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chapter 3 - Chapter 3 Adaptation to Aquatic and Terrestrial...

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Chapter 3 - Adaptation to Aquatic and Terrestrial Environments Tuesday, November 06, 2007 12:47 AM Overview Basics The physical world both provides the context for life and constrains its existence. A world of environmental factors… o Resources: water, minerals and food items o Conditions: temperature and relative humidity Most factors have extremely wide ranges: o Each type of organism is typically adapted to a narrow range of each factor Overview - Regulations Organisms typically contrast with their external environments: o Internal conditions are maintained +/- constant o Fluxes of heat and substances must be regulated o But organisms are open systems… Resources must be acquired Wastes must be eliminated How do organisms accomplish this? Overview - Bottom Line It is important for us to understand the mechanisms organisms use to interact with their environment. This understanding may lead to insights: o Why organisms are specialized o Why organisms have specific geographic distributions o Why certain adaptations are associated with certain environments What do organisms have to deal with? We examine adaptations by considering various challenges facing organisms, for example: o How do pants acquire water and nutrients from soils and transport these? o How do plants carry out photosynthesis under varied environmental conditions? o How do plants and animals cope with extremes of temperature, water stress, and salinity? Water What so special about water? Polarity of water
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Why do space scientist search for water on Mars? Hydrogen and oxygen bounds Water as a solvent Hydrogen bounds between water molecules Availability of Soil Water Water molecules are attracted to: o Each other (Causes surface tension ) o Surfaces (Causes capillary action ) When a soil is saturated and excess (gravitational) water drains: o Remaining water exists as thin films around soil particles (mineral and organic) o The greater the area of such particles (as in clayey soils), the more water the soil retains All soil water molecules are not equal It's all a matter of physical attraction… o The close a water molecule is to a soil particle, the greater the force with which it is attracted o This force is the matric potential of the soil, contributing to the overall water potential o Matric potentials (units are Mpa and atm) are considered increasingly negative as they represent greater attractive forces It's all a matter of potential… Soil water potential is: o Usually dominated by matric forces o Determined as the force required to remove the most loosely bound water molecules Typical "benchmark" values are: o -0.1 atm ( field capacity ) o -15 atm ( wilting point ) o -100 atm (exceedingly dry soil ) Plants obtain water from the soil How do water molecules move?
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