Download cellular respiration notes

Lesson Flow
Engage ➙ Explore ➙ Reflect ➙ Assess ➙ Make Career Connections ➙ Variations
Engage (20 minutes)
Discuss the concept of cellular respiration and put it in context with respiration (breathing).
What does your body need to survive and function? Can you give some examples?
Nudge the discussion as needed so that oxygen, food, water, and energy are all mentioned.
Why do we need all of these things? For example, can you explain why we need to eat? [You
might need to prompt students to get to the answer with questions like "What happens if you
do not eat for a long time?" or "Do you think you will feel more energized and can run
around faster and longer with or without food?" et cetera.]
We need food and oxygen to generate energy that our body can use for growth, repair and
movement. If we do not eat, our body will eventually run out of energy, will not be able to
function anymore, and will starve.
What happens inside our body to the food we eat?
The food we eat is digested in our stomach and digestive system. That means it is broken
down into smaller components (such as proteins, vitamins, carbohydrates, and fats) that can
be absorbed by our body to be processed. Some of these processes release energy that our
body can use for functions such as moving, thinking, or growing.
What kind of nutrients or compounds do you think foods contain that help give our body
energy? How does our body transform food into energy?
[Students may not know the answer—that is fine, and a good time to formally introduce
cellular respiration.] Many foods that we eat can be converted by our body to carbohydrates
or sugars such as glucose, which is the most important starting compound to make energy.
The process that our body uses to make energy from glucose is called cellular respiration. It
happens continuously in the cells of our body to provide energy to us nonstop. Respiration,
the process of breathing, is not the same as cellular respiration, although both are related.
Write down the chemical equation for cellular respiration and explain it to your students:
C6H12O6
+
6 O2
→
glucose
(from food)
oxygen
(from air)
(in exhaled breath)
(used by body)
(used by body)
carbon dioxide
water
6 CO2 +
6 H2O +
energy
Explain to your students that cellular respiration is a two-stage process. First, glucose is
broken down into smaller molecules, which happens in the cytoplasm of our cells and
produces some energy. The second stage takes place in the "powerhouses of our cells," the
mitochondria. Here, the smaller molecules from glucose are broken down further and, in
combination with oxygen, make the end products of cellular respiration carbon dioxide,
water, and energy. This step is the major energy contributor during cellular respiration.
Make the link between cellular respiration and breathing (respiration) by discussing the
following questions.
Where do you think the oxygen that we need for cellular respiration comes from?
The oxygen for cellular respiration comes from the air (which contains about 20% oxygen).
This is the reason why we have to breathe—to provide oxygen to the cells for breaking down
glucose to generate energy.
What do you think happens to the by-products of cellular respiration, carbon dioxide and
water?
Both, carbon dioxide and water, are carried away in our bloodstream. The water usually
leaves our body through sweating or is transported to our kidneys and ends up in our urine.
The carbon dioxide eventually ends up in the breath that we exhale.
Explain your students that you will do a series of experiments to measure the end product of
cellular respiration (carbon dioxide) that is present in their exhaled breath. Optionally, you
can show your students this introductory video to this lesson plan experiment:
Google Classroom
Tell your students that in their experiments, they will investigate what happens to cellular
respiration when they get more active and need more energy—like when exercising. Use the
following questions for them to make predictions. Write the predictions down to compare to
the results after the experiment.
What would happen if your body suddenly needed a lot of extra energy (for example, when
you exercise)? Do you think the cellular respiration rate would change? What does that mean
for the amounts of carbon dioxide and water being produced? Would the amounts increase or
decrease?
Once the prediction is made, help students understand how the indicator solution is related to
carbon dioxide and cellular respiration by asking questions and doing two short
demonstrations.
Carbon dioxide is an acidic gas. Can you think of a liquid that has carbon dioxide in it? Is that
liquid acidic, basic, or neutral?
Soda has carbon dioxide. Adding carbon dioxide to a liquid makes it acidic.
Knowing that carbon dioxide is acidic, and makes water acidic, how could we measure how
much carbon dioxide we exhale?
Knowing that carbon dioxide acidifies a solution, we can measure the amount of carbon
dioxide being produced by the time it takes to make a neutral solution acidic. We can use pH
indicators that change color dependent on if the solution is acidic, neutral, or basic. An
example of such an indicator is bromothymol blue.
Demonstrate how the indicator solution (bromothymol blue) changes color depending on if
the solution is acidic, neutral, or basic.
Place the three cups with indicator solution in front of the class so everybody can see them.
Let your students notice the color and tell them that this is a neutral solution of just water
(plus indicator).
Add one teaspoon of acid (vinegar) to one of the cups or beakers and let your students
observe the color change (to green/yellow). Tell them that you added an acid to the indicator
solution.
Add enough of the prepared baking soda solution to one of the other cups to make the color
change from green to blue and let your students observe the color change. Tell them that you
added a base to the indicator solution.
Let your students compare the different colors and recall which solution is acidic, basic, or
neutral.
Show that the indicator solution also turns green/yellow (acidic) when you breathe into it
through a straw, due to the carbon dioxide in your breath.
Explain that during their experiment they will monitor the color of the solution using cell
phones and Google's Science Journal app.
Introduce Google's Science Journal app to your students, specifically the light sensor.
Alternatively, you can assign the relevant tutorials on this Science Journal tutorial page to
them before class.
Let the students locate the light sensor on the phone they will be using for their experiments.
Demonstrate how the light sensor readings are affected by the different colors of the solution.
In the Science Journal app, open the light sensor. Then place each of the solutions (acidic,
basic, and neutral) on top of the light sensor, one after the other, and communicate the light
sensor readings for each solution to your students. The values should decrease in the order of
yellow, green, and blue.
Can someone explain why we can use the light sensor readings to monitor the color change of
the solution?
When light passes through the beaker or cup with the indicator solution, some portion of the
light will be absorbed by the solution itself. That means the light sensor can only measure the
amount of light that gets through the solution to the sensor. If the color of the solution gets
lighter, for example, because it changes color from blue-green to green-yellow (as it does
during the experiment), less light will be absorbed by the solution and the readings of the
light sensor will increase. This way, the light sensor readings will tell us when the color of
the indicator solution changed.
Explore (30 minutes)
Based on previous discussions, let each student formulate his/her hypothesis on how cellular
respiration rates (or the amount of carbon dioxide in your breath) changes after exercising.
Divide the class into groups of 2-4 students and inform them that each group will conduct an
experiment to measure the amount of carbon dioxide in their breath before and after
exercising, to test their hypotheses. Each student should perform the whole experiment
(before and after exercising) once. Within an experiment, students should divide tasks. For
example, one student could prepare the indicator solution, another could operate the phone, a
third one exhales into the indicator solution, and optionally, a fourth student could measure
the color change with an additional stopwatch. Students should then rotate through each task
so everyone can have a turn measuring the amount of carbon dioxide in their breath.
Walk the students through the experimental procedure described below. (A slideshow is
available that you can use to guide your students through the experiments.)
warning purple icon Make sure the students use a one-directional check valve with their
straws when exhaling into the indicator solutions to prevent any accidental ingestion of the
solution. The valve will only allow air flow in one direction, which prevents any suction of
the indicator solution into the straw.
Experimental Procedure
To familiarize students with the experimental procedure, first let them practice exhaling
through a straw into just water while monitoring the light intensity with Google's Science
Journal app as described in the following steps. Assign one student at a time to perform the
experiment. Students should take turns so everyone in the group can perform the experiment
once.
Fill a 9 oz cup or 150 mL beaker two thirds with water.
Cover the cup with plastic wrap and secure it with a rubber band.
With a straw, poke two holes into the plastic wrap. One should be located closer to the rim of
the cup.
Prepare the straw by cutting it into two pieces and inserting the valve in the top part as shown
in Figure 2. Each student needs to prepare his/her own straw. They can use one valve each, or
alternatively, students of one group can share a valve. In this case, the valve needs to be
passed from student to student during the experiment so each one can insert it into their
individual straw.
Prepare the straw by inserting the safety valve.
Figure 2. Inserting the check valve into the top part of the straw.
Stick the bottom of the straw through the hole that is closer to the rim of the cup.
Open the Science Journal app on the phone and clearly label your experiment. Make sure to
select the light sensor for your measurements.
Lean the phone against a box or books with the light sensor facing sideways towards the cup.
Then place the beaker or cup in front of the light sensor. Put the flashlight in front of the cup
so it shines through the dye solution directly onto the light sensor as shown in Figure 3.
Experimental setup for measuring the amount of carbon dioxide in the exhaled breath using
Google's Science Journal app.
Figure 3. Experimental setup for the experiments.
Note that the light sensor reading will be dependent on the position of the flashlight with
respect to the phone. Students might want to try different positions to get the highest sensor
readings. However, they should not move the flashlight or the phone while recording data.
Confirm that the sensor readings are stable. Then, press the record button in the Science
Journal app, take a deep breath and start exhaling through the straw into the water for as long
as you can. Try to exhale from your lungs and place the end of the straw close to the light
sensor—but do not block the sensor with the straw! Then inhale through your nose and then
continue blowing into the water. Because of the bubble formation, the sensor readings will
temporarily fluctuate. This will not affect the results of the experiment.
Stop recording after about one minute and review the light sensor readings. The maximum
sensor readings should not change much, as shown in Figure 4, but you should see
fluctuations due to bubble formation, which temporarily affects the absorption properties of
the solution.
Example graph for measuring light intensities when exhaling into just water.
Figure 4. Example graph of measured light intensity for exhaling into just water without
indicator. The x-axis is time in minutes:seconds [min:s] and the y-axis shows light intensity
in lux. The red line shows the general trend of the data, not taking into account the
fluctuations from creating bubbles in the solution.
Now, let your students do the experiment with indicator solution instead of water.
Fill a 9 oz cup or 150 mL beaker two thirds with water.
Add about 2 mL, or half a teaspoon of 0.04% bromothymol blue indicator solution.
The solution should be green or blue dependent on the pH of your water. If the solution is
already yellow or very light green, try a different water.
Repeat steps a.ii–a.viii. Students can reuse their individual prepared straws and valves.
Stop recording once the maximum sensor readings level off and are stable for more than 20
seconds. The light intensity should start to stabilize once the indicator solution has changed
color from blue-green to green-yellow. An example graph is given in Figure 5.
Example graph for measuring light intensities when exhaling into the indicator solution.
Figure 5. Example graph of measured light intensity for exhaling into the indicator solution.
The x-axis is time in minutes:seconds [min:s] and the y-axis shows light intensity in lux. The
red line shows the general trend of the data, not taking into account the fluctuations from
creating bubbles in the solution.
Let each student repeat the same experiment, following step b. again. Each one should use
his/her own straw. The safety valve can be shared. Make sure they clearly label and organize
their data in the Science Journal app. Note that the initial light intensity does not need to be
exactly the same for each experiment, since you are just measuring the amount of time it
takes for the light reading to level off.
Once all trials for the first experiment have been completed, repeat steps b. and c. again, but
before the experimenter starts exhaling into the indicator solution, he/she should do jumping
jacks or a similar exercise for one minute. Even though the students might feel a little
winded, they should try to exhale into the straw the same way they did during the experiment
before exercising. Let the students prepare a new straw for this step to avoid accidental
swapping of straws. The safety valves can be reused.
Lesson Completion
Let the students clean up their experimental supplies. All the solutions can be disposed of in
the sink.
lesson plan clock icon If time is short, break here and have students analyze their data the
next day of class.
Troubleshooting
Depending on what kind of water you use, the pH can be different. The pH of water is usually
in the range of 6.5–8.5. If your tap water results in a dark blue color when adding the
indicator solution, meaning it is slightly basic, you can still use it for the experiment. Ideally,
distilled or deionized water should have a neutral pH and should result in a blue-green color
with bromothymol blue. If your water has a light green or yellow color with the indicator,
you cannot use it for this experiment and you should try a different water source.
If your graph only shows light intensity changes in large, discrete steps instead of a smooth
continuous curve (as shown in Figure 1), remember to make sure that you are blowing
bubbles into the solution close to the light sensor to create short-term light intensity
fluctuations. This will prevent the sensor from going into "sleep mode," which can affect the
readings. If you still cannot get a smooth curve, your phone's light sensor might not have a
high enough resolution for this project, as described in the Prep Work section, and you will
need to try a different phone.
Make sure the phone, beaker or cup, and flashlight all stay in the same place during each trial.
For example, be careful not to bump them when exhaling into the solution. Moving them
around can have a significant impact on the light readings and will affect your data.
Make sure your flashlights have fresh batteries. If the batteries are dying, light intensity might
actually decrease during your experiment as the light gets dimmer.
The light sensor can be affected by shadows. Make sure people are not moving around nearby
and casting variable shadows on the phone during each trial.
Reflect (15 minutes)
Throughout the data analysis process, encourage the students to question their data. You
could ask questions like:
How reproducible was your data? Did all your trials before or after exercising result in a
similar pattern? Did all groups observe the same trend in their results?
The amount of exhaled carbon dioxide, or actual times needed to change the color of the
indicator solution, will probably vary from student to student. However, all groups should
have observed the same trend between their data from before versus after exercising.
What are possible sources of variation in your data? For example, did you see a difference
depending on which student conducted the experiment? Were your flashlight and phone
always positioned the same way throughout each experiment? Did you notice any light
interference from the surroundings that could have influenced the data?
Let each group review their recorded data in the Science Journal app. They should enter their
results in the data tables provided in the student worksheet.
How can you determine when the indicator changed color from your data recorded by the
Science Journal app?
Remind the students that the light sensor recorded the light intensity, which is dependent on
the color of the solution. The lighter the color, the more light can get through to the sensor
and the light intensity increases. Once the neutral solution changes to acidic due to the
increase of carbon dioxide, the indicator changes color from blue-green to green-yellow.
Once the indicator is green-yellow, it should not change color anymore. They can determine
the reaction time by finding the endpoint of color change, or the time at which the light
sensor readings first leveled off, in each graph. Dragging the cursor along the x-axis will give
time and measured value for each individual data point. In the example graph, shown in
Figure 6, the color change is completed at 24.2 seconds, which is when the maxiumum sensor
reading stops changing (as indicated by the red line in Figure 6). Instructions are also given in
the student worksheet.
cellular respiration ambient ligh lux
Figure 6. Example graph showing how students can determine the time when the color
change of the indicator solutions is completed from their Science Journal data. X-axis shows
time in minutes:seconds [min:s] and the y-axis shows light intensity in lux. The red line
shows the general trend of the data, not taking into account the fluctuations from creating
bubbles in the solution.
Discuss the results with the students and ask them to interpret the meaning of their data.
How many of you observed a faster color change after exercising?
All students should raise their hands. If there is a group that has opposite results, do some
joint troubleshooting to find out what led to their results. Everyone should have seen the same
trend (faster color change after exercising) in their experiments.
Why do you see a faster color change in the indicator solution after exercising?
A faster color change of the indicator solution from neutral (blue-green) to acidic (greenyellow) means that more carbon dioxide was exhaled into the solution during the same time
period, turning the solution acidic faster.
What does a faster color change tell you about your cellular respiration rate?
More carbon dioxide in your exhaled breath means that cellular respiration rates increase
when exercising, as your body needs more energy to perform the exercises.
If you have time, you can combine all the groups' average color change times before and after
exercising into a scatter plot on the board to reflect the entire class's data. This way they can
also see the trend of the data clearly, showing that after exercising, more carbon dioxide is
produced due to a higher cellular respiration rate.
Did the amount of exhaled carbon dioxide vary between different experimenters?
Even if people are doing the same activities, it does not mean that their cells respire at the
same rate. Every person's metabolism functions slightly different so the amount of exhaled
carbon dioxide can vary from person to person even if they are doing the same thing.
Assess
You can use this quiz to assess student learning after the activity; quiz is available in online
and pdf formats:
Online quiz, assignable in Google Classroom
Quiz (pdf) and answer sheet (pdf)
Make Career Connections
Discussing or reading about these careers can help students make important connections
between the in-class lesson and STEM job opportunities in the real world.
scientist performing experiments Biochemist Biochemists study the chemical composition
of living things, including our bodies, and explore how they develop, function, or react to
compounds such as drugs, hormones, or food. In fact, it was a biochemist that found out
about cellular respiration and discovered how glucose is transformed into energy that we can
use.
female doctor talking to elderly patient Physician Physicians examine patients, perform
diagnostic tests, and treat injuries or diseases. Just like in this activity, they need to know and
find out how chemical processes inside our body can be affected by certain things such as
exercise or drugs. This allows them to diagnose diseases or prescribe the right drugs to treat a
patient.
Therapist checking lung function. Respiratory Therapist Respiratory therapists deal with
respiration every day. They care for patients with breathing disorders, provide therapeutic
treatments and perform diagnostic procedures. In a pulmonary function test, for example,
they measure how much air and how quickly you exhale, similar to what you did in this
activity. Such tests allow them to assess the function of your respiratory system and diagnose
and treat any abnormalities.
Lesson Plan Variations
In addition to monitoring the amount of CO2 in their exhaled breath, you can let your
students count the number of breaths they take in a certain amount of time and record their
heart rates before and after exercising. The results will enable them to assess how the heart
rate and breathing rate are related to cellular respiration. This will allow students to explore
how body functions are linked, as well as identifying how chemicals flow through our body,
for example, how oxygen in our blood is pumped from the lungs through our heart to our
muscles.
Make the connection between cellular respiration and photosynthesis, which is the production
of sugar molecules (glucose) and oxygen from carbon dioxide and water. You can
demonstrate the photosynthesis reaction by adding an aqueous plant such as Elodea to the
indicator solution after it changed color. The excess carbon dioxide, which resulted in the
color change, will be taken up by the plant when exposed to direct sunlight and will be
transformed into oxygen and glucose. When enough carbon dioxide is used up, the indicator
color will change back to green, which indicates that carbon dioxide has been removed from
the solution. You can even demonstrate the importance of sunlight for photosynthesis by
running several parallel experiments in which you expose some plants to sunlight and keep
others in the dark. A color change should only happen in the presence of sunlight. This
variation allows the students to understand how organisms in nature depend on each other in
a diverse ecosystem.
Explore additional activities you and your students can do with Google's Science Journal app.