Temperature Flashcards
1
Q
What is the Van’t Hoff equation?
A
used to quantify effects of temperature on physiology
Q10 = (k2/k1)^10/(t2-t1)
- Q10: quotient for 10ºC temperature change
- k2 and k1: rates of reaction at temperatures t2 and t1
- can be applied to simple processes like enzyme reaction rates
- can be applied to complex processes like resting metabolic rate, growth, or locomotion
- equation can be simplified to Q10 = k2/k1 for reaction at exactly 10°C change
2
Q
What are typical Q10 values for most chemical reactions?
A
(including metabolism, growth and locomotion)
typical Q10 values are 2-3 ∴ reaction doubles or triples with 10ºC change in temperature
3
Q
What is the Q10 of purely physical processes?
A
(like diffusion) typical Q10 value is closer to 1
4
Q
Why is temperature often referred to as an ecological master factor?
A
temperature affects everything that occurs in animal, then affects everything that occurs to other animals – large impact on food webs, community structure
5
Q
What is a thermal strategy?
A
combination of behavioural, biochemical, and physiological responses that ensure body temperature (TB) is within acceptable limit
6
Q
What is ambient temperature (TA) and why is it important?
A
temperature of animal’s surroundings
- most important environmental influence on animal’s thermal strategy
- animals must be able to survive thermal extremes and thermal change
- most ecosystems exhibit spatial and temporal variation in temperature
7
Q
What is the thermal niche of all terrestrial life?
A
-60ºC to +60ºC
8
Q
What is the thermal niche of all aquatic life?
A
-2ºC to +40ºC
9
Q
What are the two major thermal strategies?
A
- tolerance: body temperature is allowed to vary with ambient temperature
- regulation: body temperature does not vary with ambient temperature – controlled (ie. humans maintain temperature at 37ºC
10
Q
What is the equation for total thermal energy?
A
ΔHtotal = Δ Hmetabolism + ΔHconduction + ΔHconvection + ΔHradiation + ΔHevaporation
11
Q
What is Fourier’s law?
A
Q = λ (ΔT/L)
- Q: heat flux (rate of transfer from warm to cold)
- λ: thermal conductivity
- ΔT: temperature gradient
- L: distance over which gradient extends
12
Q
What are the 4 heat transfer mechanisms?
A
- conduction
- radiation
- convection
- evaporation
13
Q
What is conduction?
A
transfer of thermal energy from one object or fluid to another
conduction to environment (heat loss or gain)
- transfer by direct contact
- ie. lying on cold floor when hot
14
Q
What is radiation?
A
radiation to environment (heat loss or gain)
- transfer by electromagnetic radiation
- controlled to some degree by circulation – vasoconstriction and vasodilation
- ie. emitting heat when you are hotter than environment
15
Q
What is convection?
A
convection to environment (heat loss or gain)
- transfer to moving medium
- ie. breathing air or water, wind chill
16
Q
What is evaporation?
A
evaporation to environment (heat loss)
- transfer of heat energy as a result of latent heat of evaporation – sweating, breathing, drying
- converting water from liquid to vapour uses ≅ 520 cal/g or 2.2 kJ/g
17
Q
What is the role of anatomy in heat transfer?
A
- surface area and surface insulation affect rates of heat exchange
- respiratory organs are better at transferring heat than O2
18
Q
What is the role of behaviour in heat transfer?
A
- behaviour can alter rates of heat exchange
19
Q
What is thermal conductivity?
A
ability of heat energy to move within material
- high conductivity = poor insulation
- air: 0.02 W/m per K | snow: 0.10 | water: 0.59 | rock: 1-3 | ice: 2.1 | muscle: 0.5 | fat: 0.2
20
Q
What is heat capacitance?
A
ability to store heat energy
- water can store 3000x more heat than air – water is termed heat sink (GCC)
21
Q
What do the major determinants of heat exchange via conduction influence?
A
- life in water vs. air
- insulation materials
- behaviour
ie. sitting on wooden vs. metal seat on cold day
- metal bench is very cold – great conductor, poor insulator
- wood bench is not very cold – full of air, not great conductor, good insulator
22
Q
How does SA:V ratio influence heat exchange?
A
- high SA:V ratio → increase rate of heat exchange
- SA:V ratio increases as body size decreases, therefore large animal exchange heat slower than small animals
23
Q
What is Bergmann’s rule?
A
mammals and birds living in cold environments tend to be larger
24
Q
What is Allen’s rule?
A
mammals and birds in colder climates have smaller extremities (limbs, fins) – because these are large sites for heat less
25
How does behaviour influence body temperature?
- body posture can alter exposed surface area
- huddling behaviour reduces effective surface area
26
What is insulation? What are the two types?
layer of material that reduces thermal exchange
- internal insulation: under skin – ie. blubber
- external insulation: on body surface – ie. hair, feathers, air, water
27
What are the two classes of organisms that describes the relative stability of their body temperature?
- poikilotherm: variable body temperature
- homeotherm: stable body temperature – ie. humans
28
What are the two classes of organisms that describes their source of thermal energy?
- ectotherm: environment determines body temperature
- endotherm: animal generates internal heat to maintain body temperature
29
Classify birds and mammals (poikilotherm/homeotherm and ectotherm/endotherm).
homeotherm, endotherm
- produce energy to keep body temperature at 37ºC
- most heat generated in body is by gut (internal organs)
30
Classify amphibians, reptiles, fish, invertebrates (poikilotherm/homeotherm and ectotherm/endotherm).
poikilotherm, ectotherm
31
Classify polar fish (poikilotherm/homeotherm and ectotherm/endotherm).
homeotherm, but influenced by environment
- live at freezing point of water – body temperature is constant because environment is constant
32
Classify tropical fish (poikilotherm/homeotherm and ectotherm/endotherm).
homeotherm, but influenced by environment
33
Classify polar invertebrates and tropical invertebrates (poikilotherm/homeotherm and ectotherm/endotherm).
homeotherm, but influenced by environment
34
Classify large flying insects (poikilotherm/homeotherm and ectotherm/endotherm).
poikilotherm, endotherm
- but they have to warm up flight muscles to get hot enough to work for take-off
35
Classify large reptiles (poikilotherm/homeotherm and ectotherm/endotherm).
endotherm
36
Why is the combination of increasing temperatures and decreased dissolved oxygen problematic for aquatic organisms?
- increase temperature → increase rate of biological reactions → increase aerobic metabolism demand → increase in oxygen supply needed to maintain energetic balance
- BUT increase in temperature decreases available aquatic O2 – lots of fish dying
- fish cope with changing climate by leaving, acclimating, or dying
37
What is acclimation?
process in which individual organism adjusts to change in its environment across relatively short time periods (hours, days, weeks, or months)
- generally reversible – phenotype will revert to original state if environment returns to original condition
- occurs in multiple different levels (from cells to tissues to organism)
38
Acclimation is a type of plasticity. What is plasticity?
when same genotype produces various phenotypes when exposed to different environments
- important for adjusting to new environments
- some fish have more beneficial plasticity than others – can be difficult to define what is “beneficial” because not sure what will work well in new environment, therefore need to test stressor tolerance (ie. withstanding stressors longer is probably beneficial change)
39
What is upper thermal tolerance?
temperature where fish lose equilibrium
- turn upside down – good indicator that fish are reaching ecological death point
40
When chronic temperature increases, fishes can acclimate to warm temperatures. How does upper thermal tolerance change?
increases with acclimation to warmer temperatures
41
When chronic temperature increases, fishes can acclimate to warm temperatures. How does hypoxia tolerance change?
NORMALLY decreases with acclimation to warmer temperatures – not enough available oxygen to maintain metabolic rate
- but cross-tolerance – fish that has been acclimated to warm temperatures maintains similar hypoxia tolerance at cooler temperatures
42
What is cross-tolerance?
phenomenon that occurs when mechanisms that are enhanced to protect against one stressor also elicit protection against second stressor
43
What happens to upper thermal tolerance when fish are acutely exposed to warm temperature?
- upper thermal tolerance will not change that quickly
- need time to acclimate – some fish need days, some need weeks
- depending on how long heatwaves are, fish may not be able to gain beneficial plasticity
44
What happens to hypoxia tolerance when fish are acutely exposed to warm temperature?
fish are already trying to deal with acute stressor of temperature change – adding hypoxia stressor can be detrimental (doubles/triples amount of O2 needed to deal with stressors, but warming decreases O2 availability)
45
Can fish use acclimation plasticity to cope with heatwaves?
Upper Thermal Tolerance in Heatwave Fish
- critical thermal maximum (CTMax)
- higher thermal tolerance
- do not decrease thermal tolerance at 70% oxygen
- physiological adjustments made during acclimation helps them withstand hypoxia and increasing temperatures
46
Can fish use acclimation plasticity to cope with heatwaves?
Hypoxia Tolerance in Heatwave Fish
- incipient lethal oxygen saturation (ILOS):
- bubble in nitrogen, which pushes off oxygen – eventually fish can no longer withstand environment, and will turn upside down
- as temperature acutely increased prior to hypoxia trial, hypoxia tolerance decreased – fish exposed to 20ºC before hypoxia have worse tolerance
- maintained hypoxia tolerance
- better hypoxia tolerance at all three temperatures
- hypoxia tolerance increased when brought back to 13ºC
47
Can fish use acclimation plasticity to cope with heatwaves?
fish that have gone through heatwave accrue plasticity for both thermal and hypoxia tolerance
- this is very rare in fishes (only in white sturgeon)
- complete or overcompensating: tolerance level is better than before exposure to warmer temperature
48
What does heatwave acclimation cause?
- increases whole organism plasticity
- induces cross-tolerance
- molecular and physiological changes from cell to whole organism level in response to heatwaves
- understanding individual physiological and molecular changes in response to climate changes stressors can help us predict which populations and ecosystems are threatened and can help to inform conservation efforts
49
What does increased plasticity and cross-tolerance require?
active molecular and physiological changes
- increase in mRNA transcriptional plasticity at warmer temperatures
- increase in DNA methylation plasticity at warmer temperatures
50
What are temporal heterotherms?
body temperatures changes over time
ie. hibernating animals
51
What are regional heterotherms?
body temperature varies in regions of body
- ie. billfish with heater organs near eyes
- ie. tunas and sharks retain heat in red muscle
52
Are humans homeotherms or heterotherms? Endotherms or ectotherms?
homeothermic endotherms – keep body temperature at 37ºC
53
Describe regional endothermy in fish (red muscle).
localized warming of red skeletal muscle used for sustained locomotion → faster contraction frequencies
- deeper into muscle → higher temperature
- recall Q10: animal with this muscle may swim 2x or 3x faster than prey
extensive countercurrent arrangement of arterioles and venules (rete mirabile) transmits heat from venous to arterial blood, retaining heat
54
Where is red muscle located?
different locations in different fish – important for temperature control and power generation
- most fishes have externalized red muscle
- tuna and shark have internalized red muscle
55
What is the challenge with externalized red muscle?
difficult to elevate temperature of muscle because water is direct conductor – trying to heat something that is cooling as fast as it is heated
56
Why is internalized red muscle effective?
there is insulation barrier between water and muscle – muscle generates heat when it contracts and is retained in (insulated by) large white muscle mass
57
Regional Endothermy in Tuna – Red Muscle
Is red muscle warmer or cooler than water temperature? Why?
red muscle is always warmer than water temperature (regional endothermy)
- always contracting
- rete system allows to retain heat
- goal is to have faster muscle than prey (competitive advantage)
58
Regional Endothermy in Tuna – Red Muscle
Is red muscle temperature regulated?
yes – red muscle warms faster than it cools, which implies some sort of active temperature regulation
59
Regional Endothermy in Tuna – Red Muscle
Why are there different rates of cooling and heating?
due to efficiency of rete system – can alter efficiency to change rate at which muscle temperature changes
- efficient: retain heat in muscle and slow rate of temperature change
- inefficient: (constrict inner vessels and dilate outer vessels) take advantage of environment – want to get temperature back up, have good power and contractility → reduce efficiency of rete
60
Regional Endothermy in Tuna – Red Muscle
How does warm muscle affect O2 unloading in humans?
increase in temperature right-shifts equilibrium curve, stabilizes T-state, increases P50, and enhances oxygen unloading
61
Regional Endothermy in Tuna – Red Muscle
How does warm muscle affect O2 unloading in tuna and sharks?
- Hb is relatively insensitive to temperature
- if muscle is 10-15ºC higher than ambient, there is risk of unloading lots of O2, which could elevate O2 tension, or could unload so much O2 that there would not be any left for heart (recall: single-circuit, where O2 sees blood that perfused other tissues)
- lack of temperature sensitivity could conserve O2 for heart
- convergent evolution of temperature insensitivity in tunas and sharks
- more research needed
62
Regional Endothermy in Billfish – Heater Tissue in Eyes
What is heater tissue? How does it work?
modified muscle cell (non-contractile) that generates heat
- when muscle is stimulated electrically, T-tubule activates Ca2+ release from sarcoplasmic reticulum into cytoplasm, stimulating ATP-consuming metabolic processes and mitochondria, producing more ATP, all of which generates heat
- rete system localizes heat to eyes
recall: heart and pacemaker cell are also muscle cells modified for different purpose
63
Thermal Zones of Homeotherms
What is the thermoneutral zone?
range of temperatures optimal for physiological processes – metabolic rate is minimal
64
Thermal Zones of Homeotherms
What is the upper critical temperature (UCT)?
metabolic rate increases as animal induces physiological response to prevent overheating
ie. sweating
65
Thermal Zones of Homeotherms
What is the lower critical temperature (LCT)?
metabolic rate increases to increase heat production
ie. shivering
66
Thermal Zones of Homeotherms
- body temperature stays relatively constant with ambient temperature
- body temperature eventually starts to fall when below a certain value, but before it falls, thermogenesis occurs (shivering) – increases metabolic cost to keep body temperature constant
- active cooling – metabolic rate increases, and can keep body temperature constant for some time before you start to lose control and eventually die if too high or low
67
Thermal Tolerance of Poikilotherms
Do poikilotherms have thermoneutral zone, UCT, or LCT?
no
68
Thermal Tolerance of Poikilotherms
What is preferred temperature?
ambient temperature for optimal physiological function
69
Thermal Tolerance of Poikilotherms
What is incipient lethal temperature?
ambient temperature at which 50% of animals die
- incipient upper lethal temperature (IULT)
- incipient lower lethal temperature (ILLT)
higher acclimation temperature → higher upper and lower lethal temperature
70
Thermal Tolerance of Poikilotherms
What is the range of tolerance?
range of ambient temperatures between IULT and ILLT
71
What are the two classes of thermal tolerance of animals?
- eurytherm: can tolerate wide range of ambient temperatures – can occupy greater number of thermal niches
- stenotherm: can tolerate only narrow range of ambient temperatures
72
What is aerobic scope?
represents energy available for activity above and beyond resting – ie. exercise, digestion, reproduction, immune responses, etc.
aerobic scope = maximal - resting metabolic rate
- Topt: max aerobic scope
- Tcrit: no aerobic scope
- aerobic scope = 0 means they can only survive under resting conditions
73
How does aerobic scope change with temperature?
increases with temperature up to some point (optimal temperature), then starts to decrease
74
How does temperature affect metabolic rate? (2)
- Q10 effects: for every 10ºC increase, resting metabolic rate doubles or triples
- maximum metabolic rate (VO2 max): maximum ability to extract O2 from environment – increases up to some point, then eventually decreases
75
Stressors are cumulative.
- conceptual framework for growth and abundance
- if ocean acidification, hypoxia, food restriction, disease, or competition is imposed, there is competing demands for aerobic scope – ie. adding CO2 or hypoxia reduces aerobic scope curve
- even under optimal conditions, there is less aerobic scope to deal with challenges
- width of thermal tolerance changes
76
What are van der Waal's forces?
forces that hold membrane lipids together
77
How is membrane fluidity affected by temperature?
- low temperatures cause membrane lipids to solidify (fluidity decreases)
- high temperatures increase membrane fluidity
- different species have different temperature-fluidity relationships
ie. cold-water fish fluidity is similar to birds and mammals, even though they exist at very different temperatures – related to their types of membranes
78
What do changes in membrane fluidity affect?
affect protein movement
- increased fluidity → increase protein movement
79
Is membrane fluidity constant?
membrane fluidity is maintained relatively constant in animals at their respective body temperatures
80
What is homeoviscous adaptation?
maintain membrane fluidity at different temperatures by changing composition of membrane lipids
81
What are the mechanisms of homeoviscous adaptation? (2)
- fatty acid chain length: shorter chains increase fluidity because of reduced interactions of neighbouring fatty acids
- saturation: more double bonds (and therefore more kinks – unsaturated) increase fluidity
82
What are the two phospholipid classes and how do they affect membrane fluidity?
- phosphatidylcholine (PC): decrease fluidity
- phosphatidylethanolamine (PE): increase fluidity (polar head group)
83
What does cholesterol content do to membranes?
prevents solidifying when membrane is cooled
84
How can membrane fluidity be rapidly modulated?
- by decreasing saturation in existing lipid membranes
- by synthesizing new lipids and inserting them into membranes
- changing type of lipid or cholesterol, maintaining constant level of fluidity, and therefore maintaining constant level through which proteins can work, and is important aspect of temperature effects on animals that live in range of temperatures
85
Conservation of Km
- Km of enzyme often changes with temperature
- recall: conservation of fluidity in animals living in very different temperatures
ie. Km of LDH for pyruvate increases with increase in temperature
- warmer temperature → LDH less able to bind pyruvate
- Km values are very similar across unrelated species at their different body temperatures
86
How do ectotherms respond to long-term changes in temperature? (2)
remodel tissues
- quantitative strategy: more metabolic “machinery” – ie. increase number of muscle mitochondria in low temperature
- qualitative strategy: alter type of metabolic “machinery” – ie. different myosin isoforms in winter and summer
87
What are heat shock proteins (Hsp)?
molecular chaperones that catalyze protein folding and help refold denatured proteins
- common way for all animals to help prevent negative effects of high temperature on individual proteins (keep proteins functional)
- there is always some level of Hsp in system
88
What is the heat shock response?
increase in Hsp levels in response to extreme temperatures
- rapid response – occurs within minutes to hours
89
What is endothermy (especially birds/mammals) a very successful strategy for?
trying to minimize temperature effects
90
How is endothermy intertwined with high metabolic rate?
- high metabolic rate causes increased heat production (thermogenesis) – whether animal retains or loses that heat determines if they are homeothermic endotherms or transiently heating/cooling
- advantage of high body temperature includes faster enzyme activity
91
Endothermy requires the ability to regulate what? (2)
- thermogenesis – generating too much heat is a problem
- heat exchange with environment
92
What is thermogenesis?
metabolic process through which heat is generated
- heat is byproduct of metabolic processes – energy metabolism, digestion, muscle activity
93
Do endotherms or ectotherms produce metabolic heat?
both
- BUT only endotherms can retain enough heat to elevate body temperature above environmental temperature
- endotherms possess futile cycles
94
What are futile cycles?
metabolic reactions whose sole purpose is to produce heat
ie. heater tissue in billfish, mitochondrial production of ATP
95
What is shivering thermogenesis?
uncoordinated myofiber contraction that results in only heat production, and no gross muscle contraction
- unique to birds and mammals
- works for short periods of time – muscles are rapidly depleted of nutrients and become exhausted
96
What are the 3 mechanisms of heat production in insects prior to flight?
- carbohydrate metabolism in flight muscles
- antagonistic flight muscles contract simultaneously – energy is expended and heat is produced without movement
- wing movement – frequency and orientation of wings are controlled to avoid generating lift
takes longer to elevate temperature of thorax and musculature for flight take-off in colder environments
97
Thermogenesis by Ion Pumping
What are the two main reasons why ion gradients collapse?
- membrane proteins use electrochemical energy to drive transport and biosynthesis
- ions leak across membranes
98
Thermogenesis by Ion Pumping
Why must ions be continually pumped?
- ion-pumping membrane proteins produce heat
- plasma membranes of endotherms (need to generate heat) are leakier than those of ectotherms, increasing thermogenesis due to ion pumping
99
What is brown adipose tissue (BAT)?
used for non-shivering thermogenesis
- important in thermogenesis for small mammals (high SA:V ratio) and newborns that live in cold environments
100
How does brown adipose tissue (BAT) differ from white adipocytes? (2)
- higher levels of mitochondria (which produce heat) make it brown-coloured – mitochondria have leaky membranes, therefore work hard and generate more heat
- produces protein thermogenin – thermogenin inserted into mitochondrial membranes uncouples mitochondrial proton pumping from ATP synthesis – high rate of fatty acid oxidation, energy is released as heat
101
How does the body regulate its temperature in cold environments?
must elevate heat
- vasoconstrict skin blood vessels (to keep blood closer to core to reduce heat loss)
- stimulate BAT to produce heat
- shiver
102
How does the body regulate its temperature in hot environments?
must dump heat
- vasodilate skin blood vessels
- sweat
- pant
103
Which animals are homeothermic endotherms?
birds and mammals
- most theories believe this evolved independently (convergent evolution)
104
What is the internal thermostat of mammals?
- information from central and peripheral thermal sensors is integrated in hypothalamus
- hypothalamus sends signals to body to alter rates of heat production and dissipation
105
Where is the internal thermostat of birds?
spinal cord
106
Piloerection
What does hair and feathers do? How?
act as insulation – reduce thermal conductivity
- efficiency of insulation depends on thickness
- hair and feathers are pulled perpendicular by smooth muscles (erector muscles) attached at their base
- extends fur and allows fur to lay flat – more extended and puffy → more air held
- mammals and birds get fluffier when cold
107
Vasomotor Response
Altering blood flow to the body surface can change rate of heat exchange. What happens at normal body temperature?
sympathetic nervous system maintains tonic constriction of arterioles
- mediated by 𝛼 adrenergic signals
- do not want to lose heat we worked hard to generate
- no point in generating expensive excess heat
108
Vasomotor Response
Altering blood flow to the body surface can change rate of heat exchange. What happens at low body temperature?
- increase in tonic constriction of arteriole
- decrease in constriction of AV shunt – dilates
109
Vasomotor Response
Altering blood flow to the body surface can change rate of heat exchange. What happens at high body temperature?
- decrease in tonic constriction of arteriole – dilates
- increase in constriction of AV shunt
110
How do bird feet countercurrent exchangers work?
transfers thermal energy from warm arterial blood to cooler venous blood
- heat is retained
- warm blood entering foot is being cooled by cold blood leaving foot
111
How do nasal countercurrent exchangers work?
operates to recycle and conserve water, and prevent heat loss that may occur as a result of breathing
- efficient for heating and humidifying air needed in lungs for gas exchange
- cool air is heated as it moves towards lungs (ends up at body temperature)
- oxygen is extracted from air
- air equilibrates with lower temperature as air moves back out through nose during exhalation
- recycle thermal energy required to heat air we breathe – recovered as we exhale to use in next breath
112
What organisms use sweating as a method to reduce body temperature?
used primarily by large animals
- low SA:V ratio, often making it difficult to dump heat
113
How does sweating reduce body temperature?
- reduces body temperature by evaporative cooling – transition of water to air takes lots of energy
- controlled by hypothalamus – sympathetic innervation of sweat glands
- NaCl in sweat raises heat of vapourization – greater heat loss than evaporation of pure water, but loss of salts can be problematic
- to minimize ionic and osmotic problems, amount of NaCl in sweat decreases during long periods of heat exposure
114
What are properties that make respiratory surfaces good at gas exchange? What are the challenges of this?
high vascularity, moist surface, and high airflow
- challenge is that it also enhances heat loss
115
What methods do mammals use to increase heat loss without creating problems for gas exchange?
panting
116
What methods do birds use to increase heat loss without creating problems for gas exchange?
gular fluttering
117
How does rapid ventilation increase heat loss? What is the challenge with this?
by convection and evaporation
- but CO2 loss can be big problem because humans primarily regulate ventilation to make sure CO2 levels do not change too much
- trade-off between conditions to dump heat vs. conditions to exchange gases
118
Nasal countercurrent exchanger is efficient for humidifying air and retaining heat under normal conditions.
What happens at high temperatures? What is the challenge at high temperatures?
animal has to dump heat – breathe more through mouth than nose
- air is heated by mucosa around mouth, but heat is lost because there is no efficient way of recovering it when breathing through mouth rather than nose
- results in increased breathing frequency and volume of air moved into and out of animal – but because each breath is small, it ventilates dead space more than alveolar space, therefore high air flow occurs over nasal mucosa, tongue, and other moist surfaces, increasing evaporative heat loss without altering conditions for gas transport
119
Relaxed Endothermy
temporarily lower BMR (hypometabolic state)
- relax normal TB = reset TB
hibernation over winter (seasonal) → small and large mammals
- decrease TB by ~20ºC
- downregulation of metabolism
torpor (hummingbird): overnight (diurnal) → small birds and mammals
- decrease TB by ~10ºC
saves fuel when food supply becomes limited (night and winter)
120
What are the two strategies for surviving freezing temperatures?
- freeze-tolerance: animals can allow their tissues to freeze – ie. frogs
- freeze-avoidance: animals use behavioural and physiological mechanisms to prevent ice crystal formation
121
What is supercooling (freeze-avoidance)?
when body temperature is lower than temperature at which ice would normally form, but there are no nucleation sites for ice crystals to form around
- water can remain liquid below fluid freezing point at 0°C (lowest is -40°C) in absence of nucleator
122
What is the supercooling point?
coldest you can get without ice crystals forming
123
What are the triggers for ice crystal formation?
either cluster of water molecules or macromolecule that acts as nucleator
124
What are the deleterious effects of ice crystal formation? (2)
- points and edges can pierce membranes
- crystal growth removes surrounding water, leaving salts behind – osmolarity increases
125
What role does salt content and osmolality play in preventing freezing?
can depress freezing point of solution by increasing concentration of solutes
- freezing point drops 1.86°C for every 1 Osmol/L in solution
- end up with small amount of liquid with very low freezing point (high osmolarity), which can stay liquid even at low temperatures
ions, sugars, salts, etc. do not form into ice crystals – only water is included in crystals
126
How do animals such as caterpillar larvae and larval beetles lower freezing point of a solution?
using glycerol
- some insects can consist of 25% glycerol by body weight and tolerate temperature as low as -55 to -70°C (do not freeze – can still be active)
- more concentrated glycerol → greater depression of freezing point → less likely to freeze at that temperature
- humans cannot do this – osmolarity is lethal for us
127
What 2 roles does glycerol play?
- depressing freezing point – glycerol is synthesized by carbohydrate metabolism and depresses freezing point of blood (by high osmolarity)
- changing way ice crystal forms, preventing damage – when ice does form in presence of glycerol, it freezes like bead of glass rather than ice crystal spicules (which puncture membranes), therefore induces less damage
128
What is a colligative cryoprotectant?
refers to depression of freezing point that is strictly dependent upon number of molecules in given volume
ie. osmolarity-related reductions in freezing point (higher osmolarity → greater depression)
129
What is a non-colligative cryoprotectant?
additional interactions that prevent freezing
ie. how antifreezes inhibit ice crystal growth to prevent physical damage of ice crystals
130
What is a colligative property of water?
solutes depress freezing point of liquid
131
What are antifreeze macromolecules?
proteins or glycoproteins that depress freezing point by non-colligative actions
- disrupt ice crystal formation by binding to small ice crystal and preventing growth
132
How can polar fish withstand water temperatures that are below the freezing temperature of tissues?
- freshwater-breathing organisms do not really need to worry about freeze avoidance provided there is water around – fresh water freezes at 0°C and body tissues at -0.5-0.7 °C
- the same is not true for marine waters – seawater freezes at about -1.86°C, therefore marine organism could freeze before water does
- many fishes exist within cool polar waters in supercooled state, but they must avoid ice crystals that may act as nucleation sites for ice crystal formation
- some fish in Arctic and Antarctic synthesize glycoproteins and antifreeze proteins, which regulate ice crystal formation
133
What do antifreeze proteins (AFPs) do?
- lowers freezing point of solution in non-colligative manner, but does not change melting point of solution
- regulates ice crystal formation, becomes incorporated into crystal, and depresses freezing point for ice crystal formation
- arose independently in Arctic and Antarctic fishes – convergent evolution
134
Compare the relative effectiveness of AFPs, polyols, and NaCl in lowering freezing points.
AFPs lower freezing point extremely rapidly at very low concentration
