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Photosynthesis

Photosynthesis. More energy needs = more air pollution. Researchers are turning to plants as a clean energy source. Willows: grow fast, reproduce when cut, require low fertilizers and low pesticide

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Photosynthesis

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  1. Photosynthesis

  2. More energy needs = more air pollution

  3. Researchers are turning to plants as a clean energy source • Willows: grow fast, reproduce when cut, require low fertilizers and low pesticide • Make 5-8 tons of wood/acre/year versus natural forests which make only 0.5-1 ton of wood/acre/year

  4. 2 Types of Feeders Autotroph(Producer) Heterotroph Consumers Cannot make their own food from inorganic material Must consume, plant animal or both • Plants, algae, some Protists and some bacteria • Capable of making organic from inorganic • Phototrophs use light • Chemotrophs use chemicals

  5. Figure 7.1A Forest plants.

  6. Figure 7.1B Wheat field.

  7. Figure 7.1C Kelp, a large algae.

  8. Figure 7.1D Micrograph of cyanobacteria (photosynthetic bacteria).

  9. Chloroplast • Organelle where photosynthesis occurs • Contains the pigment chlorophyll which traps energy in the form of light • CO2 enters through the pours (stomata) on the leaves of plants • H20 enters through the roots of the plant and is carried to chloroplast by veins

  10. Other parts of the leave… • Chloroplasts are concentrated in the cells of the mesophyll, the green tissue in the interior of the leaf • An envelope of two membranes encloses the stroma, the dense fluid within the chloroplast • A system of interconnected membranous sacs called thylakoids segregates the stroma from another compartment, the thylakoid space • Thylakoids are concentrated in stacks called grana

  11. Leaf Cross Section Leaf Mesophyll Vein Stoma CO2 O2 Mesophyll Cell Chloroplast Outer and inner membranes Intermembrane space Thylakoid Stroma Granum Thylakoid space  TEM 9750x

  12. Leaf Cross Section Leaf Mesophyll Vein Stoma CO2 O2 Mesophyll Cell Chloroplast

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

  14. Is the oxygen gas from the carbon dioxide or the water? How do they know which product is from which reactant? Light energy 6 + 6 H2O CO2 C6H12O6 O2 + 6 Oxygen gas Carbon dioxide Water Glucose Photosynthesis

  15. How do they know which product is from which reactant? Radioactive ISOTOPES! Experiment 1 C6H12O6 + 6 H2O + 6 O2 6 CO2 + 12 H2O Not labeled Experiment 2 C6H12O6 + 6 H2O + 6 O2 6 CO2 + 12 H2O Labeled

  16. Reactants: 6 CO2 12 H2O 6 H2O 6 O2 C6H12O6 Products:

  17. PHOTOSYNTHESIS IS A REDOX What get’s oxidized? Water….to become oxygen What get’s reduced? CO2….to become glucose

  18. In other words……… Reduction C6H12O6 + 6 O2 6 CO2 + 6 H2O Oxidation

  19. Remember: CELLULAR RESPIRATION WAS ALSO A REDOX REACTION What get’s oxidized? Glucose….to become CO2 What get’s reduced? Oxygen…….to become H20

  20. In other words…. Oxidation 6 CO2 + 6 H2O C6H12O6 + 6 O2 Reduction

  21. 7.5 Overview: The two stages of photosynthesis are linked by ATP and NADPH • Actually, photosynthesis occurs in two metabolic stages • One stage involves the light reactions • In the light reactions, light energy is converted in the thylakoid membranes to chemical energy and O2 • Water is split to provide the O2 as well as electrons

  22. 7.5 Overview: The two stages of photosynthesis are linked by ATP and NADPH • H+ ions reduce NADP+ to NADPH, which is an electron carrier similar to NADH • NADPH is temporarily stored and then shuttled into the Calvin cycle where it is used to make sugar • Finally, the light reactions generate ATP

  23. 7.5 Overview: The two stages of photosynthesis are linked by ATP and NADPH • The second stage is the Calvin cycle, which occurs in the stroma of the chloroplast • It is a cyclic series of reactions that builds sugar molecules from CO2 and the products of the light reactions • During the Calvin cycle, CO2 is incorporated into organic compounds, a process called carbon fixation

  24. 7.5 Overview: The two stages of photosynthesis are linked by ATP and NADPH • NADPH produced by the light reactions provides the electrons for reducing carbon in the Calvin cycle • ATP from the light reactions provides chemical energy for the Calvin cycle • The Calvin cycle is often called the dark (or light-independent) reactions

  25. H2O Chloroplast Light NADP+ ADP  P LIGHT REACTIONS (in thylakoids)

  26. H2O Chloroplast Light NADP+ ADP  P LIGHT REACTIONS (in thylakoids) ATP Electrons NADPH O2

  27. CO2 H2O Chloroplast Light NADP+ ADP  P LIGHT REACTIONS CALVIN CYCLE (in stroma) (in thylakoids) ATP Electrons NADPH Sugar O2

  28. Light Reactions!

  29. Light Reactions! • Chlorophyll a absorbs blueviolet and red • Chlorophyll b absorbs blue and orange • Both reflect green • Carotenoids absorb blue-green light and reflect yellow and orange. • Light is absorbed in a unit quantity called photon • The shorter the wavelength, the greater the energy

  30. Light Reflected light Chloroplast Absorbed light Thylakoid Transmitted light

  31. Light Reactions! • Reactants: NADP, ADP+P, Water and light • Products: NADPH, ATP and oxygen

  32. Light Reactions! • Pigments in chloroplasts (chlorophyll and carotenoids) are responsible for absorbing photons (capturing solar power), causing release of electrons. • The electrons jump to a higher energy level—the excited state—where electrons are unstable • The electrons drop back down to their “ground state,” and, as they do, release their excess energy

  33. Light Reactions! • The energy released could be lost as heat or light… but here it is conserved as it is passed from one molecule to another molecule • All of the components to accomplish this are organized in thylakoid membranes in clusters called photosystems • Photosystemsare light-harvesting complexes surrounding a reaction center complex

  34. Photosystem Light-harvesting complexes Reaction center complex Photon Primary electron acceptor e– Thylakoid membrane Transfer of energy Pigment molecules Pair of Chlorophyll a molecules

  35. Light Reactions! • Two types of photosystems have been identified and are called photosystem I and photosystem II • Photosystem II, which functions first, is called P680 because its pigment absorbs light with a wavelength of 680 nm • Photosystem I, which functions next, is called P700 because it absorbs light with a wavelength of 700 nm

  36. Light Reactions! • Finally, the electrons reach the reaction center where a primary electron acceptor accepts them and becomes reduced. • This solar-powered transfer of an electron from the pigment (in the reaction center) to the primary electron acceptor is the first step of the light reactions.

  37. e– ATP The easier way to explain e– e– NADPH e– e– e– Mill makes ATP Photon e– Photon Photosystem II Photosystem I

  38. Electron transport chain Provides energy for synthesis of by chemiosmosis H+ NADPH NADP+ + Photon Photon Photosystem I ATP 6 Photosystem II Stroma 1 Primary acceptor Primary acceptor e– 2 e– Thylakoid mem- brane 4 5 P700 P680 Thylakoid space 3 H2O H+ + 2 O2 1  2 The reality…..

  39. Calvin Cycle

  40. Calvin Cycle • Occurs in stroma • The ATP and NADPH made in light reactions are used to power the process of carbon fixation. • CO2 combines with 5-C ribulosebiphosphate (RuBP) to make a very unstable 6-C compound, which splits immediately into 2 3-C compounds: G3P. • What does this remind you of?!?!

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

  42. 1 Step Carbon fixation Input: 3 CO2 Rubisco 1 Step Reduction 2 P P 3 P 6 RuBP 3-PGA 6 ATP 6 ADP + P CALVIN CYCLE 2 NADPH 6 6 NADP+ P 6 G3P

  43. Calvin Cycle • For every 1 CO2 which enters the Calvin cycle, 2 G3P molecules are created. • So after 3 CO2 enter into the Calvin cycle (and 3 “turns” of the Calvin Cycle), ____ G3P molecules will be made. • 5 of the G3P molecules stay in the Calvin cycle, and 1 leaves. • The G3P that leaves will be reduced to glucose • The 5 Carbons that stay in the Calvin cycle are rearranged using ATP to reconstruct RuBP. • So to make 1 glucose, the Calvin cycle needs to be turned 6 times! • Final Products: Glucose, ADP, and NADP+

  44. CO2 ATP NADPH Input CALVIN CYCLE G3P Output:

  45. 1 Step Carbon fixation Input: 3 CO2 Rubisco 1 Step Reduction 2 P P 3 P 6 RuBP 3-PGA 6 ATP 6 ADP + P CALVIN CYCLE 2 NADPH 6 6 NADP+ P 6 G3P

  46. 1 Step Carbon fixation Input: 3 CO2 Rubisco 1 Step Reduction 2 P P 3 P 6 RuBP 3-PGA 6 ATP 6 ADP + P CALVIN CYCLE Step Release of one molecule of G3P 2 3 NADPH 6 6 NADP+ P P 5 6 G3P G3P 3 Glucose and other compounds Output: P 1 G3P

  47. 1 Step Carbon fixation Input: 3 CO2 Rubisco 1 Step Reduction 2 P P 3 P 6 RuBP 3-PGA 6 ATP 3 ADP 6 ADP + P 3 ATP CALVIN CYCLE Step Release of one molecule of G3P 4 2 3 NADPH 6 6 NADP+ P P 5 6 Step Regeneration of RuBP 4 G3P G3P 3 Glucose and other compounds Output: P 1 G3P

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