G3P is the product of the Calvin Cycle and is used by the plant to make: •Sucrose•Fructose•Starch•Cellulose•use the hydrocarbon skeleton of G3P to form fatty acids and glycerol (corn oil, olive oil)
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C 3 plants • Use CO 2 directly from the air . • Very common and widely distributed. • Example : Wheat, rice, oats, tulips
Efficient under: • cool and moist conditions • normal light Requires less machinery: • fewer enzymes • no specialized anatomy C 3 plants Adaptive Value
C 4 plants • Close stomata during the day to save water during hot and dry weather. • Great! • Water kept inside leaf • Problem! • O 2 as well, • can bind to Rubisco competing with CO 2 • Alternate mode of carbon fixation resulting in a 4-carbon product unique leaf anatomy with 2 distinct types of photosynthetic cells: bundle-sheath cells and mesophyll cells Example : corn, sugarcane
1. CO 2 first fixed and kept in a 4 Carbon molecule (malate) in mesophyll cells (surface of leaf) • contain lots of atm O 2 but NO RUBISCO 2. Malate delivered to bundle sheat cells (deeper inside leaf) and converted back into a 3 carbon sugar called pyruvate • less O 2 • Liberation of CO 2 which enters Calvin cycle C 4 plants Bundle- sheath cell Pyruvate (3 C) CO 2 Sugar Vascular tissue CALVIN CYCLE PEP (3 C) ATP ADP Malate (4 C) Oxaloacetate CO 2 PEP carboxylase Mesophyll cell
C 3 vs C 4 • Moderate weather, advantage to C 3 plants • But when the weather becomes hot and dry, advantage to C 4 plant – Early summer, • C 3 plants, Kentucky bluegrass, predominate in lawns in cooler parts of US, – By midsummer, • crabgrass, a C 4 plant, begins to take over
CAM plants • Open stomata only at night : • conserve water, 1. CO 2 taken up at night when stomata are open and incorporated into a 4- C organic acids through the crassulacean acid metabolic (CAM) pathway 2. Organic acid kept in vacuole until next day’s sun energy when light reactions can be carried out (makes ATP and NADPH) CO 2 released and enters Calvin Cycle Bundle- sheath cell Mesophyll cell Organic acid C 4 CO 2 CO 2 CALVIN CYCLE Sugarcane Pineapple Organic acids release CO 2 to Calvin cycle CO 2 incorporated into four-carbon organic acids (carbon fixation) Organic acid CAM CO 2 CO 2 CALVIN CYCLE Sugar Spatial separation of steps Temporal separation of steps Sugar Day Night
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- Fall '18
- Patricia Zuk