I. Capturing the Energy of Life All organisms require energy Some organisms (autotrophs) obtain energy directly from the sun and store it in organic compounds (glucose) during a process called photosynthesis 6CO2 + 6H2O + energy --> 6O2 + C6H12O6 II. Energy for Life Processes Energy is the ability to do work Work for a cell includes growth & repair, active transport across cell membranes, reproduction, synthesis of cellular products, etc. Work is the ability to change or move matter against other forces (W = F x D) Autotrophs or producers convert sunlight, CO2, and H2O into glucose (their food) Plants, algae, and blue-green bacteria, some prokaryotes, are producers or autotrophs Only 10% of the Earth?s 40 million species are autotrophs Other autotrophs use inorganic compounds instead of sunlight to make food; process known aschemosynthesis Producers make food for themselves and heterotrophs or consumers that cannot make food for themselves Heterotrophs include animals, fungi, & some bacteria, & protists III. Biochemical Pathways Photosynthesis and cellular respiration are biochemical pathways Biochemical pathways are a series of reactions where the product of one reaction is the reactant of the next Only autotrophs are capable of photosynthesis Both autotrophs & heterotrophs perform cellular respiration to release energy to do work In photosynthesis, CO2(carbon dioxide) and H2O (water) are combined to form C6H12O6 (glucose) & O2(oxygen) 6CO2 + 6H2O + energy --> 6O2 + C6H12O6 In cellular respiration, O2 (oxygen) is used to burn C6H12O6 (glucose) & release CO2(carbon dioxide), H2O (water), and energy Usable energy released in cellular respiration is called adenosine triphosphate or ATP IV. Light Absorption in Chloroplasts Chloroplasts in plant & algal cells absorb light energy from the sun during the light dependent reactions Photosynthetic cells may have thousands of chloroplasts Chloroplasts are double membrane organelles with the an inner membrane folded into disc-shaped sacs called thylakoids Thylakoids, containing chlorophyll and other accessory pigments, are in stacks called granum (grana, plural) Grana are connected to each other & surrounded by a gel-like material called stroma Light-capturing pigments in the grana are organized into photosystems V. Pigments Light travels as waves & packets called photons Wavelength of light is the distance between 2 consecutive peaks or troughs Sunlight or white light is made of different wavelengths or colors carrying different amounts ofenergy A prism separates white light into 7 colors (red, orange, yellow, green, blue, indigo, & violet) ROY G. BIV These colors are called the visible spectrum When light strikes an object, it is absorbed, transmitted, or reflected When all colors are absorbed, the object appears black When all colors are reflected, the object appears white If only one color is reflected (green), the object appears that color (e.g. Chlorophyll) Thylakoids contain a variety of pigments ( green red, orange, yellow...) Chlorophyll (C55H70MgN4O6) is the most common pigment in plants & algae Chlorophyll a & chlorophyll b are the 2 most common types of chlorophyll in autotrophs Chlorophyll absorbs only red, blue, & violet light Chlorophyll b absorbs colors or light energy NOT absorbed by chlorophyll a The light energy absorbed by chlorophyll b is transferred to chlorophyll a in the light reactions Carotenoids are accessory pigments in the thylakoids & include yellow, orange, & red VII. Overview of Photosynthesis 6CO2 + 6H2O C6H12O6 + 6O2 Photosynthesis is not a simple one step reaction but a biochemical pathway involving many steps This complex reaction can be broken down into two reaction systems --- light dependent & light independent or dark reactions Light Reaction: H2O O2 + ATP + NADPH2 Water is split, giving off oxygen. This system depends on sunlight for activation energy. Light is absorbed by chlorophyll a which "excites" the electrons in the chlorophyll molecule. Electrons are passed through a series of carriers and adenosine triphosphate or ATP (energy) is produced. Takes place in the thylakoids. Dark Reaction: ATP + NADPH2 + CO2 C6H12O6 Carbon dioxide is split, providing carbon to make sugars. The ultimate product is glucose. While this system depends on the products from the light reactions, it does not directly require light energy. Includes the Calvin Cycle. Takes place in the stroma. VI. Pigments in the Chloroplasts
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