Module 3. The Carbon Cycle and its acid/base chemistry –Biology
Dr. Hirrel and Ms Waggoner
Principle of the Carbon Cycle
Observation- Engage
One cornerstone in building a foundation for science literacy is an understanding of the
Carbon Cycle and how it works. Another would be gravity and how it works. However,
there is nothing we can do about changing gravity, but we can, and do, have a BIG
effect on the Carbon Cycle!
Nearly all life depends on the carbon cycle processes of photosynthesis (PS) and
aerobic respiration (AR). These processes and those supporting life in the darkness of
deep oceanic vents are driven by acid/base chemistry to harness the energy for life.
The products of photosynthesis are the substrates for aerobic respiration. Sugars and
O2 from the plant fuel the furnace of aerobic respiration in animals, fungi, and even
plants to produce ATP, the energy storage molecule of life. The CO2 released this
pathway and water plus the decomposed and recycled nutrients of all feed back to the
soil for the plants to complete the Carbon Cycle.
Both processes are accomplished by two DNA bearing, double membrane organelles:
the mitochondrion for AR found in nearly all eukaryotes and the chloroplast for PS
found in all plants and algae. The DNA is evidence of a past symbiosis because it is
bacterial like. The double membrane is the key to making ATP. Substrate compounds
of AR are stripped through a pathway of enzymes down to H ions and electrons, which
get transported from the center of the organelle to the space between the membranes
creating a concentration (energy) gradient. As H ions (H30+) diffuse back across the
inner membrane the energy generated is used by O2 and the enzyme ATPase to make
ATP.
Activity (20 -30 min). Carbon cycle. Take a walk outside to some trees with their fallen
leaves in place and discuss the cycle.
o Make students look for organisms representative of each major niche: producers =
plants, consumers = animals, and decomposer/recyclers = fungi.
o Have students follow the decomposition of leaves to the soil. Note the organisms
found along the way.
Activity (15 -20 min). What happen here? Before and after demos of PS and AR
showing what students will do.
o Photosynthesis (PS) using methyl red, pH indicator. (PreLab set-up= 60 min., 30
min. OK)
The aquatic plants, Elodea or Anacharis , are placed in CO2 charged water with
methyl red. At pH 4.5, color is red, and at pH 6.8, it is yellow. Using distilled water
or tap water left overnight to reduce chlorine add 0.1g methyl red/100mL water.
With a straw, charge the water with CO2 by bubbling air through the solution until
the color first turns pink. In two suitable containers, large test tubes, flasks, etc.,
pour an equal volume of CO2-water. In one place a leafy plant stem and add a
similar size stem to the second tube after just BEFORE class.
Discuss the PS equation. CO2 + H2O + light => Sugar (glucose) + O2
List all your observations.
RQ: Is light needed for photosynthesis?
-
+
Teachable Moment: CO2 as a pH buffer. CO2 + H2O <=> HCO3 + H . The more
CO2, the more H ion, and the redder the solution gets.
LabQuest Activity (15 -20 min). Absorbance spectrum of chlorophyll using the Vernier
spectrophotometer. Make an acetone or alcohol extract of spinach or from the
water plant used above. Grind leaves in 10mL of solvent until a green chlorophyll
solution appears. Strain or filter the solution, then pour it into a glass cuvette.
Follow the directions for running the spectral analysis. Connect LabQuest to a
laptop with LoggerLite and see the spectrum with better clarity.
o Aerobic Respiration (AR) using yeast. (PreLab set-up= 60 min., 30 min. OK)
Baker’s yeast is added to a 5-10% sugar solution (glucose is best, table sugar is
good). Wait 10 min. Using two test tubes, one half the size of the other, fill the
short tube as full as possible with the activated yeast solution, and the lager tube
about 2/3 full. Drum roll, please! Now, quickly invert the short, full tube upside
down into the larger tube. No air bubbles should be in the upside down tube. Pour
or pipet out yeast solution so that at least half of the upside down tube is visible. As
AR occurs, CO2 will collect in the inner tube. Placing tube in warm water will
increase CO2 production. Make a second tube just BEFORE class.
Discuss the AR equation. Sugar (glucose) + O2 => CO2 + H2O
Make observations and measure amount of CO2 by measuring the length (mm) of
the gas column.
Teachable Moment: What’s the volume of CO2? Determine the volume by using the
3
3
formula for the volume of a cylinder. Convert mm to cm to mL.
RQ: Is sugar needed for aerobic respiration?
Photosynthesis
RQ: Is light needed for photosynthesis?
Hypothesis- Explore
Activity (10 -15 min). Based on RQ, formulate a hypothesis about the rate of
photosynthesis with and without light.
Experiment- Explain
Activity (15 -20 min). Design the experiment to test the hypothesis.
What type of plant is needed?
What are the independent and dependent variables?
How many experimental and control groups are needed? How many
replications of each?
What data needs to be collected?
Activity (10 -15 min). Graph the expected results to support your hypothesis.
Activity (30 -40 min). Conduct the experiment. Prepare a data collection table.
pH approach. Using an aquatic plant, Elodea or Anacharis, in CO2 charged water
with a pH indicator that ranges from pH 4 to pH 6 or 8. Suitable pH indicators and
their pH range and color: Methyl red (pH 4.4, red to pH 6.2, yellow), Bromthymol
blue (pH 6.0, yellow to pH 7.6, blue), or Phenol red, the best, (pH 6.8, yellow to pH
8.2, red). Prepare CO2 charged water and plant as described in the Observation
Activity above.
Treatments
1. Experimental group: Plant with light.
2. Control group 1: Plant without light. Tube wrapped in Al foil.
3. Control group 2: No plant with light.
Teachable Moment: Why is this treatment needed? What is it controlling?
Set-up: Use a bright flood lamp (100-120v) as a light source. Place treatments in a
large beaker of water to act as a heat sink to keep temperatures from rising.
Teachable Moment: Why put treatment 2 in the light wrapped in Al foil and not just
in a dark drawer?
Record time it takes for a color change from pink to yellow occurs. Data can be
more quantitative using pH paper to measure pH every 5 min. With a plastic pipet
placed midway down the tube draw up then blow out fluid to mix before sampling.
Draw up a small amount of fluid and place it on pH paper.
Data Collection Table
Treatment
Color
Change
Time,
min.
pH at:
0 min.
pH at:
5 min.
pH at:
10 min.
pH at:
15 min.
pH at:
20 min.
1. Plant with light.
2. Plant without light
3. No plant with light
LabQuest(LQ) approach.
1. Attach a Vernier pH sensor to LQ to record pH change continually. Increase
the glassware size to accommodate both the plant and the pH sensor. The
rate of photosynthesis would be in pH units/min and calculated by doing a
Curve Fit (linear) to the data on the LQ screen.
2. Attach a Vernier CO2 sensor (~$350 ea) held by a stand (Keep OUT of
water!!) to the LQ to record the rate of PS as ppm CO2/min. Modifications
are using an floating plant, duckweed or Azolla (a fern with N fixing bacteria
in its roots). These can be collected locally from ponds and lakes in central
Arkansas. Float the plant in 50 mL water in a wide mouth 125mL Erlenmeyer
flask. A glass fish bowl or beaker is needed as the heat sink. Using two light
sources and heat sinks with the plant between optimizes PS rate.
LQ Collection set-up: Duration = 10-15 min. Sampling = 1 time every 2-5s.
Data Collection Table
Treatment
Plant PS Rate,
ppm CO2/min
1. Plant with light.
2. Plant without light
3. No plant with light
Results- Evaluate
Activity (20 -30 min). Evaluate, graph, and analyze results. Examine the graph and
highlight the region with the fastest rate. From the ANALZE menu, select curve fit, then
select linear fit (m = the rate, ppm CO2/min). Graph rate for each treatment.
Teachable Moment: What type of graph is best? Line? Bar?
Conclusion- Elaborate
Activity (15 -30 min). Do the results support or reject the hypothesis? Quantify the
differences between treatments by comparing the highest PS rate ( pH change/min).
Activity (out of class). Write a report.
Conclusion- Extension
Discuss energy flow through an ecosystem. Producers capture only 2% of the Sun’s
energy. Plants keep 70% of their photosynthetic products, Fungi get about 20% from
plants and animals, and animals get only 10% from the plant. Energy flow through the
animals is further reduced by 10% each time. Herbivores get the most energy from
plants directly; 1st carnivores get only 10%, 2nd carnivores get only 10% from the
herbivores, etc. This varies with ecosystem. Why is it important to know the
photosynthetic rates in an ecosystem?
Problem 1. How would you compare a natural ecosystem to an agricultural
system? How are they similar, how do they differ?
Problem 2. Plants have adapted three methods for PS. What are they and what
types of plants use them? What advantage does each method give the plant over the
other two?
Instructional NoteThe Compensation Point (CP)
CO2 consumption,
ppm/min
occurs when the rate of PS =
rate of AR. As light intensity
decreases so does the rate of
PS. Remember plants perform
both PS and AR. All energy for
the roots comes from AR. Plant
leaf cells contain both
chloroplasts and mitochondria
and perform both PS and AR at
the same time. Circle in graph
shows at 0 CO2 consumption,
the CP is close to 10,000 lux.
Compensation Point
Essential Equipment & Materials
aquatic plant, Elodea, Anacharis, Hornwort
pH indicator- Methyl red, Bromthymol blue, or
Phenol red –best
large diameter test tubes
flood light (100-120v)
glassware for heat sink
straws
100
50
Photosynthesis
0
-50
0
20
40
60
80
100
Aerobic Respiration
-100
Light Intensity, 1,000 lux
pH paper, range matching the pH indicator
Aluminium foil
Vernier sensors: pH, CO2
For CO2 sensor,
floating plants: duckweed, or Azolla fern
125mL wide mouth Erlenmeyer flasks
Aerobic Respiration
RQ: Is sugar needed for aerobic respiration?
Hypothesis- Explore
Activity (10 -15 min). Based on RQ, formulate a hypothesis about the rate of aerobic
respiration with and without sugar.
Experiment- Explain
Activity (15 -20 min). Design the experiment to test the hypothesis.
What type of organism is needed?
What are the independent and dependent variables?
How many experimental and control groups are needed? How many
replications of each?
What data needs to be collected?
Activity (10 -15 min). Graph the expected results to support your hypothesis.
Activity (30 -40 min). Conduct the experiment. Prepare a data collection table.
Displacement approach. Using Baker’s yeast (dried is best), Saccharomyces, weigh
0.1g/30-50mL 5-10% sugar or water. Volume varies with glassware. Be sure that
the small tube will stand upright in the larger one to make measurements easier.
The AR rate is measured as length or volume of CO2/min.
Treatments
1. Experimental group: Yeast with sugar.
2. Control group 1: Yeast without sugar.
3. Control group 2: Sugar without yeast.
Teachable Moment: Why is this treatment needed? What is it controlling?
Data Collection Table
Length, mm, or volume, mL, of CO2 bubble over time:
Treatment
1. Yeast with sugar
2. Yeast without sugar
3. Sugar without yeast
0 min.
5 min.
10 min.
15 min.
20 min.
LabQuest(LQ) approach. Attach a Vernier CO2 sensor (~$350 ea) held by a stand
(Keep OUT of water!!) to the LQ to record CO2 change continually. Use a 125mL flask
as for the PS inquiry to fit the CO2 sensor and add 25-50mL(max) of the yeast solution.
Gentle swirling or a mini stir plate can improve data collection.
LQ Collection set-up: Duration = 10-15 min. Sampling = 1 time every 2-5s.
Data Collection Table
Treatment
Yeast AR Rate,
ppm CO2/min
1. Yeast with sugar
2. Yeast without sugar
3. Sugar without yeast
Results- Evaluate
Activity (20 -30 min). Evaluate, graph, and analyze results. Examine the graph and
highlight the region with the fastest rate. From the ANALZE menu, select curve fit, then
select linear fit (m = the rate, ppm CO2/min). Graph rate for each treatment.
Conclusion- Elaborate
Activity (15 -30 min). Do the results support or reject the hypothesis? Quantify the
differences between treatments by comparing the highest AR rates (CO2 bubble
size/min).
Activity (out of class). Write a report.
Conclusion- Extension
Problem 1. In northern latitudes during the winter, large animals hibernate, but smaller
animals do not or are intermittent sleepers. When AR rates are compared, smaller
animals, mice, have higher rates than large animals, bears. Why? How can you
compare a mouse to a bear in the first place?
Problem 2. Exercise increases metabolic rate which is directly linked to AR rate. Fats
and proteins can also be used in AR to generate ATP energy. Many activities are tied to
our AR rate. Think about your school activities and your classmates, which activities or
which students might have different AR rates? Ask a RQ. Make a hypothesis. Design
an experiment. What results do you expect?
Essential Equipment & Materials
Baker’s Yeast, dried or wet
Table sugar, sucrose, or glucose
Two different size test tubes to fit inside
each other
Metric rulers
Beakers to hold test tubes
For Vernier CO2 sensor,
Lab stand to hold sensor
125mL wide mouth Erlenmeyer flasks
Module 4. Effects of pH on Carbon Cycle chemical reactions – Biology
Dr. Hirrel and Ms Waggoner
Open-ended Inquiry. Teacher teams will investigate the effects of pH on AR and PS
using techniques from Module 3. Design this as a lesson plan for your class. Using the
scientific method approach. Teams will give a 10min. report to the class on your lesson
plan. Add, delete, modify as you see fit. Include how much time for each activity, how
many periods to complete it?
Observation- Engage
Acid rain may be affecting ecosystems over large geographical areas. Soils and lakes
are changing due to pH shifts. Thus, both AR and PS are affected by pH.
Activity (
min). Examine the seeds germinated in 5% acetic acid (white vinegar,
5% acid), 5% baking soda, and distilled water. Are there differences? What are they?
Hypothesis- Explore
Experiment- Explain
Design experiment
Results- Evaluate
Present results to class. Show graphs
Conclusion- Elaborate
Report results
Conclusion- Extension
Write a problem
Essential Equipment & Materials
As in module 3, plus…what would you add?