How can you explain the shape of these two graphs that describe the rate of photosynthesis as a function of temperature and light intensity? Answers: Light intensity – this is a saturation curve graph. Initially increases light increases the production of key reaction intermediates in photosynthesis, however eventually the enzymes become saturated and the rate plateaus. Temperature- This is a bell curve. There is an optimum temperature at which the activity of the enzymes that catalyze the reactions of photosynthesis operate most efficiently.

Practice IB Bioenergetics Question The concentration of O2 was measured in the dark in a container of fixed volume for 1 hour. Next a plant was added to the container with the lights off for 1 hour. Finally high intensity lights were turned on in the container for 3 hours. Sketch a plausible graph of what would be observed during the experiment. Label the y-axis as O2 concentration and time on the x-axis.

[O2] Introduce Plant in Dark LIGHT ON TIME

The Main Product of the Light-independent Reactions In the Light-independent Reactions, the Calvin cycle uses ATP and NADPH to convert CO2 to sugar 1. Carbon fixation to a 3-carbon organic acid C3 Ribulose -1,5-bisphosphate carboxylase oxygenase 2. Reduction to an aldehyde (ATP & NADPH) The Main Product of the Light-independent Reactions VIDEO LINK OVERVIEW Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Electron transport chain Fig. 10-21 H2O CO2 CALVIN CYCLE INPUTS: CO2 + NADPH + ATP Light NADP+ ADP + P i Light Reactions: Photosystem II Electron transport chain Photosystem I RuBP 3-Phosphoglycerate Calvin Cycle ATP G3P Starch (storage) NADPH Chloroplast in Mesophyll cells Chloroplast CALVIN CYCLE OUTPUTS: G3P(or glucose) + NADP+ + ADP O2 Sucrose (export)

Figure 10.17 The Calvin cycle (Layer 1) Link to Smith College Animation

The addition of CO2 to RuBP to form 3-PGA is catalyzed by the enzyme Rubisco -Very inefficient enzyme Slow rate means that many copies of enzyme are required in each chloroplast

Figure 10.17 The Calvin cycle (Layer 2)

Figure 10.17 The Calvin cycle (Layer 3)

6 turns required to make 1 glucose molecules Link to McGraw-Hill Animation

Link to animation Light source Stop reaction at different time intervals by dropping sample into hot, boiling ethanol.

Link to Arizona Biology Project