Photosynthesis Chapter 7 Mader: Biology 8th Ed.
Outline • Flowering Plants • Photosynthetic Pigments • Photosynthesis • Light Reactions • Noncyclic • Cyclic • Calvin Cycle Reactions • C4 • CAM Mader: Biology 8th Ed.
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. Mader: Biology 8th Ed.
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. Mader: Biology 8th Ed.
Flowering Plants • CO2 enters leaf through stomata. • CO2 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. Mader: Biology 8th Ed.
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. Mader: Biology 8th Ed.
Photosynthetic Pigments and Photosynthesis Mader: Biology 8th Ed.
Photosynthetic Reaction • Light Reaction - Chlorophyll absorbs solar energy and energizes electrons. • Electrons move down electron transport chain. • Solar energy ATP, NADPH • Calvin Cycle Reaction - CO2 is taken up and reduced to a carbohydrate. • Reduction requires ATP and NADPH. • ATP, NADPH Carbohydrate Mader: Biology 8th Ed.
Photosynthesis Overview Mader: Biology 8th Ed.
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. Mader: Biology 8th Ed.
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. Mader: Biology 8th Ed.
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. Mader: Biology 8th Ed.
Thylakoid Organization Mader: Biology 8th Ed.
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 Mader: Biology 8th Ed.
Calvin Cycle Reactions • Carbon Dioxide Fixation • CO2 is attached to RuBP. The result is a 6-carbon molecule which splits into two 3-carbon molecules. • Rubisco speeds up this reaction. Mader: Biology 8th Ed.
Calvin Cycle Reactions • Reduction of Carbon Dioxide Mader: Biology 8th Ed.
Calvin Cycle Reactions • Regeneration of RuBP Mader: Biology 8th Ed.
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. Mader: Biology 8th Ed.
C4 Photosynthesis • In C4 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 C4 plants is about 2-3 times that of C3 plants. • Avoid photorespiration Mader: Biology 8th Ed.
C3 vs C4 Mader: Biology 8th Ed.
Carbon Dioxide Fixation in C3 and C4 Plants Mader: Biology 8th Ed.
CAM Photosynthesis • Crassulacean-Acid Metabolism • C4 plants partition carbon fixation in space, while CAM partitions by time. • During the night, CAM plants fix CO2, forming C4 molecules, which are stored in large vacuoles. • C4 molecules release CO2 to Calvin cycle when NADPH and ATP are available. • Water Conservation Mader: Biology 8th Ed.
Review • Flowering Plants • Photosynthetic Pigments • Photosynthesis • Light Reactions • Noncyclic • Cyclic • Calvin Cycle Reactions • C4 • CAM Mader: Biology 8th Ed.