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Photosynthesis. Chapter 7. Photosynthetic Organisms. Photosynthesis transforms solar energy into the chemical energy of a carbohydrate. Heterotrophic organisms use organic molecules produced by photosynthesizers as a source of chemical energy.
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Photosynthesis Chapter 7 Mader: Biology 8th Ed.
Photosynthetic Organisms • Photosynthesis transforms solar energy into the chemical energy of a carbohydrate. • Heterotrophic organisms use organic molecules produced by photosynthesizers as a source of chemical energy. Mader: Biology 8th Ed.
Figure 10.2 Focusing in on the location of photosynthesis in a plant Mader: Biology 8th Ed.
Flowering Plants • CO2 enters leaf through stomates. • 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 (singular granum). • Chlorophyll and other pigments within thylakoid membranes are capable of absorbing solar energy. Mader: Biology 8th Ed.
Figure 35.19 Leaf anatomy Mader: Biology 8th Ed.
Chloroplast Structure Mader: Biology 8th Ed.
Figure 36.12 An open (left) and closed (right) stoma of a spider plant (Chlorophytum colosum) leaf Mader: Biology 8th Ed.
Figure 36.12x Stomata on the underside of a leaf Mader: Biology 8th Ed.
Light • Behaves as if it has both • Particles—called photons • Wave motion—the distance between the crests of two waves is called the wavelength. Mader: Biology 8th Ed.
Figure 10.5 The electromagnetic spectrum Mader: Biology 8th Ed.
Visible Light • Has wavelength of 380-750 nm • The shorter the wavelength, the more energy. (The energy of a photon is inversely proportional to the wavelength.) • Light can excite atoms in certain molecules and move electrons to higher energy levels. Then one of three things can happen: • When the electron returns to its ground state, energy is dissipated as heat • Or energy is given off as light of a longer wavelength (fluorescence) • The electron may be lost from the atom (leaving a +ion) and may be accepted by a reducing agent (in photosynthesis NADP+) Mader: Biology 8th Ed.
Photosynthetic Pigments • Most pigments absorb only some wavelengths of light and reflect or transmit the other wavelengths. • The color seen is that which is reflected. • Chlorophyll a is the main photosynthetic pigment. • Grass-green or blue-green • Molecular formula C55H72O5N4Mg • Has a porphyrin ring (similar to hemoglobin) with a central atom of Mg Mader: Biology 8th Ed.
Photosynthetic Pigments • Chlorophyll b—yellow-green, C55H70O6N4Mg • Chlorophyll a and b absorb energy from the blue, violet, and red regions of the spectrum. • Accessory pigments—can absorb energy from other regions of the spectrum. Include • Carotenoids—orange, dark yellow • Xanthophylls—light yellow • Anthocyanins--reds Mader: Biology 8th Ed.
Figure 10.6 Why leaves are green: interaction of light with chloroplasts Mader: Biology 8th Ed.
Figure 10.7 Determining an absorption spectrum Mader: Biology 8th Ed.
Photosynthetic Pigments and Photosynthesis Mader: Biology 8th Ed.
Figure 10.8 Evidence that chloroplast pigments participate in photosynthesis: absorption and action spectra for photosynthesis in an alga Mader: Biology 8th Ed.
Figure 10.9 Location and structure of chlorophyll molecules in plants Mader: Biology 8th Ed.
Figure 10.09x Chlorophyll Mader: Biology 8th Ed.
Figure 10.10 Excitation of isolated chlorophyll by light Mader: Biology 8th Ed.
Figure 10.4 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (Layer 1) Mader: Biology 8th Ed.
Figure 10.4 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (Layer 2) Mader: Biology 8th Ed.
Figure 10.4 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle (Layer 3) Mader: Biology 8th Ed.
Photosynthetic Reactions • 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. • One Photosystem consists of a pigment complex and electron acceptor molecules in the thylakoid membrane. • Pigment complex helps gather solar energy. Mader: Biology 8th Ed.
Figure 10.11 How a photosystem harvests light Mader: Biology 8th Ed.
Figure 10.12 How noncyclic electron flow during the light reactions generates ATP and NADPH (Layer 1) Mader: Biology 8th Ed.
Figure 10.12 How noncyclic electron flow during the light reactions generates ATP and NADPH (Layer 2) Mader: Biology 8th Ed.
Figure 10.12 How noncyclic electron flow during the light reactions generates ATP and NADPH (Layer 3) Mader: Biology 8th Ed.
Figure 10.12 How noncyclic electron flow during the light reactions generates ATP and NADPH (Layer 4) Mader: Biology 8th Ed.
Figure 10.12 How noncyclic electron flow during the light reactions generates ATP and NADPH (Layer 5) 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.
Figure 10.14 Cyclic electron flow Mader: Biology 8th Ed.
Figure 10.15 Comparison of chemiosmosis in mitochondria and chloroplasts Mader: Biology 8th Ed.
Figure 10.16 The light reactions and chemiosmosis: the organization of the thylakoid membrane Mader: Biology 8th Ed.
Thylakoid Organization Mader: Biology 8th Ed.
Figure 10.x1 Melvin Calvin 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, a 5-carbon molecule. The result is a 6-carbon molecule which splits into two 3-carbon molecules. • The enzyme, 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.
Figure 10.17 The Calvin cycle (Layer 1) Mader: Biology 8th Ed.
Figure 10.17 The Calvin cycle (Layer 2) Mader: Biology 8th Ed.
Figure 10.17 The Calvin cycle (Layer 3) 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.
