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Where do we get our energy from? Photosynthesis: An Overview Some details: Water Sunlight Light Reaction ATP Carbon Dioxide NADH Dark Reaction Glucose Oxygen Today’s Goal! To explain how energy is transferred from sunlight to glucose via the light and dark reactions of photosynthesis. The Formula for Photosynthesis THE CHLOROPOPLAST Light dependent and light independent reaction locations Inner and outer membrane of chloroplast Stroma Thylakoids (Light INDEPENDENT) (Light DEPENDENT) CALVIN Pigments- Important for the absorption of light energy Three types: 1. Chlorphyll a- absorbs all spectrum of light except for green 2. Chlorophyll b- absorbs most spectrum of light except orange, yellow or red 3. Carotene- absorbs most spectrum of light except for orange So why are plant leaves green? Another Question: Why are leaves a different color in the fall? See the next slide for the answer from a celebrity presenter. 1. In the Fall the strength of the sun decreases. 2. Plants will decrease their production of chlorophyll a in order to conserve more sugar for the winter months. (remember that when the body builds something it requires energy) 3. The remaining pigments will reflect different spectrum of light depending on the species. Hey! Its David Ortiz…maybe he can explain why the leaves change color in the fall. Thanks David! Light Reactions-Does this picture look familiar? Electron Carriers What do they do? • Electron carriers take high energy electrons (stored on H) and bring them to electron transport chains (more on these later) • The electrons become high energy when exposed to sunlight Examples: 1. With electronsNADPH or FADH2 2. Without electrons NADP+ or FAD+ Light Reactions e- e- ee- eee1. Sunlight hits chlorphyll and excites the electrons (woo hoo!) Really excited electrons + NADP+ NADPH FAD+ FADH2 Electron carriers 2. These electrons are transferred to electron carriers ee- ee- e- H+’s used to help carry electrons (FAD+ becomes FADH2 when it carries electrons) H+ H+ Excited electrons splitting H20 molecule into its base elements O- leaves the plant via stomata 3. These electrons are used to split water molecules (this is why plants produce oxygen) This is a close-up shot of the pathway the light energy traveled…from beginning to end. The Electron Transport Chain is represented by the dashed line and has one side which is highly positive…shooting the Hydrogen ions against the positive gradient creates energy. + + ++ + + + + + ------------------H+ H+ H+ H+ H+ H+ H+ 4. These Hydrogen ions are also shot across an electron transport chain (against the proton gradient…remember the sledding example) H+ Energy from electron transport chain ATP Note the H+ ions returning through ATP Synthase…Oxygen picks up these ions and forms H20…more on this when we get to cellular respiration SYNTHASE ADP + P ATP 5. This produces enough energy to make a small amount of ATP which will be used in the Calvin Cycle This is a close-up shot of the pathway the light energy traveled…from beginning to end. Light-dependent Reaction-Takes Place in Thykaloid 1. Sunlight hits chlorphyll and excites the electrons (woo hoo!) 2. These electrons are transferred to electron carriers 3. These electrons are used to split water molecules (this is why plants produce oxygen) 4. Hydrogen ions are also shot across an electron transport chain (against the gradient…remember the sledding example) 5. This produces enough energy to make a small amount of ATP which will be used in the Calvin Cycle Dark Reactions (Calvin Cycle) CO2 CO2 CO2 CO2 CO2 CO2 Plant taking in CO2 Lets zoom in Electron micrograph photo of stomata(s) 1. The plant “breaths in” C02 via stomata Energy from ATP and NADPH Carbon Dioxide being split into base elements O- C O- 2. The ATP and NADPH produced in the light reaction is used to break apart the CO2 into its base elements Carbon’s from Carbon Dioxide Oxygen’s from the splitting of H20 OOO- OO- O- + C C C C C C + Hydrogen’s from the splitting of H20 H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ C6H12O6 Aka: Glucose 3. With enough C02 and H (remember when the water molecule was split?) a glucose molecule is formed (what was that formula again?) The processes we have talked about are how carbon and energy enter the food chain. Calvin Cycletakes place in Stroma 1. The plant “breaths in” C02 2. The ATP and NADPH produced in the light reaction is used to break apart the CO2 into its base elements 3. With enough C02 and H (remember when the water molecule was split?) a glucose molecule is formed (what was that formula again?) Using your notes and the diagram below, explain how energy is transferred from one form (Sunlight) to one that is stored (Glucose). Use the reactions involved in Photosynthesis in your explanation.