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24-1Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Chapter 24: Metabolism, temperature regulation and environmental stress
Energy requirements and metabolism• Energy is required to perform work• The rate of energy use for internal and external
work is known as metabolic rate. It is expressed as energy expenditure per unit time
• Aerobic metabolism requires the availability of oxygen
• Anaerobic metabolism involves the release of chemical energy without the use of oxygen
• Most animals utilise aerobic metabolism most of the time due to its greater efficiency
24-2Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Factors affecting metabolic rate• Body mass• Activity• Digestive state
24-3Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Body temperature• The rates of many physiological processes are
determined by temperature• Temperature is a critical determinant of the rate of
metabolism• Animals either thermoconform or thermoregulate;
both require body temperature to be kept in optimal range for physiological functions, but this is achieved by different methods
• Animals exchange heat with their environment through conduction, convection, radiation and evaporation/condensation
24-4Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Fig. 24.2: Heat exchange
24-5Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
24-6Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Stresses of low temperatures• Mountain and polar regions are characterised by
– low temperatures– increased solar radiation
• Animals of cold regions are more tolerant of low temperatures than other animals
• Ice formation damages cells by concentrating cytoplasm and dehydrating proteins
24-7Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Do animals freeze?• Animals in areas that experience low temperatures
may– avoid freezing by supercooling– tolerate freezing
• During supercooling, the temperature may drop below 0°C, but ice does not form in the animal’s tissues– body is evacuated of material that might seed ice
formation– they produce antifreeze that prevents ice formation
and/or lowers freezing point
24-8Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Insects at low temperatures• Insect species that live at high altitudes tend to be
small and wingless– able to make use of sheltered microhabitats
• Many species exhibit thermal melanism– dark coloration absorbs heat
• Basking in the sun increases body temperature– some insects bask on light-coloured flowers that reflect
heat
24-9Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Temperature coefficient (Q10)
• Biochemical processes take place within a range of temperatures– rate of activity increases with temperature
• Temperature coefficient, Q10, models the rate of reaction for a 10°C rise in temperature
• Quantifies effect of temperature on biochemical processes
1010
T
T
R
RQ
24-10Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Fig. 24.4: Relationship between processes and temperature
24-11Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Patterns of body temperature regulation• Endothermic animals (birds, mammals) maintain a
constant body temperature by deriving heat from internal or metabolic processes
• Ectothermic animals cannot regulate body temperature through those processes, but can reduce fluctuations in body temperature by adjusting behaviour
24-12Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Phenotypic plasticity• Some organisms can modify phenotype to
accommodate changes in environment– phenotypic plasticity
• Such changes are categorised as– acclimatisation: accommodating several changes in
environment– acclimation: accommodating one change in environment– hardening: acclimation in plants
24-13Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Thermal acclimation• Although metabolic processes in ectothermic
animals tend to increase with temperature, thermal acclimation means that metabolic rate may change between seasons– cold-water fish may have a higher metabolic rate in
winter than they do in summer
• Seasonal metabolic compensation– different sets of summer and winter enzymes with
different optimal temperatures– animals may be more active in winter than summer,
despite lower temperature
24-14Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Metabolic depression• Facing extreme conditions, many animals undergo
a reduction in metabolic rate (metabolic depression)
• Some organisms can reduce metabolic rate to less than 1% of normal resting metabolic rate
• Animals survive by dehydrating as larvae or adults, or becoming inactive
24-15Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Hypothermia and torpor• Endothermic animals undergo
– prolonged hibernation during winter– prolonged aestivation in dry conditions– shorter periods of torpor
• Body temperature is reset to a lower level– hypothermia– metabolic processes drop as a result– decreased responsiveness to stimuli
24-16Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Risks of torpor• Freezing
– use of cryoprotectants such as glucose to prevent freezing
• Lack of oxygen– many animals can tolerate anoxia
• Exhaustion of energy supply– breakdown of lipids using anaerobic pathways to avoid
using O2
• Desiccation
24-17Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Torpor• Many small mammals and some birds reduce
metabolic rate and enter torpor in response to low temperatures
• Body temperature is regulated during torpor– if it drops too far, animal becomes active for a period
before re-entering torpor
• Blood flow to skin and extremities is reduced during torpor
24-18Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Fig. 24.13: Rate of O2 consumption in dunnart
24-19Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Oxygen stress
• Hypoxia is a decrease in partial pressure of O2 from normal levels
• Occurs when rate of O2 consumption exceeds replenishment– caves, burrows– swamps, water-logged soil– tide pools
• Occurs at high altitudes where PO2 is low
Fig. 24.16: Burrow ventilation
24-20Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
24-21Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Adaptations to low oxygen
• Low environmental PO2 reduces the gradient
essential for diffusion of O2 across membranes
• Physiological and behavioural characteristics compensate for low PO2
– tolerance to anoxia– haemoglobin– high erythrocyte counts
– low rates of O2 consumption
– burrow ventilation
24-22Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Animals at high altitude• Lower partial pressure of oxygen in high altitudes
produces altitude hypoxia• Hyperventilation is a response to low PO2
– increases O2 content
• Hyperventilation also eliminates CO2 from body, causing high blood pH
• Erythrocyte count may increase as a result of acclimation– higher levels of haemoglobin
Question 1:
High-altitude training is a physiological method used to obtain an increase in haemoglobin. Why would this be referred to as blood doping? Are there any harmful effects?
24-23Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Fig. 24.15: Altitudinal elevation
24-24Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
24-25Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Oxygen stress (cont.)• When faced with a thermal gradient, animals have
a preferred temperature– behavioural thermoregulation
• When exposed to hypoxia, animals choose a lower temperature– hypoxia depresses thermogenesis (metabolic heat
production) in endotherms– set point of body temperature lowered
24-26Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Oxygen stress (cont.)• Reduced temperature decreases metabolic rate
(Q10 effect)
• Decreased requirement for O2
• Reduction in temperature increases O2 affinity of haemoglobin
• Hyperventilation and increased cardiac output are avoided
24-27Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Oxygen stress (cont.)• Depression of thermogenesis in response to
hypoxia is more common in small animals than in large animals– large animals have a lower mass-specific metabolic rate,
so they use proportionately less O2 to maintain body temperature
– smaller surface area in relation to body volume means that large animals do not absorb or lose heat as rapidly
24-28Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
Global warming• Increase in temperature as a result of global
warming may stress less thermally-tolerant organisms– increased sea temperatures have a negative impact on
penguin species– migrations of some bird species start earlier in the year– breeding is brought forward or delayed– species’ ranges are extended or retracted
Summary• Aerobic metabolism requires oxygen and is the
most efficient form of metabolism• Body mass, activity and digestion are influencing
factors of metabolic rate• Body temperature is a critical determinant of
metabolic rate and other physiological processes• Animals exchange heat with their environment• Animals may reduce metabolic rate in response to
environmental stress
24-29Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University
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