Chapter 5: How Ecosystems
Work
1. Energy Flow in the Ecosystem
2. The Cycling of Matter
3. How Ecosystems Change
p. 116-135
Key terms
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Photosynthesis
Producer
Consumer
Decomposer
Cellular respiration
Food chain
Food web
Trophic level
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Carbon cycle
Nitrogen-fixing bacteria
Nitrogen cycle
Phosphorus cycle
Ecological succession
Primary succession
Secondary succession
Pioneer species
Climax community
5.1 Energy Flow in the Ecosystem
• Describe how energy is transferred from the
sun to producers and then to consumers
• Describe one way in which consumers depend
on producers
• List 2 types of consumers
• Explain how energy transfer in a food web is
more complex than a food chain
• Explain why an energy pyramid is a
representation of trophic levels
Life Depends on the Sun
• All life is dependent on the sun for energy.
• Plants algae and some bacteria use the suns
energy and convert it into
sugars/carbohydrates by photosynthesis
From producers to consumers
• Producer- autotrophs or self-feeders makes
only energy by photosynthesis or
chemosynthesis
• Consumer- other feeders or heterotrophs- eat
other organisms to survive
Consumers- have to eat
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Heterotrophs- can not make own food, eat other
organisms
Grouped based on types of food they eat:
1. Herbivores- eat producers (antelope)
2. Carnivores- eat other consumers (lion)
3. Omnivores- eat producers and consumers (grizzly
bear)
4. Detritivores- consumers that feed on wastes, dead
organisms (vulture)
5. Decomposers- break down organisms (bacteria,
fungi)
Ecology 2010
Cellular Respiration: Burning the
Fuel
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If oxygen is available, organisms can obtain energy from
food by a process called cellular respiration. The summary
of cellular respiration is presented below.
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In symbols:
6 O2 + C6H12O6  6 CO2 + 6 H2O + ATP (Energy)
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In words:
Oxygen + Glucose  Carbon dioxide + Water + Energy
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The cell has to release the chemical energy in food
molecules (like glucose) gradually, otherwise most of the
energy would be lost in the form of heat and light.
Cellular Respiration 2009
7
Energy transfer
• All organisms need energy to carry out essential
functions, such as growth, movement, maintenance
and repair, and reproduction. In an ecosystem,
energy flows from the sun to autotrophs, then to
organisms that eat the autotrophs, and then to
organisms that feed on other organisms. The amount
of energy an ecosystem receives and the amount
that is transferred from organism to organism affect
the ecosystem's structure.
Ecology 2010
Energy Flow
• Transfer of energy from one organism to another
• Trophic levels- organism’s position in a sequence of
energy transfers
• Food chain- single pathway of feeding relationships
between organisms in an ecosystem that results in
energy transfer
• Food web- interconnected food chains
• Web cd 37 c, d, e
Ecology 2010
Food Chains
– A food chain is a series of steps in which
organisms transfer energy by eating and being
eaten.
– Food chains can vary in length. An example from
the Everglades is shown.
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Food Webs
– In most ecosystems, feeding relationships are much more
complicated than the relationships described in a single,
simple chain because many animals eat more than one
kind of food.
– Ecologists call this network of feeding interactions a food
web. An example of a food web in the Everglades is
shown.
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Ecology 2010
Limitations on trophic levels
• Only 10% of the energy available at one
trophic levels is transferred to the next
trophic level not enough to support more
levels
• Higher tropic levels contain less energy 
support fewer organisms
Ecology 2010
Ecology 2010
Pyramids of Biomass and Numbers
– The total amount of living tissue within a given
trophic level is called its biomass.
– The amount of biomass a given trophic level can
support is determined, in part, by the amount of
energy available.
Ecology 2010
Ecology 2010
Ecology 2010
Ecology 2010
5.2The Cycling of Materials
• Describe the short term and long term process
of the carbon cycle.
• Identify one way that humans are affecting
the carbon cycle.
• List the three stages of the nitrogen cycle
• Describe the role that nitrogen fixing bacteria
play in the nitrogen cycle
• Explain how the excess use of fertilizer can
affect the nitrogen and phosphorus cycles.
Recycling in the Biosphere
– Unlike the one-way flow of energy, matter is
recycled within and between ecosystems.
– Elements pass from one organism to another and
among parts of the biosphere through closed loops
called biogeochemical cycles, which are powered by
the flow of energy.
Ecology 2010
4 major cycles
1. Water cycle
2. Carbon cycle
3. Nitrogen cycle
4. Phosphorus cycle
Web cd 37 f, g, h,
10min video
http://www.youtube.com/watch?v=09_sWPxQymA&feature=related
Ecology 2010
Carbon Cycle
Short term:
• Plant convert carbon dioxide into carbohydrates during
photosynthesis
• Consumers eat the plants break down carbon during
cellular respiration
Long Term:
• carbon converted into carbonates (bones and shells)
limestone rock (largest carbon reservoirs)
• Carbon also converted into fats, oils, other energy
storing molecules release into soil or air after the
organism dies can form coal or natural gas(fossil
fuels)
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http://www.youtube.com/watch?v=U3SZKJVKRxQ
How Humans Affect the Carbon
Cycle
• Burn fossil fuels  release carbon into air
• 6 billion metric tons of carbon is released per
year about ½ will remain in the air
increasing CO2 into the air at steady rate 
global warming increase the temperature
of the Earth
The Nitrogen Cycle
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All organisms need nitrogen to build proteins
78% of the gases in the atmosphere
Must be altered in a usable form
Nitrogen fixing bacteria- bacteria that can fix nitrogen- take gas and
transform it to a usable form (nitrate), key part in the nitrogen cycle
• Legumes- beans, peas, clover that bacteria can live in nodules
• Gets released into the soil plants absorb it and then consumers
eat them
• Decomposers break down decaying and dying things putting the
nitrogen back into the cycle
• http://www.youtube.com/watch?v=1XC7xT0mIbY
The Phosphorus Cycle
• Makes up cells of living organisms (bones and teeth)
• Plants get it from soil and water consumers get it
from eating plants or other organisms
• Phosphorus goes from environment to organisms
rarely occurs as a gas
• No soluble in water sink to bottom
• Fertilizers- contain nitrogen and phosphorus, great for
plants and alga (algal bloom) can disrupt or deplete
oxygen in aquatic ecosystems
• Acid Rain- burning fuel  nitric oxide is released 
acid rain
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Video- http://www.youtube.com/watch?v=3iwL24oVpH4
Song- http://www.youtube.com/watch?v=JvZ_r-ZB8PU
Acid rain- http://www.youtube.com/watch?v=MqHw1hMEkAQ&feature=related
5.3 How Ecosystems Change
• List two examples of ecological succession
• Explain how a pioneer species contributes to
ecological succession
• Explain what happens during old-field
succession
• Describe how lichens contribute to primary
succession
THINK ABOUT IT
– In 1883, the volcanic island of Krakatau in the Indian
Ocean was blown to pieces by an eruption. The tiny island
that remained was completely barren.
– Within two years, grasses were growing. Fourteen years
later, there were 49 plant species, along with lizards, birds,
bats, and insects. By 1929, a forest containing 300 plant
species had grown. Today, the island is blanketed by
mature rain forest.
– How did the island ecosystem recover so quickly?
Ecology 2010
Succession- changes
• Ecological succession- gradual regrowth of a community of species
• http://www.youtube.com/watch?v=V49IovRSJDs
• http://www.youtube.com/watch?v=k03vxRYsJ4Y&feature=related
• Primary- development of a community in an areas that has not supported
life previously, sand dune, rock Web cd 37 b
http://www.youtube.com/watch?v=vNHnwHaSolA&feature=fvwrel
• Secondary- replace of species that follows the disruption (soil is present)
• Pioneer species- small, grow quick, reproduce quick, invade disturbed
habitats
• Climax community- stable end pt
http://www.youtube.com/watch?v=_Y9EQbKH_hA&feature=related
Song: http://www.youtube.com/watch?v=rzE6BNNLew0&feature=related
Ecology 2010
Primary Succession
– Volcanic explosions can create new land or sterilize
existing areas.
– Retreating glaciers can have the same effect, leaving only
exposed bare rock behind them.
– Succession that begins in an area with no remnants of an
older community is called primary succession.
Ecology 2010
Primary Succession
– For example, in Glacier Bay, Alaska, a retreating glacier
exposed barren rock.
– Over the course of more than 100 years, a series of
changes has led to the hemlock and spruce forest currently
found in the area.
– Changes in this community will continue for centuries.
Ecology 2010
Primary Succession
– The first species to colonize barren areas are
called pioneer species.
– One ecological pioneer that grows on bare rock is
lichen—a mutualistic symbiosis between a fungus
and an alga.
Ecology 2010
Secondary Succession
Sometimes, existing communities are not completely destroyed by
disturbances. In these situations, secondary succession occurs.
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Secondary succession proceeds faster than primary succession, in part because soil survives
the disturbance. As a result, new and surviving vegetation can regrow rapidly.
Secondary succession often follows a wildfire, hurricane, or other natural disturbance.
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We think of these events as disasters, but many species are adapted to them. Although forest
fires kill some trees, for example, other trees are spared, and fire can stimulate their seeds to
germinate.
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Secondary succession can also follow human activities like logging and farming.
Ecology 2010
Why Succession Occurs
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Every organism changes the environment it lives in.
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One model of succession suggests that as one species alters its
environment, other species find it easier to compete for resources and
survive.
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For example, as lichens add organic matter and form soil, mosses
and other plants can colonize and grow.
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As organic matter continues to accumulate, other species move in
and change the environment further.
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Over time, more and more species can find suitable niches and
survive.
Ecology 2010
Climax Communities
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Ecologists used to think that succession in a given area always proceeds
through the same stages to produce a specific and stable climax
community.
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Recent studies, however, have shown that succession doesn’t always
follow the same path, and that climax communities are not always
uniform and stable.
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Ecosystems may or may not recover from extensive human-caused
disturbances.
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Clearing and farming of tropical rain forests, for example, can change
the microclimate and soil enough to prevent regrowth of the original
community.
Ecology 2010
Ecology 2010
Mount St. Helens: Back From The
Dead
Part 1:
http://www.youtube.com/watch?v=iqG4Vi-eu5U&feature=related
Part 2:
http://www.youtube.com/watch?v=SeXpFhvLeIc&feature=relmfu
Part 3:
http://www.youtube.com/watch?v=dq-rHDEoFYw&feature=relmfu
Part 4:
http://www.youtube.com/watch?v=8Ld8vZvSOvo&feature=relmfu
Part 5:
http://www.youtube.com/watch?v=XaqEMSUlM58&feature=relmfu
Part 6:
http://www.youtube.com/watch?v=5X1JFkfcLDo&feature=relmfu
More links
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http://www.pbs.org
http://www.wiley.com/college/strahler/0471480533/animations/ch23_animations/animation1.html
http://www.life.uiuc.edu/
http://www.fire-ecology.org/
http://www.wildfirezone.org/
http://www.youtube.com/watch?v=_Y9EQbKH_hA&feature=related
http://www.geowords.org/ensci/imagesbook/04_03_succession.swf
http://www.nodvin.net/snhu/SCI219/demos/Chapter_4/Chapter_04/Present/animations/50_2_2_1.html
http://www.life.illinois.edu/bio100/lectures/f03lects/03f03-succession.html#succession
http://bcs.whfreeman.com/thelifewire/content/chp55/55020.html