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Biology
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Producers
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Producers
I. Producers
Where does the energy for life processes
come from?
Without a constant input of energy, living
systems cannot function.
Sunlight is the main energy source for life
on Earth.
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Producers
3–2 Energy Flow
Producers
In a few ecosystems, some organisms obtain
energy from a source other than sunlight.
Organisms that can capture energy from sunlight or
chemicals and use that energy to produce food are
called autotrophs.
Some types of organisms rely on the
energy stored in inorganic chemical
compounds.
Examples of autotrophs are plants, some algae, and
certain bacteria.
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Producers
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Producers
Producers are autotrophs, organisms that make
their own food.
Autotrophs use energy from the environment to fuel
the assembly of simple inorganic compounds into
complex organic molecules.
These organic molecules combine and recombine to
produce living tissue.
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Producers
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Energy From the Sun
The best-known autotrophs harness solar energy
through a process known as photosynthesis.
During photosynthesis, these autotrophs use light
energy to convert carbon dioxide and water into
oxygen and energy-rich carbohydrates.
Producers
Photosynthesis is
responsible for
adding oxygen to—
and removing carbon
dioxide from—Earth's
atmosphere.
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Producers
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Producers
Life Without Light
Plants are the main autotrophs on land.
Algae are the main autotrophs in freshwater
ecosystems and in the upper layers of the ocean
Some autotrophs can produce food in the absence
of light.
Photosynthetic bacteria are important in certain wet
ecosystems such as tidal flats and salt marshes.
Chemosynthesis is when organisms use chemical
energy to produce carbohydrates.
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Producers
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Chemosynthetic bacteria live inside
these Tube Worms and help them
digest and absorb nutrients
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Chemosynthetic bacterium
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Producers
Chemosynthesis is performed by several types of
bacteria.
These bacteria represent a large proportion of living
autotrophs.
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Producers
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Some chemosynthetic bacteria live in very remote
places on Earth, such as volcanic vents on the deepocean floor and hot springs.
Others live in more common places, such as tidal
marshes along the coast.
Consumers
Consumers
Many organisms cannot harness energy directly
from the physical environment.
Organisms that rely on other organisms for their
energy and food supply are called heterotrophs.
Heterotrophs are also called consumers.
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Consumers
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Feeding Relationships
There are many different types of heterotrophs.
•  Herbivores eat plants.
How does energy flow through living
systems?
•  Carnivores eat animals.
•  Omnivores eat both plants and animals.
•  Detritivores feed on plant and animal remains
and other dead matter.
•  Decomposers, like bacteria and fungi, break
down organic matter.
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Feeding Relationships
3–2 Energy Flow
Feeding Relationships
Feeding Relationships
The relationships between producers and
consumers connect organisms into feeding
networks based on who eats whom.
Energy flows through an ecosystem in
one direction, from the sun or inorganic
compounds to autotrophs (producers)
and then to various heterotrophs
(consumers).
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Feeding Relationships
3–2 Energy Flow
Food Chains
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Feeding Relationships
In some marine food chains, the producers are
microscopic algae and the top carnivore is four steps
removed from the producer.
A food chain is a series of steps in which
organisms transfer energy by eating and being
eaten.
Zooplankton
Small Fish
Squid
Shark
Algae
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Feeding Relationships
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Food Webs
Feeding Relationships
This food web
shows some of
the feeding
relationships in a
salt-marsh
community.
Ecologists describe a feeding relationship in an
ecosystem that forms a network of complex
interactions as a food web.
A food web links all the food chains in an
ecosystem together.
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Feeding Relationships
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Ecological Pyramids
Trophic Levels
Each step in a food chain or food web is called a
trophic level.
How efficient is the transfer of energy
among organisms in an ecosystem?
Producers make up the first trophic level.
Consumers make up the second, third, or higher
trophic levels.
Each consumer depends on the trophic level below
it for energy.
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Ecological Pyramids
3–2 Energy Flow
Ecological Pyramids
Ecologists recognize three different types of
ecological pyramids:
Ecological Pyramids
The amount of energy or matter in an ecosystem
can be represented by an ecological pyramid.
•  energy pyramids
An ecological pyramid is a diagram that shows
the relative amounts of energy or matter contained
within each trophic level in a food chain or food
web.
•  biomass pyramids
•  pyramids of numbers
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Ecological Pyramids
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0.1% Third-level
consumers
Energy Pyramid:
Shows the relative
amount of energy
available at each
trophic level.
1% Second-level
consumers
10% First-level
consumers
Only 10 % of the
energy that is stored
in one trophic level is
passed on to the next
level.
100% Producers
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Ecological Pyramids
The more levels that exist between a
producer and a top-level consumer in an
ecosystem, the less energy that remains from
the original amount.
Only about 10 percent of the energy
available within one trophic level is
transferred to organisms at the next
trophic level.
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Ecological Pyramids
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Ecological Pyramids
Biomass Pyramid:
Biomass Pyramid
The total amount of living tissue within a given
trophic level is called biomass.
Biomass is usually expressed in terms of grams of
organic matter per unit area.
50 grams of
human tissue
Represents the amount of
living organic matter at each
trophic level. Typically, the
greatest biomass is at the base
of the pyramid.
500 grams of
chicken
5000 grams
of grass
A biomass pyramid represents the amount of
potential food available for each trophic level in an
ecosystem.
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Ecological Pyramids
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Ecological Pyramids
Pyramid of
Numbers:
Pyramid of Numbers
A pyramid of numbers shows the relative number
of individual organisms at each trophic level.
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Shows the relative
number of individual
organisms at each
trophic level.
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Ecological Pyramids
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For some ecosystems, the shape of the pyramid of
numbers is the same as that of the energy and
biomass pyramids.
The main source of energy for life on Earth is
a.  organic chemical compounds.
However, in ecosystems where there are fewer
producers than there are consumers, such as a
forest ecosystem, the pyramid of numbers would not
resemble a typical pyramid at all.
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b.  inorganic chemical compounds.
c.  sunlight.
d.  producers.
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Organisms that feed on plant and animal
remains and other dead matter are
How does a food web differ from a food chain?
a.  detritivores.
a.  A food web contains a single series of
energy transfers.
b.  carnivores.
b.  A food web links many food chains together.
c.  herbivores.
c.  A food web has only one trophic level.
d.  autotrophs.
d.  A food web shows how energy passes from
producer to consumer.
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In a biomass pyramid, the base of the pyramid
represents the mass of
The amount of energy represented in each
trophic level of consumers in an energy pyramid
is about
a.  heterotrophs.
a.  10% of the level below it.
b.  primary consumers.
b.  90% of the level below it.
c.  producers.
c.  10% more than the level below it.
d.  top level carnivores.
d.  90% more than the level below it.
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