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Photosynthesis

Photosynthesis. Chapters 10. Bell Ringer. Answer the following question on a sheet of paper and turn it into the tray. You may NOT use your notes, a classmate, or your textbook.

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Photosynthesis

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  1. Photosynthesis Chapters 10

  2. Bell Ringer • Answer the following question on a sheet of paper and turn it into the tray. You may NOT use your notes, a classmate, or your textbook. A glucose-fed yeast cell is moved from an aerobic environment to an anaerobic one. How would its rate of glucose consumption change if ATP were to be generated at the same rate?

  3. What is Photosynthesis? • Conversion of light energy from the sun to chemical energy stored in sugar and other organic molecules

  4. What is the ecologial context for Photosynthesis? • Organism acquire the organic compounds that it uses for energy in two major modes: • Autotrophic • Heterotrophic

  5. What are autotrophs? • Self-feeder • Sustain themselves without eating anything derived from other living beings • Produce their organic molecules from CO2 and other inorganic raw materials • Are ultimate source of organic compounds for all nonautotrophic organism • PRODUCERS

  6. What are autotrophs? • Plants are photoautotrophs • Organisms that use light as a source of energy to synthesize organic substances

  7. What are heterotrophs? • Unable to make their own food • Live on compounds produced by other organisms • Completely dependent on other photoautotrophs for food and oxygen • “other-feeding” • CONSUMERS

  8. What is the site for Photosynthesis in plants? • Chloroplasts • Found in green parts of plants • About ½ million chloroplasts per square millimeter of leaf surface • Leaves are major site of photosynthesis in most plants

  9. Where does the green color come from? • Chlorophyll • Green pigment located within chloroplasts • Light energy absorbed by chlorophyll drives the synthesis of organic molecules in the chloroplast • Mainly found in the mesophyll

  10. What is the mesophyll? • Mesophyll- tissue in the interior of the leaf. Where chloroplasts are found. • Typical mesophyll has 30 – 40 chloroplasts

  11. What other parts of the plant are important? • CO2 enters the leaf and oxygen exits through the stomatat

  12. What is the stomata? • Stomata- microscopic pores in the leaf that allow CO2 and O2 enter and exit.

  13. What other parts of the plant are important? • Stroma – • Dense fluid within the chloroplast • Enclosed by envelope of two membranes • Thylakoids – • System of interconnected membranous sacs • Segregate the stroma from interior of thylakoid(thylakoid space) • Stacked in columns, they are called grana

  14. What is photosynthesis? 6CO2 + 12 H2O + Light energy -> C6H12O6 + 6 O2+ 6H2O

  15. Photosynthesis • The O2 given off in photosynthesis comes from H2O, not CO2.

  16. Two stages of Photosynthesis • Light Reactions • Calvin cycle (AKA Dark Reaction)

  17. Photosynthesis • Light Reactions- solar energy is captured (by chlorophyll in the thylakoids) and converted into chemical energy (ATP and NADPH). • Photophosphorylation- creates ATP through the use of the ETC in the light reactions.

  18. Photosynthesis • Dark Reactions/Calvin Cycle- chemical energy is used to make organic compounds of food. (ie: glucose) Occurs in stroma. • Carbon Fixation- CO2 (from air) is combined with molecules present in chloroplast to form organic molecules that are reduced to carbohydrates. (w/NADPH)

  19. Light Energy • What is the nature of sunlight? • Light is a form of energy known as electromagnetic energy • AKA – electromagnetic radiation • Travels in rhythmic waves • Wavelengths – distance between crests of electromagnetic waves • Electromagnetic spectrum – entire range of radiation

  20. Light Energy • What is the nature of sunlight? • Visible light – can be detected as various colors by human eye

  21. Light Energy • Photons- packets of light energy. • Pigments- substances that absorb visible light. • Chlorophyll a, chlorophyll b, carotenoids. • Spectrophotometer- instrument that measures the ability of a pigment to absorb various wavelengths of light.

  22. Absorption Spectrumand Action Spectrum • Absorption Spectrum – • Graph plotting a pigment’s light absorption versus wavelength • Action Spectrum – • Profiles the relative effectiveness of different wavelengths of radiation in driving the process of photosynthesis • Prepared by illuminating chloroplasts and then plotting wavelengths against some measure of photosynthetic rate

  23. Absorption Spectrumand Action Spectrum

  24. Absorption Spectrum and Action Spectrum

  25. Pigments • Chlorphyll a – • Considered Blue – green • Absorb violet – blue and red • Chlorophyll b – • Considered Olive green • Absorbs at slightly different wavelengths of red and blue • Carotenoids – • Hydrocarbons that are various shades of yellow and orange • Absorb violet and blue-green • Important function in photoprotection • Photoprotection – • - they absorb and dissipate excessive light that would otherwise damage the chlorophyll or interact with oxygen, forming oxidative molecules that might be dangerous to the cell

  26. What happens when chlorophyll and other pigments absorb light? • When a photon of light is absorbed, one of the molecule’s electrons is elevated to an orbital where it has more potential energy • Ground state – non-elevated electron • Excited state – elevated electron • Unstable • Can’t remain long

  27. Photosystems • Photosystems- composed of a reaction center complex surrounded by light harvesting complexes (pigment molecules + proteins). • PS II (P680) and PS I (P700)

  28. Photosystems • What is a reaction – center complex? • Includes a special pair of chlorophyll a molecules • What is a light – harvesting complex? • Includes various pigment molecules bound to proteins

  29. Photosystems • Energy is transferred from pigment molecule to a pigment molecule within the light-harvesting complex, until it is passed into the reaction-center complex. • The reaction center complex contains a molecule capable of accepting electrons and becoming reduced, called the primary electron acceptor.

  30. Photosystems • Thylakoid membrane is populated by two types of photosystems that cooperate in the light reaction • PS II (P680) and PS I (P700) • Name in order of discover

  31. Photosystems • PS II (P680) • Absorbs best at wavelength of 680 nm • PS I (P700) • Absorbs best at wavelength of 700 nm

  32. Two stages of Photosynthesis • Light Reactions • Calvin cycle (AKA Dark Reaction)

  33. Photosynthesis • Light Reactions- solar energy is captured (by chlorophyll in the thylakoids) and converted into chemical energy (ATP and NADPH). • Photophosphorylation- creates ATP through the use of the ETC in the light reactions.

  34. The Light Reactions • As electrons fall back to its ground state an electron in a nearby pigment is excited • Photon of light is absorbed by chlorophyll a pigment molecule in PS II exciting electrons. • Electrons are passed along pigment molecules in the light-harvesting complex, to the reaction center complex, and ultimately to the primary electron acceptor. • Water molecule is split into 2 e-, 2 H+ and O. These e- are transferred back to P680 and H+ is released to lumen of thylakoid. O combines with O from previous water splitting to release O2.

  35. The Light Reactions • Electrons are passed from primary electron acceptor in PS II down the ETC to PS I. As electrons pass through the ETC, ATP is generated. • Meanwhile, PS I has absorbed light, excited electrons, that are assed on to P700 and to primary electron acceptor, leaving p700 without electrons. • P700 accepts electrons from ETC (that came from PS II).

  36. The Light Reactions • Excited electrons are passed from primary electron acceptor of PS I through a second ETC. • Electrons move through a protein called ferredoxin and to NADP+ reductase, where they are accepted by NADPH. This stores the energy of the electrons into a form that can be transferred to the Calvin Cycle. (No chemiosmosis, thus no ATP in this ETC)

  37. The Light Reactions • j

  38. Cyclic Electron Flow • Cyclic Electron Flow- electrons take an alternative pathway that uses PS I but not PS II.

  39. Similarity in ETC • Potential energy stored in H+ gradient • ATP synthase • Similar electron carriers (cytochromes)

  40. Differences in ETC • Type of phosphorylation • Oxidative in mitochondria • Photophosphorylation in chloroplasts • Where electrons come from • Mitochondria – organic molecules • Chloroplasts - water • Where energy comes from • Direction/location of H+ pumping • Mito – protons pumped from matrix out to intermembrane space • Chlor – pumps from stroma into thylakoid space

  41. Light Reactions • kjh

  42. Photosynthesis • Dark Reactions/Calvin Cycle- chemical energy is used to make organic compounds of food. (ie: glucose) Occurs in stroma. • Carbon Fixation- CO2 (from air) is combined with molecules present in chloroplast to form organic molecules that are reduced to carbohydrates. (w/NADPH)

  43. Calvin Cycle • Similar to citric acid cycle, although citric acid cycle is catabolic, calvin is anabolic- • Why is it anabolic?

  44. Calvin Cycle • Similar to citric acid cycle, although citric acid cycle is catabolic, calvin is anabolic- • building carbohydrates from smaller molecules and consuming energy (endergonic)

  45. Calvin Cycle • CO2 enters the Calvin Cycle from the light reactions and exits as sugar. • The carbohydrate produced in the Calvin Cycle is not actually glucose, but a 3-carbon sugar called G3P (glyceraldehyde-3- phosphate). • To synthesize 1 molecule of G3P, the process has to happen 3x fixing 3 molecules of CO2. • Expends 9 ATP and 6 NADH.

  46. Calvin Cycle • Three phases: • 1: Carbon Fixation- • 2: Reduction- • 3: Regeneration of CO2 Acceptor (RuBP)-

  47. Calvin Cycle • 1: Carbon Fixation- CO2 is attached to 5-C molecule (ribulosebisphosphate- RuBP) to form a 6-C molecule. Enzyme: Rubisco.

  48. Calvin Cycle • 1: Carbon Fixation CO2 enters one at a time and attaches to a 5-C molecule called ribulosebisphosphate (RuBP). The enzyme involved in this first reaction is called rubisco. (This is the most abundant protein in chloroplasts and thought to be the most abundant protein on earth). Results in a 6-C intermediate, so unstable that it splits in half immediately- forms a molecule called 3-phosphoglycerate

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