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Organismal Physiology Lecture No. 3.docx

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Biology 2601A/B
Tamsen Taylor

Organismal Physiology Lecture No. 3: Thermoregulation In Ectotherms th Tuesday September 18 , 2012 RECALL: -An ectotherm does not generate internal heat and a poikilotherm has its body temperature determined by equilibration with the thermal conditions of the environment. Ectotherms: -How on Earth does an organism not producing heat manage to temperature changes within its environment? From the moderate conditions of tropical regions to the extreme conditions of dry deserts, are ectotherms merely the passive victims of their thermal environment? We will explore ways in which this statement is irrelevant. Plants Affecting Leaf Temperature (Leaf Colour): -Encelia farinosa is a species of plant that grows in extremely hot, arid environments and therefore must be white to increase its albedo (the capacity to reflect solar radiation). The black pearl pepper on the other hand, absorbs far more radiation because of its low albedo. In general, leaf colour alters provides a long-term adaptive response to altering the amount of solar radiation absorbed by a plant. Most plants don’t change their colour and utilize short term strategies for maintaining body temperature. Plants Affecting Temperature (Convection): -With regards to convection (the heat exchange with air molecules that brings organisms closer to air temperature), plants will often manipulate the shape of their leaves in order to exploit convection currents for their benefit. -In the case of the Northern Red Oak, it possesses sun leaves (more exposed to sunlight) that are small and have less surface area, which reduces the amount of exposure to the sun and wind (air molecules skim off the edge and cool the leaf down). A shade leaf is large, with greater surface area, which increases the amount of area exposed to the sun (as plants need the proper balance of sunlight). Plants Affecting Temperature (Evapotranspiration): - Evapotranspiration is the movement of water from the roots to the leaves of the tree with the eventual loss of water through the stomata of the leaves. For a plant with water readily available, this is an extremely effective way of dissipating heat. Under hot conditions, water transpiring from the plant’s stomata cools it down considerably (as water’s latent heat of vaporisation is 2270 kJ/kg). Under cooler temperatures, the plant’s stomata are tightly closed to preserve water. As a result of transpiration, some desert plants are at much cooler temperatures than the environment would usually allow. Behavioural Thermoregulation In Plants & Animals: -Organisms may engage in certain behaviour to adjust the thermal settings of their environment. For example, when corn plants are under extreme drought stress they will roll their leaves up (pointing them vertically towards the sky) so that less sun makes contact with their leaves, saving water. These behaviours are quite common among ectothermic animals such as lizard species that will often bask in the sun to regulate their metabolism. Ectothermic Metabolism: -The minor amount of heat that comes from ectotherms derives from futile cycles of cellular respiration (in plants) and from involuntary muscle contractions (in animals). Endothermy In The Skunk Cabbage: -The spadix is a physiological appendage common to certain plants (like the skunk cabbage and other endothermic plants) which is notable as the site for considerable thermoregulation. The skunk cabbage in particular exploits the ability of the spadix to generate heat in order to melt the surrounding ice and commence growth in early spring. Metabolism is however, an extremely energetically costly process. Importance of Metabolic Heat To Plants: -Thermoregulation is important to plants as it provides protection against col
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