AP Bio Unit 3 Packet – Respiration and Photosynthesis Essay Questions

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Describe the Biochemical Pathways of the Light and Dark Reactions in C3 Photosynthesis. Begin with a molecule of H2O and CO2 and end with a molecule of glucose.
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The Light Reactions (aka light dependent reactions) occur in the THYLAKOID of a chloroplast and uses H2O and light to create NADPH, ATP, and oxygen (which is the waste product). The Calvin Cycle (aka light independent reactions or Dark Reactions) occur in the STROMA and uses NADPH and ATP, which carries electrons from the light dependent reaction, as well as CO2, to create glucose (C2H12O6). Together, these reactions make up photosynthesis. The equation is written as: 6H2O + 6CO2 + light energy —–> C6H12O6 + 6O2
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Discuss how C4 and CAM Photosynthesis improve upon C3 Photosynthesis. Include both Advantages and Disadvantages of the processes. Describe appropriate leaf anatomy to complete your discussion.
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1.) One problem with the calvin cycle is PHOTORESPIRATION. The Calvin Cycle (C3 Cycle) only fixes CO2 using the enzyme RuBisCo. -Rubisco binds to O2 as well as CO2 at its active site. This is inefficient because O2 doesn’t have Carbon so it cannot produce Glucose. This wastes the cells time and energy. In Fact, RuBisCo binds to O2 better than to CO2 so if there is more O2 than CO2, the Calvin Cycle will not make glucose. This often happens in hot conditions. 1A.) In C4 Plants, however, CO2 combines with PEP to form oxaloacetate. CO2 is taken in via mesophyll cells, and malate is pumped into the bundle sheath cells. CO2 then enters the Calvin Cycle. In hot weather, though, C4 plants’ PEP does not combine with oxygen, making it more efficient. C3 Plants, however, are more efficient in moderate temperatures. 1B.) CAM Plants live in the dry parts of the world. They divide time (as opposed to C4 plants dividing space). Stomata are only opened during night, allowing CO2 to come in. CO2 attaches to PEP via PEP Carboxylase to form C4 molecules. during the day, that C4 molecule (malate) releases CO2 into the Calvin Cycle while using ATP and NADPH to create glucose. 2.) Another problem with C3 is TRANSPIRATION which is when C3 plants lose water because they have their stomata open when the weather gets hot. The stomata must open in C3 plants for photosynthesis to occur so this is bad. -Transpiration is water loss through the stomata and transpiration increases as the temperature increases. -Lack of water also leads to Cyclic Photo phosphorylation, so no Glucose is made. 2A.) C4 plants have to close stomates a lot to adapt to the hot, dry climates 2B.) CAM Plants have different adaptation to hot, dry climates, They separate carbon fixation from Calvin Cycle by time but closing their stomata during the day and opening it at night. – At night, stomates open and fix carbon in \”storage\” compounds while in the day, the stomates close and release CO2 from \”storage\” compounds to Calvin Cycle. This increases the concentration of CO2 in cells.
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Discuss the Krebs Cycle and Oxidative Phosphorylation. Specifically address ATP and Coenzyme Production, the location where these biosynthetic pathways occur, and chemiosmotic theory.
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a.) The Krebs cycle and oxidative phosphorylation are the oxygen-requiring processes involved in obtaining ATP from Pyruvate. Before pyruvate enters the Krebs Cycle, it combines with coenzyme A. During this initial reaction with coensyme A, 2 electrona dn 2H+ removed from pyruvate combine with NAD+ to form NADH + H+. NADH is a coenzyme storing enough energy to generate 3 ATP in oxidative phosphorylation. B.) The Krebs cycle occurs in the matrix of the mitochondria. Oxidative phosphorylation occurs in the cristae membranes of the mitochondria. C.) Chemiosmosis is the movement of ions across a selectively permeable membrane, down their electrochemical gradient. More specifically, it relates to the generation of ATP by the movement of hydrogen ions across a membrane during cellular respiration or photosynthesis.

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