24-1 copyright 2010 mcgraw-hill australia pty ltd powerpoint slides to accompany biology: an...

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


Factors affecting metabolic rate• Body mass• Activity• Digestive state


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


Fig. 24.2: Heat exchange



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


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


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


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


Fig. 24.4: Relationship between processes and temperature


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


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


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


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


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


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


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


Fig. 24.13: Rate of O2 consumption in dunnart


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



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


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?


Fig. 24.15: Altitudinal elevation



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


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


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


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


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