IC Lessons Photosynthesis and Respiration
This is lesson _2_ of _4_in this IC
A. Title of this lesson Floating Disks
B. Summary of this lesson
Students will conduct the leaf disk lab in groups of four. For each team of
four, 40 Leaf disks will be punched out of the leaves, compressed using the
syringe, and ten disks will be placed in each of four beakers. Two beakers
with a 2% baking soda and soap solution will have ten disks placed in each
one. The beaker with plain water will have ten disks placed inside and the last
beaker with 2% baking powder solution (no soap) will have the last 10 disks
placed in the solution. Prior to starting the lab students will make predictions
about the outcome for the leaf disks in each beaker. Following the lab
procedures, students will observe, collect and graph data. The lab should be
set up for the students with each group having the four beakers, a paper
punch, leaves, a syringe and the lab write-up forms and graphs. Review the
procedures with students and be sure each group has a scribe, materials
manager, observer and timer.
C. Objective(s)/Learning Goal(s)/ Key Student Learning(s) of this lesson
1) Students will be running a cooperative lab, sharing observations, jobs, data
collection and outcomes.
o Gas production during photosynthesis will be observed and
described.
o Alternative set-ups (no soap, beaker in the dark, plain water)
produce different results that can be documented.
o Predictions will be tested for accuracy and supported (or not) with
existing evidence.
o Students can run more than one test with this lab to check the
results.
Note: The teacher will be able to conduct formative assessments as s/he moves
through the room listening to and supporting students through the lab process.
Created by Ariel Owen (Mt.Diablo USD), Linda Templeton (Alum Rock USD), Vina Sethi (Fremont USD), and
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IC Lessons Photosynthesis and Respiration
This is lesson _2_ of _4_in this IC
Questions for student learning need to be inquiry based. For example, “How can
you show your evidence of the leaf disks rising?”
Students should be fully engaged during the lab with observations, ideas, written
outcomes, etc. By the end of the lab, at least half of the disks should have risen
with bubbles showing around the edges.
D. Teacher Background Knowledge for this lesson
The teacher needs to be familiar with the expected results of the previous
day's activity titled, "Floating Disks: Questioning Techniques. (Lesson 1)”
Although the "Floating Leaf Lab" has to do with some very general
characteristics of both photosynthesis and cellular respiration, the names of
these cellular processes are purposely withheld from students the first three
days of this IC. The first three days of activities provide an experiential basis
for which the students can draw upon when components of photosynthesis
and respiration are presented by the instructor. Nonetheless, the teacher
should be familiar with the equations for both photosynthesis and cellular
respiration and leaf structure anatomy to help them better understand the
lab results.
E. Prior knowledge that students need to understand this lesson - with an assessment to
determine what they already know (if appropriate).
Students need to have been a part of the previous day's lab activity Lesson 1.
They need to have their recorded observations. Students have prior
knowledge of the gas exchange of photosynthesis and some understanding of
leaf anatomy (stomata, cuticle, spongy mesophyll).
F. Standards covered in this lesson
Current California Science Standards
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IC Lessons Photosynthesis and Respiration
This is lesson _2_ of _4_in this IC
1. d. Students know that mitochondria liberate energy for the work that
cells do and that chloroplasts capture sunlight energy for photosynthesis.
5. a. Students know plants and animals have levels of organization for
structure and function, including cells, tissues, organs, organ systems, and
the whole organism.
NGSS
1. Asking Questions and Defining Problems: A basic practice of the
scientist is the ability to formulate empirically answerable questions
about phenomena to establish what is already known, and to
determine what questions have yet to be satisfactorily answered.
2. Planning and Carrying Out Investigations: A major practice of scientists
is planning and carrying out systematic scientific investigations that
require identifying variables and clarifying what counts as data.
3. Analyzing and Interpreting Data: Scientific investigations produce data
that must be analyzed to derive meaning. Scientists use a range of
tools to identify significant features and patterns in the data.
4. Using Mathematics and Computational Thinking: In science,
mathematics and computation are fundamental tools for representing
physical variables and their relationships.
5. Engaging in Argument from Evidence: In science, reasoning and
argument are essential for clarifying strengths and weaknesses of a line
of evidence and for identifying the best explanation for a natural
phenomenon.
6. Obtaining, Evaluating, and Communicating Information: Science cannot
advance if scientists are unable to communicate their findings clearly
and persuasively or learn about the findings of others
Crosscutting Concepts:
2. Cause and effect: Mechanism and explanation. Events have causes,
sometimes simple, sometimes multifaceted. A major activity of
science is investigating and explaining causal relationships and the
mechanisms by which they are mediated. Such mechanisms can then
Created by Ariel Owen (Mt.Diablo USD), Linda Templeton (Alum Rock USD), Vina Sethi (Fremont USD), and
Denise Torrisi (Fremont USD)
IC Lessons Photosynthesis and Respiration
This is lesson _2_ of _4_in this IC
be tested across given contexts and used to predict and explain events
in new contexts.
4. Systems and system models: Defining the system under studyspecifying its boundaries and making explicit a model of that systemprovides tools for understanding and testing ideas that are applicable
throughout science and engineering.
CCSS
Reading:
3. Follow precisely a multistep procedure when carrying out
experiments, taking measurements, or performing technical tasks
4. Determine the meaning of symbols, key terms, and other domainspecific words and phrases as they are used in a specific scientific or
technical context relevant to grades 6–8 texts and topics.
Writing:
1. Write arguments focused on discipline-specific content.
a. Introduce claim(s) about a topic or issue, acknowledge and
distinguish the claim(s) from alternate or opposing claims, and
organize the reasons and evidence logically.
b. Support claim(s) with logical reasoning and relevant, accurate
data and evidence that demonstrate an understanding of the topic
or text, using credible sources.
c. Use words, phrases, and clauses to create cohesion and clarify the
relationships among claim(s), counterclaims, reasons, and evidence.
e. Provide a concluding statement or section that follows from and
supports the argument presented.
Listening & Speaking:
Created by Ariel Owen (Mt.Diablo USD), Linda Templeton (Alum Rock USD), Vina Sethi (Fremont USD), and
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IC Lessons Photosynthesis and Respiration
This is lesson _2_ of _4_in this IC
Students will listen with respect to team member ideas. Students
will be successful in collaboration demonstrated by the group
completion of the lab report. Students will be engaged in an active
discussion about the science of the lab.
Math:
Students will be using a timer, graph, and other mathematical
measurement to determine the outcome of the lab.
G. Suggested time to complete this lesson
50 minutes
H. Materials Used in this lesson typed in a bulleted list with quantities (e.g., 10 beakers; water
of 2 liters)
Based on a class size of 32, the following supplies will be needed:
 8 lights with stands (to set at specific height above the cups with leaf
disks)
 32 cups/beakers (200 ml)
 8-16 paper punches or very stiff straws (to punch the disks out of the
leaves.
 8 boxes to cover one cup/beaker
 8 spoons
 8 sets of lab directions and lab form/graph
 8 timers (students may use their own devices to time this lab)
 Baking Soda
 Dish Soap
 Tap water (spring water is recommended if your local water is heavily
chlorinated or treated with other chemicals
 Pipette droppers (for adding soap to the Baking Soda solution)
Created by Ariel Owen (Mt.Diablo USD), Linda Templeton (Alum Rock USD), Vina Sethi (Fremont USD), and
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IC Lessons Photosynthesis and Respiration
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 4 liter container for Baking soda solution (2% solution = 1/8 tsp per 300
ml water),
 1 liter container for water
I. Materials Prep for this lesson (should include number of copies needed (e.g. one probe per
student, one set of directions per lab group)
You will be mixing a 2% CO2 (3 L) solution for this lab. It should be in the 4
liter container.
You should add a drop or two of soap to each cup of sodium bicarbonate
so that the amount is consistent.
Each group of four will need the following materials:
 Job assignment (if desired) Observer, Materials Manager, Timer, Scribe)
 1 syringe
 4 cups – 2 with 2% bicarbonate solution and soap, 1 with bicarbonate
only, and 1 with water only (approximately 120 – 140 ml per cup)
 1 spoon
 1 light set up
 1 set of directions
 1 piece of graph paper
 4 sheets of paper towels
J. Lesson Plan – detailed, numbered step-by-step plans.
Floating disks labs based on Floating Leaf Disk Assay
(Brad Williamson http://www.elbiology.com/labtools/Leafdisk.html). There
should be a copy attached to this unit.
1. Pass out syringes, one per group of four students and have them
practice creating a vacuum.
2. Pass out Ivy leaves, spinach may work also, but best results with ivy.
Pass out either a hole punch or stiff straw. Have each group member cut
out 10 leaf disks (for a total of 40 disks):
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IC Lessons Photosynthesis and Respiration
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All photos are originals by Denise Torrisi
3. 10 disks will be placed in the control beaker (water only); 10 disks in the
CO2 solution (no soap) and 10 disks each for a CO2 with soap (2 beakers), so
materials will vary.
4. Have 4 beakers or plastic cups available per group of 4 students. The
materials manager is in charge of obtaining all necessary items for this lab.
S/he may get help from other group members.
5. Place water in one cup as the Control – label the cup control;
6. Place a 2% solution of Sodium Bicarbonate in a 2nd and 3rd cup, along
with a few drops of soap - Label 2% BC and soap;
7. Place a 2% solution of Sodium Bicarbonate in the 4th cup without soap –
Label 2% BC.
8. Have a large box available for the “dark” disks.
9. Place the leaf disks in the syringe;
10. Carefully add about 10-20 ml of the Sodium Bicarbonate and soap
solution to the syringe;
Created by Ariel Owen (Mt.Diablo USD), Linda Templeton (Alum Rock USD), Vina Sethi (Fremont USD), and
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IC Lessons Photosynthesis and Respiration
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11. Gently push plunger to remove most of the air; don’t crush the disks,
draw up solution of bicarbonate, shake, tap, create a vacuum with your
thumb over the opening.
12. When disks have sunk, they are ready to place 10 disks in each of
solutions the students prepared.
13. Place the Control cup, 2% BC and soap cup, and the 2% BC under the
light source.
Created by Ariel Owen (Mt.Diablo USD), Linda Templeton (Alum Rock USD), Vina Sethi (Fremont USD), and
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IC Lessons Photosynthesis and Respiration
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14. Place the second 2% BC and soap cup under the box to prevent light
from reaching the leaf disks.
15. The timer should start as soon as the last cup is covered. The disks
under the light source are to be reported out every minute. The disks
under the box need to be reported out every five minutes. The scribe is to
write down any information provided by the observer. All students can
observe the process, and only the observer’s information is recorded. Use
the graph paper to show how many disks rise (Y axis) per minute (X axis)
16. Run the lab for at least 20 minutes, longer if possible.
17. Leave the students about 5 minutes to complete the written portion.
As the scribe and observer are completing the observations, the materials
manager and timer should be cleaning up the lab so that it can be used for
the next class.
K. Vocabulary words – key vocabulary words that are targeted or taught as part of the lesson.
sodium bicarbonate, carbon dioxide source, gas in solution, vacuum,
compression, spongy mesophyll, stomata, cuticle, chlorophyll,
photosynthesis, cellular respiration
L. Potential Pitfalls for: a. student understanding; b. laboratory mishaps and common procedural
errors; c. academic vocabulary issues, etc.
 Students erroneously believe that the sodium bicarbonate soda is what
makes the leaf sink to the bottom (rather than realizing its the
compression of the vacuum in syringe that causes of internal leaf gases
to be forced out and replacing it with water that makes the leaf disks
denser than water)
 Leaf disks rose because they got rid of (expelled through its leaf surface)
the carbon dioxide source (erroneous).
Created by Ariel Owen (Mt.Diablo USD), Linda Templeton (Alum Rock USD), Vina Sethi (Fremont USD), and
Denise Torrisi (Fremont USD)
IC Lessons Photosynthesis and Respiration
This is lesson _2_ of _4_in this IC
 Some cups/beakers may be spilled due to excitement or mishap – have
replacements and consequences ready. Lots of paper towels are a
necessity. Students will need to “restart” their lab if this happens.
 The teacher should be in motion in the classroom at all times. Listen to
student conversations to prevent misconceptions and to support deeper
understanding.
 If students are using more common language instead of scientific terms,
ask about what a good science term would be for that particular word.
For example, if a student explains that the syringe “sucked out” the air,
ask for the science term for “sucking” – created a vacuum
M.Differentiation: Modifications for English Learners, advanced learners, struggling learners, etc.
Assign EL students to teams with very competent students who also have
English as their first language. This lab is very visual and kinesthetic. The
results are obvious and can be seen without having English as a primary
language.
N. Please list all worksheets used in this lesson.
Floating Disks Lesson 2 – Procedures (See attached)
Data Table: Number of Leaf Disks Floating (See attached)
O. Please list all assessments that require a separate sheet.
Questions at the end of the Photosynthesis in Leaf Disks Procedure – graph
generated to display data.
P. Photos/Illustrations
Included in this document and credited to Denise Torrisi.
Created by Ariel Owen (Mt.Diablo USD), Linda Templeton (Alum Rock USD), Vina Sethi (Fremont USD), and
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IC Lessons Photosynthesis and Respiration
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Q. Other Resources
N/A
Created by Ariel Owen (Mt.Diablo USD), Linda Templeton (Alum Rock USD), Vina Sethi (Fremont USD), and
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IC Lessons Photosynthesis and Respiration
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Floating Disks Lesson 2 – Procedures
1. Using a paper punch or straw, have each member of your team make 10 leaf
disks from the leaves you received for this lab. Are they ivy leaves or spinach
leaves?
2. Label your cups/beakers as A, B, C and D. Cups A & D will contain sodium
bicarbonate and 2 drops of soap (provided by your teacher) Cup B will contain
sodium bicarbonate without soap, and Cup C will contain just water (as your
control to compare your results to during this lab).
3. Remove the plunger from a large clean syringe. Place all 40 of the leaf disks in
the body of the plunger. Be sure the leaf disks are near the tip of the syringe
as you place the plunger so that you do not damage the disks.
4. Insert the tip of the syringe into the beaker of Sodium bicarbonate and soap.
Draw 15-20 mL into the syringe. The leaf disks should be floating at this time.
5. Hold the syringe tip upward and expel the air by depressing the plunger
carefully. Do not allow any solution to come out of the tip.
6. Seal the tip of the syringe using the tip of your index finger. Be sure you have
it tightly sealed as you pull back on the plunger creating a partial vacuum. It
should be hard to pull on the plunger if you have a good seal.
7. Look carefully. You should see bubble coming out of the leaf disks. Hold the
plunger for 10 seconds.
8. Release the plunger and your finger from the tip simultaneously. The disks
should start to sink. Tap the side of the tube or shake gently to break any
bubbles on the edges of the disks.
9. Repeat steps 7 & 8 until all the disks sink. DO NOT overdo these steps. You
have been successful if the disks sink to the bottom. Do not repeat “just to be
sure” as you may damage the cells of the leaves and change the outcome of
this lab.
Created by Ariel Owen (Mt.Diablo USD), Linda Templeton (Alum Rock USD), Vina Sethi (Fremont USD), and
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IC Lessons Photosynthesis and Respiration
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10. Remove the plunger from the syringe and pour the solution containing the
disks into 2 plastic cups (or beakers) with the bicarbonate solution and add
the remainder of your solution equally to both beakers. There should be 10
disks per cup. Maker sure they sink to the bottom.
11. Use your spoon to place 10 disks in each cup or beaker.
12. Cover ONE beaker (Cup D) of the sodium bicarbonate and soap solution to
block light for the leaf disks. Place Cups A, B and C under a light source,
about 15 to 20 cm below the light. Begin timing the experiment as soon as the
light is turned on. Record your observations on the table provided.
13. What is happening to the leaf disks as photosynthesis proceeds? Continue to
record observations on your table. After each time check, tap the side of the
beaker to maker sure the disks are not “sticking” to the container walls.
NOTE: Check the covered beaker quickly to avoid light exposure. When
instructed, Clean the lab equipment and dispose of solutions in the sink drain.
Created by Ariel Owen (Mt.Diablo USD), Linda Templeton (Alum Rock USD), Vina Sethi (Fremont USD), and
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IC Lessons Photosynthesis and Respiration
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Names_______________________________________
Team #__________
Data Table: Number of Leaf Disks Floating
Time
(Minutes)
Cup A
Number of Disks
Floating (Light)
Bicarbonate &
Soap
Cup B
Number of Disks
Floating Bicarbonate
Only
Cup C
Number of
Disks Floating
(H2O)
Cup D
Number of Disks
Floating (Dark)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
(After 20 minutes consider the experiment over and that no more disks will rise)
What happened to the disks in the light? Provide lots of detail.
What happened to the disks in the dark? Provide lots of detail.
Created by Ariel Owen (Mt.Diablo USD), Linda Templeton (Alum Rock USD), Vina Sethi (Fremont USD), and
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IC Lessons Photosynthesis and Respiration
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Explain the differences between the light and dark condition.
You and your team are to develop a graphic method to show your data and explain
your results.
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