Download Energy Flow Review Sheet

Energy Flow Review Sheet
Courtesy of: Pamela J. Shlachtman, Miami Palmetto High School
Objectives:
The student will be able to:
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Understand
Understand
Understand
Understand
the terms energy, work and entropy
that energy transfers are not 100%
the implications of the Laws of Thermodynamics
primary productivity
Energy is the ability to do work. It is something that given the right device can be converted to a
push. Energy can be used to move an object that is considered WORK. Work always involves
movement or displacement of a body to another place. There are two type of energy, Kinetic Energy
or motion energy and Potential Energy or energy of position. If you elevate a rock so it will fall, you
give the rock potential energy. When it actually falls, the potential energy becomes kinetic energy.
Another term used in energy discussions is ENTROPY. Energy can only work if it flows somewhere.
A positive charge has no energy unless a negative charge is present. Steam energy is useful only if
it can push a piston. In order to harness energy, the energy must have some place to go. Entropy is
the amount of energy that is NOT available for work. In order to understand Entropy, one must
understand order, dispersion and randomness. Heat is relatively random energy because it disperses
quickly. If two rooms were attached by a narrow hallway and one was very hot and the other very
cold, the heat would flow into the cold room. Once the heat matched, the amount of heat energy is
zero and the entropy is 100%. It's like using a bar of soap in a large body of water. Each time the
soap is used, the amount of soap available for use is less even though the amount of soap in the
water is the same. The point is that energy tends to run to uniformity and becomes less available in
a system as it is used.
Laws of Thermodynamics
The First Law of Thermodynamics states that matter cannot be created nor destroyed. Energy can
be converted from one form to another. The energy from a "dead " flashlight battery is still around
somewhere in some form. In other words, the energy in a closed system can be changed to another
form but is never lost.
The Second Law of Thermodynamics states that heat is produced and entropy is increased each
time energy is converted to another form. This means that energy exchanges are not equal. The
movement of energy is from high quality to low quality, the lowest of which is heat which many
times is dispersed so far, it can't be used at all. A car uses gasoline, which is a high quality source
of energy to run. Only 10% of that high quality energy is used. The other 90% is converted into
heat. We can never reuse or recycle high quality heat. Look at it in form of a small sealed jar.
Suppose a small jar was filled with dirt and microorganisms. As one organism worked on the foods
available, energy would be converted to life forms and heat. The heat would be lost to the outside
of the jar until eventually the original energy of the jar would be non-existent. Now if you enlarge
that jar to an ecosystem or even the earth, you might get an idea of how energy and
thermodynamics effects you. Of course, it is not as easy as all that but the basic idea is still there.
The Source of Energy
The mass of energy in the sun is tremendous. Every second, 4.2 millions tons of the sun's mass is
converted to heat. The heat leaves the sun as electromagnetic radiation, heat radiation and other
forms of energy. Because the heat can not travel very far in the vacuum of space, we receive the
electromagnetic radiation. The grand majority of that energy is light.. About 42 % of this is
reflected by clouds and dust in the atmosphere, 14 % by snow and other things and 10 % is
absorbed in the atmosphere. The 34 % that is absorbed by water and air forming winds and
currents and the remaining 1 % is converted to energy by plants. It is this energy that we are
interested in. Plants take that energy and convert it to foods by photosynthesis. The light energy is
absorbed by chlorophyll and converted to glucose and other compounds.
Plants also release energy through respiration (15 -75%). Corn, which is one of the best energy
"catchers" converts about 3 % of the sun's energy to kernels of corn, stems, roots and leaves and
uses about 3 % for its own metabolic processes. Corn is considered excellent at 6 % !!!
Primary Productivity
Primary productivity is the rate of production of plants. The gross primary productivity is the rate
of conversion of solar energy to chemical energy in a system. Since some of the energy of plants is
used by the plant, we have another term, the Net Primary Productivity. Net primary productivity is
the rate at which plants make chemical energy available to consumers, decomposers or for storage.
Factors of Primary Productivity
Access to water and nutrients, latitude, physical complements of the soil, humidity, temperature,
slope and wind are major factors of primary production. Productivities vary according to area. Areas
of high productivity are marshes, estuaries, swamps, tropics and low productivity areas are tundras,
open ocean and deserts.
Measuring Primary Productivity
One can measure the primary productivity by:
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measuring the amount of O2 produced in a system
measuring the amount of C02 consumed in the system
harvesting, drying and measuring the amount of vegetation in the system.
Light Bottle, Dark Bottle Experiment
If two bottles are put into a lake, the light bottle would have photosynthesis and respiration
whereas the dark bottle would have only respiration The change in oxygen content in the light
bottle reflects the net production. The change in oxygen in the dark bottle reflects only the
respiration. By adding the changes together, you will receive the gross production.
Transfers of Energy in Ecosystems
When consumers eat producers, the amount of energy exchanged is between 5 and 30 %. The
average is about 10%. We have established that 10% represents a "good" exchange. This is the
reason that you can count more herbivores in the system than carnivores. Ecological efficiency for
most trophic systems is about 10%. There are other implications such as why the largest animals
eat plants. There are too many exchanges for large animals and they would be terribly reduced in
number. One of the reasons large whales eat only plankton is to avoid the tremendous number of
diatoms that would have to be made of another transfer. This also provides something that is not at
all pleasant in the ecosystem.
Biomagnification
toxins tend to accumulate the higher you go in the food web. (This is especially true of non watersoluble toxins like chlorinated hydrocarbons and heavy metals)
Waste
The waste of energy is enormous. We drive a huge car with 10 % efficiency to the corner to pick up
a 6 pack which was made with about 20% efficiency, drive home, turn on the lights that have a 5 %
efficiency. The amount of energy lost there is enormous! We could save it. In Osage, Iowa, the town
started an energy flow system in 1974. Since that time, they have saved about $ 1000/yr apiece,
reduced their use of high quality energy by 45% and converted that waste to about $ 1.2 million/yr
to spend on the town and personal needs. Miami could do that too. We don't. This is a WAD
response. WAD stands for "We are dumb" and it will be used a lot in this course.