BIO120 TEST 1: NOTES FROM LECTURES 1-4 (missing lect. 5 (7 on portal))
• Physiological vs. geographical range of tolerance
Heat balance/ thermal energy
Molecular reactions depend on enzymes, as temperature increases, enzyme
bonds weaken (and lose ability to catalyze reactions). Organisms must balance
temperatures for optimal enzyme reaction.
Homeostasis: keeping temperature (and other aspects) at ‘same’ level, despite
changing exterior temperatures.
Organisms may be limited by habitat: eg. Pronghorn: physically made to live on
horizontal planes, cannot live on nearby mountains.
Two birds (Yellow-rumped warbler) and (kirtland’s warbler) belong to same genus,
but y-r is an extreme habitat generalist, while k.w. is an extreme habitat specialist (
will only live on high trees (cognitive limitation, not due to physiology)
Tiger: Panthera tigris, broad temperature tolerance and broad habitat range. Tropical
rainforest, Sumatra, and Boreal Forest, Siberia.
• Radiation- heat is transferred by electromagnetic radiation
• Conduction- direct contact with substrate (eg. Feet to ground) (water is good
• Convection- heat transfer mediated by moving fluid (air or water) (indirect
contact) (hot and cold brick example)
• Evaporation- efficient cooling from wet surfaces (sweating)
• Redistribution- circulatory system redistributes heat among body parts, esp.
core to appendages
• Homeostasis and surface area: volume ration
• Surface area determines equilibration rate
• Volume provides the inertia
• Ratio of surface area to volume:
Radius:1 – equilibrates quickly
Radius:3 - equilibrates slowly (will not lose heat to environment (cold) if big)
(eg. Polar bears in artic vs. small bird in same env…)
Bergmann’s rule: Homeotherms tend to be larger at higher latitudes
(colder)…sometimes applies: counterargument= elephants in grassland regions/
Allen’s Rule: appendages reduced in cold climates
Shere has least SA:V, so why shouldn’t homeotherms be sheres in cold climates?
Maximum SA:V ratio is restricted to warm tropics. It will only be able to keep the
temperature of its environment. (flying snake example) Minimum SA:V ratio alpine tundra rabbit, restricted to cold habitats, note
spherical shape, reduced ears. (also consider Lepus articus (small fluffy white
bunny, limbs very short and close to body) and lepus californicus (uglier, big ears
and extracted limbs to rid of heat))
• As you leave (go N or S) from equator, productivity decreases
• Fires are crucial for nutrient enhancement in grasslands and savannahs
• Hot air, which is less dense than cold air, rises. Since it is less dense, its more
abundant mass can hold water molecules. As it rises, air cools, releasing
water molecules as precipitation. Cool air is more dense (heavier), thus
allowing it to sink to ground level and begin the cycle over again.
• Tundra: coldest of all biomes. No trees, very little vegetation and
precipitation. Composes 1/5 of land on earth. Plants include lichens, moss,
and small shrubs. Animals include caribou and artic hares (+).
• Temperate Rain(?)forests: pacific coast of N.A., (alaska to oregon). Wet, but
not as rainy as tropical. Short dry summer and long wet winter.
• Savannas: mostly grass and scattered trees. Africa, South America and
Australia. Warm temp. (20-30C0 and 25-75 cm of precipitation per year.
• Boreal/ Taiga/ Coniferous: long, cold winters and mildly warm summers. 25-
75 cm of precipitation yearly. Less plant life than most other biomes. Usually
evergreens. Conifers. Home to grizzly bears and wolverines. Moscow and
(not Toronto… deciduous)
• Deciduous: 4 seasons (D.C.). Maple, elm, oak trees. Precipitation is 75-150
cm. avg temp is 10C.
Physiological Optima and Critical Limits:
• For an endotherm within its optimal range of temperature — termed the
thermal neutral zone (TNZ) — metabolism is constant and minimized
(Figure 1A). At temperatures above and below the TNZ, endotherms elevate
their metabolic rate while inducing physiological responses to maintain a
constant body temperature (e.g., shivering to warm, sweating to cool).
Ectotherms show a very different response to changes in temperature, as
they have no TNZ (Figure 1B), but do have an optimal temperature at which
they perform most efficiently. Mobile ectotherms may behaviorally
thermoregulate a specific body temperature by moving between
environments, but doing so is energetically taxing and could reduce fitness in
• Pejus= progressively deleterious
Mechanistic Basis of Thermoregulation: • Animals that are freeze tolerant: “First, compatible solutes or osmolytes
such as glycerol and glucose are concentrated inside cells, lowering the
freezing point of the cytosolic fluid. Second, ice formation is encouraged to
occur in extracellular fluid by ice nucleators. When nucleated ice
formation begins, the remaining solutes are concentrated in the extracellular
fluids, and this creates an osmotic pressure gradient, causing water to
move out of cells, further concentrating the intracellular fluid and reducing
its freezing point.”
• Why are enzymes only marginally stable?
• Because enzymes require conformational shifts; they must be able to
alter in the common event of a reaction. They must be stable enough
to keep its shape and guide reactants to necessary enzymes, but not
too rigid as to not be able to bind reactants or release products.
Enzymes are weak bonds and easily affected by temperature. (small changes in
temp. have little to no effect on covalent bonds).
Weak bonds= enzymes.
As temperature increases, there is an INCREASE in biological reactions, and a
DECREASE in the stability of molecules(breaks the weak bonds).
Reduction in Metabolic Efficiency:
• As temperatures increase, weaker bonds break. This reduces the strength of
the membrane, allowing more H+ protons to enter the cell.
• This occurrence lowers the efficiency by which energy in food and sunlight is
converted to biological energy currency (ATP).
• Ultimately, higher temperatures lead to lower ATP production. Therefore,
organisms can compensate for that reduction by eating more food.
• As mitochondria become leakier at higher temps, they release a free radical
called hydroxyl, which damage macromolecules such as lipids, proteins and
nucleic acids. (which is why organisms can consume more food to
compensate for damaged macromolecules).
Oxygen Limitation and Fermentative Metabolism
• If organisms are living in an energy-limited environment, increased
fermentative metabolism will tax energy stor