4. Understanding that cellular respiration results in heat (energy) loss
Notes to faculty
Outcomes: Students will understand that heat is a form of energy, heat is lost by
organisms, and that loss of heat energy occurs with cellular respiration. Students will
demonstrate an understanding by identifying the source of heat energy, trace the
transformation of energy to heat, and where heat goes, using a concept map or flow
chart. Students will be able to identify on a food web illustration where energy enters the
web, how it is transferred and transformed, where cellular respiration occurs, where heat
energy is lost, and where heat energy ends up.
What students do: Students observe initial demonstration on thermal images, investigate
web sites with thermal images, and work individually or in groups to answer questions
about heat energy. Either individually or in groups, they construct concept maps or flow
charts that illustrate the results of cellular respiration in terms of energy and, specifically,
heat loss from organisms.
Logistics: The time allocated for this exercise will depend how much out-of-class time
students use to work on the four steps. Much of it can be done as homework if the
images are made available to students electronically. Depending on the initial level of
student understanding, their interest, and the time that you have allocated for this topic,
choose one or more of the following phases, but the full sequence (an example of a 5E
teaching cycle) is recommended.
• Engage – Students are “engaged” in the topic through thermal imaging and its
applications. Thermal imagers measure heat radiating from a surface; they do not
measure the temperature of an object. So thermal images indicate heat loss from a
surface. For instance, firefighters use thermal imagers to find people trapped in fires;
thermal images are also used in diagnosis of diseases in humans, other animals, and
plants. Students examine a thermal image of a handprint and discuss the patterns. You
can use “pair-share” for initial discussion of thermal handprint (e.g., what do you see and
what might explain the patterns) as a set-up for a whole class discussion. You can use a
thermal image handprint on powerpoint, on a web site, and/or live demonstration with
sheets of thermal imaging film. Also, this could be done as out-of-class/homework
assignment, preferably with students either answering questions via class management
system (e.g., Blackboard) or via hardcopy. Class-time needed: 0-10 minutes, depending
on out-of-class/homework done.
• Explore - Students then delve further into issue of heat loss. They examine thermal
images of animals (both “warm-blooded” and “cold-blooded”) and discuss what they
observe. They should formulate questions and develop hypothesizes that can be tested
by further examination of thermal photos and/or simple observations that can be
conducted anywhere, without equipment. This can be done as homework or in-class
activity; done individually or in groups. Follow-up with class discussion or electronic
discussion system. Ask: Where does the heat come from? What is the source of the
energy? What is the process that makes that energy available? What is the role of
cellular respiration? What happens to the heat energy? Class-time: 0-15 minutes,
depending on amount of out-of-class/homework done.
• Explain – Students need to arrive - themselves - at the conclusion that energy is
constantly “lost” from living organisms via cellular respiration (and so that contributes to
the relatively low level of ecological efficiency in transfer of energy across trophic levels).
Elicit as much of the following as you can from the students; try to get them to put the
storyline together themselves.
Living things need energy to carry on most of their processes. The cells of living things
oxidize carbohydrates, in the process known as cellular respiration, which provides
energy for living things. Plants produce the carbohydrates (for themselves); animals
acquire carbon-based products from plants. The balanced equation for cellular
respiration (oxidation of glucose) is as follows:
C6H12O6 + 6 H2O + 6 O2 ---> energy + 6 CO2 + 12 H2O
Exactly where does the released energy come from? Sunlight (light energy) was used
via photosynthesis to create chemical energy held in bonds of glucose molecules. Some
of that glucose will be acquired by plant-eaters. Now what happens to that glucose?
Then what happens to that released energy? Some of the energy is captured in the
chemical bonds of molecules (ATP) that power cells, and some of the energy is
dissipated as heat, which eventually is transferred to the environment. And eventually it
is transferred to the biosphere, in general, and then potentially into space. In terms of the
Earth, energy “flows”; that is, heat energy is eventually “lost”. In terms of the universe, it
is a closed system; that is, energy is not destroyed, rather it is converted to different
forms.
So energy has been transformed. And it has also been conserved because it is not used
up. All of it exists in some form somewhere. We can trace the path and amounts of all
forms of energy. At this point, students should be able to draw a concept map or flow
chart. However, they may not yet have it developed fully.
Class-time: 10-20 minutes, depending on amount of out-of-class/homework done.
• Elaborate – Students begin to apply their understanding and expand on it. They
examine thermal images of plants (e.g., skunk cabbage flower) and discuss what they
observe. This can be done as homework or in-class activity; done individually or in
groups. In general, plant metabolism has a negligible influence on plant temperature,
which reflects both the level of metabolism and insulation qualities of plants. It does not
mean that plant cells fail to produce heat from cellular respiration; they do produce heat
from cellular respiration, as can be demonstrated by germinating large seeds, such as
lima beans. For lecture courses, a digital thermal gun (relatively inexpensive due to
common industrial applications), lima beans and ziplock bags suffice for demonstration.
This can also be done as homework, by students comparing control (seeds with no
water) versus germinating seeds (with water). Furthermore, some plants produce tissue,
such as specialized flower parts, that can produce substantial heat, which facilitates
pollination by insects. The story of skunk cabbage (with interesting photos, drawings and
research reports) is available on the internet. Follow-up with class discussion or
electronic discussion. Students should be able now to generate a more sophisticated
explanation of cellular respiration, heat production, and heat loss in living organisms.
They should be able to trace energy from sun to plants to animals to environment to
space, and they should indicate where heat energy occurs due to cellular respiration and
what happens to that heat energy. At this point, students should be able to refine their
concept map or flow chart. Check for questions and confusion by reviewing and
discussing their concept maps or flow charts. Students should demonstrate an
understanding that energy is transformed, yet conserved. Class-time: 0-30 minutes,
depending on amount of out-of-class/homework done.
• Evaluate – At this point, students may be given some form of assessment of
this specific topic. For example, ask students to examine an illustration of a food web in
a textbook and identify where cellular respiration occurs and where heat energy is lost
from organisms into the environment. Every living organism exhibits cellular respiration;
all will have heat (energy) loss to the environment, even if only small amounts. Classtime: 0-10 minutes, depending on amount of out-of-class/homework done.
Hidden Curriculum addressed
• Principles - Conservation of Energy. In cellular respiration organisms transform
the chemical energy in compounds such as glucose into usable chemical energy and
some of the chemical energy is lost as heat from organisms
• Processes: Oxidation - cellular respiration occurs in the cells of all aerobic
organisms.
• Scale & Time: Students – comprehend the molecular and cellular processes
that take place in cellular respiration; where these occur within organisms such as
animals; and how these molecular/cellular processes relate to organismal processes.
• Forms & Representations: Matter & Energy Flow - Students recognize that
glucose - and other organic - molecules are a form of potential chemical energy; Energy
comes in different forms (thermal, potential, light, sound); heat is a form of energy.
Glucose is a type of energy-rich organic compound, also shown as C6H1206.
Student Directions
Your instructor will give you specific instruction for each of the steps below, including
where do locate the images.
1. Engage: Firefighters use thermal imagers to locate people in burning buildings.
Thermal imagers cannot see through solid objects, but they can detect heat that was
transferred to a surface. Some thermal imagers can detect a difference of 0.05 o C,
which is a very small amount. Using such equipment, firefighters can detect footprints or
handprints, and so track where people might have gone to try to escape a fire. One
study showed that, without the thermal imager, victims were located less than 40% of
the time, but with the imager, detected 99% of the time.
Footprints and handprints are not living! Where does the heat of the footprints and
handprints come from? How/why is heat transferred? What happens to it after transfer to
an object?
Observe a thermal image handprint. What patterns do you see? How do you explain the
patterns? Pair with a neighbor in class (or outside class) and discuss your answers.
2. Explore: Observe thermal images of a variety of animals. What patterns do you see?
How do you explain those patterns? Do “cold-blooded” animals exhibit temperature
warmer than ambient? Explain. Develop hypotheses that you can test by further
examination of thermal images and simple observations that you can conducted right
now. What are your conclusions?
Where do these animals get the heat that is detected in the thermal images? Trace this
form of energy back to the original source of energy. How/why is the heat transferred?
To what is it transferred? What happens to it after transfer to an object? What is the role
of cellular respiration?
3. Explain: Examine the balanced equation for cellular respiration (oxidation of glucose):
C6H12O6 + 6 H2O + 6 O2 ---> energy + 6 CO2 + 12 H2O
Identify each item in the equation and where it comes from. Exactly where does the
released energy come from? What happens to the released energy?
Create a concept map or flow chart. Work backwards to show the origin of energy (e.g.,
where does it come from). Work forwards to show where energy ends up (e.g., where
does it go).
In ecology/biology, what does the term “energy transfer” mean? What does “energy
transformation” mean? What does the term “conservation of energy” mean?
4. Elaborate
Observe thermal images of plants (e.g., skunk cabbage). What patterns do you see?
How do you explain those patterns? Do plant cells exhibit temperature warmer than
ambient? Explain. Develop hypotheses that you can test by further examination of
thermal images or by germinating some large seeds, such as lima beans. What are your
conclusions?
Where do plants get the heat that is detected in the thermal images? How/why is the
heat transferred? To what is it transferred? What happens to it after transfer to an
object?
Review your concept map/flow chart. Given what you have learned, refine it (e.g., make
corrections, expand it). What questions do you have now? Can heat energy from cellular
respiration be recovered? Can it be transformed to another type of energy? Can energy
be used up? Explain your answers.
5. Evaluate: Examine an illustration of a food web in a textbook and identify where
energy transformation occurs, where cellular respiration occurs, and where heat energy
is lost from organisms into the environment.
Useful images and their sources (web sites):
Illustration of energy entering biosphere (yellow = sunlight) and energy (blue = heat)
dissipating from biosphere.
www.chemistryland.com/.../GlobalWarming.html
NASA thermal image of Earth.
visibleearth.nasa.gov/view_rec.php?id=45
Place your hand on this black plastic square and create a beautiful thermal hand print.
Each color represents a different temperature. Can be used over and over again.
http://www.teachersource.com/Energy/Thermodynamics/TouchandSeeSquare.aspx
Comparison of thermal images of live person and his handprint, with Fahrenheit scale.
www.ir55.com/sc1000_sc2000_sc3000_thermacam.htm
Thermal camera's unique view of London Zoo By Roger Highfield, Science Editor,
Telegraph, UK www.telegraph.co.uk/.../2008/02/05/scizoo105.xml
Temperature Regulation by Thermogenic Flowers.
Roger S. Seymour, Environmental Biology, University of Adelaide, Australia; Kikukatsu
Ito, Cryobiosystem Research Centre, Iwata University, Moroika, Japan
www.plantphys.net/article.php?ch=e&id=126