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Honors Biology Notes: Unit 4 BioEnergy Metabolism and Energy • chemistry of life is organized into metabolic pathways – metabolism: collection of reactions that occur in organisms; facilitated by enzymes – two general categories of reactions: • catabolic: breakdown of macromolecules into monomers, releasing energy from the broken bonds • anabolic: building macromolecules from monomers, using energy to form bonds • ATP (adenosine triphosphate) powers cellular work – ATP loses one phosphate, producing ADP (adenosine diphosphate), a phosphate group, and free energy – Any time bonds are broken; energy is released – Any time chemical bonds are made, energy is used A Biochemical Pathway • Chemical elements essential to life are recycled in the cells by photosynthesis and cellular respiration (elements are recycled) • energy is not recycled Photosynthesis • General – plants and other autotrophs are producers • autotroph: organisms that can make their own food rather than ingesting or absorbing it • photoautotroph: organisms that use the energy of the sun to produce carbohydrates from CO2 and H2O • producer: organisms that are the ultimate source of organic compounds for heterotrophic organisms – heterotrophs must ingest or absorb energy from other organisms The Action Spectrum for Photosynthesis • Look for the following information in the webpage: • In 1883, Thomas Engelmann devised an experiment to learn __________________ in carrying out photosynthesis. • What organism was used? • The wavelengths that work best for photosynthesis are ___ Chloroplasts • chloroplasts are the site of photosynthesis in plants and other photoautotrophs – all green parts of a plant have chloroplasts – leaves are the major sites of photosynthesis in most plants • about ½ million chloroplasts per square millimeter of leaf surface – green color comes from the pigment chlorophyll • chlorophyll absorbs light energy Source of Reactants • chloroplasts are found in tissue in the interior of leaves called mesophyll • carbon dioxide enters leaf (and oxygen exits) by pores in the leaf called stomata • water is absorbed by the roots and moved through the plant by veins Photosynthesis • Overall (simplified) chemical equation • 6CO2 + 6H2O + light energy C6H12O6 + 6O2 • Carbon dioxide plus water, in the presence of sunlight, produces sugar (glucose, carbohydrate) and oxygen Nova Photosynthesis Overview • MEMORIZE the following diagram! HELP? • For these rather vague diagrams, focus on: • What goes in • What comes out • Where the process occurs 2 Major Stages of Photosynthesis • light reactions or photochemical reaction • the Calvin Cycle or the thermochemical reaction or dark reactions Light Reactions General • require the energy of the sun – occurs in the thylakoid membrane of the chloroplasts – rely on two clusters of pigments with different types of chlorophyll and other pigments • photosystems I and II (absorb different wavelengths of light) Light Reactions of Photosynthesis Calvin Cycle General • does not directly require light energy – occur for only a brief time after sunset, because the reactions quickly use up the ATP and NADH produced in the light reactions • occurs in the stroma of the chloroplast • 3 “turns” of the Calvin Cycle are required to produce one molecule of glucose Calvin Cycle Animations Factors Affecting Photosynthesis • Light intensity – ordinary daily sunlight yields maximum rate of photosynthesis • CO2 – more CO2 equals a higher rate only if enough light • 6x CO2 can yield 5x rate of photosynthesis – atmospheric CO2 has increased 10% in last 200 years; not enough to cause great increase in photosynthesis – greenhouse effect- greater impact on length of growing season than rate of photosynthesis • H2O- if plant goes dry stomata close, no CO2 taken in. • Temperature – primarily via enzyme activity- as temperature increases, rate goes up (until proteins denature) – low temperatures (> freezing) influence both enzyme activity and “fluidity” of chloroplast membrane – most plants have enzyme systems and membrane structure that are well matched to the temperature range they experience Cellular Respiration • Breakdown of glucose (or other organic fuel) to produce energy • Occurs in ALL living organisms (even those that photosynthesize) – overall (simplified reaction) C6H12O6+ 6O2 6H2O + 6CO2 + ATP MEMORIZE the following diagram! 3 phases • Glycolysis • Kreb’s Cycle • Electron Transport Chain and oxidative phosphorylation Glycolysis • Glycolysis: glucose, C6H12O6 is broken down – occurs in the cytoplasm of the cell – products: 2 molecules of pyruvate, C3H3O3 and 2 molecules of ATP and 2 molecules of NADH Krebs Cycle • Krebs Cycle: pyruvate is converted to CO2 – occurs in the mitochondrial matrix – transfers electrons from NAD+ to NADH – produces: 1ATP and CO2 – aerobic (oxygen requiring) process Electron Transport chain • Electron Transport chain and oxidative phosphorylation – occurs on the cristae of the mitochondria – produces up to 35 ATP – aerobic process • a maximum of 38 molecules ATP are produced per molecule of glucose during cellular respiration Fermentation • occurs instead of Krebs Cycle and Electron Transport chain when oxygen is not present – anaerobic : (“an” means not or without) absence of oxygen • Two types – Alcoholic fermentation – Lactic acid fermentation • MEMORIZE the following diagram! Alcoholic Fermentation • pyruvate from glycolysis is converted to ethanol and 2 ATP – occurs in yeast (a fungus) and some bacteria – used to produce breads and alcoholic beverages Lactic Acid Fermentation • pyruvate from glycolysis is converted into lactic acid and 2 ATP – occurs in some fungi, bacteria, and animal muscle cells that have depleted stores of oxygen – used to produce yogurt and cheeses – in humans, cells must switch from cellular respiration to lactic acid fermentation when no oxygen is present • causes muscle fatigue and pain • lactic acid is gradually carried to liver by blood, and broken down into pyruvate in the liver