Energy Flow and
Cycles of Matter
Chapter 53
Energy flow in ecosystems
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ONE WAY!
Laws of thermodynamics always apply:
1.
2.
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Energy cannot be created or destroyed, only
converted from 1 form to another
Whenever energy is converted from 1 form to
another, some of the energy is lost as heat
Simplified version: food chain
Detailed version: food web
Energy input  autotroph  heterotroph
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Note that the  shows the direction of energy flow
Bioaccumulation
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As substances move through a food chain, some
are not passed on
These substances can be stored in the bodies of
organisms in the food chain – bioaccumulation
Fat-soluble toxins tend to build up in higher
levels of a food chain – biological
magnification
Example – DDT pesticide and Bald Eagle
Ecological pyramids
Used to compare trophic levels
 Types:

 Pyramid
of numbers
 Pyramid of biomass
 Pyramid of energy
Ecosystem productivity
GPP = gross (total) energy captured
during photosynthesis
 Plants use some of this energy during
cellular respiration
 NPP = net (remaining) energy
 NPP = GPP – plant respiration
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Productivity…
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Influenced by lots of factors:
 Type
of plants
 Available solar radiation, nutrients, water
 Maturity of the community
 Human impacts
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See table 53-1 p. 1049
Biogeochemical cycles
Not one way!
 Earth is a closed system – matter cannot
escape
 Law of conservation of matter:

 Matter
cannot be created or destroyed, it can
only be changed from one form to another.
Carbon cycle
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C is in organic compounds: proteins, nucleic
acids, lipids, carbohydrates
CO2 is stored in the atmosphere (and in some
rocks)
Important processes:
 Photosynthesis
 Respiration,

decomposition, combustion
Human impact on carbon cycle – increased
combustion has increased amount of CO2 in
atmosphere
Nitrogen cycle
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N is found in proteins, nucleic acids, and chlorophyll
78% of atmosphere is N, but this is not in a form that can
be absorbed by living things
Nitrogen fixation – converts atmospheric N into a form
that can be used: combustion, volcanic action, lightning,
and nitrogen-fixing bacteria
Nitrogen-fixing bacteria – live in nodules on the roots of
plants called legumes
Nitrogen is returned to the atmosphere during
decomposition
Phosphorus cycle
P is found in nucleic acids, ATP and
phospholipids found in cell membranes
 P is not found as a gas in the atmosphere
 It cycles from the soil, into the food chain
and back

Water (hydrologic) cycle

Necessary for life:
 Provides
a medium for chemical reactions,
transports material throughout bodies, and
moderates temperatures

Important processes:
 Precipitation
 Evaporation,
transpiration