How Ecosystems Work

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Chapter 3 How Ecosystems Work
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3.1 Energy Flow in Ecosystems
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Primary Energy Source
The rate at which organic material is produced by
photosynthetic organisms in an ecosystem is
called primary productivity
Organisms that first capture solar energy, the
producers, include plants, some kinds of
bacteria, and algae.
Consumers are those organisms that consume plants
or other organisms to obtain the energy necessary
to build their molecules
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Autotrophs are organisms that use Energy from
sunlight or Inorganic substances to make Organic
compounds.
Like plants use sunlight to Make glucose.
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Heterotrophs are organisms that Must get energy
from food instead Of directly from sunlight.
We are heterotrophs because We cant make our
own food In our cells.
Instead we use cellular respiration To burn
fuel in our bodies.
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Directly or indirectly, almost all of the Energy
in living systems needed for Metabolism comes
from the sun.
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Cellular respiration is the Process of breaking
down food To yield energy.
This is essentially photosynthesis In reverse.
6CO2 6H2O Light C6H12O6 6O2
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Trophic Levels
Ecologists study how energy moves through an
ecosystem by assigning organisms in that
ecosystem to a specific level, called a trophic
level, in a graphic organizer based on the
organisms source of energy.
Energy moves from one trophic level to another
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Trophic Levels First Level
The lowest trophic level of any ecosystem is
occupied by the producers, such as plants, algae,
and bacteria
Producers use the energy of the sun to build
energy-rich carbohydrates
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Trophic Levels Second Level
At the second trophic level are herbivores,
animals that eat plants or other primary
producers. They are the primary consumers
Most herbivores rely on microorganisms, such as
bacteria and protists, in their gut to help
digest cellulose
A herbivore must be able to break down a plants
molecules into usable compounds
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Trophic Levels Third Level
At the third trophic level are secondary
consumers, animals that eat herbivores. These
animals are called carnivores
Dentrivores are organisms that obtain their
energy from the organic wastes and dead bodies
that are produced at all trophic levels
Some animals, such as bears, are both herbivores
and carnivores they are called omnivores
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Bacteria and fungi are known as decomposers
because they cause decay
Decomposition of bodies and wastes releases
nutrients back into the environment to be
recycled by other organisms
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A food chain is a sequence in Which energy is
transferred From one organism to the Next as
each organism Eats another.
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A food web shows many of the Feeding
relationships in An ecosystem.
In most ecosystems, energy does not follow simple
straight paths because animals often feed at
several trophic levels. This creates an
interconnected group of food chains called a food
web
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Energy Transfer
During every transfer of energy within an
ecosystem, energy is lost as heat.
Thus, the amount of useful energy available to do
work decreases as energy passes through an
ecosystem
The loss of useful energy limits the number of
trophic levels an ecosystem can support
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To better determine the amount of energy present
in trophic levels, ecologists measure biomass
Biomass is the dry weight of tissue and other
organic matter found in a specific ecosystem
Each higher level on the pyramid contains only
10 of the biomass found in the trophic level
below it
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The Pyramid of Energy
An energy pyramid is a diagram in which each
trophic level is represented by a block, and the
blocks are stacked on top of one another, with
the lowest trophic level on the bottom
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3.2 The Cycling of Materials
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Water moves between the Earths surface and The
Atmosphere is a process Called the Water Cycle.
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Carbon flows through Ecosystems when plants make
Food and consumers eat produces And then
decomposers start the Process over again.
But humans have a huge impact The this due to
our burning Of fossil fuels.
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The Carbon Cycle
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All organisms need Nitrogen. The good news is
that it is All around us in huge quantities.
The bad news is that almost all Organisms cant
use it from the Air.
So we get it from nitrogen- Fixing bacteria that
allows it To be used by plants.
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3.3 How Ecosystems Work
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Succession is a regular Pattern of changes
over Time in the types of species In a
community.
The community that eventually Forms if the land
is left Undisturbed is called Climax community.
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Succession that occurs on a Surface where an
ecosystem Has previously existed is
called Secondary Succession.
Pioneers are the first organisms To colonize any
newly available Area and start the process Of
succession.
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Natural fires caused by Lightning are a
necessary part Of secondary succession in Some
communities.
National forest rangers Sometimes allow natural
fires To burn unless they threaten Human life or
property.
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Succession that occurs on Surfaces where no
Ecosystem existed before is Called Primary
Succession.
Primary succession is much Slower than secondary
Succession because it begins Where there is no
soil.
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THE END