Obj. 3
ECOSYSTEMS: HOW THEY WORK
Matter, Energy and Life
Fig. 3.1 From a biological point of view, the three most important gases of the lower atmosphere are
nitrogen, oxygen, and carbon dioxide.
Fig. 3.2 Water consists of molecules, each of which is formed by two hydrogen atoms bonded to an
oxygen atom (H2O). In water vapor, the molecules are separate and independent.
Fig. 3.5 The organic molecules making up living organisms are larger and more complex than the
inorganic molecules found in the environment. Glucose and cystine show this relative complexity.
Fig. 3.3 The atoms of most elements gain or lose one or more electrons, becoming negative (-) or
positive (+) ions. The ions are held together by an attraction between positive and negative charges.
Fig. 3.6 Biological systems include levels of complexity beginning with atoms and molecules and
broadening up to the biosphere.
Fig. 3.7 Kinetic energy is energy in one of its active forms. Potential energy refers to systems or
materials that have the potential to release kinetic energy.
Fig. 3.8 Any form of energy can be converted to any other form, except heat energy. Heat
is a form of energy that flows from one system or object to another because the two are at different
temperatures. Therefore it can only be transferred to something cooler.
III. Energy
A. First Law of Thermodynamics: "Energy is neither created nor destroyed;
it only changes form." It can be related to: "You can't get something for nothing"
or "There is no such thing as a free lunch".
B. Second Law of Thermodynamics: "Systems will go spontaneously in one
direction only toward increasing entropy." It can be described as:" It takes
energy to get energy" or "In any energy conversion, you will end up with less usable
energy than you started with" or "If you think things are confused now, just wait" or
"Everything moves in the direction of increasing disorder".
Fig. 3.9 When glucose is burned, heat is released, and the atoms become more disordered, showing
increasing entropy. The fact that wood will burn but not form spontaneously is an example of the second
law of thermodynamics.
Fig. 3.11 Breaking down some of the glucose to provide additional chemical energy, producers combine
the remaining glucose with certain nutrients from the soil to form other complex organic molecules that
the producers then use for growth.
Fig. 3.13 Only a small portion of ingested food is used for growth and repair. A larger amount is used in
cell respiration to provide energy.
Fig. 3.15 This figure shows energy flow through Trophic Levels in a Grazing Food Web. Each trophic
level is represented as biomass boxes and the pathways taken by the energy flow are indicated with
arrows.
IV. Principles of Ecosystem Function and Energy Flow in Ecosystems
A. Energy Source
1. The ultimate source of energy on our planet: the sun.
2. The first basic principle of ecosystem sustainability: "For sustainability,
ecosystems use sunlight as their source of energy.'
Our planet is sustainable as long as the sun exists. Ecosystems do not use
energy at a faster rate than that available from the sun. (The same cannot
be said for humans because of our rate of fossil fuel consumption.)
B. Nutrient Cycles:
Energy flows but nutrients cycle. The molecules in an organism will eventually be
found in another organism.
1. Carbon Cycle: Changing the location of this element is the primary issue in
global warming. We are moving carbon from where it has been stored (fossil fuels) to
the atmosphere, where it acts to reduce the amount of heat reradiated to space.
·
The rate of movement (flows) between pools can be slow or fast
depending upon the nature of the pool.
Fig. 3.16 Boxes in the figure refer to pools of carbon, and arrows refer to the movement, or fluxes, of
carbon from one pool to another.
2. Phosphorus Cycle: Changing the location of this element is one of the primary
reasons for the increased nutrient load in aquatic ecosystems. We move phosphorus
from where it has been concentrated, e.g., in guano, and deposit it on soil (or in
consumer products), where it is released to water.
·
The rate of movement (flows) between pools can be slow or fast
depending upon the nature of the pool.
Fig. 3.17 This figure shows the movement of phosphates through an ecosystem.
3. Nitrogen Cycle: Changing the location of this element is the other reason for
the increased nutrient load in aquatic ecosystems. (Nitrogen and phosphorus are
limiting factors in aquatic ecosystems.)
·
The rate of movement (flows) between pools can be slow or fast
depending upon the nature of the pool.
·
The flow of nutrients into Chesapeake Bay (primarily nitrogen) has been
cited as the primary reason for the outbreak of Physteria.
Fig 3.18 This figure shows the movement of nitrogen through an ecosystem.
4. The second basic principle of ecosystem sustainability:
" For sustainability, ecosystems dispose of wastes and replenish nutrients by recycling
all elements."
Fig. 3.20 Arranging organisms by feeding relationships and depicting the energy and nutrient inputs and
outputs of each relationship show a continuous recycling of nutrients in the ecosystem, a continuous flow
of energy through it, and a decrease in biomass.
IV. Implications for Humans
1. Ecosystems are an excellent role model for humans.
2. Some examples of nonsustainable human actions: fossil fuel use, not
returning the nutrients remaining in human sewage to soil, high meat
consumption levels of the industrialized countries, energy use in homes,
consumer goods.
Fig. 3.21 To get one pound of beef requires an expenditure of 16 pounds of feed. Said another way, the
grain consumed to support one person eating meat could support 16 persons eating the grains directly.
Fig. 3.22 This figure shows one way nutrient flow in a human society.