Organismal Physiology Lecture No.1: Temperature I
Tuesday September 11 , 2012
-Human beings are one of the few organisms that inhabit environments that encompass both
temperature extremes. Accomplishing a feat most organisms cannot, they are able to do this through
the production of suitable shelters, tools, cultures, etc.
-Other life forms usually preside in one extreme environment, like penguins in the Antarctic and Baobab
trees in the African savannah, and find more primitive solutions to surviving under such conditions.
-Temperature is defined as the measure of the speed or intensity of the incessant random motions that
all the atoms and molecules of any substance undergo on an atomic/molecular scale. More exactly, the
temperature of a substance is proportional to the product of the mean-square-speed of the random
molecular motions and the molecular mass.
Distinction Between Temperature & Heat:
-While temperature is the intensity of motion by the atoms vibrating in an object, heat can be defined as
the amount of energy present in an object. It is temperature that determines the direction of heat
(energy) transfer, which is always from warmer to cooler conditions.
The Energy Balance Equation:
-Energy balance can be calculated according to the following equation: R (radiation) + H (convection) + C
(conduction) + M (metabolism) + L (latent heat) = 0. When the sum of these factors is zero, the energy
content of the organism is balanced; it is neither gaining nor losing energy.
-Radiation energy can impact organisms directly (either from the sun or the atmosphere), indirectly (by
reflecting off of other organism and their environment), or it can be emitted by the organism itself.
Convection describes the movement of heat energy through fluid mediums (e.g. wind chill), while
conduction describes the transfer of energy through solid mediums (e.g. hot rocks, soils).
-Metabolic heat production is determined by the amount of O cons2mption and is coupled with latent
heat, the amount of water evaporation or condensation present in an organism (either through
breathing or off the surface of skin).
Common Biological Temperatures:
-(-80°C) – hardened conifer leaves still survive. (-0.6°C) – melting point of ‘normal’ physiological fluids.
-(15°C) – developmental threshold for many plants. (37°C) – body temperature of most mammals.
-(53.6°C) – highest recorded temperature of a metazoan. (50-70°C) – most proteins denatured. Classifications Of Thermal Biology:
-Endotherms – generate internal heat.
-Ectotherms – rely on external temperatures to determine body temperature
-Homeotherms – defend a constant body temperature
-Poikotherms – Allow body temperature to vary.
-Heterotherms – have more than one temperature set point, or switch between homeo/poikothermy.
-Regional endothermy/heterothermy – Different body temperatures in different parts of the body.
-As oxygen consumption corresponds to metabolic activity, metabolism can be calculated according to
n (constant) x T (body temperature)
the following equation: M (metabolic rate) = a (constant) x 10 b
-Logarithmically, the equation can be modified to a linear form (y = mx + b): log(M) = nT + log(ab
The Temperature Coefficient:
-Q 10also known as the temperature coefficient, is the ratio of the rate of a process at one temperature
over the rate of the same process at a temperature 10°C lower. In other words, Q calculate10how much
the rate of metabolism changes for every 10°C drop in temperature.
-A formula for this concept would look as follows:
Q 10R (rTte of metabolism at temperature x) / R (T-10)ate of metabolism at temperature x - 10)
-Because the temperature metabolic rate relationship is not exactly exponential, the impact of a change
of temperature varies with temperature; Q is not constant. The same relationship with Q holds true
for plant functions like respiration.
-If Q10s approximately equal to 1, a physical or chemical process is taking place. If Q is ap10oximately
in between 2 and 3, a biological process is taking place.
Cause Of Temperature Changes:
-Temperature determines moti