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Biology 2601A/B Lecture Notes - Pokey, Antifreeze Protein, Cooling Bath

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BIOL 2601A/B

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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
Deal with body temp:
Burrow in soil
Bees stay in hive
A lot just take the brunt force of temperature
When its cold, water…
Water freezes!
Organisms are mostly water
One reason wh life below 0 …
Extracellular fluid and tissues freeze, then they thaw out and theyre fine
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
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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.
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