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Chapter 8 Cellular Energy 8.1 How Organisms Obtain Energy 1 Chapter 8 Cellular Energy 8.1 How Organisms Obtain Energy Transformation of Energy Energy is the ability to do work. Thermodynamics is the study of the flow and transformation of energy in the universe. 2 Chapter 8 Cellular Energy 8.1 How Organisms Obtain Energy Laws of Thermodynamics First law—energy can be converted from one form to another, but it cannot be created nor destroyed. Second law—energy cannot be converted without the loss of usable energy. 3 Chapter 8 Cellular Energy 8.1 How Organisms Obtain Energy Autotrophs and Heterotrophs Autotrophs are organisms that make their own food. Heterotrophs are organisms that need to ingest food to obtain energy. 4 Chapter 8 Cellular Energy 8.1 How Organisms Obtain Energy Metabolism All of the chemical reactions in a cell Photosynthesis—light energy from the Sun is converted to chemical energy for use by the cell Cellular respiration—organic molecules are broken down to release energy for use by the cell 5 Cells need energy for: Making new molecules Maintaining homeostasis Active transport Endocytosis Exocytosis Going against the concentration gradient Movement Cilia and flagella Muscle contraction including cardiac muscle Cell division 6 ATP stores energy in chemical bonds A= adenosine T= tri P= phosphate 7 ATP and ADP recycle 8 9 ATP is like currency Cells can only use the ATP for energy even though they store energy as fats, carbohydrates or proteins Carbohydrates, fats and proteins must be changed to ATP before they can be used by the cell (process of cellular respiration) You can only use coins in the soda machine even though you may have a $5 bill in your pocket 10 How cells tap into the energy stored in ATP Many enzymes have a site where ATP fits in like a battery to provide the energy for that enzyme to work 11 Chapter 8 Cellular Energy 8.2 Photosynthesis 12 Photosynthesis: The Big Picture Plants change solar energy (sunlight) into ATP then into glucose (chemical energy) Two step process 13 Overall reaction of photosynthesis 14 Role of Chloroplasts Chlorophyll is the pigment found in the chloroplasts of plants and algae Chloroplast is the location for photosynthesis 15 Chloroplast Structure Thylakoid membrane is the site for photosynthesis 16 Chlorophyll Plants have two types of chlorophyll Chlorophyll a is yellow green Chlorophyll b is blue green We see plants as green because green is reflected not absorbed by the chlorophyll Plants also contain red, orange and yellow pigments When leaves “turn colors” in the fall it is because chlorophyll productions ceases and the other colors are exposed 17 18 19 Photosynthesis: A Two Step Process Step One: Light Dependent Reactions Step Two: Light Independent Reactions (previously called the Dark Reactions or the Calvin Cycle) 20 Light Dependent Reactions of Photosynthesis Light strikes a chlorophyll molecule and excites an electron Electron gets passed to a series of proteins in an electron transport chain and an ATP gets made Electron goes to a second electron transport chain and another energy molecule (NADPH) gets made 21 Light Dependent Reactions of Photosynthesis Photolysis must happen to “fill in the hole” left by the electron that was excited Photolysis is the splitting of water; the hydrogen goes to fill the electron’s place and the oxygen is what we breathe (O2) 22 Light Dependent Reactions of Photosynthesis Start with sunlight and get ATP and NADPH Energy molecules used for Step Two Start with water and get oxygen 23 Light Independent Reactions of Photosynthesis Light dependent Light dependent Light independent 24 Light Independent Reactions of Photosynthesis ATP and NADPH from the light dependent reaction provide the energy to convert CO2 to C6H12O6 (glucose) Uses many enzymes in a cycle to produce glucose Cycles are important in organisms because they allow for constant production 25 Light Independent Reactions of Photosynthesis 26 Light Independent Reactions of Photosynthesis Each “turn” of the cycle produces ½ of a glucose ATP and NADPH are used to produce this glucose No sunlight is needed, reactions happen independent of light 27 Alternative Pathways C4 Plants: fix CO2 into four-carbon compounds keep stomata closed during hot days (less transpiration water loss) Sugar cane and corn 28 Alternative Pathways CAM plants: conserve water by allowing CO2 to enter only at night (stomata closed during day to conserve water) Examples: pineapple, cacti, orchids and other desert or salt march plants 29 Chapter 8 Cellular Energy 8.3 Cellular Respiration 30 Cellular Respiration Process of breaking down food to produce ATP ALL living things do cellular respiration, even: Plants Bacteria Eukaryotes in the mitochondria Prokaryotes in the cytoplasm 31 Cellular Respiration Overall reaction C6H12O6 + O2 CO2 + H2O + energy 32 Cellular Respiration Three Stage Process 1. Glycolysis: anaerobic 2. Citric Acid Cycle: aerobic 3. Electron Transport Chain: aerobic 33 Cellular Respiration Overview 34 Glycolysis Happens in the cytoplasm Need to use two ATP before can get ATP out of the process One glucose is split and converted into two pyruvate yields four ATP (two net ATP) 35 Citric Acid Cycle or Krebs Cycle Happens in the mitochondrial matrix CO2 produced Per turn of the cycle yields: 1 ATP 3 NAPH 1FADH2 36 Electron Transport Chain 37 Electron Transport Chain Located within the inner mitochondrial membrane Converts NADH and FADH2 into ATP Energized electrons are passed along a series of proteins Some energy is converted directly into ATP Other energy causes H+ ions to be forced out of the inner mitochondrial matrix 38 Electron Transport Chain cont. The force of H+ ions back into the mitochondrial matrix through the enzyme ATP synthase provides the energy for ATP synthesis Oxygen is the final electron acceptor Without oxygen the transport chain would shut down like a traffic jam Traffic (electrons) would back up and shut down the Krebs Cycle as well 39 Electron Transport Chain cont. For every NADH get 3 ATP For every FADH2 get 2 ATP Overall get a net of 32 ATP from one molecule of glucose Balanced equation: C6H12O6 + 6O2 6CO2 + 6H2O + 32 ATP 40 Fermentation Occurs when O2 is not present, no aerobic respiration, no Krebs Cycle, no Electron Transport Chain Allows the continuation of glycolysis by the removal of pyruvate Some organisms in anaerobic environments produce energy by fermentation all the time 41 Fermentation: Two Types Alcoholic Yeast Produce CO2, ethyl alcohol and 2 ATP from pyruvate Important in bread and alcoholic beverage industries Lactic Acid Animal muscle cells, some bacteria and some plants Produce lactic acid and 2 ATP from pyruvate Get sore, burning muscles Liver converts lactic acid back to pyruvate when O2 is present 42 Comparing Photosynthesis and Cellular Respiration Both Both Both Both ions use use use use electron transport chains cycles of chemical reactions electron carrier proteins concentration gradient of H+ 43 Comparing Photosynthesis and Cellular Respiration Photosynthesis Food accumulated Solar energy stored in glucose CO2 taken in, O2 given off Occurs only in presence of chlorophyll with sunlight Cellular Respiration Food broken down Glucose energy released O2 taken in, CO2 given off Occurs in all living things all the time 44