1 15 1 Thermoregulation Thermal Energy Source BIO 361T Fall 2014 1 Give a mathematical explanation for why the ratio of surface area to volume tends to decrease as animals get larger Using a sphere as an example surface area 4 r2 and volume 4 3 r3 As r increases both will increase but volume will increase a factor faster thus the ratio of surface area to volume will decrease 2 If heat transfer increases with surface area explain why larger animals have a relatively lower rate of heat transfer between their bodies and their environments Because the ratio of area for heat transfer surface area is relatively low compared to the volume generating heat volume They will lose more absolute heat but a lower percentage of their total body heat thus affecting Tb more slowly 3 Evaluate the following statement All endothermic animals are also ectothermic but not all ectothermic animals are endothermic Is this right or wrong Explain your answer One could argue that it is right if you can categorize animals as one or the other Animals that employ endothermic mechanisms also employ ectothermic mechanisms but not all animals are able to regulate internal metabolism for the sake of heat production 4 Why are the lay terms warm blooded and cold blooded inaccurate Variety of reasons temperature of blood may depend on environment in the case of poikilotherms that are primarily ectothermic or a temporal heterotherm that is primarily ectothermic A homeotherm may have cold blood if its set point is low These terms are intended to convey using primarily endothermy vs ectothermy but they do not take into account differences in environmental temperature and species exceptions 5 Use a table to compare and contrast the terms homeothermic and endothermic Homeothermic Stable Tb regardless of Ta Does not define heat source although most include endothermic mechanisms Includes most mammals and birds Also includes invertebrates and fish that live in stable climates 6 Endothermic Does not define Tb although most are also stable Generates heat by controlling metabolism Includes most mammals and birds Also includes some large flying insects and large reptiles Use a table to compare and contrast the terms poikilothermic and ectothermic Poikilothermic Fluctuating Tb usually due to Ta Does not define heat source although most are not primarily endothermic Includes most invertebrates fish reptiles and amphibians Also includes some large flying insects and large reptiles Ectothermic Does not define Tb although animals that are primarily ectothermic are often poikilothermic Controls Tb by mechanisms other than controlling metabolism behavior anatomy physiological responses Includes most invertebrates fish reptiles and amphibians Also includes invertebrates and fish that live in stable climates 2 7 What is an example of a poikilothermic endotherm Bumblebee other large flying insects large reptiles could consider hibernating mammals as poikilothermic endotherms but are more accurately temporal heterotherms 8 What is an example of a homeothermic ectotherm Arctic fish 9 For each of the following animals and thermal situations assess which direction heat will be transferred the method of heat transfer and two strategies that animal has for coping with Ta a A bumblebee in a nest as Ta is falling during the night From body to environment via radiation and conduction Endo Futile cycling of ATP synthesis and hydrolysis simultaneous contraction of antagonistic flight muscles fluttering of flight muscles without flying Ecto burrow deeper into nest where Ta fluctuates less b A notothenoid fish in Arctic waters From body to environment via radiation conduction and convection even if Tb is low metabolic reactions still generate heat which will be lost to the environment Poikilo antifreeze proteins that control ice crystal formation increase osmolarity to delay and then control ice crystal formation homeoviscous adaptations cold adapated enzymes Endo swim vigorously to increase muscle heat production Ecto move to warmer waters c A red eared slider turtle on a rock in the middle of an Austin summer day From environment to body via radiation and conduction Poikilo homeoviscous adaptations heat shock response Ecto go into water which has lower thermal inertia and will heat up slower stay still to lower metabolic rate and thus metabolic heat production d A Siberian hamster hibernating in the tundra From body to environment via radiation and conduction Poikilo temporal heterotherm lower Tb set point to reallocate thermoregulatory energy Endo non shivering thermogenesis Ecto burrow where Ta fluctuates less stay still to allow for lower metabolic rate and thus use of energy stores 10 All animals endothermic and ectothermic have pathways in which some of the potential energy stored in chemical bonds is released as heat Give a molecular mechanism for how this occurs in each of the following processes a Energy metabolism Glucose is fed into glycolysis the Krebs cycle and oxidative phosphorylation where one carbon at a time is broken off by a series of controlled enzymatic reactions Some of this energy is used to reduce NAD and FAD into NADH and FADH2 respectively while some is converted into heat 3 b Digestion Macromolecules like proteins carbohydrates and fats are hydrolyzed by proteases amylases and lipases respectively into smaller subunits by enzymes in the saliva and intestines and acid in the stomach Some of the potential energy in these chemical bonds is converted into heat c Muscle activity Muscle cells hydrolyze ATP when the actin myosin cross bridges break which releases a small amount of heat Most heat is released when glucose is hydrolyzed in cellular respiration see energy metabolism by the many mitochondria that synthesize ATP to drive muscle contraction d If all of these pathways release some heat why aren t all animals considered endothermic Ectothermic animals cannot control these pathways for the purpose of producing heat nor do they have metabolic pathways that serve no purpose other than heat production see next question 11 In addition to these common pathways endothermic animals have pathways dedicated to producing heat to keep Tb above Ta All of these pathways use potential energy stored in chemical bonds specifically to generate heat Explain how each of the following endothermic thermogenesis mechanisms accomplishes this a Simultaneous contraction of antagonistic flight muscles See muscle activity b Simultaneous
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