Guided Reading Chapter 7 In chapter 6 we learned how our cells obtain and use energy to perform work This energy was obtained in the form of organic molecules that we as animals obtain from the food that we eat In chapter 7 we will see how the chemical energy in molecules like glucose is derived from sunlight and why it is that plants are so important to us 1 Plants don t eat cookies However their cells must also obtain and use glucose to function What do plants eat Plants take in CO2 and sunlight 2 Draw a leaf mesophyll cell and label a chloroplast thylakoid grana and the stroma Beside each label provide a brief description of the item define what you have labeled Indicate where the light and dark reactions occur in this cell Chloroplast in green plant cells a plastid that contains chlorophyll and in which photosynthesis takes place Thylakoid each of a number of flattened sacs inside a chloroplast bounded by pigmented membranes on which the light reactions of photosynthesis take place and arranged in stacks or grana Grana the stacks of thylakoids embedded in the stroma of a chloroplast Stroma the supportive tissue of an epithelial organ tumor gonad etc consisting of connective tissues and blood vessels Light Reaction the reaction that occurs as the first phase of photosynthesis in which energy in the form of light is absorbed and converted to chemical energy in the form of ATP Dark Reaction the cycle of reactions the Calvin cycle that occurs in the second phase of photosynthesis and does not require the presence of light It involves the fixation of carbon dioxide and its reduction to carbohydrate and the dissociation of water using chemical energy stored in ATP 3 The process of photosynthesis requires gas exchange How does gas exchange occur in the leaf CO2 is taken up and O2 is released In the light reactions light energy is transformed into the chemical energy of ATP and NADPH In this process electrons removed from H2O pass from photosystem II to photosystem I to NADP Between the two photosystems the electrons move down an electron transport chain and provide energy for the synthesis of ATP In chemiosmosis the potential energy of concentration gradient of hydrogen irons H across a membrane powers ATP synthesis This gradient is created when an electron transport chain uses the energy released as it passes down the chain to pump H across a membrane Using CO2 energy from ATP and high energy electrons from NADPH the Calvin cycle constructs energy rich three carbon sugars glyceraldehyde 3 phophate G3P 4 Photosynthesis requires water How does water enter the leaf Explain During the light reaction water is split and its electrons are supplied one by one to P680 each replacing an electron lost to the primary electron acceptor 5 Compare and contrast photosynthesis with cellular respiration In your explanation talk about CO2 H2O O2 glucose oxidation and reduction In photosynthesis CO2 and H2O are taken up and O2 is released In cellular respiration O2 and glucose are taken up and CO2 and H2O are released Both oxidation and reduction occur In photosynthesis CO2 is reduced to glucose and H2O is oxidized to O2 In cellular respiration glucose is oxidized to CO2 and O is reduced to H2O 6 What happens to the oxygen and hydrogen atoms when water is split in the light reaction When water is split in the light reaction the oxygen atom combines with a second oxygen from another split water molecule forming O2 The exergonic fall of electrons provides energy for the synthesis of ATP by pumping H across the membrane 7 The carbon cycle constructs sugar molecules in the stroma from CO 2 and energy rich products derived from the light reactions occurring in the thylakoids Which energy rich products derived from the light reaction are used in the Calvin cycle The light reactions provide the chemical energy ATP and reducing power NADPH for the next stage of photosynthesis the Calvin cycle 8 In general where does the mass of a tree come from Most college graduates cannot answer this very fundamental question Carbon
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