Todd Bennethum, Department of Biological Sciences, 1392 Lilly Hall, Purdue University, West Lafayette, IN 47907-1392, (317) 494-8107
Bruce Parker, Department of Biology, Utah Valley State College, 800 W. 1200 So., Orem, UT 84058-5999, (801) 222-8000 x.8650
For more info: contact Bruce Parker
Student successfully completing this exercise should be able to:
- Define energy as it applies to biological systems. This definition
should include the concepts of work, energy transformation, potential
energy, and heat.
- Describe cellular respiration and how this process converts energy to
useable forms. The description should include the input components and
the output products of respiration.
- Understand and be able to design the experiments to test for the those
measurable aspects of cellular respiration and the factors which
influence respiration.
In aerobic respiration, a molecule of glucose is broken down completely to CO2
and water, with the assistance of enzymes, according to this basic equation:
The occurrence of cellular respiration in an organism can be demonstrated in
several ways. Some energy is give off as heat, and some biological systems use
energy to reproduce light. The amount of glucose used can be determined, and
the amount of oxygen consumed can be measured. In this laboratory, cellular
respiration will be determined by measuring CO2 production. In aquatic systems,
CO2 produced during cellular respiration will result in acidification of the
fluid medium. Thus, CO2 production can be estimated by monitoring pH changes in
the fluid medium. These changes can be measured with high grade litmus paper or,
preferable, a calibrated pH electrode.
Campbell, N.A. (1993) Biology, 3rd Edition. Benjamin/Cummings Publishing
Co., Inc., Redwood City, CA, 1190 pp.
Keeton, W.T. and J.L. Gould (1993) Biological Science, 5th Edition.
W.W.Norton & Co., New York, NY, 1194pp.
Taylor, M.T. (1993) Student study guide: An introduction to concept
mapping for Campbell's Biology, 3rd Edition. Benjamin/Cummings Publishing
Co., Inc. Redwood City, CA, 452pp.
Eberhard, C. Saunders general biology laboratory manual to accompany
Villee, et al BIOLOGY. Saunders College Publishing, 1990. pp. 64-66.
Procedure
We suggest the following introductory demonstration, with no prior
discussion of the topic.
1. Bring in a narrow necked bottle (pop bottle works well) containing
a white powder (baking soda - sodium bicarbonate). Pour into the
white powder a clear liquid (vinegar - dilute acetic acid,
concentrated does not work well). (This will go faster if the
baking soda is 1st dissolved in water). Place a balloon over the
opening of the bottle and capture the gasses emitted - the balloon
will inflate rapidly. Shake the bottle a bit to facilitate mixing
and increase gas production. Remove the balloon and let it go - it
will fly around the room until it is empty. Alternatively, use one
of those balloon-powered toys that come in breakfast cereals, etc.
2. Ask the students, "What just happened here?" Try to get them to list as
many concepts as possible that they can identify with experimental
demonstration they just witnessed. If you and they are already familiar
with concept mapping, this is a good opportunity to use it. Try to center
(or steer) the conversation around the concept of energy. This is a
demonstration of chemical energy in an inorganic system - what about a
biological system? Try to get the students to identify the different
components in the demonstration and what they might be analogous to in
a biological system:
white powder - "food",
liquid - enzymes to aid in energy transformation,
gas - potential (stored) energy (ATP),
movement of balloon - using potential energy to do work.
3. An optional exercise at this point is the classic "burn a peanut"
demonstration. Light a peanut that is suspended beneath a test tube with
a known volume of distilled water. Measure heat production via a
temperature change in the water. One calorie (4.2 J) can heat 1g (1 ml
distilled water) through 1oC. The energy released by burning the peanut
is used to heat the known quantity of water. This demonstration may
help lead you from a discussion of inorganic chemical bond energy seen in
#1, to biological energy used to work.
4. Demonstrate the need for oxygen to do biological work. Have one student
at each table squeeze a tennis ball or racquet ball as rapidly as possible.
Have the other students time how long this can be done, and the
frequency of squeezes. This can be plotted out for better visualization.
Ask the students why they couldn't continue squeezing the ball
indefinitely. Relate this to the basic formula for cellular respiration-
and the concept of aerobic vs. anaerobic cellular respiration. Also,
encourage the students to connect the idea that work is exhibited in
the maintenance of the structure of living things. An alternative to
this demonstration is to have the students list some ways that they
do biological work, such as exercise and have each group analyze the
rate at which the work may be maintained. If it can be done in a
sensitive manner, it may be interesting to point out the differences
between different students and their levels of work capacity.
Examples of work might be doing "arm curls" with a small weight, or
climbing stairs. Be careful not to be too strenuous or involve
students who may present a health risk. As the students analyze the
data, encourage them to explore reasons for the decrease in the
capacity to work over time. Some explanations may involve depletion
of food resources or lack of circulation. The idea of oxygen
depletion may crop up and also lead to a discussion on the
difference between physiological "respiration" and cellular
respiration. Be able to tie the two concepts together.
5. Ask the students to generate a list of the different kinds of
organisms which might be expected to use energy and carry-out
respiration. The diversity should be useful in pointing to the
universal nature of some form of respiration. Continue the class
discussion in a large group, or small groups, to cover the topic of
cellular respiration - pull out the major concepts mentioned earlier
to help the students in hypothesis formulation. Discuss ways of
measuring cellular respiration to give the students an idea of how
to proceed with actual experimentation. The ideas could include the
production of CO2 with the resulting decrease in pH, the release of
heat as the energy is lost due to the inefficiency of respiration,
or the loss of oxygen in the enclosed system. Which approach the
students are allowed or encouraged to pursue will depend on the
available equipment. Some discussion as to why the levels of CO2
result in the change in pH is appropriate since many of the students
may not connect the ideas. ( CO2+H2O-> H2CO3-> 2H+ + CO3-- ) It
may be useful to have them do the classic demonstration of blowing
through a straw into lime water or into distilled water containing
a pH electrode to show that they are producing the changes simply by
their own exhalation of CO2.
At this point, provide the students with materials to set up their
own experiments to demonstrate the occurrence of cellular
respiration. The use of adequate controls should be discussed. We
suggest using Elodea for one organism, to reinforce the fact that
plant cells also have mitochondria and respire. Other animals may
include small aquatic animals such as Daphnia guppies or snails.
Demonstrate the use of litmus paper or pH electrodes, if necessary.
Be sure to start with water that is pH 7.5-8.0 for best results.
Water - use spring water if available. Otherwise, ???...Do not use
straight tap water. If the water is below pH 7.5, adjust the pH up with
NaOH. Don't use sodium bicarbonate if you are then assaying for a CO2
based pH change. Be careful not to introduce anything which would act as a
buffer.
Elodea - ask the students to think about what circumstances would increase
respiration in a plant. Test tubes sealed with rubber stoppers work well
for Elodea. Some could be placed in the dark and others left in the light
for comparison.
Daphnia - Use the bulb end of a cut off, small, disposable (reusable!)
plastic pipette for a respiration chamber. We found a pH change of >0.5
pH units with as few as 6 Daphnia in the pipette for 20 minutes.
Larger animals - use an Erlenmeyer flask with a rubber stopper to minimize
dead space for gas exchange. Use animals that have not recently been fed
(24h for Daphnia, longer for fish and snails) and the shortest possible
run times to minimize ammonia production. (This also makes a good
discussion topic - what other factors may alter the pH?)
The pH can be monitored over time, and a graph depicting rate of CO2
production generated (change in pH/time).
If time allows, the students may desire to investigate the differences
that occur in respiration rates under varying environments for the
organisms they are using. They may try varying the temperature, exposure
to light versus darkness, increased number of organisms, exposure to mild
poisons such as detergents or heavy metals, etc. If Daphnia are used, they
may be placed in an ice bath and the decrease in activity noticed and
related to respiration. Their recovery once returned to room temperature
may also be investigated.
Just to reemphasize some points:
1. Don't use tap water for the experiments.
2. Adjust the pH to 7.5-8.0 starting to see a pH change.
3. Use starved animals to minimize ammonia production.
4. pHydrion papers from Sigma work very well if pH meters are
unavailable.
5. Try to limit the surface area of the water as much as possible to
reduce the amount of gas exchange which may occur at the air-water
interface.
6. Larger organisms like snails or fish may be placed in 100 ml of water
to concentrate the CO2 to measurable levels. A stoppered erlenmeyer flask
works well.
Students should have tremendous variations in the rates at which
physiological fatigue occurs, but their muscles should show signs of
stress within 3-15 minutes.
We have observed easily measurable changes in pH in 15-30 minutes of at
least one-half a pH unit and as many as 2 units.
Overall, students should gain the following:
1. An improved understanding of energy, cell respiration, and associated
concepts.
2. Reinforce the fact that plants also respire.
3. Build hypothesis formulating and testing skills.
4. Data collection, tabulation, and graphing skills.
5. Practice in writing a lab report.
1/2 hour - 1 hour for introduction; 2 hours for the remainder
Today's lab will explore the concepts of energy and cellular respiration.
In cellular respiration, chemical bonds (Carbon) are broken to release energy
that is stored as ATP. ATP can be used as a source of energy to fuel the
metabolic needs of the organism. The metabolic needs constitute biological
"work" including transport, reproduction, movement, synthesis, waste removal, and
growth.
The initial step in cellular respiration is glycolysis, a series of
chemical reactions found in every known living organism. Respiration can proceed
without oxygen (anaerobic) or it can be oxygen requiring (aerobic). Aerobic
respiration utilizes the Krebs Cycle and electron transport chain to generate
ATP. This lab will be concerned only with aerobic respiration. For more detail
about glycolysis, the Krebs Cycle and the electron transport chain, refer to your
text.
How might cellular respiration be demonstrated and measured? What is the
basic chemical reaction for cellular respiration? Cellular respiration in a
controlled aquatic system can be estimated by measuring the amount of CO2
produced. An increase in CO2 will result in a decrease in the pH in a closed
aquatic system - why? You will choose from a variety of aquatic organisms and
use a pH electrode or pH litmus paper to indirectly measure CO2 production by
monitoring changes in pH.
1. The primary objective is to develop a better understanding of the concepts
of energy and cellular respiration, and related concepts.
2. Through this lab you will gain experience in hypothesis formulation,
hypothesis testing through direct experimentation, and reporting and
discussing results and findings.
3. Through direct experimentation, you will become familiar with cellular
respiration in both plants and animals.
After an introduction to energy and cellular respiration, a number of
organisms will be available for direct experimentation. Try to formulate
hypotheses that can be tested with the available materials. What factors might
affect cellular respiration in plants? Animals? Why? What will be your
control(s)? What data will you collect? Discuss your possible hypotheses with
your instructor, and select one that is testable in the allotted time. Proceed
with setting up your experiment. Be sure to record your starting times, initial
pH, and any behavioral observations. At time intervals you and your instructory
decide upon, measure the pH in the fluid medium and record the pH and time on a
data table.
A graph of your results can be constructed. What is the dependent
variable? The independent variable? How do your results compare with your
hypotheses? What were some possible problems with your experimental
technique? What are some further questions that might be interesting to address
with future experimentation?
Address the following questions:
1. Which of your experiments produced the most dramatic results? Speculate
why this might be so?
2. What were some of the major findings of the other groups in the lab?
3. How would you explain cellular respiration to a person with no prior
knowledge of the concepts involved?
4. How do your results show that cellular respiration is occuring? What are
some other experiments that might be used to demonstrate other aspects of
cellular respiration?
5. What are some of the conditions which you might alter which would affect
respiration and why? What would be the expected outcome of altering these
conditions?
KEYWORDS:
energy, cell respiration, chemical reaction, carbon dioxide
production, oxygen consumption, glucose, work, food potential
energy, ATP, energy conversionABSTRACT:
Energy conversion/transformation and its application to biological
systems is a difficult subject for many students. The goal of this
lab is to make a connection between potential energy stored in
present in chemical bonds of organic nutrient molecules, and
biological "work" performed by organisms as a result of ATP
production in cellular respiration. Demonstrations, concept
mapping, group discussions, and investigation are all used to
enhance learning.FAIR USAGE:
BIOLAB and LABSHOP are supported by NSF. The teaching materials placed on BIOLAB
may be freely copied and disseminated for all noncommercial educational
activities provided that appropriate credit is given to the authors, this source,
and its NSF support.INSTRUCTORS GUIDE
Background Information
Objectives:
Students often have misconceptions and misunderstandings about
energy, energy conversions/transformations, and energy in biological systems.
The primary objective of this lab is to reinforce the concept of energy, and to
explore its relationship to biological work, via experimentation with plant and
animal cellular respiration.Concepts:
The focus of the lab is the concept of energy transformation.
Cellular respiration is the mechanism by which chemical energy is converted from
one form to a more usable form, with a release of a certain amount of heat.
Energy is defined as the capacity to do work and students can be directed to
envision energy as being necessary for biological work. Biological work includes
the simple maintenance of life and energy comes from food/nutrient molecules
which are broken down. Stored (potential) energy is transformed to be used to
fuel biological processes. Nearly all of the energy used to maintain life is
ultimately derived from the sun.Factual background:
Organisms need energy to perform many of the essential
functions of life, such as growth, repair, movement, reproduction, and transport.
Plants and other primary producers transform energy from solar or lithochemical
sources into storage products that are used as energy sources ("food") by
consumer organisms. Energy needed to do biological work comes from the
potential energy stored in chemical bonds in these food or nutrient sources.
Respiration is the conversion of chemical bond energy in nutrient molecules into
forms directly usable by the cell, such as ATP. Respiration can be aerobic
(oxygen) or anaerobic (without oxygen). This lab is designed to explore the
subject of aerobic respiration only. However, some discussion of anaerobic
respiration may be useful as well in the initial portion of the lab.
The potential energy in the glucose molecule is released in glycolysis (not an
oxygen requiring step), the Krebs Cycle and the electron transport chain. Refer
to a textbook for a detailed discussion of these processes.Bibliography:
6. Experimentation
Hints, Suggestions, and Special Instructions
Materials, Supplies, Recipes, Special Instructions
Materials:
pop bottle, vinegar, baking soda, balloon,
peanut, ring stand, clamp, pin, bunsen burner, test tube,
distilled water, thermometer,
live animals such as Daphnia, guppies, snails , spring water,
Erlenmeyer flasks, rubber stoppers, large test tubes,
disposable plastic Pasteur pipettes, litmus paper - 3 colour
comparison type (or pH meter + pH electrode and pH 2, 7, 10
buffers)
Expected Student Outcomes
Time frame
STUDENT PROTOCOL
Introduction
Objectives
Specific Instructions
Reporting results
Conclusions