Name
Then a hawk might eat the snake. The hawk would be a fourth-level
consumer. Each level of consumers eats animals from the level
below.
Food Chains and Food Webs
By Cindy Grigg
The example above is a food chain with five parts: grass,
grasshopper, toad, snake, and hawk. Other food chains are short.
For example, a horse might eat the grass. Few animals eat horses, so
that food chain might only have two parts.
Plants are special living
things. They are special
because they can make
their own food using
energy from the sun.
Plants are primary
producers that produce
food from sunlight, carbon
dioxide, and water.
Knowing the links of a food chain helps you see how energy
moves through an ecosystem. Each time an animal eats, only a
small amount of the energy is stored to become food for the next
level consumer. For example, when an herbivore eats grass, some of
the energy is used by the herbivore to live. Some of the energy is
lost as waste. Only a small amount of energy is stored in the
herbivore's body. When a carnivore eats the herbivore, it receives
only a fraction of the energy that the herbivore took into its body.
Carnivores must eat many herbivores to get enough energy.
Animals cannot make
their own food. Animals
are consumers, because
they must consume, or eat, to get energy to live. Some animals eat
plants. Some animals eat other animals.
Scavengers are animals that eat dead animal remains.
Decomposers, like fungi, bacteria, and some insects, break down
dead organisms, both plants and animals. Decomposers use some of
the dead organisms as food. What they don't use becomes part of
soil, enriching it so that it can grow more producers. Decomposers
join together the top and bottom of the food chain.
When an animal eats food, some of the food's energy is used to
carry out the animal's life processes. Animals need energy to breathe,
keep the heart beating, and excrete wastes, as well as to move around.
Whatever food energy isn't used by the animal is stored in its tissues.
When an animal eats another animal, it gets the energy that was
stored in the dead animal's body tissues. Energy is passed from the
producers (plants) to the consumers (animals). Some consumers eat
only plants. They are called herbivores, and they are the first-level
consumers. A second-level consumer eats first-level consumers.
Second-level consumers are carnivores- animals that eat the meat of
other animals. Third-level consumers eat the second-level
consumers. Carnivores in the food chain that eat other carnivores are
also called tertiary consumers (tertiary means third). A food chain
shows how food energy is passed along from producers to
consumers.
Grass is a producer that makes its own food. Grasshoppers
(first-level consumers) eat grass. Then a toad may eat the
grasshopper. The toad would be a second-level consumer. Then a
snake might eat the toad. The snake would be a third-level consumer.
There are more producers in a food chain than consumers.
Producers use most of the energy they make, passing on only about
ten percent to the consumers that eat them. The consumers, also,
only pass on about ten percent of their energy to the next level
consumer. An energy pyramid shows this relationship among food
chains, with a larger number needed below to support the next level
above. For example, grasshoppers eat ten stems of grass. A toad
might eat ten grasshoppers. These grasshoppers would need to eat
one hundred stems of grass. An ecosystem must have many primary
producers to support a pyramid of consumers. The energy
relationship limits the amount of higher-level consumers. There is
not enough energy to support a large number of carnivores in any
given area.
A food web shows many different food chain relationships.
Many animals eat a variety of different foods to get enough energy
to live. Food energy doesn't always move in a straight line like a
chain. Often the energy moves in various ways so that a drawing of
it looks more like a spider web than a chain-that's why we call it a
food web.
2. What are plants?
Name
All food chains begin with energy from the sun, but we don't
often show the sun as part of the chain. Food chains or webs show
living organisms. Producers use sunlight to make their own food
energy. Consumers eat producers. Other consumers may eat the
first-level consumers. Decomposers break down the tissues of dead
organisms. Soil is enriched by what is left over. It helps more
producers grow. Food webs show the links among several animals.
Most of the food energy taken in is used by the organism. Only ten
percent of energy is passed on in the next higher level of a food
pyramid.
Food chains and webs make a circle of life. Living things take in
food and die. They provide food for other living things. It is another
of nature's cycles with no beginning and no end. When decomposers
break down dead organisms, nutrients and carbon dioxide are
released. Nutrients enrich the soil and help new plants grow. Plants
need carbon dioxide to make their food, and in the process of making
food, they give off oxygen, which is needed by people and animals
to breathe. All living things are connected and help maintain a
balance for life on Earth.
Food Chains and Food Webs
Questions
1. Which of these is the correct order?
A. herbivore, carnivore, producer
B. producer, herbivore, carnivore
C. carnivore, producer, herbivore
D. producer, carnivore, herbivore
3. ______ are animals that eat dead animal remains.
A. Scavengers
B. Carnivores
C. Herbivores
D. Decomposers
4. Carnivores that eat other carnivores are ______.
A. tertiary consumers
B. third-level consumers
C. shown above the second level in the energy pyramid
D. all of the above
5. Which of these is NOT a decomposer?
A. some insects
B. tree
C. bacteria
D. fungi
6. When decomposers break down dead organisms, what are
released?
A. oxygen and sugar
B. nutrients and carbon dioxide
C. carbon dioxide and water
D. oxygen and water
7. Which of these is NOT a fact?
A. Third-level consumers are also called tertiary consumers.
B. An ecosystem must have many primary producers to
support a pyramid of consumers.
C. Herbivores are first-level consumers.
D. All food chains begin with animal protein.
Choose an ecosystem and describe one or more food chains or webs in
that ecosystem.
Name
8. What do second-level consumers eat?
(Compare and contrast) How are food chains and food webs
different? How are they alike?