22-Agric-A1 Applied Plant, Animal or Human Physiology · May 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. 04-Agric-A1 Animal or Human Physiology, National Exams May 2017 — a three-hour closed-book examination; one of two approved calculator models (Casio or Sharp) is permitted. The rubric states that five (5) questions constitute a complete exam paper and that the first five questions appearing in the answer book are marked (worth 20 marks each, 100 marks total); all six (6) printed questions are worked here as a complete study resource.
Reference texts. M.K. Yousef (ed.), Stress Physiology in Livestock, Vol. I — Basic Principles, CRC Press (thermoregulation, thermoneutral zone, endotherm/ectotherm physiology, external stressors); J.A. DeShazer (ed.) and ASABE Standards (American Society of Agricultural and Biological Engineers), Livestock Energetics and Thermal Environmental Management (sensible heat production, metabolic body-size scaling, animal housing design); P. McDonald et al., Animal Nutrition, 7th ed. (gross/digestible/metabolizable/net energy, feed-energy partition); K. Schmidt-Nielsen, Animal Physiology: Adaptation and Environment, 5th ed. (Bergmann's rule, comparative thermal biology, calorimetry); R.L. Curtis, Environmental Management in Animal Agriculture, Iowa State University Press (animal housing microclimate).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Part (a) — predation on ectotherms shortly after dawn. Reptiles and amphibians are ectotherms: overnight, with no sun and no internal thermogenesis to speak of, their body temperature falls toward the (typically cool) ambient temperature. Because locomotor muscle contraction speed, nerve conduction velocity, and overall metabolic rate are all strongly temperature-dependent in an ectotherm (governed by the Arrhenius/Q10 relationship — enzyme-catalysed reaction rates roughly double for every 10°C rise), a reptile or amphibian that has cooled overnight is sluggish, slow to strike or flee, and has not yet basked long enough after sunrise to reach its preferred operating temperature. Endothermic mammals and birds, by contrast, hold their core temperature constant around the clock via internal thermogenesis, so their own locomotor performance at dawn is unimpaired. The dawn window is therefore a period of maximal performance asymmetry between predator and prey — the endothermic predator is at full capacity while the ectothermic prey is still thermally handicapped — which is exploited as an energetically cheap hunting opportunity.
Part (b) — large body size in cold-region endotherms (Bergmann's rule). Metabolic heat production scales with body mass roughly as M0.75 (volume-related), while the surface area available for heat loss scales roughly as M0.67 (area-related, since surface area ∝ length² and mass ∝ length³, so surface area ∝ mass2/3). Because the exponent for heat production is larger than the exponent for heat loss, the ratio of surface area to body mass (and hence heat loss per unit of heat produced) decreases as an animal gets bigger. A large-bodied endotherm such as a polar bear or a whale therefore loses proportionally less heat per kilogram of tissue than a small one, which is a substantial thermoregulatory advantage in a cold climate: for a given level of insulation (fur, blubber), the large animal can sustain a lower critical temperature and spend less of its metabolizable energy intake on cold-induced thermogenesis. This body-size–versus–climate pattern is known as Bergmann's rule, and the same surface-area logic underlies the companion pattern (Allen's rule) that cold-climate endotherms also tend to have shorter, more compact extremities (ears, limbs, tails) to further minimize surface area for heat loss.
