Your name: Sara Painter
Title of Lesson: Can You Handle the Pressure?
School: Culver City Middle School
Grade Level: 7th
Subject(s): Life Science
In this lesson the students will learn about how the circulatory and respiratory system
work together to provide all the cells of our body with oxygen. They will learn about the
different structures of the two systems and how they function. The students will learn why
scuba divers have a special interest in how the respiratory system functions. The students
will complete a lab activity where they will examine the case of Scuba Steve, a diver with
the bends. The students will carry out several tests in the lab to determine how changes in
pressure can affect the function of our respiratory system.
In what way is your lesson/activity inquiry-based?
The first part of this lesson is inquiry based because the students will be making
hypotheses about how their respiratory rate and the amount of time they can hold their
breath may differ between resting and active states. They will carry out two simple tests
and make an inference as to the function of the respiratory system. The latter part of the
lesson is inquiry based because the students will be carrying out a scientific investigation
to determine what caused Scuba Steve to get the bends. The students will be performing
several tests on samples of “scuba diver blood” and using the data they collect to form
conclusions about some of the dangers associated with scuba diving.
Time Required
Intro Demo ~ 5 min
PowerPoint intro to respiratory and circulatory systems ~ 10 min
Respiratory rate activity ~ 10 min
The case of Scuba Steve intro and directions ~ 15 min
Lab investigation ~ 30 min
Lesson Closure ~ 10 min
Group Size
3-4 students
Cost to implement
~$65 for food coloring, plastic cups and 40 bottles of carbonated water
Learning Objectives
After this lesson, students should be able to:
List the major components of the respiratory and circulatory system
Explain the function of the respiratory system
Describe how changes in pressure may affect the respiratory system
Define diffusion and give examples of where diffusion takes place in the human
Introduction / Motivation
Diffusion demo:
To begin the lesson, start by having a beaker of water in the front of the classroom. Drop a
few drops of food coloring into the beaker. Hold the beaker up and slowly walk about the
classroom so the students can observe the contents. Ask the students if they can explain
what is happening and what it is called (this should be a review of concepts they learned
early in the year). Ask the students if they can think of any places in their bodies that
diffusion might be happening.
Powerpoint and activity:
The students will next be introduced to human respiratory and circulatory system using
the associated PowerPoint. Begin by reviewing the basic structures and functions of the
respiratory system (this should be a review of concepts they been learning over the last 2
weeks). Explain that 02 and CO2 are constantly being exchanged between our blood and
the environment because of diffusion.
During the next 10 minutes or so lead them through the first activity on their work sheet
which requires them to take some data on their respiratory system. Before completing
each test the students will make hypotheses regarding how many breaths they take and
how long they think they will be able to hold their breath. Following your instructions they
will next count how many breaths they take in 30 second while sitting in their seats. They
will write the number down on their worksheets. Next the students will stand and run in
place for 15 seconds and again count the number of breaths they take in 30 seconds. Next
they will hold their breath as long as they can. And finally they will again run in place for
15 second and then try to hold their breath as long as they can. As a class discuss the
answers to the next four questions on their worksheet.
Following the discussion use the PowerPoint to introduce why someone would want to
study the respiratory and circulatory systems. Start by asking the students what kind of
people or activities would require a good understanding of the respiratory system? Reveal
and review each of the four categories on the slide. This is list is not exclusive so feel free
to add more as needed
- Doctors
- Athletes
- Emergency Responders
- Scuba Divers?
What’s going on here? Why would scuba divers care about the respiratory system? Let’s
think about what scuba divers experience as they are underwater. Ask the students if they
have ever swum to the bottom of a swimming pool or deep in a lake and felt some pain or
discomfort in their ears. Describe that that this occurs because of water pressure. Water is
very heavy and can therefore exert great pressure even at a relatively shallow depth.
Divers experience an increase of 1 atmosphere of pressure every 33 feet of depth.
I use the PowerPoint to aid a discussion about how the pressure affects the density of air
molecules that a diver is inhaling with each breath. In reality the increasing pressure
increases the solubility of the gas into the blood stream, but rather then presenting it as
solubility you can present it as simple diffusion.
Scientific Case Study:
Now explain to the students that they are going to examine how pressure affects the
functioning of the respiratory system by examining the case of Scuba Steve. Read allowed
the following from the student worksheet:
- Scuba Steve just finished a fantastic weekend of diving in the Bahamas! Scuba Steve
spent all weekend diving on coral reefs and saw many interesting fish and
invertebrates. After his weekend of diving he hopped on a plain and returned to his
home in Los Angeles. The next morning Scuba Steve didn’t feel very good. He was
experiencing some aching pain in his elbows and shoulders. He was also
experiencing some itching in his neck and arms. But, none of these symptoms were
as terrible as his head ache so Scuba Steve decided to visit the doctor. The doctor
diagnosed Scuba Steve with a case of the “bends.”
To introduce the students to the lab tell the students that you were able to collect some
blood samples from Scuba Steve and his Friends from the doctors office. Explain to the
students that they will be completing two different lab tests to see if they can discover why
Scuba Steve isn’t feeling so well today.
The students will complete two activities in the lab that will allow them to examine the
affects of scuba diving on a scuba divers blood and respiratory system. Set up an even
number of lab stations in the classroom so that there will be 3-4 students per group. Half of
the lab stations will have activity 1 and the other half of the stations will have activity
number 2. Have the students start at one lab station and after ~15 minutes have the
groups switch locations. The students at lab activity 2 should go to lab activity 1 and vice
versa. Print out and tape down the directions for completing each lab activity at the
associated lab stations.
Test 1 - Depth: The first of these activities will examine the diffusion of a “gas” from a
scuba tank into a divers blood stream at different depths.
The students will have eight cups at their lab station. Four of the cups will be labeled as a
different depth, 20, 40, 60 and 80 feet and contain about 50ml of blue colored water. The
other four cups will be used to complete the tests. Tell the students that the four cups
labeled with a depth represent the concentration of gas in the scuba tank. Each cup will
contain 50ml of water with blue food coloring. Before the lab begins alter the density of
this water by adding some sugar according to the table below. Changing the density will
change the apparent time to dissolve as the heavier blue water will tend to sink and spread
out along the bottom quickly. When the students pier down into the cup the dye will
appear uniformly distributed and completely dissolved even though it actually has just
spread out along the bottom of the cup. As a scuba diver goes deeper, the pressure from
the surrounding water will increase and thus, the blue water will appear to dissolve faster.
# ¼ tea spoon sugar/ ml water
20 feet
40 feet
60 feet
80 feet
The students will be told that they are going to test to see how quickly the “gas” (blue
colored water) will dissolve into a scuba divers blood stream at each depth. The students
will need to measure out 100ml of “scuba diver blood” (water with red food coloring) into
the test cup. Starting with the shallowest depth the students will use the pipet or dropper
to add 5 drops of the scuba tank air to the scuba diver blood. Using a stop watch, or clock
with a second hand, the students will time the number of seconds it takes for the gas to
completely dissolve into the blood stream. Have the students check the cup every 15-20
seconds and look carefully for any signs of blue color. Once the blue water has completely
dissolved the students will record the time in seconds that it took to completely dissolve.
They will repeat this process for each scuba tank depth. As the students record their data
they will also be plotting a bar graph and answering a few simple questions about their
results. After they have tested all four depths they should empty the contents of their test
cups into a waste container or a sink.
Test 2 - Time: The second test will examine how time under water affects how much gas
has dissolved into a scuba divers blood stream.
As a scuba diver is underwater the gas from his lungs dissolves into his blood stream. Soda
water is an excellent analogy to a scuba divers blood stream because carbonated water
have C02 gas dissolved into them. This activity will allow the students to explore the
question: How does time underwater affect what happens to the diver when he returns to
the surface?
Three bottles of carbonated water will be placed at each lab station. The students will be
told that the soda bottles are filled with samples of scuba divers blood. Add a small
amount of red food coloring to each bottle of carbonated water. The students will be told
that each of these scuba divers had all gone diving to a depth of 30 feet, but each diver
remained at that depth for a different time. The soda bottles will be labeled with 3 times,
20 min, 40 min and 60 min.
Before the start of the lab shake some of the soda bottles and release some of the carbon
dioxide from solution. The soda labeled as 60min should not be shaken, the soda labeled
as 40 min will need to be semi flat (shake 2-3 times and release the pressure) and the soda
labeled as 20 min will be nearly flat (shake 4-5 times or mix with water). The students will
be completing two mini tests at this lab station. First instruct them to test for gas in the
divers blood stream by simulating what happens when that diver quickly returns to the
surface. The students will need to fill a test cup half way with the scuba divers blood to be
tested by gently pouring from the labeled bottle into the test cup. The students will then
take a large syringe and suck up 20ml of scuba divers blood. Next they will cap the end of
the syringe by tightly placing their finger over the top. Instruct the students to pull back on
the syringe until it reads and observe closely to see what happens (pulling back on the
syringe will decrease the pressure inside. The students should see CO2 bubbles come out
of solution). They should pull back on the plunger as far as they can while being careful to
not pull it all the out. They will need to record their observations, both what they see
happening inside the syringe and how hard it was for them to pull back on the plunger.
Next the students should complete the second mini test. They will need to fill the syringe
again with 20 ml of the scuba diver blood to be tested. To test for the amount of gas in the
scuba divers blood they will recap the syringe and vigorously shake for 1-2 minutes. The
students will be instructed to keep one finger over the cap to secure it while shaking. The
students will need to measure the difference between the plungers initial and final location
to observe the amount of gas released. The students will plot a bar graph of their results
and answer the associated questions on their worksheet. Any tested scuba diver blood
should be discarded by pouring into a waste cup or down the drain.
Materials List
Each group will need:
Per group (6 groups):
- Activity 1 - depth:
o 8 plastic cups
o 1 large plastic container
o 2-3 droppers or pipettes
- Activity 2 - time:
o 3 bottles of soda water
o 3 plastic test cups
o 2 large syringes
o 1 large waste container
Safety Issues
The students will be instructed to be very careful to not spill water with food coloring as it
may stain clothing.
Lesson Closure
After the students have completed the lab activity have them return to the classroom and
hold a review of their results. To help clarify what they observed show a sample set of
results so that they can see the patterns even if their group’s data was not very accurate.
Use the PowerPoint to help the students interpret the meaning of their results. Be sure to
emphasize how pressure is causing the observed patterns by changing the density of air
molecules the scuba diver is inhaling with each breath. At these higher pressures more gas
will dissolve into the blood stream of the diver. Explain what is meant by “the bends,” how
this disease occurs as well as prevention and treatment. Leave plenty of time for questions
during this section. The students will complete the final section of the worksheet “advice
for Scuba Steve and his friends” for homework.
Is this lesson based upon or modified from existing materials? If yes, please specify
source(s) and explain how related:
Not stated
Not provided
Student worksheet
Lab tests instructions
List CA Science Standards addressed
Standard 5. B. - Students know organ systems function because of the contributions of
individual organs, tissues, and cells. The failure of any part can affect the entire system.
Standard 6. J. - Students know that contractions of the heart generate blood pressure and that
heart valves prevent back flow of blood in the circulatory system.
Lesson Implementation Comments
How did the lesson or elements of the lesson work as desired?
The students appeared to really enjoy the first mini activity where I had them examine
their own respiratory system. I never intended to make it a competition, but it happened
anyway and it was great to see the motivation and excitement in the students.
How did the lesson or elements of the lesson not work as desired?
The students really needed 15 min for each activity and in some cases even longer. The
activity really does take 10 minutes to complete but the students need an extra 5 min or so
to read directions, figure out who is going to complete which part, and ask questions if
necessary. An additional 5 min of clean up time should also be planned for the end.
Another issue I had when implementing this lesson was the inaccuracy of the students’
data. I only had 1-2 groups per class that had correct looking data, while most students
were quite a ways off. I had planned for this and decided to show some sample results
after completion of the lab so that the students could observe the patterns they were
suppose to find. I instructed them at this time to make some changes to their data if they
were missing pieces or if their data was way off.
Other comments about this activity
Diffusion rate is a function of pressure and temperature. I toyed with the idea of altering
the temperature of the water but decided that it would be too much of a stretch to ask the
students to imagine that a variation in temperature was related to scuba diving depth.
My solution was to alter the density of the blue colored water by adding a little sugar.
Although this doesn’t actually change the rate at which is dissolves it certainly appears to
dissolve faster. The denser blue water quickly falls to the bottom of the cup and spreads
out. The densest blue water will spread out and appear uniform after only about 45
seconds while the blue water with no sugar takes more than 5 minutes to dissolve
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