MetLab.09s - Biology 05B Spring Quarter 2009 Lab 5 page 1...

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Biology 05B –– Spring Quarter 2009 Lab 5 – page 1 ENERGY METABOLISM Contents: Topic Page I. Introduction 1 II. Metabolic Rate And Temperature in a Mouse 3 III. Metabolic Rate And Temperature in an Insect 4 IV. Calculations 4 I. INTRODUCTION In photosynthesis, plants extract electrons from H 2 O, excite these electrons to a higher energy level using light energy and then entrap these high-energy electrons in the chemical bonds of various sugars which can then be converted into several other organic molecules. The presence of these high- energy electrons within the chemical bonds of these molecules thus represents stored chemical potential energy. Animals, lacking the ability to carry out photosynthetic reactions, must consume these organic molecules derived directly or indirectly from plants so that they can extract and utilize this energy to carry out life processes. Heterotrophic organisms use one of two methods to extract this energy. The first occurs in the absence of oxygen (i.e., is anaerobic) and is termed fermentation. Fermentation produces a limited amount of ATP and by products (either lactic acid or ethanol) that are not completely oxidized. The other way that organisms extract energy from organic molecules requires oxygen and is known as cellular respiration. Following is a summary equation for the multi- step oxidation of glucose by cellular respiration: C 6 H 12 O 6 (686 kcal/mole) + 6O 2 + 38ADP + 38 Pi ± 6CO 2 + 6H 2 O + 38ATP (7.3 kcal for each Pi added to ADP x 38 or 277 kcal total) + heat (409 kcal) This process produces about 19 times as much ATP as fermentation. Here, the energy of the excited electrons captured during photosynthesis has been completely dissipated. In other words, no usable chemical potential energy remains in the products (CO 2 and H 2 O). Evidence for this is that these electrons have been passed to oxygen to form water and therefore have been returned to the energy status of their origin in photosynthesis. Obviously, oxygen consumption is an integral part of energy metabolism because it occurs only when all of the usable energy in food molecules has been released. Further, by monitoring the rate of oxygen consumption, an estimate of the rate of energy utilization can be determined. In today's lab, we will make such determinations by measuring the rates of oxygen consumption by a mouse and an insect. In addition to confronting the basic issue of estimating the rate of energy utilization, today's lab will also address the relationship between energy metabolism and the regulation of body temperature. Not all of the energy liberated from glucose (or other food molecules) is captured in ATP. In fact, less than half of this energy is captured in ATP with the rest being lost as heat (see the above summary equation). In organisms with comparatively high metabolic rates, this heat production contributes to the regulation of body temperature. These organisms are classified as endotherms. Among this broader class of animals are some groups, including mammals, which are
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MetLab.09s - Biology 05B Spring Quarter 2009 Lab 5 page 1...

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