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ECOSYSTEMS AND ENERGY FLOW
CH 36
I. Feeding Relationships and Energy Flow
A. Types of Organisms
All organisms require an input of energy to carry out their life processes like
growing, moving, and reproducing
Producers: obtain energy from the sun by converting it to glucose
(autotrophs)
Consumers: obtain energy by eating producers or other consumers
(heterotrophs)
Decomposers (detrivores): obtain energy from the waste of organisms
and from dead organisms (heterotrophs)
No matter the type of organism, once the energy is obtained, the organic molecules
enter into cellular respiration to release the energy for use
B. Food Chains
Sun →producer → primary consumer → secondary consumer → tertiary
consumer → quaternary consumer
Each level is called a trophic level or feeding level
At each trophic level, decomposers break down waste and dead
organisms
C. Food Webs
In an ecosystem, feeding relationships are rarely linear, but are
branching forming a food web
In a food web, some consumers can be both primary and secondary
consumers, feeding at different trophic levels
a. Describe a food chain with 4 trophic levels
b. Describe the effects on this food web if the mouse had a toxin in it
II. Energy Flow Through Ecosystems
The amount of energy produced at the first trophic level limits how large the
other trophic levels can get
About 1% of solar energy is captured by producers to do photosynthesis
About 10% of the energy stored in each trophic level is available to the next
trophic levels
The remaining 90% of the energy is
o Used by the organisms in that trophic level
o Released as heat
o Lost as waste
10%
10%
Sun → producer →primary →secondary
consumer consumer
90% of energy in each trophic level is lost as
heat, waste, or used by that trophic level
A. Productivity and Biomass
Biomass: the mass of the organisms in a particular trophic level
Primary productivity: rate at which producers make glucose
o The higher the rate, the more energy available to higher trophic
levels
B. Productivity and Ecological pyramids
Producers set how much energy will be available to each subsequent
trophic level
However, only 10% of the energy of a trophic level is available to a
subsequent one
The rest of the energy is lost as heat, waste, or is used by the organisms
in that trophic level
This creates an ecological pyramid
III. Chemical Cycles in ecosystems
A. Basic pattern of chemical cycling
Producers use chemicals from the environment
Consumers eat producers incorporating some of those chemicals into
themselves
Decomposers break down consumers and producers returning those
chemicals to the environment for producers to use
B. The Carbon Cycle
Producers use CO2 in atmosphere to make organic compounds
(photosynthesis)
Consumers eat producers and other consumers and they break down organic
compounds releasing CO2 to air (cellular respiration)
Dead organisms are decomposed by detrivores which release CO2 to air
Volcanic eruptions and burning of fossil fuels release more CO2 into air
http://www.nodvin.net/snhu/SCI219/demos/Chapter_3/Chapter_03/Present/a
nimations/51_1_2_1.html
C. The Nitrogen Cycle
Nitrogen fixing bacteria convert N2 gas to NH4
Plants use NH4 to make protein
Consumers eat plants
Decomposers return NH4 to soil
Some bacteria in soil recycle N2 to atmosphere
http://www.classzone.com/books/ml_science_share/vis_sim/em05_pg20_nitro
gen/em05_pg20_nitrogen.html
D. Water Cycle
Water exits plants by transpiration and becomes water vapor
Water evaporates off of large bodies of water and becomes water vapor
Water vapor in atmosphere condenses and precipitates down to earth to be
used by plants and animals
http://earthguide.ucsd.edu/earthguide/diagrams/watercycle/index.html