Photosynthesis: Light Reactions & The Calvin Cycle PDF

Photosynthesis Energy for life in 2 steps … 2 steps  Photosynthesis & Energy Organic Matter - source of food – Autotrophs (plants) – Heterotrophs (animals) 3 Types of Photosynthesizers Plants Protists Bacteria Figure 8.1  Photosynthesis: The Big Pi...

Photosynthesis Energy for life in 2 steps … 2 steps  Photosynthesis & Energy Organic Matter - source of food – Autotrophs (plants) – Heterotrophs (animals) 3 Types of Photosynthesizers Plants Protists Bacteria Figure 8.1  Photosynthesis: The Big Picture ❑3 inputs ❑ Sunlight ❑ H2O ❑ CO2 ❑2 products ❑ O2 ❑ sugar  “Photo” - “Synthesis” O2 CO2 Synthesize Sugar Capture Glucose Light E H 20  2 Stages of Photosynthesis 1st - Light Reactions – H2O Electrons excited by photons – Electrons passed to E carriers NADPH & ATP – E used in 2nd Stage 2nd – Dark Reactions – Calvin Cycle E used to fix CO2 Carbohydrate (sugar) produced  Chloroplasts “Photo” – Thylakoids “Synthesis” - Stroma  “PHOTO” O2 Capture Light E H 20  Light E travels in waves: Plant pigments absorb specific wavelengths ❑ kinetic energy ❑ E packets = photons High E Low E  Light Energy ❑ Photons carry diff. amts. of E, carried as waves. ❑ Wavelength = amount of E photon contains ❑ Shorter the wavelength = higher E High E Low E  Electromagnetic Spectrum Range of E organized into waves of different lengths Chlorophyll Pigments on surface of thylakoid membranes Thylakoid  Low High Plant Pigments ❑ Plant pigments absorb / reflect E ❑ Chlorophyll a (reflects G) ❑ Chlorophyll b (reflects Y-G) ❑ Carotenoids (reflect Y-O, R) Why are plants green?  Visible Spectrum ❑ Range of E humans see as light ❑ ROYGBIV ❑ Pigments = molecules that absorb light  Photons → Excited State ❑ Kinetic E → chemical E  Light Reactions 2 actions take place in light reactions. 1. 2. H20 is split→ Electrons from H20 electrons transferred to primary H+ electron acceptor O2 Photons of λ kick e- up orbital level →→→ excited state  “Photo” Part ❑Photosystem II ❑Electron Transport Chain 1 thylakoids ❑Photosystem I Capture ❑Electron Transport Chain 2 Light E  primary electron Reaction Center molecules acceptor – accept excited electrons from H2O Primary Electron Acceptors e– Electrons collected after being E boosted. sunlight reaction center antennae pigments photosystem Figure 8.5  Collecting Solar Energy primary electron primary acceptor electron acceptor e– Energy scale e– sunlight sunlight to Calvin cycle electrons photosystem I photosystem II electron fall supplies energy that will ATP lead to ATP synthesis Figure 8.6  Electron Transport Chain Couples transfer e- → proton gradient (H+) Gradient powers ATP synthesis (ATP Synthase) Transfer E to NADPH ETC Protons (H+) rush out of thylakoid sacs with kinetic E harnessed to build ATP molecules. Light Reactions H2O is split → H+, e-, O2 PII ETC 1 PI ETC 2 Split H2O e- used pump H+ e- to acceptor e- to make NADPH inside → gradient e- to 1°acceptor Potential→ kinetic H+, O2 released used make ATP The Light Reactions Figure 8.7 E storing molecules “SYNTHESIS” Calvin Cycle Part 2 CO2 Synthesize Sugar E  The Calvin Cycle (Stroma) ❑ Use ATP & NADPH to synthesize sugar ❑ Enzymes Nobel Prize in Chemistry in 1961  The Calvin Cycle CO2 + RuBP (sugar) joined by Rubisco (an enzyme) This makes 6-carbon sugar that splits into 3- carbon sugars 3-PGA ATP + NADPH from light reactions is used to make ➔ high-energy sugar G3P One turn of cycle makes ½ of Glucose, the other leftovers are recycled So 2 times around Calvin Cycle makes 1 Glucose  This slide is the level of detail I expect you to Calvin Cycle know… what follows are images of the cycle to help you study but are more detailed. CO2 (from atmosphere) fixation Rubisco enzyme 3-PGA (intermediate 3-carbon sugar) RuBP (5-carbon sugar) reduction regeneration ATP NADPH Energy from light reactions in this form used to make Other than 1 G3P ½ of glucose G3P, rest gets molecule recycled ½ of Glucose  The Calvin Cycle 3-PGA 1. Fixation: C from CO2 using Rubisco → 6 C sugar 2. Reduction: Make G3P and Sugar using ATP and NADPH 3. Regenerate 5 G3P use 1 G3P for glucose (ATP) 1. Carbon fixation ▪ Enzyme Rubisco ➔ CO2 + 5-C 6 ATP RuBP sugar 3 ATP Calvin cycle 6 ▪ Result = 6 3-C six 3-PGA molecules sugar ▪ (3-phosphoglyceric acid) 3 molecules 2. Energizing the sugar 3 molecules Rubisco ▪ ATP transfers electrons to 3-PGA 6 molecules of 3 molecules 1. Carbon of RuBP 3-PGA ▪ Energy-rich G3P sugar fixation from light ▪ glyceraldehyde 3-phosphate 3 ADP reactions 6 ATP 3 ATP 4. Regeneration 3. Exit of product of RuBP from light 6 ADP ▪ 1 molecule G3P exits reactions 2. Energizing ▪ 2 turns of cycle ➔ 1 glucose 5 molecules the sugar 6 molecules of of G3P 3-PGA 3. Exit of derivative product 4. Regeneration of RuBP 6 from 1 molecule light ▪ Remaining 5 molecules G3P of G3P 6 molecules reactions ▪ Transformed back into RuBP of G3P glucose and other derivatives Figure 8.8  Evolutionary Adaptations ❑ Adaptationsfor plants that live in hot or dry environments ❑ How do plants reduce evaporative water loss?  Stomata Plant leaf pores Open / Close – CO2 IN – H2O OUT  Stomata: Pores for gas exchange How to get CO2 when stomata are shut? Water evaporates from plant Stop water loss from plant Release O2 No C for sugar Take up CO2 to make sugar Plant growth stops / Plant can die Three Photosynthetic Pathways Most plants “CO2-sticky ‘Nocturnal Plants’ have temperate climate tape” enzyme CO2 – holding molecule  C4 Pathway In plants, the enzyme rubisco frequently binds with O2 rather than CO2 This is called photorespiration that undercuts photosynthesis. Most CROP plants are C4 plants because they do less photorespiration and can better deal with drought conditions. C4 plants grab CO2 and hold CO2 it to feed the Calvin Cycle O2 C4 CO2 pathway Calvin cycle sugar mesophyll cells bundle-sheath cells vein cells Figure 8.10 CAM Photosynthesis Nocturnal Plants Plant’s stomata open only at night So can only fix CO2 at night CO2 is “banked” until sunrise Day – light Rxns to power the Calvin cycle Desert plants (cacti)