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Lecture 2

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Department
Biology
Course
BIO120H1
Professor
Scott Browning
Semester
Fall

Description
BIOLOGY LECTURE #2 Physiological Optima and Critical Limits - Distribution limits + responses to climate change depend on their performance, which varies as the environment shifts from OPTICAL to EXTREME conditions - Distribution limits: depend on biotic + abiotic environmental factors - Adaptations + energetics: limit size of optimal enviro + range of enviro between critical limits - “Performance curve” diagram that shows variation in fitness between enviro (abiotic) factors that define critical limits Thermal Performance Curves - Hard to measure fitness - Correlated measures of org’s performance are used as indirect measure - Performance = max fitness under range of optimal temp = Decline to 0 just beyond upper + lower critical temp - Critical temp defines org’s thermal tolerance range - Critical Thermal Limits: breadth of temp that org can tolerate @ short exp - Only survive short periods in conditions that exceed a threshold in their “critical tolerance limits” - 2 metrics: upper + lower LT or50T maxand CT min - EURYTHERMAL: org’s have wide thermal breadth, live in wide range - STENOTHERMAL: org’s restricted to narrow thermal enviro OR thermoregulate - Categorize animals based on their thermal interactions with the environment - ENDOTHERM OR ECTOTHERM - TNZ = THERMAL NEUTRAL ZONE (optimal range of T) Endotherm: IN TNZ: metabolism is constant + minimized - ABOVE +BELOW TNZ: elevate their metabolic rate while inducing physiological responses to maintain a constant temp (SHIVERING/SWEATING) Ectotherms: DON’T HAVE TNZ, but… do have an optimal temperature where they can perform most efficiently. - Mobile: thermoreg a specific body temp by moving between enviro - Energetically taxing + reduces fitness in food limited places THERMAL PERFORMANCE CURVES (TPC): - Before reaching upper + lower CLs, org perform less and less well. - T increase/decrease from optimal point = PERFORMANCE IS REDUCED - AKA PEJUS TEMPS (where performance begins to decline) - Less extreme than CL’s - Thermal transitions that are more ecologically relevant: before death org required to use mech to divert energy away from performance Mechanical Bases of TPC Performance optima occur when physiological rate + metabolic efficiency = maximized LOWER CRITICAL TERMAL LIMIS - Thermodynamic FP: orgs that can survive use physiological echs to stop formation of intracellular ice - Can’t survive with ice formed inside cells, but can form outside of cells as long as it grows in a controlled manner - TOLERANT vs RESISITANT - Freeze tolerant: org’s that allow extracellular ice to form but not intracellular (eg. Ectothermic terrestrial vert, invert, marine intertidal invert) HOW: COLLIGATIVE PROPERTIES OF WATER 1) Compatible solutes/osmolytes (glycerol and glucose) are C inside cell to lower FP of cytosolic fluid 2) Ice formation encouraged in extracell fluid by ice nucleators 3) Osmotic pressure gradient created by ice formation where remaining solutes C in extracell fluids… causes water to move out of cell = further C intracell fluid = reduce FP - Other org’s are freeze resistant: they prevent freezing body tissues by limiting size of ice crystals using antifreeze proteins + glycoproteins - Antifreeze proteins: coat growing ice crystals + prevent from growing too big - Hibernation: energy saved (reduced met), but periodic arousal leads to large temporary increases in metabolic rate during - Lower CL’s of tropical ectotherms ABOVE FP of tissues… diff mech to lower thermal tolerance limits: MARGINAL STABILITY - Enzyme function needs conformational shifts (changes in 3D molecule shape) to bind reactions + release products - confo shift = enzyme needs to be stable enough to maintain its shape to recognize + bind its substrates + position R in active site, BUT, not so stable that it becomes rigid + unable to bind R/ release P: JUST RIGHT STABILITY - 3D structure depend on many weak bonds that together stabilize molecule, ALL HIGHLY T SENSITIVE - Small increase in temp have large impact on weak bonds: stability, flexibility, structure of molecule - THERMODYNAMIC IMPACT: increase in rate of biological reactions + reduction in stability of enzymes REDUCTION IN METABOLIC EFFICIENTY (diagram pg.5) - Increase in T = more thermal energy to break more weak bonds for marginal stability - Broken weak bonds = mem brain of a barrio to protons (H+) - reduces efficiency for energy in food/sun to be converted to ATP
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