Energy Flow DQC’s
Unlike matter, which cycles within the Earth’s ecosystems, energy flows directionally, entering the
Earth’s ecosystems as sunlight and leaving as reflected sunlight or heat. The biosphere is an “open”
system with respect to energy. However, energy and matter are coupled, but are not interchangeable;
students struggle to understand this relationship. A common misconception is that matter is converted to
energy during transformations of organic material, and is often accentuated by commonly used phrases
(e.g. “Cereal at breakfast provides the energy needed for an active day”). Plants capture solar energy and
store it as chemical energy within carbon compounds, and most of this chemical energy is converted to
heat energy during cellular respiration. Two Diagnostic Question Clusters (DQC’s), Energy Pyramid
and Rainforest provide parallel questions to diagnose student reasoning about energy flow through
ecosystems. Both DQC’s ask students to reason about an ecosystem scale energy flow question, and
subsequent questions diagnose their ability to trace energy through individual processes involved in
energy flow through ecosystems. The goal is to identify the knowledge gaps, misconceptions and
misapplications that prevent students from understanding ecosystem scale questions. The names of
individual questions categorized by process are shown in the table below.
Processes
Multiple Process
Photosynthesis
Energy Pyramid
ENERPYR1 (1)
CORNGROW (7),
Transformation – Plant – Plant
Transformation Plant – Animal
GRAPGLUC (4)
Transformation – Plant to Decomposer
Transformation – Animal to Animal
Transformation – Energy Loss
Respiration – Decomposition
BREADMOLD (6)
TREEENER (3)
DEERWOLV (2)
TROPHERNER (5)
BREADMOLD (6),
TREEENER (3)
Rainforest
TROPFOREST (1)
ECOENER1 (2a),
OWLSUN (2b)
ENERGYL1 (3),
TREEFOREST (6)
TREEFOREST (6)
ENERGAINA (4a)
OWLSUN (2b)
BREADMOLD (5)
ENERGAINB (4b)
COMPOST (7),
BREADMOLD (5)
Energy Pyramid Diagnostic Question Cluster
Tracing energy is a necessary principle for understanding ecosystem ecology. Many students incorrectly
consider higher trophic levels to contain more energy than lower trophic levels, which is often based on
their own experiences consuming vegetables vs. meat products. This DQC specifically asks students to
trace energy through trophic levels, and properly identify that energy is lost as heat as matter is
transferred within organisms and between trophic levels. Following the initial ecosystem scale, multiple
process question, students are asked about processes regarding energy flow, with questions at molecular,
organismal and ecosystem scales.
General Instructions for Coding DQC Responses
Responses to DQC questions can be grouped into three general categories; Informal, Mixed or
Scientific. These three categories encompass a wide range of reasoning abilities, but all three categories
are common among college students. The table below describes the general types of responses that
would be associated with each level of reasoning. In addition, the levels of reasoning are assigned a
numerical value for coding purposes. Codes 2-4 are used for responses that attempt to answer the
question, while codes 1a-1e are reserved for missing responses or those that provide no information
about student reasoning. Mixed reasoning presents itself in several different ways, thus level 3 answers
are divided up into subcategories to reflect different types of responses.
Code
4
3
2
1a
1b
1c
1d
1e
Level
Scale
Successful use of
other scales to
explain macroscopic
phenomena
Processes described
in terms appropriate
for that scale
Partially successful
attempts to connect
scales, but with some
inappropriate use of
macroscopic ideas at
other scales
Matter
Reactants and products described
as chemical substances
Accounts of processes describe
Principled
transformation of reactants into
reasoning
products in ways that conserve
atoms at the atomic-molecular
scale and mass at larger scales.
Less than completely successful
attempts to conserve matter.
Reactants and products described
as material kinds, but atoms not
Mixed
traced through chemical processes
reasoning
and matter-energy
transformations may be used as a
“fudge factor.)
No attempt to make
Material inputs or needs and
connections across
products or results are mentioned,
scales for questions
but not in ways that clearly
posed at
distinguish matter, energy, and
macroscopic scale
conditions.
Informal
Inappropriate use of
No indication that the student is
reasoning
macroscopic scale
reasoning about transformation of
ideas at other scales
matter: no account of how
material inputs are transformed
into results.
Missing data (e.g. responses or codes lost after exam was taken and coded)
Student did not reach question
Student skipped question
I don’t know or equivalent
Nonsense answer that is not responsive to question
Energy
Forms of energy are clearly
identified and distinguished
from forms of matter.
Energy transformation
described in ways consistent
with energy conservation.
Energy is recognized as a
distinct entity, but sometimes
in ways that do not clearly
distinguish energy from matter
(e.g., glucose, ATP) and/or
conditions (e.g., temperature).
Accounts fail to conserve
energy.
“Energy” used in an informal
sense as something that makes
events happen.
No clear distinction between
energy sources and other
needs or inputs.
These general ideas for coding above are applied to each individual question below to provide specific
details for how to code each question. Still, you will find that the specific coding rubric for each
question does not list every possible answer that you might see. In these cases, refer back to the general
rubric above, and try to be as objective as possible. You will undoubtedly find responses that don’t quite
fit a specific category, but seem to be in between. For these scenarios, we suggest that you assign a 2.5
or 3.5 code to the student.
Energy Pyramid Diagnostic Question Cluster
Please answer the questions below as carefully and completely as you can.
1. Consider the three diagrams below. They represent three situations in which 100 kg of green
plants serve as the original source of food for each of the food chains. In situation II, for
example, cattle eat 100 kg of green plants and then people eat the beef that is produced by the
cattle as a result of having eaten the plants.
In which of the three situations is the most energy available to people?
A) I
B) II
C) III
D) Situations I and II will roughly tie for the most energy.
E) The same amount of energy will be available to people in all three situations.
Please explain your answer.
As matter is transferred between trophic levels, not only is matter lost to the ecosystem, but energy is
also lost as heat. Therefore, the most energy is available to the person in diagram III, where the fewest
steps are taken to get to the person.
Processes = Multiple Process, Principles = Tracing Matter and Energy, Scale = Ecosystem ->
Atomic/Molecular
Interpreting Student Responses: This question requires students to be able to trace matter and energy
through an ecosystem and to know that energy is expended as matter is transferred from one trophic
level to the next. Students who choose I or II are not effectively tracing matter and/or energy through the
ecosystems, and are relying more on their perception of the question based on personal experiences that
do not include principled reasoning.
Coding Rubric – Energy Pyramid #1
Code
4 - Scientific
3a - Mixed
3b – Mixed
3c - Mixed
2 - Informal
1a
1b
1c
1d
1e
Example Student Responses
“Energy is used at each step. Some must be
lost.”
“The sun provides the most energy we use. The
plants use the sun so really all energy comes
from the sun. Every chain away from the plants is
less energy because each animal uses some of the
energy provided from the link before them.” –
EP20
“Energy is not destroyed, so it is transferred
evenly through the animals to people.” –EP8
“Food gives energy no matter how it is
made/consumed or which level of the food
pyramid is there.”– EP16
“because each additional link to that food chain
adds their energy to the original product.” EP17
Description
Student chooses C
Student chooses E
Student chooses A
“B/c ther are more steps in the food chain more
and more energy is produced and ultimately
available to people.” EP18
“Cattle for 100kg provides more calories for less Student chooses B
compared to fish and green plants.” -EP19
“Your getting higher quality food because your
Student chooses D
eating protein which gives you more energy than
plants.” EP21
Missing data (e.g. responses or codes lost after exam was taken and coded)
Student did not reach question
Student skipped question
I don’t know or equivalent
Nonsense answer that is not responsive to question
2. A remote island in Lake Superior is uninhabited by humans. The primary mammal populations are
white-tailed deer and wolves. The island is left undisturbed for many years. Select the best answer(s)
below for what will happen to the average populations of the animals over time.
_____a. On average, there will be more deer than wolves.
_____b. On average, there will more wolves than deer
_____c. On average, the populations of each would be about equal.
_____d. The populations will fluctuate, with sometimes more deer than wolves, sometimes more wolves
than deer
_____e. None of the above.
Please explain your answer to what happens to the populations of deer and wolves.
Wolves are carnivores, which mean that they consume herbivores such as deer. Although the wolves kill
some deer, there are many more deer than wolves in the ecosystem. If the populations were equal, the
wolves would quickly run out of food – as not enough deer would survive to reproduce. In addition, a
small proportion of the matter and energy in a deer is actually transferred to a wolf that eats it; most is
lost as carbon dioxide (matter) or heat (energy).
Processes = Transformation, Principles = Tracing Matter, Scale = Ecosystem -> Atomic/Molecular
Interpreting Student Responses: Many students who recognize the food pyramid pattern in the more
conventionally worded #1 fail to recognize it for this question. This is an indicator that their
understanding of food pyramids is shallow—something that they recite in response to certain cues—
rather than being based on a principled understanding of the necessity of food pyramids: If herbivores
and carnivores are both losing biomass through cellular respiration, than there has to be less available
for the carnivores.
Coding Rubric – Energy Pyramid #2
Code
4 - Scientific
3a - Mixed
3b – Mixed
3c - Mixed
2 - Informal
1a
1b
1c
1d
1e
Example Student Responses
Description
No student responses in the pilot data
exemplified a Level 1 response
“an equilibrium is reached where deer are
reproducing enough to support a healthy wolf
pop, or the wolves don't reproduce too much and
wipe out the deer pop.” EP60
“Too many wolves = too few deer= wolves die =
deer repopulate.” EP-7
Student chooses A and they cite incomplete energy
transfer through trophic levels in their explanation.
Student chooses A, but they do not explain their
choice or the explanation does not include ideas about
transfer of energy through trophic levels.
Student chooses D or E and explains that the
populations would cycle (e.g. wolves would deplete
deer enough that wolves would decline and then, when
the wolf population was low, the deer population
would grow again). This answer indicates a lack of a
complete understanding of predator-prey dynamics
because the student does not account for the
incomplete transfer of energy from one trophic level
to the next.
Student Chooses C
“The more the wolves populate, the more deer is
needed to feed them. In the long run, there would
be more wolves because they only die of age,
disease or each other.” EP-6
"The fluctuation will occur to try to meet
Student Chooses B OR Student chooses C, D, or E
balance." EP-8
and explicitly states that the populations remain
"They would most likely reproduce with their
approximately equal due to the concept of "balance."
same species consistently and roughly the same
amount."EP-23
Missing data (e.g. responses or codes lost after exam was taken and coded)
Student did not reach question
Student skipped question
I don’t know or equivalent
Nonsense answer that is not responsive to question
3. A tree falls in the forest. After many years, the tree will appear as a long, soft lump barely
distinguishable from the surrounding forest floor. Do you think that the process of decay involves
energy? Circle Yes or No.
Please explain your answer.
Energy is stored as chemical potential energy within the bonds that hold the matter together within the
tree. During the decay process, some of this energy is transferred to the decomposers, remaining in the
form of chemical potential energy, now stored within the decomposer. However, some of the energy is
converted to heat energy, and is lost to the atmosphere.
Processes = Respiration, Principles = Tracing Energy, Scale = Organismal -> Atomic/Molecular
Interpreting Student Responses: This question requires students to understand that potential energy is
stored in molecules within organisms. When an organism dies, the potential energy stored in
biomolecules does not leave the tree until the process of decomposition occurs. Some students think that
dead trees do not have energy. These students are not properly applying the principle of conservation of
energy.
Coding Rubric – Energy Pyramid #3
Code
Example Student Responses
Description
4 - Scientific
-Yes: Decomposers use the organic material in
the tree in their energy harvesting pathways
3a - Mixed
-Yes: As it decomposes, it is used by critters for
food energy and it probably releases some form
of it as well.
-Student chooses Yes and explains that the energy is
located in the carbon containing compounds of the
tree, and that this energy is transferred to the
decomposers during decomposition, (NOT converted
to energy). They may also discuss heat loss as a form
of energy during decomposition.
-Student chooses Yes but provides a vague
explanation or an explanation with incorrect details
about the energy involved.
3b – Mixed
- Yes: Energy is involved by using carbon
dioxide,
-Student chooses Yes and incorrectly converts matter
to energy, or vice versa.
3c - Mixed
NA
NA
2 - Informal
- No
-Yes: The tree breaks down itself because of lack
of nutrients provided from the soil
--Yes: Energy is needed to decompose the tree
-Student chooses No
-Student chooses Yes and describes that energy is
“needed” to break down the tree.
1a
1b
1c
1d
1e
Missing data (e.g. responses or codes lost after exam was taken and coded)
Student did not reach question
Student skipped question
I don’t know or equivalent
Nonsense answer that is not responsive to question
4. You eat a grape high in glucose content. How could a glucose molecule from the grape provide
energy to move your little finger?
A) The glucose is digested into simpler molecules having more energy.
B) The glucose reacts to become ATP (Adenosine Triphosphate).
C) The glucose is converted into energy.
D) The energy of the glucose is transferred to other molecules.
E) The energy of the glucose is transferred to CO2.and H2O.
Processes = Transformation, Principles = Tracing Matter and Energy, Scale = Organismal / AtomicMolecular
Interpreting Student Responses: This question explores whether students understand how chemical
potential energy is stored and released through molecular transformations of carbon. Very few students
answer this question correctly, showing us as instructors that they do not understand the flow of energy
at an atomic-molecular level. Students who answer A are not properly applying the principle of
conservation of energy because they believe one molecule with a certain amount of energy can be
broken into molecules that have MORE energy. Students who answered B are not properly tracing
matter - they do no know the correct chemical composition of glucose and ATP or they think one atom
can become another (e.g. carbon can become phosphorus). Students who answer C think that matter can
be converted to energy and do not understand conservation of matter. D is the correct answer. Students
who answer E are confused, but know the equation for respiration.
Coding Rubric – Energy Pyramid #4
Code
Example Student Responses
Description
4 - Scientific
D
Student chooses D
3a - Mixed
C
Student chooses C
3b – Mixed
B
Student chooses B
3c - Mixed
E
Student chooses E
2 - Informal
A
Student Chooses A
1a
1b
1c
1d
1e
Missing data (e.g. responses or codes lost after exam was taken and coded)
Student did not reach question
Student skipped question
I don’t know or equivalent
Nonsense answer that is not responsive to question
5. The top of a food web:
A) accumulates all of the energy that existed in the consumed organisms that were lower in the food
web.
A) has less available energy than trophic levels below it.
A) has the same amount of accumulated energy as each of the trophic levels below it.
A) has available to it all of the energy of the food web.
Please explain your answer.
As energy is transferred between trophic levels, much of it is lost as heat and leaves the ecosystem.
Therefore, the organisms at the top of the food web must have less energy than the trophic levels below
them because there is no other way to acquire energy, except by consuming organisms in lower trophic
levels (unless it is a plant).
Processes = Transformation, Principles = Tracing Energy, Scale = Ecosystem
Interpreting Student Responses: This question requires that students understand that not all energy is
transferred from one trophic level to the next because acquiring and assimilating biomolecules requires
an expenditure of energy. Many students assume that the top of the food web contains the same amount
of energy as levels below them (C), which means that they are incorrectly conserving energy within the
ecosystem. Other students assume that higher trophic levels have more energy than lower trophic levels
since they are often larger and consumer more animals (A,D).
Coding Rubric – Energy Pyramid #5
Code
Example Student Responses
Description
4 - Scientific
EP68 - B; energy is lost in each transaction, so
as you go up the food web you lose energy (that's
why there are a lot of plants and small animals,
but fewer big predators - it takes more energy to
sustain them.
Student chooses B and describes energy lost as heat
from cell respiration at every preceding level. May
also attributes lower numbers and biomass at higher
trophic levels to this loss of energy during transfer.
3a - Mixed
EP36 - B; Similar to the answer I gave earlier,
more energy is used up as it passes through more
organisms.
EP28 - B; Farther down the food web not all the
nutrients get passed on because its converted into
energy and then used in the process.
EP9 - C; The top of the food web can only have
as much energy as what's below it.
Student chooses B with incorrect or no rationale
given, especially where matter and energy are
confused.
3b – Mixed
3c - Mixed
2 - Informal
1a
1b
1c
1d
1e
Student Chooses C
EP42 - A; the top needs to consume energy
Student Chooses A
passed on from all levels below. Top levels need
more energy than lower ones.
EP49 - D; The energy is consumed by predator
Student Chooses D
after predator till it reaches the top of the food
chain, therefore all the energy goes upward.
Missing data (e.g. responses or codes lost after exam was taken and coded)
Student did not reach question
Student skipped question
I don’t know or equivalent
Nonsense answer that is not responsive to question
6. A loaf of bread was left uncovered for two weeks on a balance measuring its mass. Three different
kinds of mold grew on it, decomposing the bread. Assuming that the bread did not dry out, which of the
following is a reasonable prediction of the weight of the bread and mold together?
A) The mass has increased, because the mold has grown.
B) The mass remains the same as the mold converts bread into biomass.
C) The mass decreases as the growing mold converts bread into energy.
D) The mass decreases as the mold converts bread into biomass and gases.
Please explain your answer and indicate any important transformations.
Correct, Scientific Answer: When mold grows on the bread, it is actually decomposing the bread and
breaking down organic molecules. Some of the carbon in these organic molecules is converted to carbon
dioxide during cellular respiration and some is incorporated into the biomass of the mold. The mold is a
heterotrophic organism and cannot photosynthesize, thus (a) is incorrect. Choice (b) assumes that the
mold is not respiring, and subsequently losing mass, which is incorrect. Choice (c) is incorrect because
matter cannot be converted to energy.
Processes = Respiration, Biosynthesis Principles = Matter, Scale, Scale = Organismal ->
Atomic/Molecular
Purpose of Question: Most students recognize that mass is transferred from the bread to the growing
mold. Very few students, however, account for the carbon cost (loss to atmosphere during metabolism)
during the process of assimilating bread carbon into biomolecules within the mold. Students more
readily use an overly simplified solid-solid cycle rather than incorporate solid-gas matter conversions.
Several students improperly cited “conservation of mass” as a reason why the mold + bread combo
would not lose mass.
Coding Rubric – Energy Pyramid #6
Code
Example Student Responses
Description
4 - Scientific
D: The mold will grow, buit also gives off waste
gasses like CO2 and water vapor, which will
decrease the mass of the bread and mold (GJ8)
Student chooses D, and describes how some bread
biomass is incorporated into the mold, but some is lost
as CO2 to the atmosphere, likely due to cellular
respiration.
3a - Mixed
C: The molds were using the bread as a source of
energy therefore the nutrients from the bread
were being lost. (GJ9).
Student chooses C and says that some of the mass is
being converted to energy or student chooses D and
confounds matter and energy in their explanation.
D: The mold takes resources from the bread and
converts it into energy for itself to grow and
expand, what it cannot use will turn into waste
and gas (GJ46)
3b - Mixed
D: The mold uses the bread to grow by
consuming it. The mold doesn't use all it
consumes so the waste is expelled (GJ55).
Student chooses letter D, but provides a vague
explanation that does not explicitly explain that gases
are a product of respiration by the mold, often talking
about waste from mold.
3c - Mixed
B: The mold uses bread and water to grow by
decaying it however molds mass increases
(GJ53).
Student chooses B and provides no explanation or
recognizes transformation but not oxidation. They
may cite conservation of matter in their answer OR
student chooses A and thinks that the bread is not the
only source of mass for the mold.
A: not very sure but, I would assume the bread is
not the only source of food for the mold.
Therefore the biomass would still increase even
though some of the bread is gone.” (RF-16)
2 - Informal
1a
1b
1c
1d
1e
A: It’s a growing fungus (GJ48).
Student chooses letter A and provides no explanation
or chooses A or B, but their explanation does not show
a commitment to tracing matter or energy.
Missing data (e.g. responses or codes lost after exam was taken and coded)
Student did not reach question
Student skipped question
I don’t know or equivalent
Nonsense answer that is not responsive to question
7. Each Spring, farmers plant about 5-10 kg of seed corn per acre for commercial corn production. By
the fall, this same acre of corn will yield approximately 4-5 metric tons (4,000 – 5,000 kg) of dry,
harvested corn. What percent of the mass of the harvested corn was once in the following substances and
locations? Fill in the blanks with the appropriate percentages; you may use 0% in your response if you
feel it is appropriate.
2.5
<1
95
2.5
0
% from absorption of mineral substances from the soil via the roots
% from absorption of organic substances from the soil via the roots
% from incorporation of CO2 gas from the atmosphere into molecules by green leaves
% from incorporation of H2O from the soil into molecules by green leaves
% from absorption of solar radiation into the leaf
Processes = Photosynthesis, Principles = Tracing Matter and Energy, Scale = Ecosystem ->
Atomic/Molecular
Purpose of Question: Many students can recite and/or write the chemical equation for photosynthesis,
but do not properly apply it to questions about mass gain in plants. Most often, students think that mass
is gained by absorbing materials through their roots – including carbon based substances. Some students
misinterpret the question, not considering only dry biomass, and thus provide a much larger value for
water than the correct value. Other students falsely convert energy to matter by supplying a positive
value for the last blank.
Coding Rubric – Energy Pyramid #7
Code
Example Student Responses
Description
4 - Scientific
EP15 - 1,1,89,0,0; all living things are made
from carbon that comes from CO2
3a - Mixed
EP61 - 15,15,20,20,30; water and sunlight are
two of the most important necessities in a
phototrophic plants' life cycle. Therefore it must
have more food and water and CO2 to convert
into energy.
10,10,50,30,0 (Sample)
3b - Mixed
EP3 - 30,30,20,10,10
EP7 - 20,50,10,10,10
EP6 - 25,25,25,25,0
EP20 - 33,0,33,33,0
3c - Mixed
EP62 - 8,10,4,75,3; the water will be the cause of
most of the weight. Absorption of minerals and
organic matter are what is next as gas and solar
energy do not have much mass they do not take
up much of the weight.
EP36 - 20,25,5,45,5; Most is water, then
minerals and organic substances.
EP25 - 20,20,20,20,20; It uses all to grow.
Student attributes approximately a fifth of the mass
EP11 - 18,14,25,25,18; Well w/ the process of
gain to each of the five sources, often arguing
photosynthesis I feel each is about equal but H20 explicitly or implicitly that all five are necessary for
and CO2 play a bigger role.
plant growth.
Missing data (e.g. responses or codes lost after exam was taken and coded)
Student did not reach question
Student skipped question
I don’t know or equivalent
Nonsense answer that is not responsive to question
2 - Informal
1a
1b
1c
1d
1e
Student attributes the vast majority of the weight gain
to incorporation of CO2 (>75%), and 0% to solar
radiation, which must not provide any mass.
Student argues that solar radiation is responsible for a
substantial portion (>10%) of the plants' mass,
demonstrating a confusion of matter and energy.
Exception: solar radiation is shown as equivalent to
the other factors in terms of mass increase (see
below). OR Student attributes 50-75% of the mass to
CO2, and attributes the remaining mass to other
factors.
Student attributes more than 60% of the mass to the
sum of uptake from organic and mineral components
of the soil. OR Student attributes approximately one
fourth of the mass gain to each of the first four
categories, excluding solar radiation. OR Student
attributes a third of the mass gain to the soil, one third
to CO2 and one third to water
Student argues that most of the mass gain is due to
uptake of water (>40%), even though the question
makes very clear that the corn is measured with dry
biomass.