BIO120H1 Chapter Notes - Chapter Part 5: Metabolic Water, Arteriole, Bipedalism

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27 Nov 2018

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BIO120: Struggle for Existence, James D. Thomson (Part 5
Physiological Ecology as a Way of Thinking About Organisms)
In association with Lecture 15 & 16 and Reading Quiz 7
- In biological sciences, we focus on tangible physicochemical attributes and natural causes of
living entities; we stay within the realm of direct evidence even within that scope, we look at
an organism in different ways
- We can focus on subset of reactions that direct development of complex adult forms from
unicellular zygotes (development), or on the subset that carries out metabolic processing of
energy and materials to fuel and supply all of that growth, maintenance, and reproduction
- Alternatively, organisms can be viewed as a library of information, bearing detailed sets of
genetic instructions written in DNA information has two special aspects:
o Necessary and sufficient to direct assembly of complex organism
o Heritable and connects that organism to other organisms in a family tree of relatedness
- Informationally viewed, we’re all twigs on that tree we have a phylogenetic position on that
tree, with understandable relationship to others that can be inferred from similarities and
differences in our DNA
o Information lets us classify organisms in term of relatedness into taxonomy that has
analogous characteristics to a pedigree
How Environmental Factors Determine Distribution and Abundance
- All organisms have restricted spatial distributions if environmental factors in particular habitat
are too harsh for a particular species, it will not be able to persist there
- Environmental factors can be classified in a few different ways
o One distinction is between abiotic and biotic factors
Biotic factors arise from actions of other organisms while abiotic factors are
manifestations of non living, physico chemical world
o Abiotic factors are subdivided into two categories, conditions and resources
Resources are necessary physical entities that organisms use up; they can be
depleted (E.g. water, chemical nutrients, space)
Conditions are physical states that cannot be depleted, such as temperature or pH
- Factors most important in determining whether a species can or cannot persist in an area are
called limiting factors
o At broadest level, two factors most likely to limit distributions of terrestrial species are
temperature (a condition) and water (a resource)
o For terrestrial organisms, water availability depends on precipitation, so water and
climate are most important determinants of what sorts of organisms are found in different
parts of world
- Organisms affected simultaneously by all factors in environment choose only to focus on one
factor at a time; standard concept is of an environmental gradient
o Simplest gradient occurs along a line drawn across a real habitat E.g. if you walk from
shore of a lake toward higher ground, you’re walking along a gradient of soil moisture; at
lake’s edge, soil is hydric, so if you laid out a 1m wide strip to walk along, and counted
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number of plants in each meter of strip, sample strip is called a transect since you’d see a
gradient of soil mixture
o Another way to construct gradient of samples; suppose you locate a large number of
sample points scattered randomly throughout lake valley; at each point, you set up a 1m
square sampling plot, conduct a census of organisms in each plot and measure soil
moisture content in each plot On computer, sample plots are sorted from lowest to
highest soil moisture and samples are arranged along a gradient of soil moisture so you
can see how different species sort themselves out along the gradient
o Other factors include temperature, pH, salinity, organic content of soil, altitude above sea
level etc.
o Since many of these factors are critical to success or failure of organisms, most species in
montane regions are restricted to well defined ranges of elevation, tempered by
- Any particular species is likely to be restricted to only a portion of an ecological gradient, if the
factor varying along gradient is a limiting factor portion that species is restricted to constitutes
the range of tolerance for that particular factor and considered as defining part of niche of species
- Ranges of tolerance graphed as curves showing how organism’s ability to function changes along
gradient at increasing distance from optimum/peak, organisms find environment increasingly
stressful; they become unable to grow well enough to reproduce and then become unable to grow
at all, then finally unable to live (death zones)
Why are Temperature and Water so Important?
- Processes that permit life are essentially chemical reactions that occur in aqueous solutions
reaction rates depend strongly on temperature and on concentrations of reactants
o In very cold conditions, molecules move slowly so reactions come to a stop
temperature dependence characterizes simplest inorganic reactions and is more important
in organisms because most important reactions are catalyzed by enzymes
Enzymes are proteins whose ability to catalyze a reaction depends on way that
protein molecule is folded or configured
o At high temperatures, proteins denature and lose characteristic shapes and functionalities
natural selection can produce heat resistant enzymes, but resistance is limited
- Due to fundamental temperature dependence of chemical reactions, all forms of life are limited
by extremes of cold and heat
- Water is important because it affects concentrations of chemical reactants, but especially because
cells and tissues depend on membranes to compartmentalize chemical processes and reactants
- Proper functioning depends on osmotic balance
o If cells get too dry, concentrations of dissolved salts increase, chemical reactions are
slowed and changed, and eventually come to a stop; salt can precipitate and crystallize
o If too much water enters cells, reactants get diluted and fail to combine as needed
- Organisms are characteristically in danger of overheating, over cooling, drying out and getting
waterlogged; physico chemical reason has three parts:
o Environments typically contain a far broader range of physical conditions than narrower
ranges of tolerance characterizing organisms; death zones are out there
o Things tend to equilibrate; objects, whether organisms or inanimate objects, will tend to
reach same temperature as environment; in dry environment, objects will lose water and
become saltier
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