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Photosynthesis i n Detail

Photosynthesis i n Detail. Light Reactions and Calvin Cycle Honors Biology. The Two Stages of Photosynthesis: A Preview. Photosynthesis consists of two processes 1) The Light reactions NEEDS LIGHT Light Dependent Reactions 2) The Calvin cycle

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Photosynthesis i n Detail

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  1. Photosynthesis in Detail Light Reactions and Calvin Cycle Honors Biology

  2. The Two Stages of Photosynthesis: A Preview • Photosynthesis consists of two processes 1) The Light reactions • NEEDS LIGHT • Light Dependent Reactions 2) The Calvin cycle • A.k.a- Dark Reactions or Light Independent Reactions • DOES NOT NEED LIGHT

  3. The Light Reactions • Occur in the grana (& thylakoids) • Convert solar energy to chemical energy • Chlorophyll absorbs solar energy • Split water • release oxygen gas (a by-product) • produce ATP (using chemiosmosis) • Forms NADPH from NADP+ (an e- acceptor) • Temporarily stores high energy e-’s • “Electron shuttle bus”

  4. The Calvin Cycle • Occurs in the stroma • Forms SUGAR from carbon dioxide • Carbon fixation occurs (CO2 fixed carbon) • using ATP for energy and NADPH for reducing power (adding e-s to fixed carbon) • Fixed carbon  carbohydrate

  5. H2O CO2 Light NADP  ADP + P LIGHT REACTIONS CALVIN CYCLE ATP NADPH Chloroplast GLUCOSE (sugar) O2 • An overview of photosynthesis G3P Starch

  6. Photosynthesis • Occurs in the chloroplast • Divided into 2 sets of reactions: - Light Dependent Reaction - Calvin Cycle (Dark Reaction) Photosynthesis

  7. Light Reaction • Requires Light!! • Occurs in the thylakoid/grana(in chloroplast) • Electron Transport Chain (ETC) makes ATPand NADPH sends it to the Calvin Cycle • WASTE PRODUCT: O2 Gas

  8. Part 1 – Light Reactions You need to be able to draw this picture! Photosystem II ETC PhotosystemI H2O Splits 

  9. What are the main steps in the light reactions? • Uses energy from sunlight • Splits water into H+ and O2 • Converts ADP into ATP and NADP+ into NADPH • Use sunlight and water • Produces Oxygen, NADPH, and ATP WRITE Light Rxn Sequence of Events… Photosystem II ETC Photosystem I

  10. How is light absorbed in the thylakoid? • Photosystemsabsorb light • Clusters of chlorophyll and proteins trap energy from the sun • Energy is transferred to electrons  makes “excited” electrons

  11. What are Electron Carriers? • Compound (NADP+) that can accept a pair of high-energy electrons and transfer them to another molecule • NADP+ grabs/carries 2 electrons and a H+ becomes NADPH

  12. Photosystem II • Photosystem II Steps→ 1) Chlorophyll and other light-absorbing pigments absorb energy from the sun • Energy transferred to e-  high energy e- leave the chlorophyll and go to the ETC (electron transport chain) 2) H2O molecules are broken down • - Electrons come from H2O • - O-, H+ and e- are separated • For everyTWOH2Os we get 4e-, 4H+, and 1 O2

  13. Photosystem II (cont’d) • 3) The excited e- jump from protein to protein and enter the ETC (electron transport chain) on the thylakoid membrane • As e- jump through the ETC, they lose energy • This energy pumps/pulls H+ from the outside(stroma) to the inside (lumen - aka - thylakoid space) • H+ ions start to build up inside the thylakoid • Next, e- move to Photosystem I

  14. Photosystem I • Photosystem I → 4) More energy is absorbed from sunlight • Energy is added to e- from Photosystem II • Excited e- leave the molecules 5) E- are added to NADP+which then becomes NADPH

  15. Photosystem I (cont’d) • Now, remember…those H+ ions are building up inside the lumen 6) H+ ions diffuse through a protein channel embedded in the thylakoid membrane • The protein channel is part of an enzyme called ATP Synthase 7) As the H+ ions flow through the protein channel, the enzyme (ATP Synthase) makesATPby adding a P group to ADP

  16. #7 #5 #3 #6 #1 #4 #2

  17. Light Reaction Summary… • Summary: • Chemiosmosis The process that uses the proton gradient and ATP synthase to make ATP • e- travels from PS II  PS I  added to NADP+ makes  NADPH • BothATP(via ATP Synthase) and NADPHare produced • During the light reaction  these • then enter the • Calvin Cycle • NADP+ is the finale-acceptorin photosynthesis

  18. Calvin Cycle! • Second part of PS • Occurs in the • stromaof the • chloroplast • Can occur withor • withoutlight Three turns shown above

  19. Calvin Cycle Summary of Steps: • ATPand NADPHused for energy • CO2 is taken into the plant • High-energysugarsare made • Also known as the sugarfactory

  20. Carbon dioxide & Calvin Cycle • Enters cycle from the atmosphere • Carbon from the carbon dioxide molecule is used to make glucose (C6H12O6) • Plants then use the glucose for: • Food! • Plant energy! • Stored in bonds of the glucose molecule

  21. Carbon “fixing” – process of turning CO2 into a solid compound Calvin Cycle! • Main job: • Incorporates CO2 and rearranges the C’s to form sugar using the energy (ATP/NADPH) from the Light Reaction • The CC “fixes” CO2 • - Carbon enters as CO2 and • leaves as sugar • Goal is to produce a sugar (G3P) • Each turn “fixes” one molecule of carbon, so one G3P takes 3 turns of the Calvin Cycle INPUT: Each turn needs: - 3 ATP - 2 NADPH - 1 CO2 Three turns shown above

  22. The Calvin cycle has three phases 1. Carbon fixation 2. Reduction 3. Regeneration of the CO2 acceptor (RuBP)

  23. The Calvin Cycle Steps CARBON FIXATION 1. CO2 enters cycle and attached to a 5-carbon sugar called ribulose biphosphate (RuBP) forming 6-C molecule (unstable) • Enzyme RUBISCOcatalyzes reaction 2. Unstable 6-C molecule immediately breaks down to 3 3-C molecules called 3-phosphoglycerate (3-PGA)

  24. REDUCTION 3. Each 3-phosphoglycerate (3-PGA) gets an additional phosphate from ATP (from LIGHT RXN)  becomes 1,3 phosphoglycerate 4. NADPH reduces 1,3 phosphoglyceratetoGlyceraldehyde-3-phosphate (G3P) • G3P = a sugar that stores potential energy • Every 3 CO2 yields 6 G3P’s BUT only 1 can be counted in net gain for carbohydrate (GLUCOSE) production

  25. REGENERATION OF CO2 ACCEPTOR (RuBP) 5. The C- skeletons of 5 G3P molecules are rearranged into 3 RuBP molecules • ATP is used !!!!

  26. The Calvin cycle NOTE: MORE ATP is needed than NADPH!! Phase 1: Carbon fixation Phase 3:Regeneration ofthe CO2 acceptor(RuBP) Phase 2:Reduction Also known as PGAL

  27. Calvin Cycle Overview • For 1 G3P molecule made • 9 ATP molecules are used • 6 NADPH molecules are used • G3P (aka PGAL)= starting material to make other organic molecules (glucose, starch, etc.)

  28. Calvin Cycle Note: RuBP and Rubisco are NOT the same thing! Steps: EnzymeRubiscoattaches CO2 to RuBP creates 6 x 3-PGA 6 x PGA are reducedto = 6 x G3P (sugar) via ATP/NADPH 1 x G3P exitsasglucose 5 x G3P remain in the cycle. ATP rearranges the atoms  3 x RuBP

  29. 6CO2 + 6H2O + sunlight  C6H12O6 + 6O2

  30. Rate of Photosynthesis • The rate of PS is affected by 3 factors: • Light intensity • Amount of CO2 • Temperature • Why wouldn’t roots need chloroplasts? Root cells don't have chloroplasts, because chloroplasts catch sunlight! Since roots are underground, they are not exposed to the sun!

  31. Alternate Pathways • If it is too hot out, the plant will close the stomata so that it doesn’t lose too much water and become dehydrated • However this eliminates the gas exchange!! • SO  the levels of CO2 drop and the levels of O2 increase • This results in…. PHOTORESPIRATION • Photorespiration adds oxygen to the Calvin Cycle instead of carbon dioxide - This makes NO sugar or ATP - This wastes all of the plants resources! • Two types of plants: 1) CAM 2) C4 plants

  32. Alternate Pathways • Therefore, certain plants, (cacti, pineapple, etc.) only open their stomata at NIGHT! • This prevents them from drying out and still lets them get CO2!

  33. What is wrong with this picture?

  34. For the test, you will need to know these pictures and labels: • Flower Reproductive • Leaf Structure • Chloroplast • Light Reactions • Calvin Cycle

  35. Exit Slip-April 9, 2014

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