Chapter 10 Summary: Thermal Relations

What determines an animal's body temperature?

The balance between heat gains and heat losses. Body temperature remains constant only when total heat gain equals total heat loss.

What is conduction?

Heat transfer through a stationary material substance by direct contact between molecules

What is convection?

Heat transfer caused by movement of a fluid or gas, such as water or air.

How does convection differ from conduction?

oth involve movement of heat through matter, but convection occurs when the substance is moving. Convection is much faster than conduction.

Why is evaporation an effective cooling mechanism?

Evaporation absorbs a large amount of heat because water changing from liquid to gas requires energy.

How does evaporation cool an animal?

Heat is absorbed from the body surface and carried away by water vapor.

What is thermal radiation?

Heat transfer through radiant energy emitted by all objects.

Why can thermal radiation transfer heat at a distance?

Radiant energy travels between objects at the speed of light and does not require direct contact.

What wavelengths are most important for thermal-radiation heat transfer in animals?

Infrared wavelengths.

How does heat move during thermal radiation?

Net heat movement is from the object with the higher surface temperature to the object with the lower surface temperature.

Does visible color strongly affect infrared heat transfer?

No. Most objects behave nearly like black bodies at infrared wavelengths.

Why is visible color still important in thermoregulation?

It influences how well an object absorbs visible and near-visible solar radiation.

What is a poikilotherm (ectotherm)?

An animal whose body temperature is determined primarily by environmental thermal conditions.

Do ectotherms thermoregulate?

Yes. They often thermoregulate behaviorally.

How do ectotherms regulate body temperature?

By moving between environments that bring body temperature closer to their preferred set point.

How does resting metabolic rate relate to body temperature in ectotherms?

Resting metabolic rate is usually an exponential function of body temperature.

What is Q10?

A measure of how much metabolic rate changes with a 10°C increase in temperature.

What is the typical Q10 value for ectotherms?

Between 2 and 3.

Why are metabolism-temperature curves often plotted on semilogarithmic graphs?

Because exponential relationships appear as straight lines on semilogarithmic coordinates.

What is partial compensation?

An acclimation response that returns metabolic rate toward its original level following a temperature change.

Why is partial compensation beneficial?

It reduces the impact of environmental temperature changes on metabolism.

What is the most common mechanism of partial compensation?

Changes in the concentration of key rate-limiting enzymes within cells.

How do species adapt evolutionarily to different body temperatures?

Through molecular specialization of proteins and membrane phospholipids.

What is molecular specialization?

The evolution of structurally distinct proteins and membrane lipids that function optimally in different thermal environments.

Why do cold-adapted and warm-adapted species often have similar enzyme performance?

Molecular specialization preserves enzyme-substrate affinity and membrane fluidity despite different temperatures.

How do lizard species demonstrate thermal adaptation?

Each species runs fastest at its preferred body temperature.

How do polar fish demonstrate thermal adaptation?

They function at higher rates in cold environments than temperate fish could.

What is a freezing-tolerant ectotherm?

An ectotherm that can survive actual freezing of extracellular body fluids.

Where must freezing be restricted in freezing-tolerant animals?

To extracellular fluids.

What is a freezing-intolerant ectotherm?

An animal that survives by avoiding freezing rather than tolerating it.

What are the three strategies freezing-intolerant ectotherms use to avoid freezing?

Behavioral avoidance, antifreeze production, and supercooling.

What do biological antifreezes do?

They lower the freezing point of body fluids.

What is supercooling?

Remaining unfrozen at temperatures below the normal freezing point.

What is homeothermy?

Thermoregulation through physiological mechanisms that maintain a relatively constant body temperature.

Is homeothermy energetically expensive?

Yes.

What is the thermoneutral zone?

The range of ambient temperatures where endotherms regulate body temperature primarily by changing insulation rather than heat production.

What is the driving force for dry heat loss?

The difference between body temperature (TB) and ambient temperature (TA).

How do mammals and birds regulate heat loss within the thermoneutral zone?

By adjusting insulation.

What mechanisms can alter insulation?

Posture changes, skin blood flow, changes in trapped air layers, and regional heterothermy.

What is thermogenesis?

Metabolic heat production.

What is the primary method of thermoregulation below thermoneutrality?

Increasing metabolic heat production.

What are the two major mechanisms of heat production below thermoneutrality?

Shivering and nonshivering thermogenesis (NST).

What is shivering thermogenesis?

Heat production through involuntary muscle contractions.

Which animals use shivering thermogenesis?

Both mammals and birds.

What is nonshivering thermogenesis (NST)?

Heat production without muscle contractions.

In which animals is NST most common?

Placental mammals.

What tissue is the primary site of NST?

Brown adipose tissue (brown fat).

What protein makes brown fat capable of producing heat?

Uncoupling Protein 1 (UCP1).

How does UCP1 generate heat?

By uncoupling oxidative phosphorylation, causing energy to be released as heat rather than ATP.

What is regional heterothermy?

Maintaining different body regions at different temperatures.

What mechanism usually produces regional heterothermy?

Countercurrent heat exchange.

What is countercurrent heat exchange?

Heat transfer between closely adjacent arteries and veins flowing in opposite directions.

How does countercurrent heat exchange conserve heat?

Heat from warm arterial blood is transferred to cooler venous blood before reaching appendages.

What are the first lines of defense against overheating in many desert-adapted animals?

Hyperthermia and cycling of body temperature.

What is hyperthermia?

Allowing body temperature to rise above normal levels to reduce water loss from evaporative cooling.

What is sweating?

Evaporative cooling through the secretion and evaporation of sweat.

Which animals sweat?

Only certain mammals.

What is panting?

Rapid breathing that increases evaporative heat loss from respiratory surfaces.

Which animals pant?

Mammals and birds.

What is gular fluttering?

Rapid vibration of throat tissues to enhance evaporative cooling.

Which animals use gular fluttering?

Birds.

Why can metabolic rate increase above thermoneutrality?

Because active evaporative cooling and hyperthermia require energy.

What are the three forms of seasonal acclimatization?

Acclimatization of peak metabolic rate, acclimatization of metabolic endurance, and insulatory acclimatization.

What is controlled hypothermia?

A deliberate reduction in body temperature to conserve energy and water.

Why do animals use controlled hypothermia?

To avoid the high energy and water costs of homeothermy.

What happens to body temperature during hibernation, estivation, and daily torpor?

Body temperature is allowed to fall close to ambient temperature.

What is torpor?

A temporary reduction in body temperature and metabolism.

What is hibernation?

A prolonged period of controlled hypothermia, usually during winter.

What is estivation?

A prolonged period of controlled hypothermia or dormancy associated with hot or dry conditions.

Which fish exhibit regional endothermy?

Tunas, lamnid sharks, and billfish.

Which fish exhibits whole-body endothermy?

The opah.

Which tissues are endothermic in tunas and lamnid sharks?

Red swimming muscles and sometimes the stomach, viscera, brain, and retinas.

Which tissues are endothermic in billfish?

The brain and retinas.

What is required for a fish tissue to be endothermic?

A countercurrent vascular system that prevents heat from escaping to the gills.

What is the heat source for endothermy in most warm-bodied fish?

Ordinary metabolic heat production.

What makes billfish unique among warm-bodied fish?

They possess specialized heater organs derived from eye muscles.

Why do many insects warm their flight muscles?

Warm flight muscles generate greater power output.

Why is body temperature important for flight in insects?

Many insects require a minimum flight-muscle temperature before flight can occur.

How do insects warm their thorax before flight?

Through shivering of the flight muscles.

How do bees thermoregulate while in the hive?

By adjusting the amount of shivering performed.

What is preflight warm-up?

Shivering of flight muscles to raise thoracic temperature before flight.

How do flying insects regulate thoracic temperature?

By changing heat transport out of the thorax through circulation.

How do social bees and wasps regulate hive temperature?

Through coordinated group thermoregulation.