Mrs. Engelbrecht
Objective #4 Activities
Ecology Unit
Ecosystem Interactions—How Feeding Interactions Promote Energy
Flow Through Ecosystems
MCHS Biology
2010-2011
Ecosystem Interactions—Objective #4
Objective #4:
4a:I can explain the roles of autotrophs (producers) and heterotrophs (consumers) in ecosystems.
4b. I can identify food chains within food webs, and label the trophic levels to which each organism
belongs.
4c. I can explain why decomposers are very important to organisms in ecosystems.
4d. I can interpret an energy pyramid to determine what happens (and why it happens) to the amount
of energy as you move up the trophic levels.
Vocabulary Practice
A. Word Parts
Fill in the chart below concerning the word parts. These will help you figure out the definitions for some of the
vocabulary words for this unit.
Word Part
Meaning
autohetero-troph
-ic
B. Partner Knowledge Rater:
Word
1st Try—Guess
or Draw
2nd Try—Share
with a Partner
autotrophs
(producers)
heterotrophs
(consumers)
food chain
food web
2
3rd Try—After
Rename the
Reading (p. 41-44) word in 3 words
or less
Word
1st Try—Guess
or Draw
2nd Try—Share
with a Partner
3rd Try—After
Rename the
Reading (p. 41-44) word in 3 words
or less
trophic levels
energy pyramid
decomposers
10% rule
Making Connections—First Try
Word Sort & Summary
Using the list of words below, decide which words go together (in other words, which words are related to each
other in some way). Then, in the boxes below the words, write those words together in the same box. After you
have done that, then give each box a title that indicates why those words go together. You must have AT LEAST
TWO GROUPS. You may use a word more than once.
autotrophs (producers)
trophic levels
heterotrophs (consumers)
energy pyramid
decomposers
food chain
food web
10% rule
Connection: _______________________________________
After filling in the boxes, use ALL the
words and the connections you just made
to write 2-3 sentences that summarizes
how all the words are connected. So, not
only do you have to write out the
connections you just made, but you also
have to connect all the groups of words
you formed. Do this on a separate sheet
of paper.
Connection: _______________________________________
Connection: ________________________________________
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Reading For Understanding—Practice
Read the passage below concerning interactions that occur between organisms in ecosystems. Remember,
while you’re reading, do the following:
A. As you are reading, underline any definitions of vocabulary words you find. Change your definitions in the
chart if you need to.
B. Mark the following as you read:
DGT = I don’t get this. I had to re-read this to try and understand it.
!! = I am surprised to find this out
?? = I have a question about this (write your question in the margin)
Ecosystem Interactions—Eat or Be Eaten!
At this point in your wonderful journey through ecology, you have learned what ecology is, how the number
of organisms in a population increase and decrease in size, and how different populations of different species
interact with each other. I know that you’re wondering what could be left to study in ecology, since you have
already learned so much that your brain is about to burst. However, there’s so much more exciting ecological
goodness to learn! All of the interactions we have studied so far regarding populations and communities have
involved biotic factors interacting with other biotic factors; now that we are studying ecosystems, we will now
include how abiotic factors interact with biotic factors, mainly in terms of energy. So, the central question that you
need to keep in mind for this objective is, “How does energy flow and get recycled in ecosystems?”
In order to start answering that question, we need to first start by discussing the two main ways organisms
can obtain energy for growth and reproduction—organisms that are autotrophic (called autotrophs, or
producers) and organisms that are heterotrophic (called heterotrophs, or consumers). If an organism is an
autotroph, that organism can synthesize, or make, its own food using an abiotic energy source of some kind. For
example, any organism that is photosynthetic (plants, algae, some bacteria) is an autotroph, because they convert
the sun’s thermal (kinetic) energy into the chemical (potential) energy of molecules that they then use for energy or
to build cell structures. Other types of autotrophs make their own food without ever seeing the sun, believe it or
not! Some bacteria that live at the bottom of the ocean (which the sun‘s rays do not ever reach) can synthesize
their own food using chemicals that are released by geysers of very hot, magma-heated water. Heterotrophs, on
the other hand, must consume other organisms for food. They then break down these organisms into molecules, and
then use those molecules for energy to power their cells’ activities. Examples of heterotrophs include animals, some
protists, fungi, and some bacteria. Thus, there are two ways any organism in an ecosystem can obtain energy—
they can either convert energy from an abiotic energy source into the molecules their cells need for cell activities,
or they can consume another organism and break it down to get the molecules their cells need for cell activities.
However, autotrophs and heterotrophs are more than just two words that will eventually be in a
differences chart on your test—in ecosystems, they both serve very important roles. Photosynthetic autotrophs
capture energy from the sun and convert it into the potential energy of molecules their cells need to function, as
was said before. This energy transformation is vital to supporting life in ecosystems; indeed, without autotrophs
transforming the sun’s energy, food webs and food chains would soon collapse. Why? Well, autotrophs aren’t
called producers for nothing! When they transform the sun’s energy into the chemical energy of molecules, they use
these molecules to grow and add to their bodies; in other words, they produce more mass to their bodies. The
bodies of the autotrophs are, in turn, eaten, or consumed, by other organisms—namely, the heterotrophs. These
heterotrophs are then eaten by other consumers, which are eaten by other consumers, and so on and so forth, all
the way up the food chain. Thus, autotrophs are called producers because they ultimately produce the food, or
energy, that the heterotrophs, or consumers, must consume to survive.
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Stop and Think
a) What is the main role of autotrophs in ecosystems?
b) What is the main role of heterotrophs in ecosystems?
c) Predict two possible consequence of all autotrophs becoming extinct at this very moment in time:
1.
2.
Now that you know the roles that autotrophs and heterotrophs play in ecosystems, we can now start
answering the first part of our central question: “How does energy flow through ecosystems?” When trying to
answer this part of the question, you should first start by looking at the one thing that all organisms must get in
order to obtain energy to live—food. In order to determine ecosystem energy flow, you must look at which
organisms are feeding off each other, and connect those feeding relationships together to form a food chain. For
example, in a deciduous forest ecosystem, a possible food chain might be: grass  grasshopper  frog 
snake. What this means is that the grasshopper eats the grass, the frog eats the grasshopper, and the snake eats
the frog. In ecology, we consider each organism in a food chain to be at a certain “feeding level;” these feeding
levels are called trophic levels, and each trophic level in a food chain has a name (because, in science, everything
must have a confusing name!). If an organism is a producer (autotroph), it is always first in a food chain, and that’s
why they’re called primary producers. Heterotrophs that consume the autotrophs for food are at the second
trophic level, and they are called primary consumers because they are the first organisms to consume other
organisms in the food chain. Any organisms that feed on the primary consumers are called secondary consumers,
and any organism that feeds on the secondary consumers are called tertiary consumers. (“Tertiary” is a fancy
way of saying “third.” Use it sometime when you’re talking to your friends or family so you can sound smart, such
as: “I got in trouble at the tertiary level of discipline in the student handbook, so now I have a SCAP.”) Whenever
we speak of “moving up” the trophic levels, we mean moving from the primary producers to the tertiary consumers.
Study the diagram of the food chain below, which has the trophic levels labeled for you, as well as other names
for these organisms below each organism’s picture.
Links of food chain (source - Flint, M.L. and Gouveia P. 2001)
While intensely scrutinizing the food chain above and marveling at its energy-flowing glory, you may have
noticed that there is an earthworm at the end of the chain, and it is labeled as a “decomposer.” What do
decomposers do? The answer to this question will lead us to the answer to the second part of our central question:
“How is energy recycled in ecosystems?” Decomposers are an ecosystem’s “clean-up crew;” that is, they are the
ones that will break down organisms after they have died. Decomposers include animals such as earthworms and
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some insects, but they also include fungi and some bacteria. While these helpful organisms keep an ecosystem free
of dead animals littering the landscape by breaking down dead things for their own energy needs, this
decomposition by them serves another purpose—to put nutrients back into the soil, so they can be recycled and
used again by other organisms in the ecosystem (mainly plants or any other organism that obtain nutrients from the
soil). Even though decomposers break down the dead bodies of organisms for their own energy, they also end up
releasing some of the molecules from the dead organisms back into the soil. These molecules are then available to
those organisms that get nutrients from the soil to grow. By putting nutrients back into the soil, decomposers are, in
essence, recycling energy. They are recycling the energy of molecules that would have been “trapped” in the
dead bodies of organisms forever if they were not decomposed.
Stop and Think
a) Why are decomposers necessary in any ecosystem?
b) You and your BFF are at lunch, happily fulfilling your roles as carnivores, feasting away on hamburgers. A
vegetarian comes over from another table and says, “How can you eat cow muscle on a bun?!? Don’t you CARE
about the cow that was KILLED just so you could EAT IT?” You, having just learned all about energy flow
through the trophic levels in Mrs. E’s Biology class, retort, “I’ll have you know that I’m not eating cow muscle; I’m
simply eating stored energy from the sun in this hamburger, just like YOU do when you eat your salads, tofu, and
hummus!”
Explain why your retort was very accurate about how energy flows through the trophic levels.
c) At what trophic level are the vegetarians from question b? ___________________________
d) At what trophic level are you and your BFF from question b? __________________________
e) The next day at lunch, Mrs. E wanders into the cafeteria and observes that very few people are using the
recycling bins for their plastics. She then gets the microphone out and makes an announcement: “Everyone in
here will be a part of a larger recycling effort in our ecosystem one day!”
Explain what she means when she makes this strange announcement.
Food chains in ecosystems are a simple way to illustrate one path of energy flow through ecosystems;
because organisms usually have a taste for more than one animal when they want dinner, food chains are not
enough when mapping out all of the feeding relationships seen in an area. Thus, in order to connect an organism
to all of its possible food sources, all of the food chains in an ecosystem must be connected to each other. When all
of the food chains in an ecosystem are connected, we have created what is called a food web. An example of a
food web is shown on the next page:
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A schematic diagram of a food web in alfalfa. Each arrow represents a transfer of food, or energy from one organism to
another. The web becomes more complex as more species are introduced into the system. (Source - Flint, M.L. and Gouveia,
P. 2001).
Notice that a food web is made of many interconnected food chains, and shows the complex feeding
relationships often present in an ecosystem. This means that energy flow through ecosystems is often not as simple
as a single food chain makes it seem; energy in the form of foods can flow in many “directions” and “places” in a
food web. Also notice that the food web above shows you at which trophic level each organism is located; not all
food web diagrams will be kind enough to show that to you—much like the one pictured on the next page!
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Stop and Think
a) List THREE food chains in the space below. Two of the chains must have 4 trophic levels; 1 chain must have
only 3 trophic levels.
1.
2.
3.
b) In the diagram above, color the organisms listed below the colors indicated:
 Color the primary producers GREEN.
 Color the primary consumers BLUE.
 Color the secondary consumers ORANGE.
 Color the tertiary consumers PURPLE.
 Color the decomposers BROWN.
c) In 3-4 sentences, summarize the relationship between food webs and food chains. Use ALL of the following
words: food web, food chain, trophic levels, autotrophs, heterotrophs, decomposers, producers, primary
consumers, secondary consumers, tertiary consumers.
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While food webs show how energy flows between organisms in an ecosystem, they do not show the
amount of energy that is flowing from one trophic level to the next. In order to show the amount of energy
available to each trophic level in an ecosystem, scientists use what’s called an energy pyramid. Organisms at the
bottom, or largest, part of the energy pyramid have the most available energy to use; organisms at the top, or
smallest part, of the pyramid have the least amount of energy available to them. In the energy pyramid below,
the amount of energy available to each trophic level is listed in kilocalories (kcal), which is a unit of energy. Study
the numbers in the energy pyramid pictured below, being careful not to get caught up in the energy pyramid’s
powerful pyramidal properties:
Did you notice that the amount of kilocalories, or energy, decreases as you move towards the top of the pyramid?
Did you also notice that only ten (10) percent of the energy at each trophic level is available to the level above it?
(If not, go back and look at those numbers again!) This is called the ten percent rule—no matter how much energy
is available at each trophic level, the trophic level above it only gets about 10% of that energy to use to survive.
Where does the 90% of energy go that doesn’t make it to the next trophic level? Well, some of that energy is
used by organisms themselves for energy to grow and add to their own bodies. For example, a rabbit eating
grass uses some of the energy from the grass to add cells to its own body to grow and as energy to fuel cell
metabolism. The rabbit is also giving off heat as a result of this metabolism, which is lost to its environment.
Further, the parts of the grass the rabbit cannot use for energy is eventually excreted as waste (you might know
this better as “poop”), which is basically lost energy that cannot be passed on to the next trophic level (but, thanks
to decomposers, the poop can be broken down so nutrients return to the soil for use by producers and other
decomposers).
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Stop and Think
Study the energy pyramid below:
a) What happens to the amount of energy as you move up the trophic levels? (one-word or one-sentence answers
are unacceptable!)
b) Why does your answer to a) happen?
c) Does the number of organisms increase or decrease as you move towards the top of the energy pyramid?
_______________________________________ Explain why you think this happens, using the 10% rule to support your
answer.
**If you can satisfactorily answer the three questions above, you are at a level 3 understanding of Objective #4d.
Answer the questions below to practice your level 4 understanding of the I can statement.
c) Explain how quote below is simply a different way to state the 10% rule:
Three hundred trout are needed to support one man for a year.
The trout, in turn, must consume 90,000 frogs, that must consume 27 million
grasshoppers that live off of 1,000 tons of grass.
-- G. Tyler Miller, Jr., American Chemist (1971)
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Stop and Think (continued)
d) You are a marine biologist studying a marine (ocean) ecosystem. Specifically, you are studying how much
biomass (organic material in organism’s bodies; organisms add more mass to, or grow, their bodies when they get
energy from the sun or by consuming other organisms) is made at each trophic level. This biomass is consumed
for energy at each trophic level except for the primary producers. You gather data to construct your own biomass
pyramid of the aquatic ecosystem, and you fully expect it to look like a biomass pyramid of a terrestrial ecosystem
(terrestrial biomass pyramids and energy pyramids are similar in shape). However, after you compile your data,
the diagram below is what you come up with:
Write a scientific explanation for why the biomass pyramid for this ecosystem would be inverted, or upsidedown, when compared to an terrestrial biomass pyramid. Use your knowledge of energy flow through
ecosystems to support your answer. (HINT: Think about the differences in producers between a terrestrial
ecosystem and an aquatic ecosystem—are they going to be the same? Will you see different amounts of them?
Why or why not?)
As you can see, energy flow through ecosystems involves a lot of interactions between abiotic and biotic
factors. The source of all energy, the sun, is the primary abiotic factor involved in energy flow, since it is the
ultimate source of all the energy in any ecosystem. After the energy from the sun has been converted to chemical
energy in the primary producers, this chemical energy is then consumed by heterotrophs at the upper trophic levels.
But, no matter what trophic level the organisms in an ecosystem are at, when they die they become food for the
decomposers. The decomposers then break down the dead organisms, obtaining energy for themselves, but also
releasing nutrients back into the soil for use by other organisms in the ecosystem.
Stop and Think
a) You now have enough information to answer the central question of this objective: “How does energy flow and
get recycled in ecosystems?”
b) Explain why energy flow through an ecosystem should be drawn as a circle, and not a straight line:
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Making Connections—Putting It All Together
Below is a choice menu. You must choose ONE choice from each ROW. That means you will be working on two tasks!
Objective #4 Choice Menu
Vocab Puzzle
Get a vocabulary puzzle at either a level 3 or a
level 4. Write the words in the puzzle pieces
according to how they are connected, draw a
picture of each word or concept you place in a
puzzle piece, and write why they are
connected along the borders between the
words.
Vocab Sentences
Analogies
Using the Objective #4 vocabulary words:
Write analogies for the following concepts:
a) Write 4 “differences” sentences
(______________ and _____________ are
DIFFERENT because _______________.)
a) the role of autotrophs in ecosystems
b) the role of heterotrophs in ecosystems
c) the trophic levels in a food web
d) how energy flows through ecosystems
e) the role of decomposers in ecosystems
f) the relationship between a food chain and a
food web
b) Write 4 “connections” sentences
(______________ and _______________ are
CONNECTED because ______________.)
(“Connected” does NOT mean “similar!”)
Concept Map
Comic
RAFT
On a piece of poster paper, make a concept
map that uses all of the Objective #4
vocabulary words AND answers all of the
Objective #4 I can statements. Label all
connectors.
Get an 11 x 17 piece of paper, and fold it into
sixths. In 6 panels, make a comic strip that:
Role: A photon of light from the sun (a photon
is a particle of energy in sunlight)
a) uses all of the Objective #4 vocab words
b) answers all of the I can statements for
Objective #4.
Audience: Television audience
Remember, only 1-2 words in a box, and only
2-3 words on a connector are allowed!
Remember, comics have a STORY LINE. You
must make up a story and illustrate it, and
your story and illustrations must answer the I
cans and use all the vocabulary words.
Format: TV Travel show called “Egon’s Energy
Adventures “
Topic: Episode titled, “I Lost Myself in This
Trip!”
Develop a TV show that reveals to viewers
what really happens to energy as it travels
through an ecosystem. (Make sure you answer
all of the I can statements!)
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Rate Your Understanding of the I Can Statements
When you’re finished, rate yourself on the I cans using the chart below:
Ecosystem Interactions
0 = No
evidence
1=
Beginning
2=
Progressing
3=
Proficient
4A. I can explain the roles of
autotrophs (producers) and
heterotrophs (consumers) in
ecosystems.
4B. I can identify food chains
within food webs, and label the
trophic levels to which each
organism belongs.
4C. I can explain why
decomposers are very important
to organisms in ecosystems.
4D. I can interpret an energy
pyramid to determine what
happens (and why it happens) to
the amount of energy as you
move up through the trophic
levels.
Determine Your Understanding of the I Can Statements
1) Take the Exit Ticket provided by your instructor.
2) Check your answers when you are finished.
3) Mark whatever you did not get correct on your exit ticket.
4) Re-rate yourself on how well you have mastered the I can statements in the rubric above.
5) Staple this page to the back of your Exit Ticket and turn it in to your period’s box.
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4=
Advanced