Concept 2: Analyzing the Processes of Photosynthesis PART 2 – Adaptations to Dry Climates Refer to pg 81-90 in Holtzclaw, Ch 10 in Campbell and media resources Refer to pg 321-323 in Holtzclaw, Lab 4 in LabBench

Try This! Where does the organic biomass of a tree primarily come from? Oxygen Water Carbon dioxide Light Fertilizer Carbon dioxide!

A building block for organic molecules! Try This! Where does the organic biomass of a tree primarily come from? Oxygen Water Carbon dioxide Light Fertilizer CO2 Carbon dioxide! A building block for organic molecules!

Chapter 10 You must know: How photosystems convert solar energy to chemical energy How linear electron flow in the light reactions results in the formation of ATP, NADPH, and O2 How chemiosmosis generates ATP in the light reactions How the Calvin cycle uses the energy molecules of the light reactions to produce G3P The metabolic adaptations of C4 and CAM plants to arid, dry regions

AP Lab 4 You must know: The equation for photosynthesis and understand the process of photosynthesis The principles of chromatography and how to calculate Rf values The relationship between light wavelength or intensity and photosynthetic rate How to determine the rate of photosynthesis and then be able to design a controlled experiment to test the effect of some variable factor on photosynthesis

Photosynthesis – The Basics CO2 + H2O → C6H12O6 + O2 Light Reactions “photo” Calvin Cycle “synthesis”

The Light Reactions

The Light Reactions Light energy excites electrons in chlorophyll Removal of electrons from H2O Formation of O2 Electron Transport Chain Reduction of NADP+ to NADPH Proton Motive Force ATP Synthase to produce ATP

H+! Proton Motive Force

Try This Unlike in cellular respiration, the proton motive force generated by the light reactions in photosynthesis happens in three ways… Can you remember the three ways? Electron transport chain powering the active transport of H+ into the thylakoid space H+ produced in the thylakoid space from the splitting and oxidation of water Removal of H+ from stroma during the reduction of NADP + to NADPH

The Light Reactions The whole point was to transfer light energy to chemical energy in the form of: electrons in NADPH ATP Why? To power carbon fixation in the Calvin Cycle…

Carbon Fixation! The Calvin Cycle CO2 enters as a gas through the stomata (openings) of the leaves Through the power of NADPH and ATP, CO2 gets converted into an organic compound: a 3-carbon sugar called glyceraldehyde-3-phosphate (G3P) Can be converted to glucose, sucrose, starch, etc…

The whole point…

How does this affect YOU?

Chapter 10 You must know: How photosystems convert solar energy to chemical energy How linear electron flow in the light reactions results in the formation of ATP, NADPH, and O2 How chemiosmosis generates ATP in the light reactions How the Calvin cycle uses the energy molecules of the light reactions to produce G3P The metabolic adaptations of C4 and CAM plants to arid, dry regions

NOW… Adaptations to hot, arid climates… CAM plants and C4 plants Sugarcane – C4 plant Pineapple – CAM plant

Hot, Dry Climates What’s the big deal? Stomata – water loss Rubisco – photorespiration

Stomata…

Stomata… Water exits via stomata during transpiration (evaporation of water through the stomata - which pulls water up the plant from the roots) If it’s a hot, dry day, plants need to minimize water loss! Solution? Close/minimize stomata BUT? Lowers CO2 intake…

Rubisco… Remember rubisco? It’s the enzyme that fixes CO2 in the Calvin cycle of C3 plants The thing is… rubisco will also bind O2 in absence of CO2 Causes breakdown of Calvin Cycle products… Photorespiration Solution? Adapt!

Try This! The presence of only Photosystem I, not Photosystem II, in the bundle sheath cells of C4 plants has an effect on O2 concentration. What is that effect, and how might that benefit the plant?

Try This! The presence of only Photosystem I, not Photosystem II, in the bundle sheath cells of C4 plants has an effect on O2 concentration. What is that effect, and how might that benefit the plant? Without PS II, no O2 is generated in the bundle-sheath cells! This avoids the problem of O2 competing with CO2 for binding to rubisco No photorespiration

Now… Practice Re-Read about CAM plants and C4 plants and do worksheet Try #12 – 15, 17-19, 21-22 p. 91-92 Go over Comparison Charts Try animation activities (Campbell Online) Re-Read about CAM plants and C4 plants and do worksheet P. 88-89 Holtzclaw P. 200-202 Campbell Activity: Photosynthesis in Dry Climates (Campbell Online) Get Ready for Lab 4 Go through Lab 4 LabBench Checkpoint Next Class on Photosynthesis (Concept 2)