Ch3 Adaptations to the Physical Environment8.pdf

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University of Toronto St. George
University College Courses
Spencer Barrett

Body Size and Thermal Inertia  exchanges of NRG and materials b/w an orgnm and envmt occurs across body surfaces  larger orgnm have less SA compared w/ their tissues than smaller orgnms  exchanges are more diff.  when orgnm differs only in size:  S increases as square of L, V increases as cube of length  surface-to-volume ratio decreases in proportion to length  larger orgnms lose heat less rapidly; this ththermal inertiatendency to remain at same temp.) is advantageous in cold envmts  but can’t rid excess heat rapidly (risk of overheating)  easier to maintain a constant internal envmt Homeothermy Increases Metabolic Rate and Efficiency  homeostasis is an organism’s ability to maintain constant internal conditions in the face of a varying envmt  all homeostatic systems exhibit negnegative feedbackhen the system deviates from its desired state, or set point, internal response mechanisms act to restore that state)  homeothermy is the maintenance of a constant body temp. (homeothermic) in the face of a fluctuating envmtal temp. (displayed by most mammals and birds)  poikilothermic organisms conform to the external temp. (ex. frogs, grasshoppers)  can’t function at temp. extremes; are active only a fraction of the range of mammals Ectotherms  ectotherms use heat outside their body to elevate their body temp. (ex. reptiles, insects,
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