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Org Phys Lec oct 4.docx

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Western University
Biology 2601A/B

Org Phys Lec Oct 4 Insect Cold Tolerance Heath Macmillan Ectotherms- body of the stone fly is about 0 degrees Just because we don’t see things out in the wild doesn’t mean theyre not there Daily and seasonal temperature changes How do organisms deal with cold? Endotherms defending the temp they think is optimal, Ectotherms allowing their body to change with the environment Endotherms/ homeotherms Turn the low temp problem into an energy problem Ectotherms Deal with body temp: Migration Burrow in soil Bees stay in hive A lot just take the brunt force of temperature When its cold, water… Water freezes! Expands! Organisms are mostly water One reason wh life below 0 … Extracellular fluid and tissues freeze, then they thaw out and theyre fine How?! Water doesn’t always freeze at 0 degrees Sometimes as low as 20 degrees Insects tend to be small so avoding freezing is a popular tactic Smaller volume= less likely to freeze Large volume more likely Ice cant form unless it can make this lattice structure In an orgamism it isn’t just water, theres other stuff which impedes the lattice Alex How insects survive the cold Chill susceptible- suck at surviving cold (majority) will migrate, avoid cold Freeze avoiding- keep themselves from freezing – small insects, ice wont form inside their bodies Freeze tolerant: survive freezing How do we know an insect has frozen Tape a thermocup to them and measure their temp, put them in a cooling bath, body temp will go down as temp in environment goes down, bump in the graph is when ice forms (alex) Supercooling point because it is always below 0 All of these insects are dead before freezing happens, freezing doesn’t kill them it’s the effects of cold Chill susceptible insects die well before they freeze Chill susceptible insects Chil injury- effects from cold that kill them before freezing 2 types of chilling injury; Acute chilling injury- caused by any quick exposure to low temps (no freezing), probably related to membrane phase changes Chronic chilling injury- exposure to mild temperatures for a relatively longer time, loss of iron homeostasis (20-70% of the ATP you consume is going to keeping sodium on one side and potassium on the other) Loss of iron homeostasis means loss of water If you let all the sodium go into your cells they would explode Chronic chilling inury Actotransportive ions: direction of this is different for different ions In this we have sodium being removed from the cell into the cytoplasm, enzymatic process, consuming energy Channels: allow ions to move down the gradient (not up) Rate of ion movement has a relationship with temp, all ions will speed up as temp increases, exponential rise in ion pumping activity, pump rate is dependent on temp, leak rate (moving through the channel) is not dependent on temp Means that at higher temp our ion pump rate is above the leak rate (can keep ions on the side of membrane we want them) Threshold temp at which leak rate exceeds rate at which we can pump (drift of ions down the gradient) Why is that bad? We need to keep ion balance, critical to all cells function especially nerves and muscles. Loss of ion homeostasis means a loss of cell potential As temp ecreases muscle potential slowly rises, they reach a critical nerve/ uscle potential and they cant make muscle actions any more Chill coma Chill coma Before they die they enter chil coma Loss of ion balance leading to paralysis, if you warm them back up they reverse this. Bee on a string Chill coma temp varies among species Drosphila collected from all over th
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