PHOTOSYNTHESIS. Botany Department B.N.D. College

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1 PHOTOSYNTHESIS Botany Department B.N.D. College

2 Photosynthesis An anabolic, endergonic, carbon dioxide (CO 2 ) requiring process that uses light energy (photons) and water (H 2 O) to produce organic macromolecules (glucose). photons SUN 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 glucose

3 Plants Autotrophs: self-producers. Location: 1. Leaves a. stoma b. mesophyll cells Mesophyll Cell Chloroplast Stoma

4 Stomata (stoma) Pores in a plant s cuticle through which water and gases are exchanged between the plant and the atmosphere. Oxygen (O 2 ) Carbon Dioxide (CO 2 ) Guard Cell Guard Cell

5 Mesophyll Cell Cell Wall Nucleus Chloroplast Central Vacuole

6 Chloroplast Organelle where photosynthesis takes place. Outer Membrane Inner Membrane Stroma Thylakoid Granum

7 Thylakoid Thylakoid Membrane Granum Thylakoid Space

8 Chlorophyll Molecules Located in the thylakoid membranes. Chlorophyll have Mg + in the center. Chlorophyll pigments harvest energy (photons) by absorbing certain wavelengths (blue-420 nm and red-660 nm are most important). Plants are green because the green wavelength is reflected, not absorbed.

9 Wavelength of Light (nm) Short wave (more energy) Long wave (less energy)

10 Absorption of Chlorophyll Absorption violet blue green yellow orange red wavelength

11 Redox Reaction The transfer of one or more electrons from one reactant to another. Two types: 1. Oxidation 2. Reduction

12 Oxidation Reaction The loss of electrons from a substance. Or the gain of oxygen. Oxidation 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 glucose

13 Reduction Reaction The gain of electrons to a substance. Or the loss of oxygen. Reduction 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 glucose

14 Breakdown of Photosynthesis Two main parts (reactions). 1. Light Reaction or Light Dependent Reaction Produces energy from solar power (photons) in the form of ATP and NADPH.

15 Breakdown of Photosynthesis 2. Calvin Cycle or Light Independent Reaction or Carbon Fixation or C 3 Fixation Uses energy (ATP and NADPH) from light rxn to make sugar (glucose).

16 1. Light Reaction (Electron Flow) Occurs in the Thylakoid membranes During the light reaction, there are two possible routes for electron flow. A. Cyclic Electron Flow B. Noncyclic Electron Flow

17 A. Cyclic Electron Flow Occurs in the thylakoid membrane. Uses Photosystem I only P700 reaction center- chlorophyll a Uses Electron Transport Chain (ETC) Generates ATP only ADP + P ATP

18 A. Cyclic Electron Flow SUN Primary Electron Acceptor e - Photons e - P700 e - e - ATP produced by ETC Accessory Pigments Photosystem I

19 B. Noncyclic Electron Flow Occurs in the thylakoid membrane Uses PS II and PS I P680 rxn center (PSII) - chlorophyll a P700 rxn center (PS I) - chlorophyll a Uses Electron Transport Chain (ETC) Generates O 2, ATP and NADPH

20 B. Noncyclic Electron Flow Primary Electron Acceptor 2e - 2e - ETC Primary Electron Acceptor 2e - Enzyme Reaction SUN Photon H 2 O 2e - ATP P680 1/2O Photosystem II 2 + 2H + Photon 2e - P700 NADPH Photosystem I

21 B. Noncyclic Electron Flow ADP + P ATP (Reduced ) NADP + + H NADPH (Reduced) Oxygen comes from the splitting of H 2 O, not CO 2 H 2 O 1/2 O 2 + 2H + (Oxidized)

22 Chemiosmosis Powers ATP synthesis. Located in the thylakoid membranes. Uses ETC and ATP synthase (enzyme) to make ATP. Photophosphorylation: addition of phosphate to ADP to make ATP.

23 Calvin Cycle Carbon Fixation (light independent rxn). C 3 plants (80% of plants on earth). Occurs in the stroma. Uses ATP and NADPH from light rxn. Uses CO 2. To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH.

24 Chloroplast Outer Membrane Inner Membrane Stroma Thylakoid Granum

25 Calvin Cycle (C 3 fixation) (6C) 6CO 2 (30C) 6C-C-C-C-C RuBP 6ATP (36C) 6C-C-C-C-C-C (unstable) 6C-C-C 6ATP 6NADPH 6C-C-C 6C-C-C 6ATP 6NADPH 6C-C-C 12PGA (36C) (36C) 12G 3 P C 3 glucose (30C) (6C) C-C-C-C-C-C Glucose

26 Calvin Cycle Remember: C3 = Calvin Cycle C 3 Glucose

27 Photorespiration Occurs on hot, dry, bright days. Stomates close. Fixation of O 2 instead of CO 2. Produces 2-C molecules instead of 3-C sugar molecules. Produces no sugar molecules or no ATP.

28 Photorespiration Because of photorespiration: Plants have special adaptations to limit the effect of photorespiration. 1. C4 plants 2. CAM plants

29 C4 Plants Hot, moist environments. 15% of plants (grasses, corn, sugarcane). Divides photosynthesis spatially. Light rxn - mesophyll cells. Calvin cycle - bundle sheath cells.

30 C4 Plants CO 2 Malate C-C-C-C Malate C-C-C-C Transported CO 2 C 3 C-C-C PEP ATP C-C-C Pyruvic Acid glucose Vascular Tissue Mesophyll Cell Bundle Sheath Cell