Lecture 3 Energetics: Background (Chap 3 and 22 book)

Wednesday Chap 3 (book notes)
Temperature limits and occurrence of life
Sun provides warmth and energy

  • tolerable temps 1-100 degrees Celsius

Heat and Biological molecules

  • heat > kinetic energy > molecules move faster
  • heat accelerates chemical reactions
  • for every 10 degrees Celsius biological processes quicken by 2x or 4x

Q10 -ratio of rate of a physiological process @ one temperature to it's rate @ a temp 10 degrees Celsius or cooler.

  • in higher temperatures things develop more rapidly

metabolic theory of ecology- temperature has consistent effects on a multitude of important ecological processes

  • proteins become less stable in higher temperatures

Thermophilic- heat loving bacteria with strong protein bonds

Cold Temperatures and Freezing

  • marine vertebrates can freeze in cold water (the blood and body tissues of vertebrates have less than 1/2 the salt content of seawater, and freeze at a higher temperature, that's why Jack froze to death in Titanic…kinda)

Organisms and Temperatures

  • all organisms are particularly adapted to function with in certain limits.

Heat/Gain Loss

  • solar radiation reach the earth (most) absorbed by H2O, plants and animals
  • each object on earth continually exchanges heat with it's surroundings.

radiation- the emission of electromagnetic energy by a warm surface, which may then be absorbed by any cooler surface (sources: sun, sky, landscape).
conduction- transfer of kinetic energy of heat by two things in contact with one another
convection- transfer of heat by movement of liquids and gases.
wind chill factor- wind steals heat.

Global warming- with global warming temperatures will increase in boreal forests and tundra areas, not in already humid climates.

heat budget- gains and losses of heat by an organism
change in heat content = metabolism - evaporation +/- radiation +/- conduction +/- convection

Calculating heat budgets provides insight into the conditions that allow survival of an organism as well as what adaptations it may make to survive under other conditions:

  • Since plants cannot readily move to another location to avoid harsh levels of heat, humidity, or water availability, plants may cope by altering leaf sizes, shapes, or orientations to control radiation, evaporation, and convection.
  • An animal may vary its metabolic rate (warm-blooded) or body temperature (cold-blooded) to remain in its "climate space", referred to as the "comfort zone" for humans. Levels of radiation and convection may be altered by controlling blood flow to surface regions and extremities, sweating, or fluffing one's fur/hair or feathers. Some birds (e.g., flamingos, penguins) have specialized "heat exchanger" mechanisms to transfer heat to and from their surroundings.

[Source: Environmental Physics, Clare Smith, chapter 3]

Larger organisms have less surface area to bulk tissue ratio than smaller animals
S = surface V = cube of length L= Length

(someone should insert the equation from the book here, cause I don't know how)

  • thermal inertia- the fact that larger organisms loose heat across their surface area less rapidly than smaller organisms.
  • larger size and lower surface area:volume area allows organisms to better maintain their internal environment (: = ratio).

Homethermy Increase metabolic rate and efficiency
• Homeostasis - organisms ability to maintain constant internal conditions in the face of varying external environment.
• All organisms exhibit homeostasis , although occurrence and effectiveness vary
• Negative feedback - exhibited by all homeostatic systems and is when internal mechanisms act to restore the system when it deviates from its desired state, or set point. (example is thermometer in home to regulate temperature)
• Homethermy is the regulation of temperature within cells, under which biochemical processes can proceed efficiently
• Ectoterms - organisms that use heat from outside of their body to elevate their temperatures (reptiles, amphibians)
• Endotherms - organisms that generate sufficient heat metabolically to raise their body temperatures.
• Homeostasis requires energy when a gradient between internal and external conditions must be maintained. Endotherms must generate heat metabolically to balance loss of heat to cooler surroundings
• Organisms employ mechanisms to control heat loss.
§ Countercurrent circulation - blood flowing from the body toward the extremities encounters blood returning to the body, thus transferring heat from arterial to venous blood. The extremities are kept cooler then rest of body , minimizing heat transfer to environment.

Chapter 22

Ecosystem functions
Lotka: systems and energy/material transformation rates obey thermodynamic principles in proportion to their size and efficiency
Lindeman: trophic levels (food chain) and pyramid of energy (less energy reaches higher trophic levels)
Ecosystem ecology: concerns matter cycling and energy passage through ecosystem—major energy flow measurements from Odum
Primary production: capturing energy from light and transforming it into chemical energy, in plants, algae, and some bacteria

  • only small fraction of solar radiation absorbed
  • photosynthesis pigments absorb little light energy (1/3 at most), and lose the rest as heat

Gross Primary Production: total energy assimilated through photosynthesis
Net Primary production: assimilated energy minus energy lost through respiration
Units of productivity: kilojoules per meter squared per year or Watts per meter squared

Influences on Primary production
Light and Temperature

Solar constant: intensity of solar radiation at outer limit of atmosphere
Compensation point: light intensity level where photosynthesis assimilation= respiration
Saturation point: intensity level above which photosynthesis no longer responds to light
Photosynthetic efficiency: % of energy in sunlight converted to NPP in growing season—the rest of the light is respired, reflected, or released as heat


Water transpires during energy conversion and is released through stomata opened to take in CO2.
Water Use Efficiency: grams of dry matter (NPP)/kg water transpired


Include phosphorus (for ATP), nitrogen, potassium, calcium, and others
Nutrient use efficiency: dry matter production/grams of nutrients

Primary production varies among land and water ecosystems

Trophic levels only produce 5-20% of energy than level below it
Ecological efficiency: percentage of energy use for each member of the food chain
Egested energy: energy in indigestible components of food (hair, feathers, exoskeletons, cartilage, bone) that is defecated or regurgitated
Assimilated energy: energy in food digested and absorbed
Respired energy: energy used in metabolic needs, mostly released as heat
Excreted energy: energy in nitrogen-excess excrement
Assimilation efficiency: percentage of ingested energy that is assimilated
Stoichiometry: study of balance of intakes and outputs of matter, energy, etc.
Net production efficiency: amount of assimilated energy channeled into growth and reproduction
Some life forms are adapted to consume detritus (remains of plants and indigestible plant matter in excrement)
Residence time: amount of energy stored at each trophic level, the inverse of energy transfer rate: energy stored in biomass (kJ/m2)/net productivity (kJ/m2/year)
Biomass accumulation ratio: same as residence time, only replace energy with biomass
Net Ecosystem Production: balance of carbon gain and loss in ecosystems

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License