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PHOTOSYNTHESIS

PHOTOSYNTHESIS. Autotrouphs. SUN. photons. glucose. Photosynthesis. Anabolic (small molecules combined) Endergonic (stores energy) Carbon dioxide (CO 2 ) requiring process that uses light energy (photons) and water (H 2 O) to produce organic macromolecules (glucose).

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PHOTOSYNTHESIS

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  1. PHOTOSYNTHESIS

  2. Autotrouphs

  3. SUN photons glucose Photosynthesis • Anabolic (small molecules combined) • Endergonic (stores energy) • Carbon dioxide (CO2) requiring process that uses light energy (photons) and water (H2O) to produce organic macromolecules (glucose). 6CO2 + 6H2O  C6H12O6 + 6O2

  4. Question: Where does photosynthesis take place?

  5. Chloroplast Mesophyll Cell Stoma Plants • Autotrophs – produce their own food (glucose) • Process called photosynthesis • Mainly occurs in the leaves: a. stoma - pores b. mesophyll cells

  6. Oxygen (O2) Carbon Dioxide (CO2) Guard Cell Guard Cell Stomata (stoma) Pores in a plant’s cuticle through which water vapor and gases(CO2 & O2) are exchanged between the plant and the atmosphere. Stoma Found on the underside of leaves

  7. Question: Why are plants green?

  8. Chlorophyll Molecules • Located in the thylakoid membranes • Chlorophyll have Mg+ in the center • Chlorophyll pigments harvest energy (photons) by absorbing certain wavelengths (blue-420 nm and red-660 nm are most important) • Plants are green because the green wavelength is reflected, not absorbed.

  9. 400 500 600 700 Short wave Long wave (more energy) (less energy) Wavelength of Light (nm)

  10. violetbluegreenyelloworangered Absorption of Light by Chlorophyll Chlorophyll absorbs blue-violet & red light best Absorption wavelength

  11. Question: During the fall, what causes the leaves to change colors?

  12. Fall Colors • In addition to the chlorophyll pigments, there are other pigments present • During the fall, the green chlorophyll pigments are greatly reduced revealing the other pigments • Carotenoids are pigments that are either red, orange, or yellow

  13. Redox Reaction The transfer of one or more electrons from one reactant to another. This allows atoms to be rearranged into new molecules. Two types: 1. Oxidation is the loss of e- 2. Reduction is the gain of e-

  14. Question: What do cells use for energy?

  15. Energy for Life on Earth • Sunlight is the ULTIMATE energy for all life on Earth • Plants store energy in the chemical bonds of sugars • Chemical energy is released as ATP during cellular respiration

  16. Parts of Photosynthesis

  17. Photosynthesis Overview Reactants Products 3 carbon sugar (G3P)

  18. Two Parts of Photosynthesis Two reactions make up photosynthesis: 1.Light Reaction or Light Dependent Reaction - Produces energy from solar power (photons) in the form of ATP and NADPH. SUN

  19. Two Parts of Photosynthesis 2. Calvin Cycle or Light Independent Reaction • Also called Carbon Fixation or C3 Fixation • Uses energy (ATP and NADPH) from light reaction to make sugar (glucose).

  20. Energy Carriers Nicotinamide Adenine Dinucleotide Phosphate (NADP+) NADP+ = Oxidized Form (Empty, needs e-) Picks Up 2 high-energy electrons and H+from the Light Reaction to form NADPH (Full) NADPH formed in the light reactions carries high energy electrons to be passed on to another molecule in the calvin cycle. 22

  21. NADPH 23

  22. Light Reactions

  23. STEP 1 – Photosystem II • Sun Light hits pigments • excites 2 electrons. • Electrons jump from pigment to pigment • Electrons reach P680 (reaction center – a specialized chlorophyll) • Passed to primary electron acceptor (Protein)

  24. STEP 2 – Replacement of Electrons • Water is split 2. 2 electrons (from H) replace those lost in PS II 2. H+ builds a gradient (High concentration) in Thylakoid space 3. Oxygen gas is released out

  25. STEP 3 – Electron Transport Chain • Electrons are passed down a series of electron acceptor proteins • As electrons are passed down – energy is lost with each transfer • Energy is used by to create H+ gradient in thlylakoid for production of ATP

  26. STEP 4 - Photosystem I SAME AS PHOTOSYSTEM II • Light excites 2 electrons in pigment • Electrons are passed until reach reaction center (P700) • Electrons are sent to second primary electron acceptor. • Electrons from first ETC fill missing space.

  27. STEP 5 – ETC • Electrons are passed from Primary acceptor to NADP+ reductase • Energy from small ETC is used to add electrons to NADP+ to form NADPH and H+ (electron carrier)

  28. ATP SYNTHESIS Enzyme in thylakoid membrane called ATP Synthase As H+ ions passed through thylakoid membrane, enzyme attaches a free phosphate group to ADP Forms ATP in stroma to be used in CALVIN CYCLE 30

  29. Chemiosmosis • Powers ATP synthesis • Takes place across the thylakoid membrane • Builds H+ (hydrogen ion) gradient (high concentration in thylakoid space) • Uses ETC and ATP synthase (enzyme) • H+ move down their concentration gradient through channels of ATP synthase forming ATP from ADP

  30. Chemiosmosis 32

  31. 33

  32. Calvin Cycle • Light Independent Reaction • Uses CO2 + RuBP (5 C) andan enzyme called RuBISco to carry out Carbon Fixation • C3 plants (80% of plants on earth) – product is a 3 – carbon sugar called G3P • Occurs in the stroma of chloroplasts • A series of steps modify the molecule RuBP until final product is produced (biochemical pathway) • 1 G3P is the product for sugar production; 5 G3P are rearranged to form the starting molecule 3 RuBP • Uses ATP for energy and NADPH for reduction from light reaction • To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH.

  33. Carbon dioxide added 1 at a time! 3 turns to make 1 G3P 6 turns to make 1 glucose. RuBISco: control enzyme RuBP ATP used; ADP and Pi released ATP and NADPH;release ADP, Pi, and NADP +; molecules rearranged and split to form 6 (3C) G3P 2 G3P make glucose; It can make any monomer!

  34. Photorespiration • Occurs on hot, dry, bright days • Stomates close • Fixation of O2 instead of CO2 • Produces 2-C molecules instead of 3-C sugar molecules • Produces no sugar molecules or no ATP

  35. Photorespiration Because of photorespiration, plants have special adaptations to limit the effect of photorespiration: 1. C4 plants 2. CAM plants

  36. C4 Plants • Hot, moist environments • 15% of plants (grasses, corn, sugarcane) • Photosynthesis occurs in 2 places to prevent oxygen build up. • Light reaction - mesophyll cells • Calvin cycle - bundle sheath cells

  37. CAM Plants • Hot, dry environments • 5% of plants (cactus and ice plants) • Stomates closed during day • Stomates open during the night • Light reaction - occurs during the day • Calvin Cycle - occurs when CO2 is present

  38. Question: Why do CAM plants close their stomata during the day?

  39. Cam plants close their stomata in the hottest part of the day to conserve water

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