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Get out your reading that is due today, Quiz on Thursday Without using notes, talk to your group about the answers to these question…. 1. Essentially, what is the job of ATP? 2. Why can’t we store ATP for later use? 3. What is the difference between endergonic and exergonic reactions? RECAP AND PREQUEL • All life needs a constant input of energy – Heterotrophs (Consume) • get their energy-filled organic molecules from “eating other organisms” • make usable cellular energy through cell respiration – Autotrophs (Producers) • • • • produce their own energy-filled organic molecules Photo-autotrophs convert energy from sunlight build organic molecules through photosynthesis Also break down these organic molecules to make energy through cell respiration. PHOTOSYNTHESIS YOU WOULD BE DEAD WITHOUT IT. Light Plants actually take in 12 water molecules, and six water molecules are created, so to simplify, this is the equation you usually see only showing the ‘net consumption of water’. Obtaining the reactants… Sunlight Pigments in the chloroplasts of (mostly) plant leaves absorb light energy called photons. CO₂ Water Gas Exchange occurs at the stomata, tiny pores on the leaves. Photosynthesis takes place inside the cell’s chloroplasts in the leaf of a plant. PHOTOSYNTHESIS LIGHT-DEPENDENT PHASE (Requires Sunlight) LIGHT-INDEPENDENT PHASE (Does Not Require Sunlight) FIRST PHASE Light Dependent Reactions: The first phase involves reactions that convert: 12 H₂O and solar light energy into 6 O₂ which is released as a waste 18 ATP, and 12 NADPH which are used later (in light independent) to make carbohydrates…. Light Dependent Reactions Reactants Products 8 Photons (light energy) get absorbed into pigments, which are clustered into a protein complex called a photosystem. Which wavelengths of light are not absorbed by each pigment? Chlorophyll a, Chlorophyll b, Carotenoids? The feathers of male cardinals are loaded with carotenoid pigments. These pigments absorb some wavelengths of light and reflect others. Sunlight minus absorbed wavelengths or colors equals the apparent color of an object. Why are plants green? Transmitted light • PS II chlorophyll molecules absorbs light – An electron from a chlorophyll molecule, absorbs the energy and becomes EXCITED, pops out of the molecule and leaves the photosystem…. Once energized it then goes through an electron transport chain. Passing from one protein to the next, losing a little bit of energy along the way. (still pretty energized at the end) The energy that is being released as it travels through the ETC is being used by the proteins to actively transport H⁺ (protons) into the inside of the thylakoid. The electron then enters photosystem I (PSI), where the electron gets RE-ENERGIZED again by photon light, enters a second ETC, where more H⁺ is pumped into the thylakoid… At the end of the 2nd E.T.C. the 2 electrons and a H⁺ attach to a molecule called NADP, which is referred to as the FINAL ELECTRON ACCEPTOR. Once the electron and the Hydrogen ion attach, the molecule is now called NADPH, an electron carrier. 12 of these are created in all for this process… Let’s go back to PSII for a sec, when our electron first got energized… It is important to replace the lost electrons from the chlorophyll molecules because then the chlorophyll wouldn’t be able to absorb more light energy. • To replace the lost electrons, molecules of water are split. This reaction is called photolysis. Electrons from the Hydrogens replace the ones that popped out of the chlorophyll molecules in Photosystem II. 2 Hydrogen Ions (protons) are released into the inside of the thylakoid. From the ETC and photolysis, you have all these H⁺ built up causing a concentration gradient, and they want to GET OVER TO THE OTHER SIDE OF THE MEMBRANE (chemiosmosis)….the only channel protein they can use is an enzyme called ATP Synthase. ATP SYNTHASE The Hydrogen ions pass through ATP synthase to even out the concentration of molecules. As they do this, the energy they contain is used to add a Phosphate to ADP, creating ATP!!! (PHOSPHORYLATION) 18 ATP are made in all In Summary: Light and water are used to make the energy charged molecules (ATP and NADPH) that will fuel the second phase of photosynthesis. ATP And Oxygen is released as a waste. 18 ATP + 12 NADPH