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Food Chains and Webs ---
Every organism needs to
obtain energy
in order to
live. For
example,
plants
get energy from the sun
, some animals
eat plants, and
some animals eat other
animals.
A
food
chain
is the sequence of
who
eats whom
in a biological
community (an ecosystem) to obtain
nutrition. A food chain starts with
the
primary energy
source
, usually the
sun
or boiling-hot deep sea
vents. The next link in the chain is
an
organism that makes its own
food
from the primary energy
source -- an example is
photosynthetic
plants
that make their own
food from sunlight (using a process called
photosynthesis
) and
chemosynthetic bacteria
that
make their food
energy from chemicals
in hydrothermal vents. These are called
autotrophs
or
primary producers
.
Next come
organisms that eat the autotrophs; these organisms
are called
herbivores
or
primary consumers
-- an
example is a rabbit
that eats grass.
The next link in the chain is animals that eat
1
herbivore -
these are called
secondary
consumers
-- an example is a
snake that eats rabbits. In turn,
these animals are eaten by larger
predators
-- an example is
an owl that eats snakes. The
tertiary
consumers
are eaten by
quaternary consumers
-- an
example is a hawk
that eats owls. Each
food chain ends with a
top
predator
and animal
with
no natural enemies
(like an
alligator, hawk, or polar bear).
Food
Chain Questions
1.
What travels through a food chain or
web?
2.
What is
the ultimate energy for all life on Earth?
3.
Food chains
start with what?
4.
The 1
st
organism
in a food chain must always be what type of
organism?
5.
Name
2 food making processes.
6.
Where do chemosynthetic bacteria get
their energy?
7.
Define herbivore.
8.
Herbivores are
also called _________________________.
9.
What are
animals called that feed on herbivores?
10.
Secondary
consumers are eaten by larger ________________.
11.
_________________ consumers eat
secondary consumers.
12.
Make a food chain with a producer and 3
consumers.
2
The arrows in
a food chain show the
flow of
energy
, from the sun or
hydrothermal vent to a top predator.
As the energy flows from organism to
organism, energy is lost at each step.
A network of many
food
chains
is
called a
food web
.
Trophic Levels:
The trophic level of an organism is the
position it holds in a food chain.
1.
Primary
producers
(organisms that make their
own food from
sunlight and/or chemical
energy from deep sea vents) are the
base of every food chain - these
organisms are called
autotrophs
.
2.
Primary
consumers
are animals that eat primary
producers; they
are also called
herbivores
(plant-eaters).
3.
Secondary
consumers
eat primary consumers. They
are
carnivores
(meat-eaters)
and
omnivores
(animals that
eat both
animals and plants).
4.
Tertiary
consumers
eat secondary consumers.
5.
Quaternary
consumers
eat tertiary consumers.
6.
Food chains
no natural enemies.
When any organism dies, it is
eventually eaten by
detrivores
(like
vultures, worms and crabs) and broken
down by
decomposers
(mostly
bacteria and fungi), and the exchange
of energy continues.
Some
organisms' position in the food chain
can vary as their
diet
differs.
For example, when a bear eats
berries, the bear is
functioning as a
primary consumer
. When a
bear eats a plant-eating
rodent, the
bear is functioning as a
secondary
consumer
. When the
bear
eats salmon, the bear is functioning as a
tertiary consumer
(this
is because salmon is a secondary
consumer, since salmon eat herring
that
eat zooplankton that eat phytoplankton, that make
their own
3
energy from sunlight). Think about how
people's place in the food
chain varies - often within a single
meal!
Food Web Questions
1.
What is used
to indicate the flow of energy in a food chain or
web?
2.
What
happens to energy as we move from step to step in
a chain or web?
3.
Define food web.
4.
What is meant
by trophic levels?
5.
Define autotroph.
6.
The
1
st
trophic level consists
of _______________ consumers called
_________________.
7.
Name the
2
nd
trophic level (both
names).
8.
Secondary consumers may be
_______________ eating meat or
_______________ that eat both plants
and animals.
9.
What is the 3
rd
trophic level called?
10.
What is the 4
th
trophic level called?
11.
At the 5
th
trophic level would be _____________ consumers
that eat
_____________ consumers.
12.
Give an
example of 3 detrivores. On what do they feed?
4
13.
What organism feeds on dead plants and
animals and helps recycle them?
14.
Both
______________ and ______________act as
decomposers
15.
Can an organism fill more than one
trophic level --- yes or no? Give an
example.
Numbers
of Organisms:
In
any
food web
,
energy is lost each time one organism
eats
another
. Because of
this, there have to be many
more plants
than
there are plant-eaters
.
There are
more autotrophs than
heterotrophs
, and more
plant-eaters than meat-eaters. Each level has
about
10% less
energy
available to it because
some of the energy is
lost
as heat
at each level. Although there
is
intense competition
between animals, there is also
interdependence
. When one
species
goes
extinct
, it can affect an entire chain
of other species and have
unpredictable
consequences.
1.
In food chains and webs, what trophic
level must you have more of than
others?
2.
Each trophic level has how much LESS
energy?
3.
What may happen if a species goes
extinct?
Equilibrium
As the number of
carnivores
in a community increases
, they eat
more and more of the herbivores,
decreasing the herbivore population.
It then becomes harder and harder for
the carnivores to find
herbivores to
eat, and the population of carnivores decreases.
In this
way, the carnivores and
herbivores stay in a
relatively stable
equilibrium
, each limiting
the other's population. A similar equilibrium
exists between plants and plant-eaters.
5
Complete the Food Chains Worksheet
Circle the organisms that complete the
food chains below.
6