Photosynthesis Chapter 7 Outline Flowering Plants Photosynthetic Pigments Photosynthesis Light Reactions! Noncyclic! Cyclic Calvin Cycle Reactions C 4 CAM 1 2 Photosynthetic Organisms Photosynthesis transforms solar energy into the chemical energy of a carbohydrate. All organisms use organic molecules produced by photosynthesizers as a source of chemical energy. 3 4
Flowering Plants The green portions of plants, particularly leaves, carry on photosynthesis. Leaf of flowering plant contains mesophyll tissue.! Contains cells specialized to carry on photosynthesis. Flowering Plants CO 2 enters leaf through stomata. CO 2 and water diffuse into chloroplasts. Double membrane surrounds fluid (stroma).! Inner membrane system within stroma form flattened sacs (thylakoids). " Often stacked to form grana. Chlorophyll and other pigments within thylakoid membranes are capable of absorbing solar energy. 5 6 Fig. 7.2 Photosynthetic Pigments Most pigments absorb only some wavelengths of light and reflect or transmit the other wavelengths. Absorption Spectra! Organic molecules and processes within organisms are chemically adapted to visible light. 7 8
Photosynthetic Pigments and Photosynthesis Fig. 7.3 9 10 Photosynthetic Reaction Light Reaction - Chlorophyll absorbs solar energy and energizes electrons. Electrons move down electron transport chain.! Solar energy # ATP, NADPH Photosynthesis Overview Calvin Cycle Reaction - CO 2 is taken up and reduced to a carbohydrate. Reduction requires ATP and NADPH.! ATP, NADPH # Carbohydrate 11 12
Light Reactions Light reactions consist of two electron pathways: Noncyclic electron pathway Cyclic electron pathway Both pathways produce ATP, but only the noncyclic pathway also produces NADPH. Noncyclic Electron Pathway Electron flow can be traced from water to a molecule of NADPH. Uses two photosystems, PS I and PS II. Photosystem consists of pigment complex and electron acceptor molecules in the thylakoid membrane.! Pigment complex helps gather solar energy. 13 14 Cyclic Electron Pathway Cyclic pathway begins when PS I pigment complex absorbs solar energy and is passed from one pigment to another until it is concentrated in a reaction center. Pathway only results in ATP production. 15 16
Thylakoid Organization 17 18 Calvin Cycle Reactions Calvin cycle is a series of reactions that produce carbohydrates before returning to the starting point again. Utilizes atmospheric carbon dioxide to produce carbohydrates. Includes:! Carbon dioxide fixation! Carbon dioxide reduction! RuBP Regeneration 19 20
Calvin Cycle Reactions Carbon Dioxide Fixation Calvin Cycle Reactions Reduction of Carbon Dioxide CO 2 is attached to RuBP. The result is a 6- carbon molecule which splits into two 3- carbon molecules.! Rubisco speeds up this reaction. 21 22 Calvin Cycle Reactions Regeneration of RuBP Importance of Calvin Cycle PGAL (glyceraldehyde-3-phosphate) is the product of the Calvin cycle that can be converted to a variety of organic molecules. A plant can utilize the hydrocarbon skeleton of PGAL to form fatty acids and glycerol, which are combined in plant oils. 23 24
C 4 Photosynthesis In C 4 leaf, bundle sheath cells and mesophyll cells contain chloroplasts. Mesophyll cells are arranged concentrically around the bundle sheath cells. In hot, dry climates, net photosynthetic rate of C 4 plants is about 2-3 times that of C 3 plants. Avoid photorespiration 25 26 C 3 vs C 4 Carbon Dioxide Fixation in C 3 and C 4 Plants 27 28
CAM Photosynthesis Crassulacean-Acid Metabolism C 4 plants partition carbon fixation in space, while CAM partitions by time.!during the night, CAM plants fix CO 2, forming C 4 molecules, which are stored in large vacuoles. " C 4 molecules release CO 2 to Calvin cycle when NADPH and ATP are available. $ Water Conservation 29 30 Review Flowering Plants Photosynthetic Pigments Photosynthesis Light Reactions! Noncyclic! Cyclic Calvin Cycle Reactions C 4 CAM 31 32