATP and NADPH (from light RXN)  PGA gets converted to G3P (PGAL) using ATP and NADPH.  ATP  ADP + P  NADPH  NADP  PGA  G3P (PGAL)  The reduction of CO 2 to CH 2 O results in 6 total PGAL molecules.  5 molecules of G3P (PGAL) will be used to regenerate RuBP.  It takes 3 turns of the Calvin Cycle to have a net gain of 1 G3P (PGAL)

42 Fig Ribulose bisphosphate (RuBP) 3-Phosphoglycerate Short-lived intermediate Phase 1: Carbon fixation (Entering one at a time) Rubisco Input CO 2 P P P P P ATP 6 6 ADP P P 6 1,3-Bisphosphoglycerate 6 P P NADP + NADPH i Phase 2: Reduction Glyceraldehyde-3-phosphate (G3P) 1 P Output G3P (a sugar) Glucose and other organic compounds Calvin Cycle

43 G3P (PGAL)  Glucose  Glucose is used to produce ATP  Plants need several other organic compounds.  G3P (PGAL) can be converted to many other compounds such as: fatty acids, Amino Acids, and of course Glucose.  Technically, the Calvin cycle ends with the production of G3P (PGAL)

44 Step 3 - RuBP Regeneration  5 (PGAL) G3P  3 RuBP  3 ATP  3 ADP + P  ATP comes from the light dependent reactions

45 Fig Ribulose bisphosphate (RuBP) 3-Phosphoglycerate Short-lived intermediate Phase 1: Carbon fixation (Entering one at a time) Rubisco Input CO 2 P P P P P ATP 6 6 ADP P P 6 1,3-Bisphosphoglycerate 6 P P NADP + NADPH i Phase 2: Reduction Glyceraldehyde-3-phosphate (G3P) 1 P Output G3P (a sugar) Glucose and other organic compounds Calvin Cycle 3 3 ADP ATP 5 P Phase 3: Regeneration of the CO 2 acceptor (RuBP) G3P

46 Fig Light Reactions: Photosystem II Electron transport chain Photosystem I Electron transport chain CO 2 NADP + ADP P i + RuBP 3-Phosphoglycerate Calvin Cycle G3P ATP NADPH Starch (storage) Sucrose (export) Chloroplast Light H2OH2O O2O2

47 Variations in Photosynthesis  The C-3 Pathway –  CO 2 is fixed during the Calvin cycle, and the first detectable molecule is a 3 Carbon compound (PGA).  The C-4 Pathway –  CO 2 is fixed to a 3 C compound (forming a 4 C compound) prior to the Calvin Cycle.  CAM Plant Pathway –  Similar to the C- 4 Pathway, but at a slightly different time.

48 C-3 Pathway  Occurs in the mesophyll of the leaf  RuBP  PGA  P3G (PGAL)  See Figure

49 C-4 Pathway  CO 2 is attached to a 3 C compound called PEP with an enzyme called PEP-carboxylase.  This process forms oxaloacetate and occurs in the mesophyll.  Oxaloacetate enters the bundle sheath cells where the Calvin Cycle takes place  Occurs in warm dry climates  Partition PSS in space  See Figure 10.14

50 Fig b Sugar CO 2 Bundle- sheath cell ATP ADP Oxaloacetate (4C) PEP (3C) PEP carboxylase Malate (4C) Mesophyll cell CO 2 Calvin Cycle Pyruvate (3C) Vascular tissue The C 4 pathway

51 CAM plant Pathway  A C4 compound is produced similar to the C-4 pathway.  That compound is produced during the night, and stored in the vacuole until day.  Occurs in the mesophyll  Occurs in hot, dry and stressful environments  Allows Stomates to open at night when it is cooler and less water is lost to evaporation.

52 Fig CO 2 Sugarcane Mesophyll cell CO 2 C4C4 Bundle- sheath cell Organic acids release CO 2 to Calvin cycle CO 2 incorporated into four-carbon organic acids (carbon fixation) Pineapple Night Day CAM Sugar Calvin Cycle Calvin Cycle Organic acid (a) Spatial separation of steps (b) Temporal separation of steps CO 2 1 2

53 The Importance of Photosynthesis: A Review  The energy entering chloroplasts as sunlight gets stored as chemical energy in organic compounds  Sugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the organic molecules of cells  Plants store excess sugar as starch in structures such as roots, tubers, seeds, and fruits  In addition to food production, photosynthesis produces the O 2 in our atmosphere


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