ANSWERS TO REVIEW QUESTIONS – CHAPTER 24
1. Differentiate between aerobic and anaerobic metabolism. (p. 558)
These concepts were first introduced in Chapter 3. Aerobic metabolism involves the release of
chemical energy in reactions consuming oxygen, whereas anaerobic metabolism uses reactions that do
not consume oxygen.
2.
What factors affect metabolic rate? Describe the effects of each of these factors. (pp. 558–
560 Figure 24.1)
Body mass–Larger animals have a higher absolute metabolic rate than smaller animals.
Activity–Metabolic rates are lowest in inactive animals (basal metabolic rate), but then rise with
different levels of activity to a maximum level five to ten times the basal metabolic rate.
Digestive state–Metabolic rate increases during digestion at a rate proportional to the amount of food
and inversely proportional with the ease of digestion.
3.
How can burrowing, diving and high altitude animals overcome the problems associated
with anoxic conditions? (pp. 568–571 Figures 24.15–24.17)
During most dives, well-adapted divers take enough O2 to provide the needs of their tissues. However,
there is the potential for unexpectedly long dives if the animal is pursued by a predator, has difficulty in
dealing with prey or is unable to regain access to the atmosphere. Under these circumstances there is a
high risk of damage to vital organs, particularly the heart and brain, which are sensitive to low levels of
O2. Diving animals have a complex cardiovascular mechanism, the diving response, which can be
invoked to reserve O2 for sensitive organs. The advantage of the diving response is that it maintains
circulation to the heart, brain and lungs but limits circulation to all other organs. This allows the animal
to survive dives that are unexpectedly long, a risk that is possible with every dive that an animal takes.
The diving response is best developed in diving mammals such as whales and dolphins, and also in
diving birds like penguins and shearwaters.
The initial physiological reaction in the diving response is bradycardia, an intense slowing of the heart.
In conjunction with bradycardia, vasoconstriction of the major peripheral arteries slows or stops blood
flow to the muscles, skin and visceral organs. This reduced blood flow is called ischaemia and results
in depleted O2 in the peripheral tissues. The lactic acid that accumulates in the O 2-depleted organs does
not enter the blood due to the restricted flow. O2 supply to the heart, lungs and brain is maintained by a
constant, or slightly elevated, central blood pressure.
The diving response places the animal under physiological stress. It takes several minutes to flush out
the accumulated lactic acid after the dive and the diving response is not invoked in any immediate
subsequent dives.
The initial short-term effect of exposure to low O2 pressures at high altitude is an increase in both the
heart and respiration rates. Acute responses, known as altitude sickness or sorroche, occur with rapid
accents to high altitude. These include hyperventilation, which may have deleterious effects on blood
pH due to a fall in the partial pressure of CO 2 in the lung. A redistribution of body fluids can cause
pulmonary or cerebral swelling (oedema), which may be fatal if the affected individual remains at the
high altitude.
Long-term effects, such as increases in capillaries and a decrease in the ventilatory response, reverse
many of the short-term effects. Other long-term effects include a lower fertility and a higher rate of in
utero mortality in people living at high altitude, particularly immigrants.
4.
What are the physiological changes that occur in response to high altitude? (p. 570 Figure
24.15)
As altitude increases, the atmospheric pressure of O2 decreases by about one-half every 5500 m. This
decreases the total amount of O2 for gas exchange since the O2 partial pressure gradient between the air
and the body’s delivery system is reduced, which decreases the rate of diffusion. For athletes training at
high altitude there is an advantage since the body’s response to the lower partial pressure of O2 is an
increased production of red blood cells and eventually an increase in the number of capillaries in some
tissues. These physiological responses increase the body’s efficiency in obtaining and distributing O 2,
which assists the athlete in their capacity to perform at lower altitudes.
The initial short-term effect of exposure to low O2 pressures at high altitude is an increase in both the
heart and respiration rates. Acute responses, known as altitude sickness or sorroche, occur with rapid
accents to high altitude. These include hyperventilation, which may have deleterious effects on blood
pH due to a fall in the partial pressure of CO 2 in the lung. A redistribution of body fluids can cause
pulmonary or cerebral swelling (oedema), which may be fatal if the affected individual remains at the
high altitude.
Long-term effects, such as increases in capillaries and a decrease in the ventilatory response, reverse
many of the short-term effects. Other long-term effects include a lower fertility and a higher rate of in
utero mortality in people living at high altitude, particularly immigrants.
5.
What is metabolic depression? Provide examples of some species that metabolically depress
in response to environmental stress. (pp. 566–567 Table 24.1)
Metabolic depression is a reduction in metabolic rate in response to environmental stress, such as
extremes in temperature, low O2 levels or starvation. There is a comprehensive list of examples in
Table 24.1.
6.
Describe the Q10 effect and explain why it is important in the physiological functioning of
animals. (p. 561 Figure 24.4)
The rates of most chemical reactions are temperature dependent, and the rate of both physical and
chemical processes increases. This thermal dependence is because higher temperatures increase the
kinetic energy of molecules, and so the probability of reactant molecules colliding with sufficient
energy to react with one another increases. The temperature coefficient, or Q 10, quantifies this
temperature effect; it is defined as the increase in the rate of a physiological process or reaction for a
10°C rise in temperature. Q10 is calculated by dividing the rate at a certain temperature (RT) by that at a
temperature 10°C lower (RT – 10).
Most biological reactions, such as metabolism, have a Q10 value between 2 and 3, whereas physical
processes, such as diffusion, have a Q10 value of about 1 (Fig. 24.4). Q10 is a useful concept because it
can be used to distinguish between physical and biological reactions and quantify the effect of
temperature on physiological processes, such as breathing and levels of metabolism in whole animals.
Deviations from the expected Q10 range may indicate that the system is no longer functioning properly
(e.g. that an enzyme is denaturing at high temperature) or factors other than temperature are influencing
reaction rates (e.g. metabolic depression).
7. Explain the four major avenues of heat exchange in animals. (pp. 560–561 Figure 24.2)
Conduction–the transfer of heat between two solid bodies in direct contact.
Convection–the transfer of heat from an object by the movement of a fluid such as air or water.
Radiation–the transfer of heat from a warmer to a cooler body via electromagnetic waves.
Evaporation/condensation–terrestrial animals may lose heat to the environment via evaporation of
water from a body surface.
8.
Discuss the basis for the difference in the relationship between metabolic rate and ambient
temperature between reptiles and mammals. (pp. 564–565 Figure: 24.12)
Mammals maintain a constant body temperature. The mammalian metabolic rate varies with increasing
ambient temperature. At low ambient temperatures mammals can increase their metabolic rate, which
also increases heat production. At warm temperatures (within the range of the mammals’ internal body
temperature) mammals maintain a constant metabolism. At high temperatures the mammalian
metabolic rate increases again.
Reptiles cannot regulate their body temperature. The metabolic rate of reptiles increases with
increasing temperature. Reptiles maintain constant body temperature during the day by behavioural
adjustments—for example, by orientating their body at various angles to the sun, by seeking out
microclimates such as tree branches or burrows with different temperatures, or by changing skin
colour.
9.
How may torpor reduce an animal’s energy expenditure during cold conditions? (pp. 567–
568 Figures 24.13–24.14)
Torpor results in substantial energetic savings, as there are no thermoregulatory costs if ambient
temperature is above the torpor set-point, and there are lower thermoregulatory costs if ambient
temperature is below the torpor set-point than for normothermic animals. The Q10 effect also reduces
metabolic rate as the body temperature is lower than normal of heat generated by active skeletal
muscle.