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Lecture 4

Lecture 4 - Endothermic Homeotherms

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Western University
Biology 2601A/B
Graeme Taylor

LECTURE 4: ENDOTHERMIC HOMEOTHERMS Endothermic Homeotherms  Climatic fluctuations in temperature are a part of everyday for all living organisms o Daily – for example, night vs. day, fluctuations in tides o Seasonal o Temporal  Animals and plants need to manage climatic fluctuations  Endotherms adjust to this variation in their environment by adjusting their physiology o Such as by increasing or decreasing the body heat produced as part of the metabolic breakdown of food o Resulting in constant internal body temperatures relative to environmental fluctuations  Regulating internal body temperature is necessary for cellular function  Departures from the set core body temperatures can lead to cellular damage or death of the individual  Homeotherm – an animal that thermoregulates by physiological means, rather than simply by behavior o More independence from external thermal conditions o Highly stable core body temperature  Adaptation of endothermic homeothermy has only arisen in birds and mammals o Humans are classified as homeothermic endotherms  Origin of birds was nested within the dinosaurs and there was no close relation between mammals and birds – thus the origin of endothermic homeothermy was independent between the two groups  Endothermy clearly permits mammals and birds to have an active life in harsh environments  Also permits long distant migration in birds and mammals  Being and endothermic homeotherm is expensive – there is a cost o Breaking down food releases heat, thus constant consumption of food is needed to maintain body temperature  Basal metabolic rate – resting metabolic rate, relatively still  Each single point represents a single species  Shows exponential growth  Body mass has an effect on metabolism – smaller animals relatively have a higher metabolism than larger animals  10-12 fold difference between mammals and reptiles – more expensive to be a mammal  Homeotherm – when small mammals hibernate, they allow their body temperature to fall into environmental temperature  Mammals and birds must have a high degree of control minimizing their energetic cost o Heat production – internal furnace o Heat retention – insulation o Regulation – good example of negative feedback control Effect of Temperature on Endothermic Homeotherms  Can be observed by examining an organism’s metabolic rate over an n range in temperature  In the thermoneutral zone (TNZ) – metabolic rate is maintained at stable interval  Once within TNZ, organism will experience modulation of insulation and blood flow o Outside the TNZ, species will exhibit increased energy consumption due to heat generation at colder temperatures and increased energy consumption due to heat loss at higher temperatures  Regulation of body temperature in homeotherms requires a set point for which there are many biological sensorts – skin, spinal cord, hypothalamus, and scrotum (in males) 
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