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Biology
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33-2 Controlling Body Temperature
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33-2 Controlling Body Temperature
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Body Temperature and Homeostasis
How is the control of body temperature important to vertebrate life?
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Body Temperature and Homeostasis
Body Temperature and Homeostasis
The control of body temperature is important for maintaining homeostasis in vertebrates, particularly in habitats where temperature varies widely with time of day and with season.
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Body Temperature and Homeostasis
Vertebrates have many ways to control body temperature.
All of these incorporate three important features:
• a source of heat for the body
• a way to conserve that heat
• a method of eliminating excess heat when necessary.
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33-2 Controlling Body Temperature
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Body Temperature and Homeostasis
What is the difference between ectotherms and endotherms?
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Body Temperature and Homeostasis
Ectotherms
An ectotherm is an animal whose body temperature is mainly determined by the temperature of the environment.
Most reptiles, fishes, and amphibians are ectotherms.
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Body Temperature and Homeostasis
Ectotherms have relatively low rates of metabolism when they are resting, and their bodies do not generate much heat.
When active, an ectotherm’s muscles generate heat, but that heat is lost to the environment fairly easily.
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Body Temperature and Homeostasis
Endotherms
An endotherm is an animal whose body temperature is controlled from within.
Endotherms have relatively high metabolic rates that generate a significant amount of heat, even when they are resting.
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Body Temperature and Homeostasis
Birds and mammals are endotherms.
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Comparing Ectotherms and Endotherms
Comparing Ectotherms and Endotherms
Neither endothermy nor ectothermy is superior. Each strategy has advantages in different environments.
Endotherms do well in cool weather because they generate and conserve body heat. However, their high metabolic rate requires a lot of fuel.
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Comparing Ecotherms and Endotherms
Ectothermic animals need much less food than similarly sized endotherms.
In environments where temperatures stay warm and constant, ectothermy is a more energy-efficient strategy.
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Evolution of Temperature Control
Evolution of Temperature Control
The first land vertebrates were ectotherms.
Modern reptiles are ectotherms, but some dinosaurs may have been endotherms.
Scientists are not sure when endothermy evolved. Endothermy may have developed twice: once in the reptile line leading to birds, and once in the line leading to mammals.
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33-2
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33-2
The control of body temperature is important for
a. maintaining homeostasis.
b. marking a territory.
c. eliminating wastes.
d. delivering oxygen to cells.
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33-2
Of the following animals, which can maintain a constant internal temperature?
a. shark
b. elephant
c. desert lizard
d. frog
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Lizards often bask in the sun because they are
a. chordates.
b. ectotherms.
c. endotherms.
d. slow moving.
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33-2
Animals that do not rely on their surroundings to gain or lose body heat are
a. fish.
b. endotherms.
c. ectotherms.
d. amphibians.
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33-2
One disadvantage endotherms have compared to ectotherms is that
a. endotherms cannot stay warm in cold weather.
b. far more food is required to maintain constant temperature.
c. endotherms are more limited in the habitats they can occupy.
d. endotherms cannot live in the ocean where the water is too cold.
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