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Photosynthesis

Photosynthesis. Photosynthesis. Photosynthesis is the way that plants make food from sunlight You take in food which is digested and then transferred to cells for use by mitochondria Plants can’t “eat” so they make food which is then transferred to the mitochondria

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Photosynthesis

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  1. Photosynthesis

  2. Photosynthesis • Photosynthesis is the way that plants make food from sunlight • You take in food which is digested and then transferred to cells for use by mitochondria • Plants can’t “eat” so they make food which is then transferred to the mitochondria • Mitochondria then transform the “food energy” into chemical energy

  3. Photosynthesis • Why does it matter? • Source of nearly all the energy on Earth • Process by which atmospheric gases are maintained in the ratios we need to survive

  4. Photosynthesis • Who photosynthesizes? Some bacteria

  5. Photosynthesis • Who photosynthesizes? Some bacteria Some protists

  6. Photosynthesis Most plants

  7. Photosynthesis • Heterotroph: organism that must consume food • Autotroph: organism that makes its own food (photosynthesis)

  8. Photosynthesis 6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2 Carbon dioxide Water Carbohydrate Oxygen

  9. Photosynthesis 6CO2 + 6 H2O + light energy → C6H12O6 + 6 O2 Carbon dioxide Water Carbohydrate Oxygen

  10. Epidermis Mesophyll Guard cells Epidermis Vein Vein Stoma

  11. Photosynthesis • Vein: water delivery

  12. Photosynthesis • Epidermis: water-proof covering of the surface of the leaf • Prevents unwanted loss of water and gases

  13. Photosynthesis • Stoma: Opening in the leaves • water exits • O2 exits • CO2 enters

  14. Photosynthesis • Stoma: Opening in the leaves • water exits • O2 exits • CO2 enters Transpiration

  15. Photosynthesis • Guard cells: surround stoma • Open and close stoma

  16. Photosynthesis • Mesophyll: central layer of cells • contains chloroplast-rich cells • site where most photosynthesis occurs

  17. Photosynthesis

  18. Photosynthesis • 2 sets of reactions:

  19. Photosynthesis • 2 sets of reactions: • LIGHT DEPENDENT REACTIONS

  20. Photosynthesis

  21. Photosynthesis • 2 sets of reactions: • LIGHT DEPENDENT REACTIONS • LIGHT INDEPENDENT REACTIONS (Calvin cycle)

  22. Photosynthesis

  23. Light Dependent Reactions

  24. Light Dependent Reactions • Thylakoids contain pigments

  25. Light Dependent Reactions • Pigments: molecules that absorb light energy

  26. Light Dependent Reactions • Pigments: molecules that absorb light energy • Electrons are energized by absorbing energy and “jumping” energy levels

  27. Light Dependent Reactions • Pigments: molecules that absorb light energy • Electrons are energized by absorbing energy and “jumping” energy levels • A specific amount of energy is required in order for the electron of a specific atom to jump and land in another energy level • Ex. Long jumping versus hopscotch

  28. Light Dependent Reactions • Thylakoids contain the pigment chlorophyll • Chlorophylls a and b • Absorb light on opposite ends of the visible light spectrum • Between 500 and 600 nm light is reflected • Why chlorophyll appears green

  29. Light Dependent Reactions • Thylakoids contain the pigment chlorophyll Absorbed Reflected Absorbed

  30. Light Dependent Reactions • Thylakoids contain pigments called carotenoids • Absorb light below 550 nm • Appear red, orange, and yellow

  31. Light Dependent Reactions • Thylakoids contain pigments called carotenoids Absorbed Reflected

  32. Light Dependent Reactions • Thylakoids contain pigments • Which pigment is dominant in deciduous trees right now?

  33. Light Dependent Reactions • Pigment in the thylakoids form Photosystems • Network of pigments held together within a protein matrix • Channel energy absorbed from light to a specific pigment molecule: reaction center chlorophyll

  34. Light Dependent Reactions • Pigment in the thylakoids form Photosystems • Reaction center chlorophyll passes the energy (via an energized electron) to a primary electron acceptor: Ferredoxin

  35. Light Dependent Reactions • Process of replacing the electrons that follows this step depends on the organism: • Bacteria: cyclic • Algae and plants: non-cyclic

  36. Light Dependent Reactions • Cyclic phosphorylation • Bacteria • Contain only 1 photosystem: Photosystem I • From electron acceptor, electrons go through electron transport system from which ATP is produced • Electrons then return to Photosystem I

  37. Light Dependent Reactions • Non-cyclic phosphorylation • Algae and plants • Contain 2 photosystems: Photosystem I, and Photosystem II • PS II acts first

  38. Light Dependent Reactions • Non-cyclic phosphorylation • Photon of light energy excites electron which is passed from PS II to electron transport chain and then to PS I • Another photon of light re-excites the electron now in PS I which passes the electron to the primary electron acceptor and through a series of reactions

  39. Light Dependent Reactions • Non-cyclic phosphorylation • Electrons lost from PS II must be replaced • PS II takes an electron from protein Z • Protein Z then takes an electron from water by splitting a water molecule into H+ ions and O • H+ ions are used later, O forms O2 and is “exhaled”

  40. Light Dependent Reactions • Electron transport chains • Series of enzymes embedded in membrane called the cytochrome complex • Receive excited electrons from PS II and PS I • Electrons are passed from 1 molecule to the next

  41. Light Dependent Reactions • Electron transport chains • Energy from the electrons energized in PS II powers a proton pump • Proton pump pumps protons into the thylakoid space • Results in high concentration of protons in the thylakoid space • Concentration gradient powers ATPase

  42. Light Dependent Reactions • Electron transport chains • ATPase allows protons back out of membrane • Rush of protons provides enough energy to attach a phosphate to an ADP forming • This process is called chemiosmosis ATP

  43. Light Dependent Reactions • Electron transport chains • Energy from the electrons energized in PS I is passed to a reduction complex • At the reduction complex NAD+ is transformed into NADH

  44. Light Dependent Reactions • Electron transport chains • NAD+ is an electron acceptor: it holds on to the energy from the electrons until it can be used to bind a phosphate group to an ADP

  45. Light Dependent Reactions • Electron transport chains • and NADH produced leave the thylakoid to participate in the next set of reactions: the light independent reactions or Calvin cycle ATP

  46. Light Dependent Reactions Ferredoxin

  47. Light Dependent Reactions Ferredoxin Z

  48. Light Dependent Reactions Ferredoxin Z Energy is taken from the electrons and is used to make ATP from ADP

  49. Light Dependent Reactions Ferredoxin Feredoxin Z Energy is taken from the electrons and is used to make ATP from ADP

  50. Light Dependent Reactions Ferredoxin Ferredoxin Energy is taken from the electrons and is used to make NADPH from NADP Z Energy is taken from the electrons and is used to make ATP from ADP

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