Organismal Physiology 10/24/2013
Up to and including October 17 Lecture
Temperature, Energy, gas and fluids topics covered for midterm Lecture 2: Temperature: Principles of Thermal Biology : Sept 12
Temperature of a substance is proportional to the product of the mean square speed of the random
molecular motion and molecular mass
Temperature: intensity of motion by the atoms in the object
Heat: Amount of energy in the object
Temperature determines the direction of heat transfer
Warm ▯ Cold
Endotherms: Generate internal heat
Ectotherms: Rely on external temperatures to determine Tb
Homeotherms: Defend a constant body temperature Lecture 2: Temperature: Principles of Thermal Biology : Sept 12
Poikilotherms: Allow body temperature to vary
Heterotherms: Have more than one temperature set point, or switch between homeo and
Regional endothermy/ heterothermy: Different Tb in different parts of the body
The relationship between temperature and metabolism in an ectotherm Lecture 2: Temperature: Principles of Thermal Biology : Sept 12
Q10: The Temperature Coefficient
The ratio for the rate of a process at one temperature over the rate of the same process at a temperature
Since temperaturemetabolic rate relationship is not exactly exponential, the impact of a change of
temperature varies with temperature.
Q10 = 1 for many physical/chemical processes
Q10=23 got most biological processes
Temperature determines motion, and therefore the rate at which molecules encounter one another
More interactions = More reactions
Temperature also determines the conformation and efficiency of enzymes (Q10 ~ 23 in biological)
Most enzymes have a temperature optimum Lecture 2: Temperature: Principles of Thermal Biology : Sept 12
Temperature can affect the rate at which the substrate and enzyme encounter one another
Warmer = more often = more reactions
Enzymes activity site can change shape with temperature
change in binding affinity for substrate
generally warmer = weaker
High Km = low affinity
Low Km = high affinity Lecture 2: Temperature: Principles of Thermal Biology : Sept 12
An animals rate of energy consumption; the rate at whoich it converts chemicalbond energy to heat and
This rate is determined by enzyme activity; thus temperature dependent
Processes of Ectotherms governed by Temperature:
Fruit production and ripening
Thermal inertia: body size and thermal biology Lecture 2: Temperature: Principles of Thermal Biology : Sept 12
Why are there temperature limits?
Prevent ice formation or damage from freezing
Mismatch of oxygen demand and delivery
Alter aerobic/ cardiovascular capacity
Modify membrane composition
More fluid for lower temperatures, less fluid for higher temperatures
Change the enzyme Lecture 3: Temperature: Plants and Ectotherms : Sept 12
Poikilotherm: an animal in which body temperature is determined by equilibrium with the thermal
conditions and environment
R + H + C + L + M = 0
R = Radiation
Minimize or maximize radiation absorption
Leaf color / angle
H = Convection
C = Conductance
Not much of an issue for plants
L = Latent heat Exchange
M = Metabolism
Metabolic heat generation in some plants
Plants can affect their leaf temperature
leaf color alters radiation absorption
longterm, adaptive response
Rolling leaves and pointing them vertically reduced sun interception
Shape affects convection – heat exchange with air molecules Lecture 3: Temperature: Plants and Ectotherms : Sept 12
Latent Heat of vaporization of water = 2270 kj/kg
transpiration is a very effective way to cool if you have water
Why do plants need metabolic heat?
To warm up tissues to a more optimal physiological temperature
To attract pollinators in early spring:
Increase odor diffusion
Provide warmth for ectotherm pollinators
Thermogenesis in the aroid spadix
Not inhibited by CO, cyanide or azide
Alternative oxidase pathway
Thermoregulation: is the ability of an organism to keep its body temperature within certain
boundaries, even when the surrounding temperature is very different
CNinsensitive respiration in plants
Heat generation in flight muscles of bees and moths
Note both heat production and heat loss in flying bees Lecture 3: Temperature: Plants and Ectotherms : Sept 12
Why are fish ectotherms
Fish can generate heat, but have problems keeping it
Surrounded by thermally conductive water
Ectotherms don’t generate internal heat that contributes meaningfully to body temperature.
Fish gills act as a heat sink
Fish are ectotherms because the high blood flow across their large gill surface means that they loose heat
to the environment very quickly
Heat retention is a major issue Lecture 3: Temperature: Plants and Ectotherms : Sept 12
A reoccurring theme – especially in fish (not exclusively)
Oxygen delivery to retina
Allows for VERY effective countercurrent exchange of heat
Red muscle temperature is elevated above water temperature Lecture 3: Temperature: Plants and Ectotherms : Sept 12
This heat comes from the normal heat produced by contractile activity of the red muscles
Only difference is the heat is retained
To allow long migration through water of different temperatures
To allow better performance as a predator chasing prey into cold water
Improvements of power output of muscles Lecture 4: Endothermic Homeotherms : September 19
Climatic fluctuations in temperature are a part of everday life for all living organisms
Night vs day
Animals and plants need to manage climatic fluctuations
Endotherms adjust to this variation in their environment by adjusting their physiology
such as by increasing or decreasing the body heat produced as part of the metabolic breakdown of food
Resulting in constant internal body temperatures relative to environmental fluctuations
Regulating internal body temperature is necessary for cellular function
Departures from the set core body temperatures can lead to cellular damage or death of the individual
Homeotherm: An animal that thermoregulates by physiological means, rather than simply by behavior.
More independence from external thermal conditions
Highly stable core body temperature
Thermal Adapatation in Endotherms: climate and phylogeny interact to determine population
level responses in a wild rat Lecture 4: Endothermic Homeotherms : September 19
In thethermoneutral zone metabolic rate is maintained at a very stable interval. The size of the zone
varies for different homeothermic species. Large animals will exhibit a naturally large thermoneutral zone,
while small animals, a small one.
Endothermy clearly permits mammals and birds to have an active life in harsh environments
in day or night
swimming in cold water
Endothermy clearly permits long distant migration in birds and mammals
Being an endothermic homeotherm has a cost…
Need more energy
When small mammals hibernate, they allow their body temperature to fall to environmental temperature
Brown adipose tissue is very useful for small animals and newborns as it provides an alternative means of
heat production. Futile cycles refer to metabolic pathways such as glycolysis (conversion of glucose to
pyruvate) and gluconeogenesis (conversion of pyruvate to glucose) that are useful not in their products but
by their cancellation, in that they generate necessary heat.
Mammals and Birds must have a high degree of control minimizing their energetic cost
regulation Lecture 4: Endothermic Homeotherms : September 19
How does metabolic rate of an animal remain constant in all different temperatures in TNZ?
Modulation of insulation against a background of constant metabolic heat is the principle means by which a
mammal or bird thermoregulates in its thermoneutral zone
exposed body parts are often cooler than core temperature
heat & energy conservation
Testes and brains are often kept cooler
Most birds and mammals actively increase the rate at which water evaporates from certain of their body
surfaces, a process called active evaporative cooling. (Sweating, panting and gular fluttering)
Once within the thermoneutral zone, the organism will experience the modulation of insulation and blood
flow. Lecture 4: Endothermic Homeotherms : September 19
Outside the thermoneutral zone, species will exhibit increased energy consumption due to heat generation
at colder temperatures and increased energy consumption due to heat loss at higher temperatures.
Regulation of body temperature in homeotherms requires a set point for which there are many biological
sensors like: the skin, spinal cord, back of the brain, hypothalamus, and scrotum (in males). Lecture 5: Behavioural, Physiological and Biochemical Changes: Sept 24
loss of membrane fluidity and loss of ion homeostasis
3 Classifications of Cold Tolerance
1) Die before freezing – chill susceptible
2) Keep from freezing – Freeze avoiding
lower freezing point
3) Survive Freezing – Freeze tolerant
We can always tell for certain if an organism has frozen by looking at thesupercooling point (SCP)
whereby all of the water molecules should be frozen and examining the exotherm point which is also
referred to as the latent heat of crystallization
Chillsusceptible insects die from physiological processes that have nothing to do with freezing (they die
before their bodies have frozen).
This injury caused by the effects of cold (not ice) is known aschilling injury .
There are two types of chilling injuryacute chilling injury and chronic chilling injury .
Acute chilling injury is the result of quick exposure to low temperatures (not freezing) and is possibly caused
by phase changes in the cell membrane.
Chronic chilling injury is caused by the loss of ion homeostasis which eventually leads to the loss of water
Ice nucleating agents and pest control Lecture 5: Behavioural, Physiological and Biochemical Changes: Sept 24
topical application of ice nucleators
Cause ice formation = death
Glyercol, sorbitol, trehalose (carbs or polyols)
Colligative properties (freeze avoiders)
Freeze point depression based on number of solutes in solution
Noncolligative properties (freezetolerators)
Protect membranes, enzymes during freezing
Draw water out of cells
Keep the ice nucleators
Only freeze extracellular fluids
Freeze at a higher temperature
Rapid cold hardening
Prior exposure to cold enhances protection against more cold
Stabilize membranes (increase fluidity)
Repeated freezing and thawing is obviously bad
Cold activation of immune system
Cold can upregulate the immune system
Cold active pathogens Lecture 6: Metabolism 1 : Photosynthesis: Sept 26
Autotrophs make food from sunlight Lecture 6: Metabolism 1 : Photosynthesis: Sept 26
Heterotrophs use the food to do work
Photosynthesis is by far the most important biological process on Earth due to carbon fixation happening
because of algae hotspots in the oceans and Canada’s boreal forest
There is an annual cycle of CO 2concentration in the atmosphere that constantly increases, and then
decreases. This is referred to as “planetary breathing” and it is the respiring of 2O in the atmosphere.
Plants are far more efficient than solar panels and other commercial photovoltaic cells.
The range of wavelengths and frequencies of the visible spectrum of light is the only kind used in
PIGMENTS Lecture 6: Metabolism 1 : Photosynthesis: Sept 26
Molecules that absorb photons are generally observed as being the same colour as the wavelengths they
In the case of green chlorophyll, it reflects green light.
The absorption of the photon increases the energy level of the molecule.
As chlorophyll absorbs a photon of blue light, it gets to a higher excited state, which will be lost due to heat
As chlorophyll absorbs a photon of red light, it reaches its lowest excited state
which returns to ground state by fluorescence (the loss of energy by the emission of light of longer
Absorption spectrum of a plant (or leaf pigment extract) describes how much a pigment is
absorbing a particular wavelength of light. Lecture 6: Metabolism 1 : Photosynthesis: Sept 26
A ction spectrum describes the O2 evolution rate (relative rate of photosynthesis) at each wavelength
The chloroplast contains a double membrane (an outer envelope and an inner envelope) with an
intermembrane space in between.
Inside the chloroplast, within the space of thstroma , thethylakoids are stacked as grana lamellae
(the site of Photosystem II) and connected by stroma lamellae (the site of Photosystem I).
Under weak blue light, chloroplasts will try to maximize their exposure to photons, while under strong blue
light, chloroplasts will try to minimize their exposure to photons (hiding behind cell walls).
Energy harvested photons is transferred to the reaction centre
A group of pigment molecules will form an antenna complex with thereaction centre denoting a
special pair of chlorophyll molecules.
This reaction centre (comprised of either P680 or P700) will receive the transfer of energy (light) by other
chlorophylls in the antenna complex in order to accept and then donate electrons ( electron transfer ).
The combination of a reaction centre and its antenna complex is known as a photosystem . Lecture 6: Metabolism 1 : Photosynthesis: Sept 26
The chlorophylla molecules (comprising the antenna complex) each have an Mgcontaining porphyrin
group (related to the Heme group in haemoglobin).
2 Reactions of Photosynthesis
Uses water and produces oxygen
Use ADP NADP+ to produce ATP, NADPH
Energy input from transfer of photons
Can use rate of O2 production to measure photosynthetic rate
Uses Co2, produces sugars
Uses ATP, NADPH, produces ADP, NADP+
Energy input from lightdependant reactions
Can use rate of net CO2 consumption to measure photosynthetic rate
As red light hits PSII and is transferred to the P680 (strong oxidant) reaction centre, two water molecules
are split and the electrons are transferred from the high energy state P680* (weak reductant) through the
electron transport chain.
As the electrons are moved and managed through the ETC towards PSI, H ions are being pumped into
the lumen (by plastiquinone).
After the plastiquinone pool, the electron are transported to the Cytochrome complex, then to plastocyanin
(not part of the membrane), and finally to PSI.
Simultaneously, far red light is hitting PSI and is transferred to the P700 (weak oxidant) reaction centre
where the electrons are transferred from the high energy state P700* (strong reductant) to Ferredoxin,
After which NADP becomes the final electron acceptor (by way of NADP reductase) and results in the
production of NADPH.
The overload of protons in the lumen form an electrochemical gradient that fuels the production of ATP as
the H ions pass the thylakoid membrane and into the stroma by way of the protein channel ATP synthase.
Key Actions Of The Electron Transport Chain:
Oxygenevolving complex (still a mystery) oxidizes water.
The reducing potential is transferred via plastiquinone (PQ) and plastiquinol (PQH ).
The energy lost includes driving a proton gradient.
Coppercontaining plastocyanin transfers electron to PSI. Lecture 6: Metabolism 1 : Photosynthesis: Sept 26
Ferredoxin complex reduces NADP . +
Protons drive ATP synthase.
Photosynthetic Carbon Reduction (PCR) Cycle:
Ribulose 1,5 – biphosphate enters the first step of the PCR cycle (Carboxylation)
With the input of 3 carbon dioxide and 3 water molecules, the enzyme Rubsico carboxylate the substrate to
form two stable 3carbon (C3) molecules (3PGA).
Rubsico is the most abundant protein on Earth, which both functions as a carboxylase and an oxygenase.
Its small subunit is encoded in the nuclear genome, while its large subunit is encoded in the chloroplastic
Second step of the PCR cycle (Reduction), ATP and NADPH from the lightdependent reaction is
consumed in order to fuel the reduction of 3PGA to G3P.
In the third and final step of the PCR cycle (Regeneration), ATP from the lightdependent reactions is
consumed in order to convert G3P molecules (through several pathways of other molecules) into ribulose
1,5 – biphosphate.
For every 3 turns of the PCR cycle, only 1 G3P molecule actually goes to become sugars, the rest are
used to make three molecules of RuBP.
Key Actions of PCR
Rib1,5 + 3CO2 + 3H20 ▯ 2(3PGA)
3PGA + 6ATP + 6 NADPH ▯ G3P
Rubisco acting as an oxygenase Lecture 6: Metabolism 1 : Photosynthesis: Sept 26
Consumes ATP and NADPH
Net loss of previously fixed carbon
This is more likely to occur at low2CO concentrations or high temperatures.
While Rubisco is the most abundant protein on earth, isn’t efficient today because..
evolved 3.5 bya
low oxygen environment
oxygenation wasn’t a trait selected against
There is little variation in Rubisco O2 binding among higher plants
Most variation in photosynthesis efficiency in the plant arises from changes in CO2 concentrating
I.e Easier to increase CO2 than make a new rubisco
C4 and CAM Photo
CO2 concentrating Mechanisms
Seperates initial CO2 fixation using from the PCR cycle and Rubisco.
C4 uses spatial separation
CAM uses temporal separation
By concentrating CO2 around rubisco, photorespiration is reduced
Highly efficient and very productive
Uses nitrogen and water efficiently
More heat tolerant than normal C3 photosynthesis
1) Co2 fixed by PEPcase
2) C4 acid is pumped into the bundle sheath
3) C4 acid is decarboxylated releasing CO2
4)pyruvate diffuses back
5) Pyruvate reconverted into PEP Lecture 7: Metabolism 2: Plasticity Oct 1
Homeostasis: Lecture 7: Metabolism 2: Plasticity Oct 1
Homeostasis can be defined in a variety of ways.
In terms of animals, homeostasis is the internal constancy and the physiological regulatory systems that
automatically make adjustments to maintain it.
In terms of plants, homeostasis is the condition of a relatively stable internal physiological environment,
usually involving extensive feedback mechanisms.
Homeostasis works by having bodily sensors constantly monitoring body temperature with reference to a
set point (the standard for body temperature), working almost exclusively as a household thermostat.
Negative & Positive Feedback:
Homeostasis of body temperature is an excellent example of a negative feedback loop where the
process works to return the value to the set point.
When body temperature is too hot, there is an attempt at increasing heat loss (such as vasodilation and
sweating) in order to cool the body towards the set point.
When body temperature is too cold, there is an attempt at decreasing heat loss (vasoconstriction) and
increasing heat production in order to heat the body towards the set point.
Positive feedback loops result in an amplification of the deviation from the set point and are a rare
occurrence in biology.
In examining the ice albedo effect, there is evidence of a positive feedback loop as the low albedo of the
surrounding soil absorbs the progressively warmer effects of climate change and continuously melts the
Control In Homeostasis:
Homeostasis is present at many levels of control in the body:
Hormonal Lecture 7: Metabolism 2: Plasticity Oct 1
Insulin and glucagon regulating mammalian blood sugar
Cellsignalling pathways that regulate cytoplasm composition
Vasoconstriction and dilation regulating heat loss in vertebrates
Maintaining rates of reactions by altering pathways and enzymes
Compensation maintains an organism’s physiological performance in the face of varying conditions.
Compensation requires a shift away from the acute response.
Some species of ectotherms settle for no compensation and thus, their body temperature is dictated by
In comparing polar fish and temperate fish, we see that polar fish have a very narrow temperature range for
optimal enzyme function, while temperate fish have a much more stable temperature range for proper
After compensation, the rate of metabolism of a given organism will be lower than normal and graphically
expressed as a less steep (smaller slope) curve.
This is seen in the compensatory response of warmgrown vs. coolgrown black spruce as the warmgrown
trees have a lower rate of metabolism than the cool grown. This downregulation of warmgrown trees is
Origin Of Acute Perturbations: Lecture 7: Metabolism 2: Plasticity Oct 1
Acute distresses may come from mismatches in biochemical pathways.
This is seen with the rates of pumping in vs. the rates of diffusing out ions
As well as with the rates of production vs. the use of reducing equivalents (temperature effects on
In the electron transport chain of photosynthesis there are three main types of processes in relation to
Fast physical processes that are largely temperature independent (very fast absorbance of light),
Diffusions that are a bit temperaturedependent (electron shuttling)
Enzymecatalyzed processes, which are quite temperaturedependent (NADP reduction and +
Also, the lightdriven reactions of photosynthesis are less temperaturedependent
Carbon reactions are more temperature dependant; since the Calvin cycle is largely enzymatic.
The Effects Of Light Intensity & Decreased Temperature:
Under increased light intensity, more reducing equivalents are produced in the lightdriven reactions than
are consumed in the stroma and there is also potential buildup of ROS.
Although there is an increase in the output of the electron transport chain, there appears to be no change
in the Calvin cycle.
Decreased temperature tends to have the same effect
The enzymatic Calvin cycle slows down
This allows for the similar buildup of ROS and excess of reducing equivalents in the ETC. Lecture 7: Metabolism 2: Plasticity Oct 1
Acute & LongTerm Responses To Temperature:
Acute response to temperature include the increase production of ROS and decreased phosphate
availability (ATP specifically) as the phosphate is locked up in phosphorylated intermediates.
Longterm responses to temperature include
Either decreasing the rate of light harvesting or increasing the capacity of the Calvin cycle.
Methods Of Compensation In An Organism:
Compensation can work in two ways:
Either by changing the enzymes involved in a pathway
Changing the enzyme’s environment,
Changing the pathways themselves
Have the pathway proceed in a different direction.
Enhancing The Activity Of Enzymes: Lecture 7: Metabolism 2: Plasticity Oct 1
Changing the activity of an enzyme will alter the rate of that enzyme’s reaction.
Abundance of enzyme
In temperate fish, isozymes (two different enzymes, same function) are used to compensate for
fluctuations in temperature their preserving their respective affinities and thus, their function.
Changing the activity of an enzyme will alter the rate of reaction
phosphorylation of an enzyme can activate it, change its conformation, or alter activity
The process is mediated by protein kinases.
We can also change the enzyme’s environment (either lipid environment, pH or substrate availability) in
order to induce more activity within an enzyme.
Phospholipid Membrane Changes & Compensation:
Phospholipid membrane changes contribute to compensation by way of homeoviscous adaptation
Maintaining the same viscosity across temperatures
This is accomplished by:
shortening chain length
Incorporating double bonds
Changing head groups Lecture 7: Metabolism 2: Plasticity Oct 1
All of which increases membrane fluidity.
The membrane environment also affects transmembrane function as well.
The modification of pathways can be achieved by:
Changing the direction or rate of the reaction
Turning pathways on or off
Using different pathways.
For example, when energy supplies are low, glycolysis is favoured, but when energy supplies are high,
gluconeogenesis is favoured.
Reactions can be reversed simply by manipulating the balance of substrates, or by employing different
enzymes for the forward and reverse pathways of each reaction.
Instead of pathway modification, plants use a completely different pathway to compensate to
An example of this is cyanideinsensitive respiration
Where some plants can actually salvage some of the products of mitochondrial respiration via alternative