BIOL 1107 1nd Edition Lecture 18 Outline of Last Lecture I Photosynthesis II Chloroplasts and Chlorophyll III Cyclic vs Noncyclic Electron flow Outline of Current Lecture I Calvin cycle II C4 Plants III CAM Plants Current Lecture I Calvin Cycle Uses ATP and NADPH to convert carbon dioxide to sugar Location stroma It is a metabolic pathway similar to Krebs cycle in that a starting material is regenerated after molecules enter and leave the cycle Carbon enters the cycle in the form of CO2 leaves in the form of sugar Cycle spends ATP as an energy source and consumes NADPH as reducing power for adding high energy electrons to make the sugar Carbohydrate produced directly from the cycle is actually not glucose but a 3 carbon sugar name G3P G3P is a sugar the same 3 carbon sugar formed in glycolysis by the splitting of glucose These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute II C4 Plants so named because they preface the Calvin cycle w an alternate mode of carbon fixation that forms a 4 carbon compound as its first product Examples sugarcane and corn members of the grass family In C4 plants there are two distinct types of photosynthetic cells bundlesheath cells and mesophyll cells Bundle sheath cells are arranged into tightly packed sheaths around the veins of the leaf Between the bundle sheath and the leaf surface are the more loosely arranged mesophyll cells First step is addition of CO2 to PEP to form the four carbon product oxaloacetate In effect mesophyll cells of a C4 plant pump CO2 into bundle sheath keeping the CO2 concentration in bundle sheath cells high enough for rubisco to accept carbon dioxide rather than oxygen In this way C4 photosynthesis minimizes photorespiration and enhances sugar production This adaptation is especially advantages in hot regions w intense sunlight and it is in such environments that C4 plants evolved and thrive today III CAM Plants Second photosynthetic adaptation to arid conditions has evolved succulent water storing plants including ice plants many cacti pineapples and representative of several other plant families At night these plants open their pores stomata During day they close those stomata So how do light reactions occur in these plants During night when their stomata are open these plants take up CO2 and incorporate it into a variety of organic acids This mode of carbon fixation is called CAM The mesophyll cells of CAM plants store the organic acids they make during the night in their vacuoles until morning when the stomata close During the day when the light reactions can supply ATP and NADPH for Calvin cycle CO2 is released from organic acids made the night before to become incorporated into sugar in the chloroplasts CAM pathway is similar to C4 pathway in that carbon dioxide is first incorporated into organic intermediates before it enter Calvin cycle The difference is that in C4 plants the initial steps of carbon fixation are separated structurally from Calvin cycle whereas in CAM plants the two steps occur at separate times
View Full Document
Unlocking...