Chapter 4 Photosynthesis

Photosynthesis is the process by which certain organisms use light energy To make sugar and oxygen gas from carbon dioxide and water What does it need? (Input) What does it make? (Output) Light energy PHOTOSYNTHESIS 6 CO2 + H2O Carbon dioxide Water C6H12O6 O2 Glucose Oxygen gas

Trophic Roles Autotrophs  Producers of the biosphere: produce organic molecules from CO2 & inorganic raw materials Heterotrophs  consumers

Learning Target 1. Describe Oxidation & Reduction reactions

REDOX Reactions LEO the Lion Says GER

REDOX Reactions Oxidation Reduction CO2 + H2O + energy → C6H12O6 + O2 When a compound loses electrons Reduction When a compound gains electrons CO2 + H2O + energy → C6H12O6 + O2 CO2 is reduced to form glucose Water is oxidized to form O2

Photosynthesis is a redox process, as is cellular respiration Photosynthesis is a redox process, as is cellular respiration In photosynthesis H2O is oxidized and CO2 is reduced Reduction Oxidation 6 O2 6 H2O 6 CO2  C6H12O6 Figure 7.4A, B

Learning Check If H2O is losing electrons than it is being reduced/oxidized Co2 is being reduced/oxidized, which means it is gaining/losing electrons.

Photosynthesis Overview Light reactions Depend on light Occur in Thylakoid Membrane Light Independent (“Dark”) reactions Does NOT need light Occurs in the Stroma

Learning Target Compare & contrast the structure & function of mitochondria & chloroplast 15. Determine what factors affect the process of photosynthesis & cellular respiration

Location, location, location Where does the Light Dependent Reaction occur? The Light Independent reaction?

Chloroplast Structure Found in mesophyll 1 mesophyll cell may have 30 chloroplasts Stomata regulate passage of CO2, O2 and H2O

Learning Check Where does the Light Dependent Reaction occur? The Light Independent reaction? What factors could affect the process of photosynthesis?

Learning Targets 11. Describe the purpose of Chlorophyll & Accessory pigments.

Pigments Pigments Absorb light energy Boost e- become unstable! Chlorophyll Chlorophyll a  main pigment  blue-green Chlorophyll b  accessory pigment  yellow-green Other accessory pigments  absorb different wavelengths of light Carotenoids  yellow-orange Xanthophyll yellow Rhodophyll  red Fucoxanthin  brown Why are plants green? Why are plants changing color?

Photosystems Pass energy  reaction center (chlorophyll a molecule)  transfers energy to primary electron acceptor antenna pigments are primarily chlorophyll b, carotenoids & xanthophyll

Learning Check What is the purpose/function of pigments?

Photosynthesis Overview Light reactions light energy  chemical energy (ATP and NADPH) and produce O2 Light Independent (“Dark”) reactions Using ATP and NADPH from the light reactions form sugar from CO2

Learning Target 6. Explain how electron transport chains (ETC) establish an electrochemical gradient across membranes. 7. Contrast Chemiosmosis in Cellular Respiration and Photosynthesis

ETC, Chemiosmosis & ATP Synthase Powers ATP synthesis in light reactions electrons (e-) are passed along a chain of proteins (called the ETC) in the membrane  H+ pumped into Thylakoid space (chemiosmosis) H+ diffuse back across the membrane through ATP synthase  powers the phosphorylation of ADP to produce ATP (photophosphorylation)

Photophosphorylation http://vcell. ndsu. nodak

Learning Check! ETC uses the energy of e- being passed along to pump _______ from the ________ into the thylakoid _______ Chemiosmosis is the movement of ______ to create a ________concentration.

Learning Target 3. Identify the inputs and outputs and location of the light reactions and Calvin Cycle. 4. Explain the role of NADH, FADH2, and NADPH. 14. Summarize how energy is transferred during photosynthesis and cellular respiration.

Electron Carriers NAD+ NADP+ ADP  ATP Reacts with C-H bonds to become NADH NADP+ Reacts with free e- and H+ ions ADP  ATP diffusion of H+ through ATP Synthase

LDR Inputs? Outputs? Two types: Noncyclic Photophosphorylation

Non-cyclic photophosphorylation

Learning Target 12. Describe the connection between PS2 & PS1

Cytochrome complex synthase reductase LIGHT REACTOR NADP+ ADP ATP NADPH CALVIN CYCLE [CH2O] (sugar) STROMA (Low H+ concentration) Photosystem II H2O CO2 Cytochrome complex O2 1 1⁄2 2 Photosystem I Light THYLAKOID SPACE (High H+ concentration) Thylakoid membrane synthase Pq Pc Fd reductase + H+ NADP+ + 2H+ To Calvin cycle P 3 H+ 2 H+ +2 H+

Light Dependent RXN animation http://www.science.smith.edu/departments/Biology/Bio231/ltrxn.html http://vcell.ndsu.nodak.edu/animations/photosynthesis/movie-flash.htm

Cyclic Photophosphorylation Primitive  used by bacteria Electron boosted out of P1  ETC  returned to P1 Electron drives proton pumps chemiosmosis  ATP

Learning Targets 3. Identify the inputs and outputs and location of the light reactions and Calvin Cycle. 4. Explain the role of NADH, FADH2, and NADPH. 15. Summarize how energy is transferred during photosynthesis and cellular respiration.

Calvin Cycle/Light Independent Reactions Occur in the dark or the light Light independent reactions 3 steps Carbon fixation Reduction Regeneration of RuBP

Step 1: Carbon Fixation RuBP (ribulose bisphosphate) 5 C sugar Catalyzed by Rubisco (RuBP carboxylase) Adds CO2 Creates an unstable 6 C molecule that splits Creates PGA (3 C moleucle

Step 2: Reduction PGA gets phosphorylated by ATP (gets it’s energy) Reduced by NADPH (gets it’s e-) Produces G3P (PGAL) some G3P  glucose most G3P  regenerate RuBP

Step 3: Regeneration of RuBP 1 G3P moves out to eventually become glucose G3P  rearranged into RuBP Requires input of 3 ATP Takes 6 turns of cycle  1 glucose

http://www.science.smith.edu/departments/Biology/Bio231/calvin.html

Alternative mechanisms: Photorespiration C3 plants  rice, wheat, soybeans Uses Co2 directly to make PGA On hot, dry days they close their stomata no CO2 taken in and O2 builds up rubisco substitutes O2 for CO2 Creates a 2 C compound 2 C compound gets broken down  releases CO2 & water Called photorespiration Uses light, releases CO2 and water Doesn’t make glucose

Alternative mechanisms: C4 Plants Sunny ecosystems C is fixed into 4 C molecule Carbon fixed outside cells (in bundle sheath cells  very efficient  requires extra ATP Only fixes C, not oxygen Donates the carbon to Calvin Cycle Balances out photorespiration & saves water Corn and sugarcane are a C4 plants

Alternative mechanisms: CAM Plants Crassulacean acid metabolism  Hot/dry climates Orchids, cacti, pineapple etc. Stomates open at night to reduce water loss  evaporation CO2 is fixed into a 4 C compound, used later