Van't Hoff's Rule states that biochemical reaction rates double for every 10 degree Celsius increase in temperature, up to a point. Animals regulate their body temperature through physiological and behavioral adaptations. Endotherms like birds and mammals generate their own body heat through metabolism, while ectotherms rely on environmental heat sources. Smaller animals have higher mass-specific metabolic rates than larger animals due to greater surface area to volume ratios and heat loss. Increased stamina through endothermy provided evolutionary advantages over ectothermy.

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2. Van’t Hoff’s Rule: for every temperature rise
of 10o C, rate of biochemical reactions double up
to a point.
This is why it is bad to get too hot or too
cold
– Too cold = body functions slow due
to Van’t Hoff’s Rule.
– Too hot = proteins break down and
body functions slow; that’s why
Van’t Hoff’s Rule only works up to a
point.

3. Energy Pie: distribution of
individual’s energy among:
• Growth
• Reproduction
• Activity
• Maintenance: includes body temp
• Storage

4. How plants and animals gain and
lose heat
• Radiation (+/-): to/from nearby objects
– E.g., lizard gains heat from sun, or loses heat to
surroundings in shade
• Conduction (+/-): to/from touching objects
– E.g. lizard gains heat laying on warm rock or loses heat
laying on surface of cool burrow
• Convection (+/-): into wind/moving water
– E.g. body is warmed by hot wind or cooled by cold wind
• Metabolism (+): from body’s generation of heat
• Evaporation (-): from moist body surfaces

5. Types of animals based on way
body temp is maintained
• Poikilotherms – have a variable body
temperature
• Homeotherms – have a stable body temp
• Endotherms principal source of body heat
is body’s metabolism (erroneously called
warm-blooded)
– Birds & Mammals
• Ectotherms principal source of body heat
is from environment (erroneously called
cold-blooded)
– Everything else (with a few exceptions)

6. Surface Area to Volume Ratio
• Small, thin things have a greater
surface area to volume ratio thus gain/
lose heat faster than large, thick
things.

7. SA:V Ratio
• However… larger endotherms also
generate more heat per unit volume
as well – and have a harder time losing
it.
– Elephant & Kangaroo

9. Types of Thermoregulation
• Physiological thermoregulation:
altering body’s metabolic generation
of heat to regulate body temp.
• Behavioral thermoregulation:
altering posture, orientation, and/or
microclimate to regulate body temp.

10. Impact of Van’t Hoff’s Rule
• Since rates of reaction double for every
10oC – this applies to cell respiration too.
• Oxygen consumption doubles, and so
does ATP production.
Internal Temp = POWER

11. What happens to a lizard in a fur
coat?
• Gets colder & dies of hypothermia
• WHY?
– Can’t absorb the heat & doesn’t
generate enough of its own heat.

12. HOT ENVIRONMENT
Lizard Mammal
•Absorbs heat from enviro. •Generates body heat
• Metabolism at max. •Must cool down (sweat, slow
metabolism)
COLD ENVIRONMENT
Lizard Mammal
•Metabolism slows (less food needed) •Generates extra body heat
•Sleep, curl-up, burrow •HOW? More ATP… means more
FOOD req’d
•Possible Hibernation or TORPOR
Hot Blood = a short life spent
eating long & dangerously
•More exposed to predators, more food
req’d/indiv, less food for reprod,
lifespan drops

13. Torpor: lowering of body temp
below activity temperature.
• Daily Estivation: <24 hr torpor in response to
heat and/or dryness
• Seasonal Estivation: seasonal torpor in
response to heat and/or dryness
• Daily Torpor in Response to Cold: daily torpor
in response to cold and insufficient energy
uptake. Note: name and definition are same.
• Hibernation: seasonal torpor in response to
cold and insufficient energy uptake

14. Torpor:
Adaptive Values
• Reduces Energy Needs
– 2 ways
• Reduces Water Needs
– 3 ways

15. Torpor:
Adaptive Values
• Reduces Energy Needs
– Lowers temp gradient which is the difference
in temp between body and environment: this
slows rate of heat loss
– Less tissue demand because lower body temp
Quick
34 o
heat 34o Slow
heat
loss loss
99o 35o
High temp gradient Low temp gradient

16. Torpor:
Adaptive Values
Reduces Water Needs
– Decreases cutaneous (outer surface such as skin)
water loss
• Less evaporation
– Decreases excretory water loss
• Less waste products produced
– Decreases respiratory water loss
• Less breathing (colder body temp slows metabolism)
and less water lost per breath (colder exhaled
air contains less water)

17. Advantages and Disadvantages of
Endothermy versus Ectothermy
• Endothermy • Ectothermy
– Advantage – Advantage
• Always ready • Uses 10x less
to go energy
– Disadvantage – Disadvantage
• Uses 10x • Prisoner of
more energy environment (cold
and slow when no
source of heat)

18. What are the gains of
endothermy?
• Nocturnal Ability • Larger body size
• Niche expansion – Bigger brain
– Climate zones
Not enough to offset the cost of a
population size reduction, higher &
more consistent food needs, lower
life span, and number of offspring...
(FITNESS)

19. BUILD A MUSCLE RPG

20. What are the strengths of your muscle?
What problems might it have?
• High # fibres • High # Mito & Caps
– Powerful muscle – Weaker muscle
– Less stamina – More stamina

21. Trade-Offs
High Power/Low Stamina
vs
Low Power/High Stamina
Reptiles are built for speed
bursts – SPRINTERS
Mammals are built for
STAMINA

23. STAMINA IS THE MAIN
ADVANTAGE ENDOTHERMS HAVE
High stamina  Ability to outrun
= predators
Increased activity  More energy to eat
longer
=
 Can be a TRUE
Increased Aerobic herbivore [N-issues]
Capacity
 More energy to
= reproduce/care for
Increased Metabolic offspring
Rate

24. Increasing stamina
• All mitochondria
created equal • Bony Palate
• Incr. # Mitochondria • 4 Chambered Heart
• Incr. organ size • Larger nasal
passages
– PGC1α gene • Nasal Turbinates
– Oncogenes
– Brown fat “baby fat”

25. Where’s the HEAT?
• Inner membrane not PMF = electrochemical gradient
100% impervious to
H+ ‘leaky’
• THERMOGENIN
allows H+ to leak &
release PMF energy as
heat

26. Summary of
Endothermy versus Ectothermy
Endothermy Ectothermy
– Advantage – Advantage
• Stamina • Uses 10x less
– Disadvantage energy
• Uses 10x – Disadvantage
more energy • Prisoner of
environment

28. Metabolic rate per gram is
inversely related to body size
among similar animals
• One of animal biology’s most intriguing, but largely
unanswered questions has to do with the relationship
between body size and metabolic rate.
– Physiologists have shown that the amount of energy it
takes to maintain each gram of body weight is
inversely related to body size.
– For example, each gram of a mouse consumes about 20
times more calories than a gram of an elephant.

29. • The higher metabolic rate of a smaller
animal demands a proportionately
greater delivery rate of oxygen.
– A smaller animal also has a higher
breathing rate, blood volume (relative
to size), and heart rate (pulse) and
must eat much more food per unit of
body mass.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

30. • One hypothesis for the inverse relationship
between metabolic rate and size is that the
smaller the size of an endotherm, the greater
the energy cost of maintaining a stable body
temperature.
– The smaller the animal, the greater its
surface to volume ratio, and thus the greater
loss of heat to (or gain from) the
surroundings.
• However, this hypothesis fails to explain the
inverse relationship between metabolism and
size in ectotherms.
• Nor is it supported by experimental tests.
• Researchers continue to search for causes
underlying this inverse relationship.