REVIEW : Chapter 10: Photosynthesis: Pages 172- 187 Energy from Sunlight Photosynthesis, the metabolic process by which plants capture energy from sunlightand store it in carbohydrates (sugars, and starch) is the very basis of life on Earth.  AUTOTROPHS and HETEROTROPHS?1. Photosynthesizing plants take in CO2, water, and light energy, producing O2 andcarbohydrate. Photosynthesis occurs in the chloroplast. - Structure of a chloroplast: Chloroplasts have two organelle membranes. Thylakoids? Granum? The fluid-filled space around the grana is the stroma.The overall reaction is: 6 CO2 + 12 H2O + light  C6H12O6 + 6 O2 + 6 H2O. Water is the source of O2 produced.2. Photosynthesis, like metabolism, is a result of many steps  not just a single step.When looked at as a whole, it can be separated into two main pathways.• The first pathway is called the light reactions and is driven by light energy. It produces O2 (from water), ATP (from electron flow and photophosphorylation), and the reduced electron carrier NADPH  in the Thylakoid membrane• The second, The Calvin cycle, does not use light directly. It uses the energy in ATP, NADPH to reduce CO2 to carbohydrate. First 3C sugar produced is G3P. glucose  sucrose and starch  in the Stroma3. How does chlorophyll capture light energy? Reaction center and the Photosystems?- Light is a type of electromagnetic radiation. Fig 10.3- Light with shorter wavelength has more energy than light of longer wavelength.- Pigments absorb light of specific wavelength. Transmitted light? Why are plants green?Chlorophyll a and b absorb red and blue light and transmit green.Carotenoids absorbs blue and green and transmit yellow, orange or red. I. Which wavelengths of light drive Photosynthesis? Most effective Red and Blue- Each type of pigment has a characteristic absorption spectrum- Action spectra and absorption spectra? Fig 10.5 - CHLOROPHYLL is the main photosynthetic pigment. Structure: Head (contain Mg) with large ring structure absorbs light. Tail anchors the molecule to the thylakoid membrane.- Plants have two predominant chlorophylls: chlorophyll a and chlorophyll b. These molecules differ slightly in their structure.These chlorophylls absorb blue and red wavelengths, which are near the ends of the visible spectrum.- Other accessory pigments absorb photons (light) that are intermediate in energy between thered and blue wavelengths and then transfer that energy to chlorophylls. Accessory pigmentsfunction to extend the range of wavelengths that can drive photosynthesis. They also function to protect chlorophyll from free radical damage  “sun screen”!1Chlorophylls and accessory pigments form antenna systems (complex) for absorption of light energy. A Photosystem = Antenna complex, Reaction center and many proteins Two photosystems  Photosystem I (P700) and Photosystem II (P680)II. Photosynthetic Pigments absorb light in the visible spectrum. Absorption of a photon puts a pigment molecule in an excited state that has more energy than the molecule has in its ground state. An excited pigment molecule may lose its energy by transferring it to another pigment molecule  resonance, until it reaches the reaction center. Fig 10.9 III. What happens when an electron in the reaction center is excited?  the excited electron is passed from the reaction center to a molecule that acts as the primary electron acceptor ( Pheophytin in photosystem II and Ferrodoxin in photosystem I)  redox reactions4. How does photosystem II work? Produces ATP, O2 and reduced electron carriers-Primary en acceptor accepts electrons and transfers them to the electron transport chain (ETC). -ETC is similar to the one found in mitochondria.-It also contains mobile electron carrier, and a cytochrome complex.-The ETC sets up a proton gradient and drives ATP synthesis. Protons are pumped across the thylakoid membrane. Protons diffuse back to stroma through the ATP synthase complex  protein motive force and photophosphorylation (Chemiosmosis is the source of ATP in photophosphorylation).5. Photosystem II obtain electrons by oxidizing water – Oxygenic vs anoxygenic?- A photosystem that can split water is called oxygenic, whereas a photosystem that cannot oxidizewater is called anoxygenic. 6. How does photosystem I work? Produces NADPH and oxidized electron carriers- When the reaction center of photosystem I absorbs a photon of light, the excited electron is eventually passed to ferredoxin  NADP+ to form NADPH. NADPH is an electron carrier like NADH. Steps that occur in the photochemical reaction centers:Light excitation of Antenna chlorophyll  Transfer of excited electron to neighboring chlorophyll  excitation of Reaction center chlorophyll  passage of excited electron to electron acceptor and to electron transport chain  Replacement of the electron in the reaction center chlorophyll27. The Z scheme: Photosystems II and I work together:Noncyclic electron flow, depicted by the Z scheme, uses two photosystems, (I and II), producing ATP, NADPH, and O2. P680 and P700? Oxidized P680 + takes electrons from water, splitting the water molecule.Path of electrons through the photosystem I and II? PS II  pheophytin  PQ  cytochrome complex  PC  PS I  Ferrodoxin  NADP+8. Cyclic electron flow produces only ATP. Its operation maintains the proper balance of ATP and NADPH in the chloroplast. Only Photosystem I involved. What is/are the overall function(s) of photosystem I?- In noncyclic photosphosphorylation, photosystem I produces NADPH. - In cyclic photophosphorylation, photosystem I produces ATP.Questions: 1. Compare Photo phosphorylation and Oxidative Phosphorylation?2. The processes of oxidative phosphorylation coupled with electron transfer (in mitochondria) and photophosphorylation (in chloroplasts) resemble each other in certain respects. Describe five ways in which the two processes are similar, and describe three significant differences between the two processes.3. During photophosphorylation in plants, electrons flow through a series of carriers in the chloroplast. What is the ultimate donor of electrons, and what is the ultimate acceptor? Whatprovides the energy to move those electrons?9. The Calvin cycle consists of three phases: fixation of CO2, reduction of 3PG to form carbohydrate, and regeneration of RuBP. CO2 acceptor in calvin cycle is 5carbon, RuBP.First 3C