Van’t Hoff’s Rule: for every temperature riseof 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.
Energy Pie: distribution of individual’s energy among:• Growth• Reproduction• Activity• Maintenance: includes body temp• Storage
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
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)
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.
SA:V Ratio• However… larger endotherms also generate more heat per unit volume as well – and have a harder time losing it. – Elephant & Kangaroo
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.
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
What happens to a lizard in a furcoat?• Gets colder & dies of hypothermia• WHY? – Can’t absorb the heat & doesn’t generate enough of its own heat.
HOT ENVIRONMENTLizard Mammal•Absorbs heat from enviro. •Generates body heat• Metabolism at max. •Must cool down (sweat, slow metabolism)COLD ENVIRONMENTLizard 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
Torpor: lowering of body tempbelow 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
Torpor: Adaptive Values• Reduces Energy Needs – 2 ways• Reduces Water Needs – 3 ways
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 Quick34 o heat 34o Slow heat loss loss 99o 35oHigh temp gradient Low temp gradient
Torpor: Adaptive ValuesReduces 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)
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)
What are the gains of endothermy?• Nocturnal Ability • Larger body size• Niche expansion – Bigger brain – Climate zonesNot enough to offset the cost of apopulation size reduction, higher &more consistent food needs, lowerlife span, and number of offspring...(FITNESS)
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
Trade-OffsHigh Power/Low Stamina vsLow Power/High Stamina Reptiles are built for speed bursts – SPRINTERS Mammals are built for STAMINA
STAMINA IS THE MAINADVANTAGE 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
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”
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
Summary of Endothermy versus EctothermyEndothermy Ectothermy – Advantage – Advantage • Stamina • Uses 10x less – Disadvantage energy • Uses 10x – Disadvantage more energy • Prisoner of environment
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.
• 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.
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