Photosynthesis Dark Reaction Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Review Two Stages of Photosynthesis Capturing energy from sunlight to make ATP and NADPH. Storing energy in carbohydrates ATP and NADPH powering carbon fixation. Chloroplast Structure Internal membranes organized into sacs of thylakoids and stacked in grana. Semiliquid fluid (stroma) surrounds thylakoid membrane. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Leaf Organization Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Photosystems I and II “Z” Scheme Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Two Photosystems Work Together Two-stage photosystem referred to as non-cyclic phosphorylation. Photosystem II acts first. High energy electrons generated by photosystem II used to synthesize ATP, and then passed to photosystem I to drive NADPH production. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Raven - Johnson - Biology: 6th Ed Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Light and Dark Reactions occur in different parts of the chloroplast Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Carbon Fixation- The Calvin Cycle CO2 attaches to ribulose bisphosphate (RuBP). Splits to form 2 three-carbon molecules of phosphoglycerate (PGA). Also called C3 photosynthesis. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Photorespiration-Why photosynthesis is not very efficient Photorespiration incorporates O2 into ribulose1,5-bisphosphate instead of CO2. Under normal conditions, 20% of photosynthetically-fixed carbon is lost to photorespiration. Loss rises as temperature increases. Why does this happen? Oxygen competes with CO2 for RuBP 21% of the atmosphere is O2, only 0.03% is CO2 Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

C4 Plants are Adapted to Hot Climates In hot climates, plants close their stomata to reduce water loss This reduces the amount of CO2 that can be taken in even more! C4 photosynthesis produces a four carbon compound which does not go through photorespiration. C4 plants conduct the Light Reaction in mesophyll cells and the Calvin Cycle in bundle sheath cells. Creates high levels of CO2 Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Raven - Johnson - Biology: 6th Ed Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Crassulacean Acid Metabolism (CAM) plants CAM plants are adapted to hot environments Open stomata during the night and close them during the day to minimize water loss. Use C4 during the night and C3 during the day. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Raven - Johnson - Biology: 6th Ed Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies