Lecture+14+-+Metabolism+and+Metabolic+Rate (4)

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Unformatted text preview: Thursday’s Class: METABOLISM & METABOLIC RATE Chapter 2 Pages: 39-­‐44, 71-­‐74 Chapter 2 Pages: 22-­‐27, 57-­‐60 What you should be able to do by the end of today’s lecture •  Explain how metabolic rate is measured directly and indirectly and how metabolic rate can be calculated from indirect measures •  Understand the reason for the differences in metabolic rate between ectotherms and endotherms •  Explain what factors affect metabolic rate •  Describe how metabolic rate varies with body size and the implicaWons for small animals Metabolism “The set of processes by which cells and organisms acquire, rearrange and void commodiWes in ways that sustain life” (Hill, Wyse & Anderson) “The sum of all chemical reacWons in a biologic enWty” (Moyes & Schulte) Metabolic Rate “An [organism’s] rate of energy consumpWon; the rate at which it converts chemical-­‐bond energy to heat and external work” (Hill, Wyse & Anderson) Metabolic Rate Principles in Animal Physiology Metabolic rates are significant because: •  Determinant of how much food an animal needs •  QuanWtaWve measure of the total acWvity of all its physiological mechanisms •  Measurement of the drain the animal places on the energy supplies of an ecosystem/ agricultural system What goes into metabolic rate? Endotherms Figure 3.5 Willmer et al. 2005 Endotherms vs. Ectotherms •  High MR •  Maintain body temp via adjustments of metabolic heat producWon •  Narrow range of body temps •  RelaWvely low MR •  Body temp depends mainly on external sources and behavior Endotherms vs. Ectotherms At the same body temperature, similar sized endotherms & ectotherms differ in oxygen consumpWon on average by at least 4 to 5 fold High demand for food (for energy) in endotherms Ectothermy allows for less energeWcally costly mode of living Eckert & Randall – Animal Physiology How can we measure metabolic rate? C6H12O6 + 6O2 6CO2 + 6H2O + 2820 kJ/mol Direct Calorimetry Accurate to 0.00001°C Antoine Lavoisier, 1873 335 J melts 1 g ice 1 calorie heat required to raise 1g of water 1o C Direct Calorimetry on vertebrates Walsberg & Hoffman (2005) J. Exp. Biol. 208: 1035-­‐1043 Indirect Calorimetry C6H12O6 + 6O2 6CO2 + 6H2O Indirect Calorimetry Factors affecWng metabolic rate •  •  •  •  •  •  Temperature AcWvity DigesWon StarvaWon ReproducWve State Dormancy –  (HibernaWon/ AesWvaWon/ Torpor) •  Time of Day Factors affecWng metabolic rate: Endotherms Temperature Ectotherms? Factors affecWng metabolic rate: InacWve AcWvity 8 7 Raw data 6 SMR Oxygen Consumption (ml/hr) 5 4 3 2 1 0 0 8 6 12 18 24 30 36 42 48 24 30 36 42 48 AcWve 7 6 5 4 3 2 1 0 0 6 12 18 Time (hours) Factors affecWng metabolic rate: Feeding/DigesWng Specific Dynamic AcWon (SDA) •  Increase in metabolic rate caused by food ingesWon •  Also called the heat increment of feeding Factors affecWng metabolic rate: ReproducWon •  Humans: MR increases 30% near term –  growth of fetus –  fetal metabolic requirements –  growth of mammary Wssue •  Golden-­‐mantled ground squirrels –  lactaWon takes up 1/3 of yearly energy! Factors affecWng metabolic rate: Time of Day •  Metabolic rate is typically higher during acWve period Nocturnal: Diurnal: MR MR night What other factor affects MR? Body Size MR Whole animal MR Mass-­‐specific MR Body mass What other factor affects MR? Body Size * Small animals have higher mass-­‐specific MR’s For a given unit of mass, the MR is greater in smaller animals…1 gram of shrew consumes O2 at 100 Wmes the rate of 1 gram of elephant! The effect of body size on weekly food requirements Costs & Benefits of Endothermic Homeothermy LimitaWon with Body Size Principles in Animal Physiology Shrews & small hummingbirds must maintain enormous mass specific metabolic rates to regulate their body temperature near 37-­‐40°C Can only pack so many mitochondria into a cell & can only supply metabolic fuels up to a certain rate Eckert & Randall – Animal Physiology Friday’s Class METABOLISM & METABOLIC RATE CONT’ * If needed Chapter 1: pages 9-­‐11 Chapter 14: pages 628-­‐631 Chapter 2 Box 2.2 Chapter 11: pp 529-­‐530 ...
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