AP Biology Ch. 40


how organisms obtain, process, and use energy resources

Convergent Evolution

causes similar forms of speedy fishes, birds, and marine mammals; occurs because natural selection shapes similar adaptations when diverse organisms face the same environmental challenge

Metabolic Rate

the sum of all the energy-requiring biochemical reactions occurring over a given time interval


Birds and mammals; maintaining their body temperature within a narrow range by heat generated by metabolism; high-energy strategy that permits intense, long-duration activity of a wide range of environmental temperatures


fishes, amphibians, reptiles, and invertebrates; gain their heat mostly from external sources; requires much less energy than is needed by endotherms, because of the energy cost of heating (or cooling) an endothermic body; generally incapable of intense a

basal metabolic rate

metabolic rate of a nongrowing endotherm at rest, with an empty stomach and experiencing no stress

standard metabolic rate

minimal metabolic rate of an ectotherm must be determined at a specific temperature; metabolic rate of a resting, fasting, nonstressed ectotherm

Claude Bernard

physiologist; made the distinction between external environments surrounding an animal and the internal environment in which the cells of the animal actually live; many animals tend to maintain relatively constant conditions in their internal environment,

interstitial fluid

internal environment of vertebrates; exchanges nutrients and wastes with blood contained in microscopic vessels called capillaries


internal balance; depends on feedback circuits


animal uses internal control mechanisms to moderate internal change while external conditions fluctuate


animal allows its internal conditions to vary as external conditions fluctuate

homeostatic control system

three functional components: a receptor, a control center, and an effector


detects a change in some variable in the animal's internal environment

control center

processes the information it receives from the receptor


directs an appropriate response

Negative-feedback mechanisms

prevent small changes from becoming too large; most homeostatic mechanisms in animals operate on this principle

positive feedback

change in some variable that triggers mechanisms that amplify rather than reverse the change;


process by which animals maintain an internal temperature within an optimal range, enabling cells to function effectively as external temperature fluctuates

Ectotherms gain most of their heat from the environment

ectotherms have such a low metabolic rate that the amount of heat it generates is too small to have much effect on body temperature; thermoregulate by behavioral means, such as basking in the sun or seeking out shade

Endotherms can use metabolic heat to regulate their body temperature

In a cold environment, an endotherm's high metabolic rate generates enough heat to keep its body substantially higher than its surroundings; enables endotherms to perform vigorous activity for much longer than is possible for most ectotherms; endothermic

Animals regulate the exchange of heat with their environment by four physical processes

conduction, convection, radiation, and evaporation


mammals and birds hair, feathers, or fat layers; reduces the flow of heat between an animal and its environment and lowers the energy cost of keeping warm

endotherms and ectotherms can alter the amount of blood flow between the body core and the skin

vasodilation & vasoconstriction


Elevated blood flow in the skin; increase in the diameter of superficial blood vessels near the body surface- increasing the transfer of body heat to a cool environment


reduces blood flow and heat transfer by decreasing the diameter of superficial vessels

countercurrent heat exchanger

circulatory adaptation is an arrangement of blood vessels which reduces heat loss; can be passed or go through; relative amount of blood that flows through the two paths varies, adjusting the rate of heat loss


is the only way to keep body temperature from rising if environmental temperature is above body temperature; Water absorbs considerable heat when it evaporates; it is 50 to 100 times more effective than air in transferring heat

endotherms and ectotherms use behavioral responses to control body temperature

hibernate or migrate to a more suitable climate; amphibians