Flows of Energy and Matter
Significant Ideas
 Ecosystems are linked together by energy and matter
flows.
 The Sun’s energy drives these flows, and humans are
impacting the flows of energy and matter both locally
and globally.
Energy Flows, Materials Cycle
 Almost all ecosystems are driven by energy from the
sun.
 Energy (heat) continually flows through systems
 Matter (nutrients, oxygen, carbon dioxide, water) are
cycled and recycled.
 Biosphere systems are dependent on amount of
energy reaching the ground.
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Affected by time of day, season, cloud cover, etc.
 Most solar energy is not used to power living
systems; it is reflected or reradiated as heat
(infrared).
Solar Radiation
Solar Radiation Continued
 A study of a cornfield suggested that only 1.6% of
solar energy was used by the corn. So what
happened to the rest?
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35% is reflected back into space by snow, ice, water, and land
60% is absorbed by the atmosphere
< 5% available at Earth’s surface and is absorbed, heating up
land and the ocean (this can be used by plants for
photosynthesis)
Pathways of Energy in an Ecosystem
 Conversion of light energy into chemical energy
(photosynthesis)
 Transfer of chemical energy from one trophic level to
another with varying efficiencies (moving up the
food chain/food web)
 Overall conversion of ultraviolet and visible light to
heat energy by an ecosystem
 Re-radiation of heat energy into the atmosphere
(infrared)
Biomass and Productivity
 Productivity: The conversion of energy into biomass
over a given period of time.
 Biomass: Living mass of an organism or organisms
(sometimes referred to as dry mass).
 Gross: Refers to the total amount of something
 Net: Refers to the amount left over after deductions.
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Gross Income: $60,000 per/year
Net Income: $50,000 per/year after taxes, social security,
retirement, health care, etc.
 Primary Production: to do with plants
 Secondary Production: to do with animals
Gross vs. Net Productivity
 Gross Productivity: Total gain in energy or biomass
per unit area per unit time.
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Biomass that can be gained before deductions
But all organisms have to respire to stay alive so some energy
is used up to stay alive instead of used to grow.
 Net Productivity: Gain energy or biomass per unit
area per unity time that remains after deductions
due to respiration.
Gross Primary Productivity (GPP)
 All light energy fixed by plants is converted to sugars
 Can estimate plant’s energy uptake by measuring
amount of sugar produced: Gross Primary
Productivity.
 However, measuring sugar produced is difficult
because it is used almost as soon as it is produced.
 Easier to measure Net Primary Productivity (NPP)
Net Primary Productivity (NPP)
 NPP: An ecosystem’s NPP is the rate at which plants
accumulate dry mass (actual plant material).
 Measured in grams per square meter.
 It is a measure of potential food for consumers in the
ecosystem.
 Calculation for NPP: GPP – R, where GPP is Gross
Primary Productivity (production of sugar) and R is
respiratory loss.
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In theory, any glucose that’s left over after photosynthesis and
respiration should be material deposited in and around cells to form
new plant matter.
NPP is Biomass
Gross Secondary Productivity (GSP)
 The total food ingested including the food not used
for energy and is excreted as waste.
Net Secondary Productivity (NSP)
 Dry mass of plants that is stored in new tissue (the
tissue of an animal)
 Calculate: NSP = GSP – R
 GSP is equal to food eaten minus energy in waste
(feces and urine)
 R is respiratory loss
Maximum Sustainable Yield
 Equivalent to the NSP or NPP of system.
 Important number for farmers who are trying to predict
how much money they will get for their product.
 Farmers are often paid by how much biomass (often
measured by weight/acre) that their crop yields.
 Modern agricultural economists spend many months
predicting yields which drives prices of the food you buy.

Corn Futures are a good example. People bet on how much corn will
be grown in a particular year…even before it is ever planted!
Matter Flows
 Matter flows through ecosystems linking them
together. The flow of matter involves transfers and
transformations.
 Carbon Cycle
 Nitrogen Cycle
Carbon Cycle
 Carbon flows through ecosystems through feeding, death
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and decomposition, photosynthesis, respiration,
dissolving, and fossilization.
Carbon is stored in organisms and forests, the
atmosphere, soil, fossil fuels, and in the oceans.
Places where carbon is stored are called Carbon Sinks
The oceans are the largest carbon sinks, holding many
times more carbon than all the forests on earth
combined.
Climate change is affecting how much carbon the ocean
can hold.
Nitrogen Cycle
 Nitrogen flows include nitrogen fixation by bacteria
and lightning, absorption, assimilation,
consumption, excretion, death, decomposition, and
denitrification by bacteria in water-logged soils.
 Nitrogen is stored in organisms, soil, fossil fuels,
atmosphere, and bodies of water.
 Places where nitrogen is stored are called Nitrogen
Sinks
Human Impact on Energy Flows
 Human activities such as burning of fossil fuels,
deforestation, urbanization, and agriculture impact
energy flows as well as the carbon and nitrogen cycle.
 How does the burning of fossil fuels or deforestation
affect the carbon cycle?
 How could urbanization and agriculture affect either
the carbon cycle or nitrogen cycle?
 Take 5 minutes to write down your thoughts
To Do: Calculating Productivity
 Pg. 67 of Course Companion, Do question 1, a-e.
 Calculating productivity worksheet