PHOTOSYNTHESIS

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). 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 glucose SUN photons

3 Question: Where does photosynthesis take place?

4 Plants Autotrophs – produce their own food (glucose)Autotrophs – produce their own food (glucose) Process called photosynthesisProcess called photosynthesis Mainly occurs in the leaves:Mainly occurs in the leaves: a.stoma - pores b.mesophyll cells Stoma Mesophyll Cell Chloroplast

5 Stomata (stoma) Pores in a plant’s cuticle through which water and gases are exchanged between the plant and the atmosphere. Guard Cell Carbon Dioxide (CO 2 ) Oxygen (O 2 ) Found on the underside of leaves

6 Mesophyll Cell of Leaf Cell Wall Nucleus Chloroplast Central Vacuole Photosynthesis occurs in these cells!

7 Chloroplast Organellephotosynthesis Organelle where photosynthesis takes place. Granum Thylakoid Stroma Outer Membrane Inner Membrane Thylakoid stacks are connected together

8 Thylakoid Thylakoid Membrane Thylakoid Space Granum Grana make up the inner membrane

9 Question: Why are plants green?

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

11 Wavelength of Light (nm) Short waveLong wave (more energy)(less energy)

12 Absorption of Light by Chlorophyll wavelength Absorption violet blue green yellow orange red

13 Question: During the fall, what causes the leaves to change colors?

14 Fall Colors In addition to the chlorophyll pigments, there are other pigments presentIn addition to the chlorophyll pigments, there are other pigments present During the fall, the green chlorophyll pigments are greatly reduced revealing the other pigmentsDuring the fall, the green chlorophyll pigments are greatly reduced revealing the other pigments Carotenoids are pigments that are either red, orange, or yellowCarotenoids are pigments that are either red, orange, or yellow

15 Redox Reaction The transfer of one or more electrons from one reactant to another Two types: 1.Oxidation is the loss of e - 2.Reduction is the gain of e -

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

17 Reduction Reaction The gain of electrons to a substance or the loss of oxygen. glucose 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 Reduction

18 Two Parts of Photosynthesis Two reactions make up photosynthesis: 1.Light Reaction or Light Dependent Reaction - Produces energy from solar power (photons) in the form of ATP and NADPH. SUN

19 Two Parts of Photosynthesis 2. Calvin Cycle or Light Independent Reaction Also called Carbon Fixation or C 3 FixationAlso called Carbon Fixation or C 3 Fixation Uses energy (ATP and NADPH) from light reaction to make sugar (glucose).Uses energy (ATP and NADPH) from light reaction to make sugar (glucose). ATP

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

21 Cyclic Electron Flow Occurs in the thylakoid membraneOccurs in the thylakoid membrane Uses Photosystem I onlyUses Photosystem I only P700 reaction center- chlorophyll aP700 reaction center- chlorophyll a Uses Electron Transport Chain (ETC)Uses Electron Transport Chain (ETC) Generates ATP onlyGenerates ATP only ADP + ATP ADP + ATP P

22 Cyclic Electron Flow P700 Primary Electron Accepto r e-e- e-e- e-e- e-e- ATP produced by ETC Photosystem I Accessory Pigments SUN Photons Pigments absorb photons, excite electrons, which produce ATP

23 Noncyclic Electron Flow Occurs in the thylakoid membraneOccurs in the thylakoid membrane Uses PS II and PS IUses PS II and PS I P680 reaction center (PSII) - chlorophyll aP680 reaction center (PSII) - chlorophyll a P700 reaction center (PS I) - chlorophyll aP700 reaction center (PS I) - chlorophyll a Uses Electron Transport Chain (ETC)Uses Electron Transport Chain (ETC) Generates O 2, ATP and NADPHGenerates O 2, ATP and NADPH

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

25 B. Noncyclic Electron Flow ATPADP +  ATP NADPHNADP + + H  NADPH Oxygen comes from the splitting of H 2 O, not CO 2Oxygen comes from the splitting of H 2 O, not CO 2 H 2 O H 2 O  1/2 O 2 + 2H + (Reduced) P (Oxidized)

26 Chemiosmosis ATP synthesisPowers ATP synthesis. thylakoid membranesLocated in the thylakoid membranes. (enzyme)Uses ETC and ATP synthase (enzyme) to make ATP. Photophosphorylation: phosphateADPATPPhotophosphorylation: addition of phosphate to ADP to make ATP.

27 Chemiosmosis

28 Calvin Cycle Carbon Fixation (light independent rxn).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.

29 Chloroplast Granum Thylakoid Stroma Outer Membrane Inner Membrane

30 Calvin Cycle (C 3 fixation) 6CO 2 6C-C-C-C-C-C 6C-C-C 6C-C-C-C-C 12PGA RuBP 12G 3 P (unstable) 6NADPH 6ATP C-C-C-C-C-C Glucose (6C) (36C) (30C) (6C) 6C-C-C C3C3 glucose

31 Calvin Cycle Remember:C3 = Calvin CycleRemember: C3 = Calvin Cycle C3C3 Glucose

32 Photorespiration hot, dry, bright daysOccurs on hot, dry, bright days. Stomates close. Fixation of O 2 instead of CO 2. 2-C molecules3-C sugar moleculesProduces 2-C molecules instead of 3-C sugar molecules. Produces no sugar molecules or no ATP.

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

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

35 C4 Plants Mesophyll Cell CO 2 C-C-C PEP C-C-C-C Malate ATP Bundle Sheath Cell C-C-C Pyruvic Acid C-C-C-C CO 2 C3C3 Malate Transported glucose Vascular Tissue

36 CAM Plants Hot, dry environmentsHot, dry environments. 5% of plants (cactus and ice plants).5% of plants (cactus and ice plants). Stomates closed during day.Stomates closed during day. Stomates open during the nightStomates open during the night. Light rxn - occurs during the day. Calvin Cycle - occurs when CO 2 is present.

37 CAM Plants Night (Stomates Open)Day (Stomates Closed) Vacuole C-C-C-C Malate C-C-C-C Malate C-C-C-C CO 2 C3C3 C-C-C Pyruvic acid ATP C-C-C PEP glucose

38 Question: Why would CAM plants close their stomates during the day?