1 / 18

Temperature

Temperature. Chapter 8. Temperature. Average kinetic energy of a system Arguably the most important aspect of the physical environment for life Influences geographic distributions of species Influences interspecific competition. Temperature Ranges. For most living, active animals:

marcel
Download Presentation

Temperature

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Temperature Chapter 8

  2. Temperature • Average kinetic energy of a system • Arguably the most important aspect of the physical environment for life • Influences geographic distributions of species • Influences interspecific competition

  3. Temperature Ranges • For most living, active animals: • -2 °C (polar aquatic species) to 50 ° C (desert spp.) • Few species can survive entire range

  4. Terminology of Thermal Biology • Various terms used to describe thermal biology of animals: • Cold-blooded vs. Warm-blooded • Poikilothermic vs Homeothermic • Ectothermic vs. Endothermic

  5. Cold-blooded vs. Warm-blooded • Description of relative body temperature • “Warm-blooded” = high body temperature • Mammals and birds • “Cold-blooded” = low body temperature • Reptiles, amphibians, fish, invertebrates • Tend to be inaccurate • Many “cold-blooded” animals have high body temperatures (e.g. desert reptiles and invertebrates) • Many “warm-blooded” animals may have low body temperatures (e.g. hibernating mammals)

  6. Homeothermic vs. Poikilothermic • Description of variation in body temperature • Homeothermic – body temp. strictly regulated • Mammals and birds • Poikilothermic – body temp. may fluctuate widely • “Lower” vertebrates and invertebrates • Problems • Many “poikilotherms” normally have stable body temperatures under natural conditions • Some “homeotherms” have broad seasonal changes in body temperature (hibernation, etc.)

  7. Endothermic vs. Ectothermic • Description of heat production • Endothermic – most body heat is physiologically generated (muscle contraction) • Ectothermic – most body heat derived from the environment (solar radiation, etc.) • Problems • Some animals generate lots of heat but do not use it to regulate body temperature

  8. Determinants of Body Temperature • Temperature depends on the amount of heat (calories) contained per unit mass tissue • # calories contained per °C determined by the heat capacity of the tissues (~ 0.8 cal*°C-1*g-1) • Amount of heat in body depends on… • Rate of heat production • Rate of external heat gain • Rate of heat loss to the environment • Body heat = heat produced + heat transferred

  9. Heat Transfer Three ways of transferring heat • Conduction – transfer of heat between objects in contact with one another • Radiation – transfer of heat by electromagnetic radiation • Evaporation – transfer of heat to water as it changes from liquid to gaseous phase Fig 8.3

  10. Conduction • Transfer of kinetic energy between two objects in contact • Heat moves from warmer region to cooler region • Rate of transfer: • H = rate of heat transfer per cross sectional area • k = thermal conductivity of the conductor • d = distance between two points • T1 and T2 = temperature at points 1 and 2

  11. Conduction and Convection • Conduction rate is increased by convection • Movement of gas or liquid over the surface of transfer • Continuous replacement of fluid maximizes temperature difference and facilitates heat transfer

  12. Radiation • Transfer of heat via electromagnetic emission • Objects do not require contact • Stefan-Boltzmann law: H = εσTs4 • H = rate of heat exchange per unit area • ε = emissivity (wavelengths at which EM radiation is emitted,~3-4 μm for most objects on earth) • σ = Stefan-Boltzmann constant • Ts = surface temperature of the object • Net heat exchange is from the object with the higher Ts to the one with the lower Ts

  13. Evaporation • Only means by which heat can be lost to a hot environment • Vaporization of water requires heat • ~ 2400 kJ per g water absorbed from the surface of the animal • Evaporative cooling used to dissipate heat • Sweating, panting

  14. Heat Storage • Animals can store heat in their bodies by moderating heat transfer to the environment • Factors Affecting Heat Transfer • Surface Area/Volume Ratio • Larger animals have proportionately lower heat flux • Temperature Gradient • Between body and environment • Lower gradient, slower heat transfer • Specific Heat Conductance • Insulation – reduces heat conductance

  15. Total Body Heat Htotal = Hv + Hc + Hr + He + Hs Hv = heat produced by metabolism (+) Hc = heat loss/gain by conduction and convection (+/-) Hr = heat transfer via radiation (+/-) He = heat loss by evaporation (-) Hs = stored heat (+)

  16. Effects of Body Temperature Change • Temperature affects the rate of chemical reactions • Affects chemical reactions needed to maintain homeostasis • Too low • metabolism not fast enough to maintain homeostasis • Too high • reactions in metabolic pathways uncouple, enzymes denature, etc.

  17. Changes in Metabolism with Body Temperature • Temperature Coefficient (Q10) – factorial increase in a rate with a 10 °C increase in temperature Q10 = (R2/R1) 10/T2-T1 • R2 and R1 • reaction rates at temperatures T2 and T1 respectively • If T2 and T1 differ by 10 °C, Q10 = (R2/R1) • Typical Q10 values for biological rates (metabolic rate, etc) range from 2 to 3 (doubling or tripling of rate)

  18. Changes in Metabolism with Temperature • Q10 values often change across a range of temperatures • Performance curves • Initial large increase, followed by smaller increases

More Related