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Photosynthesis Chloroplast Structure & Reactants Products Plant Cells Contain Chloroplast – the organelles that carry on photosynthesis converting light energy into sugar! Gas Released Gas Used Light energy 6 CO2 + 6 H2O Carbon dioxide Water C6H12O6 Photosynthesis + 6 O2 Glucose Oxygen gas Raw Materials Simple Sugar Photosynthesis • Chloroplasts are concentrated in mesophyll, the green tissue in the interior of a leaf • Membranes in the chloroplast form the framework where many of the reactions of photosynthesis occur Fig. 7-2a Leaf Cross Section Leaf Mesophyll Vein CO2 O2 Stoma Mesophyll Cell Chloroplast The Chloroplast • A chloroplast contains two membranes (as do mitochondria) • A thick fluid called the stroma fills the inner compartment of the chloroplast • Suspended in the stroma are the thylakoids, a system of interconnected individual membranous sacs, which enclose another compartment known as the thylakoid space • The thylakoids are arranged in stacks called grana Chloroplast Outer and inner membranes Thylakoid Stroma Granum Thylakoid space Intermembrane space The Chloroplast • Built into the thylakoid membranes are the chlorophyll molecules that capture light energy • Photosynthesis occurs throughout a plant (all the green parts), but is concentrated in the leaves • A plant will invest much of its energy into the production of its leaves in order to capture as much light energy as possible Make like a tree and… • Leaves are designed to capture light and increase the absorption of carbon dioxide • Carbon dioxide enters the leaf (and oxygen exits the leaf) via the stomata, tiny pores protected by guard cells • Water is supplied to the tree via its roots, but may exit the leaves when the stomata are open (a catch 22!); why stomata open at night in many plants Pigments • Pigments are light-absorbing molecules built into the thylakoid membranes • Pigments absorb some wavelengths of light, but reflect others • We do not see the absorbed wavelengths (because their energy has been absorbed by the pigment molecules); we see the wavelengths that the pigment reflects! Pigments • A leaf is green because chlorophyll absorbs colors other than green; absorbs light most strongly in the blue and red, but poorly in the green • Different pigments absorb different wavelengths • Chloroplasts contain different types of pigments Pigments • Chlorophyll A (a type of chlorophyll pigment) absorbs light mainly in the blue-violet (high energy) and Chlorophyll B red (low energy) wavelengths Light Chloroplast Thylakoid Reflected light Absorbed light Transmitted light •In addition to chlorophyll, other pigments, known as accessory pigments are present in plants; these include carotene, and cyanins, colors like orange & brown. Pigments Light Chloroplast Reflected light Absorbed light Transmitted light Autumn color change • Autumn leaf color is a phenomenon that affects the normally green leaves of deciduous trees and shrubs, changing to reds and yellows (and various shades in between) • In late summer, the veins that carry fluids into and out of the leaf are gradually closed off, and chlorophyll decreases Autumn color change • When chlorophyll concentrations decrease at the end of summer, some of these other pigments – which are usually masked by chlorophyll – reveal their colors • Carotene, for example, is especially longlasting variations of orange color http://ohad.me/?showimage=53 The Chloroplast Structure Cont. Fig. 7-2b Chloroplast Outer and inner membranes Thylakoid Stroma Granum Thylakoid space Intermembrane space Fig. 7-2a Leaf Cross Section Leaf Mesophyll Vein CO2 O2 Stoma Mesophyll Cell Chloroplast Fig. 7-6b Light Reflected light Chloroplast Absorbed light Thylakoid Transmitted light Fig. 7-0c Light energy 6 CO2 + 6 H2O Carbon dioxide Water C6H12O6 Photosynthesis + 6 O2 Glucose Oxygen gas