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Lecture 3

Lecture 3 - Temperature II - Plants and Ectotherms

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Biology 2601A/B
Graeme Taylor

LECTURE 3: TEMPERATURE II – PLANTS AND ECTOTHERMS Thermoregulation  Constant body temperature that is well above its ambient surroundings is maintained despite the water temperature surrounding the organism What if you are an Ectotherm?  Ectotherm – does not generate internal heat  Poikilotherm – an animal in which the body temperature is determined by equilibration with the thermal conditions in the environment  Are ectotherms passive victims of their thermal environments? No, they are not – will be discussed throughout lecture as to why this statement is irrelevant o Going with the flow is better in some places than others R + H + C + L + M = 0  R = radiation  C = conductance o Minimize (to cool) or maximize (to warm) o Not much of an issue for plants radiation absorption  L = latent heat exchange o Leaf color or leaf angle o Transpiration o Example – black t-shirt absorbs more o Has to do with how much water is lost heat, keeping your warm, whereas white through the stomata reflects heat, keeping you cool  M = metabolism  H = convection o Metabolic heat generation in some plants o Leaf shape Plants can Affect their Leaf Temperature  Leaf color alters radiation absorption  Long-term, adaptive response to altering the amount of solar radiation absorbed by plant o Encelia farinosa – species of plant that grows in hot, arid environment; white to increase its albedo (capacity to reflect solar radiation) o Black pearl pepper – absorbs far more radiation because of its low albedo Behavioral Thermoregulation  Minimizes amount of radiation hitting the surface, which minimizes the amount of energy gained, which keeps them cool – useful for plants under drought  Rolling leaves and pointing them vertically reduces sun interception, saving water  Lizards were found in their native habitat, and their body temperature ranged from 30-40°C  To maintain body temperature, on average, the lizards choose specific areas Plants can affect their Leaf Temperature  Shape affects convection – heat exchange with air molecules that brings organisms closer to air temperature  As wind is passing over leaf’s surface, kinetic energy is transferred o Middle of the leaf’s surface is warmer, however, cause convection is less effective in comparison to the edges of the leaf’s surface  When radiation is high, there is more heat to dissipate o e.g. sun leaves – small and have less surface, which reduces the amount of exposure to the sun and wind (air molecules skim off the edge and cool the leaf down)  No need to actively cool as radiation is low, less heat to dissipate – e.g. shade leaves (bigger in size, so there is an ecological advantage in comparison to sun leaves)  Evapotranspiration – 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  Latent heat of vaporization of water = 2270 kJ/kg  Transpiration is a very effective way to cool if you have water  Under cool temperatures, the plant’s stomata are tightly closed to preserve water What about Metabolism?  Where does ectotherm heat come from? o Futile cycling in plants o Muscle contractions in animals Why do Plants need Metabolic Heat?  Provides protection against cold temperatures and helps warm up tissues to a more optimal physiological temperature  To attract pollinators in early spring: o Increase odor diffusion which is favored by ectothermic pollinators o Provide warmth for ectothermic pollinators Thermogenesis in the Aroid Spadix  Generation of internal heat in the spad
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