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APES CHAPTER 2
Energy

The ability to accomplish WORK and:
 Move or change position
 Physical composition
 Absorb energy & use it to organize and
reorganize molecules
 Change temperature
○ Example: photosynthesis, cellular respiration
 Ultimate source of energy on Earth:
○ The sun
○ Radioactive decay in core (Geothermal)
Energy: Forms, Quality, Changes and Laws

Energy - The
capacity to do work
or transfer heat

Radiation - form of energy,
ultimate source is the sun (or
other stars)
Transfer of Energy
Radiation – transfer of energy by waves or
rays
Conduction – the transfer of heat between two
parts of a stationary system at different
temperatures. Usually solids.
Convection – transfer of heat by movement in
liquids or gases. Density differences account
for motion.
How the Sun Heats the Earth
Radiation
Conduction
Convection
Evaporation absorbs energy
Condensation releases energy
Know these!!!!!
Energy: Forms, Quality, Changes and
Laws
 Kinetic Energy (of motion)
○ Energy contained in moving objects.
○ Ex: Wind, flowing water, electricity, heat
 Potential Energy (of position)
○ Stored, latent energy available for use.
○ EX: Water behind a dam, chemical energy stored in
bonds
 Measurements of Energy
○ Joule (J), kilowatt-hour (kWh), calorie (c), Calorie
(C), British thermal unit (Btu)
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Energy: Forms, Quality, Changes and
Laws

Thermodynamics
 First Law – Conservation of Energy
○ Energy is neither created nor destroyed, but can be
transferred or transformed.
 All energy sources are finite (limited).
 Second Law – Change in Quality
○ Change from more-ordered to less-ordered
○ The quantity of energy remains the same, but the ability to
do work diminishes (quality)
○ With each energy transfer or transformation, some energy
is lost as waste.
○ Heat is usually the “waste”
 No process is 100% efficient.
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Second Law of Thermodynamics
Solar
energy
Chemical energy
(photosynthesis)
Waste
heat
Mechanical
energy
(moving,
thinking,
living)
Chemical
energy
(food)
Waste
heat
Waste
heat
Waste
heat
Rule of 10
Fig. 2-11, p. 32
Second Law in Nature
Energy flows through
food chains and is
never recycled.
 Must be continually
renewed by
consumption.
 Energy must be
constantly supplied to
an ecosystem . . . .
By?

ENERGY TRANSFER BETWEEN TROPHIC LEVEL IS ONLY 10% EFFICIENT
Energy Efficiency & Quality

Energy Efficiency - The ratio of the
amount of work that is done to the total
amount of energy that is introduced to
the system.
Ex: Difference between woodstoves and fireplaces

Energy Quality – the ease of which an
energy source can be used for work.
Ex: Gasoline vs. wood
Energy: Forms, Quality, Changes and Laws

High quality energy
 Concentrated and can do useful work
 Oil in Saudi Arabia, Gasoline, food

Low quality energy
 Dispersed and does little useful work
 Oil in Ocean, wood
A fireplace that is 10% efficient
would require 14 kg of wood to
heat a room to 68F.
A modern woodstove that is 70%
efficient uses 2 kg of wood to
heat a room to 68F.
Calculating Efficiencies
Multiply efficiencies to determine overall efficiency:
0.35 x 0.90 x 0.05 = 0.01575 or 1.6%
Entropy

Randomness
 Always increasing in a system unless energy
is added to create order.

Energy Conversions underlie all
ecological processes
 All living things work against entropy to
maintain order
 Less energy available = less life to be
supported
Entropy:
Is this a system?
What happens to your room if
you don’t expend energy to
put things away?
Where would the energy to
pick up your room come
from?
In using food energy to clean
your room, you are decreasing
the entropy of your room, but
Increasing the entropy in the
universe by producing body
heat.
Connecting Laws of Matter and
Energy to Environmental Problems

High-throughput (high waste) economy
Matter is stored as waste; continuous seeking of both
matter and energy to maintain economy

Matter Recycling economy
Matter is conserved by recycling therefore resources
are preserved; more energy maybe needed to recycle
materials.

Low-throughput (low waste) economy
Matter and energy are both conserved; minimizing waste
and energy needed to recycle or create new materials.
ENERGY IS A LIMITING FACTOR IN
SYSTEMS
Life requires order.
 All living things work against entropy by
using energy to maintain order.
 The form and amount of energy
available in an environment determines
what kinds of organisms can live there.

 Ex: Rainforest vs Arctic Tundra;
photosynthesis vs chemosynthesis
Energy: Limiting Factor
vs
vs