Unit 8 Investigation 2 Daily Cycle
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Daily Cycle
Contents
• Introduction
• Thinking About the Question
• Materials
• Safety
• Trial I : Air in a bag
• Trial II : Paper leaf versus living leaf
• Technical Hints
• Analysis
• Further Investigations
Introduction
Discovery question: What happens to a living plant throughout the day and night?
cartoon of sun and moon. [dayandnight.jpg]
This activity investigates a 24-hour cycle of exchanging water vapor of plants.
Thinking About the Question
How does the 24-hour day/night cycle affect release of water vapor by plants?
The turning of the earth on its axis has caused a regular and predictable daily
cycle of light and darkness. Animals, plants and even microbes have built-in
timepieces that help them know when to eat, when to rest, and when to wake up.
Draw your impression of a 24-hour day/night cycle.
[Answer: Student drawings will vary. Student drawings probably will show the sun
and the moon.]
How does the day differ from the night? Label your drawing to show the lightest
and darkest parts of the day. Label the warmest and coolest parts of the day.
[Answer: Student drawings will vary. The temperature should be the warmest
several hours after noon. At noon, when the sun is directly overhead, is not the
hottest time of the day. This is because the sun heats up objects on the Earth’s
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surface that retain and radiate energy throughout the day. It is the radiation of
energy from these objects that provides us with much of the warmth. So the
warmest time of the day will be after noontime. The temperature should be the
coolest several hours after midnight. It also takes time for the heat of an object to
disperse during the night, making midnight not the coolest time of the day.]
Materials
• relative humidity sensor [linked to Technical Hint Choosing the relative
humidity sensor]
• light sensor [linked to Technical Hint Choosing the light sensor]
• small potted plant with broad leaves
• paper leaf (from Trial I)
• 3 re-sealable plastic bags (per student)
Safety
No specific safety features needed for this investigation.
Trial I
24-hour cycle
1. During a 24-hour cycle does the amount of moisture in air change with
varying light? Place your thoughts in Notes.
[All air contains some water vapor, especially if plants, trees, and animals
are present. The moisture holding capacity of air depends on the air's
temperature. The capacity increase dramatically with increasing
temperature.]
2. Refer to Technical Hints to run the relative humidity sensor software.
3. Refer to Technical Hints to run the light sensor software.
4. Bag some air from the room and place the relative humidity sensor and
light sensor into the bag immediately. Place your bag near a window.
Make sure the slots on the relative humidity sensor are not blocked and
are open to the air in the bag by standing the sensor on one end. Seal the
bag and start both sensors. Stop recording after 24 hours.
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[[baggedair24hours.jpg] Now it becomes tricky. We are working with 7
companies and we need to not show a preference. Most of the companies
have a separate relative humidity and light sensors. So I am adding a light
sensor along with the black square box with slots that represents the
relative humidity sensor. It should also be black and cylindrical with a cord.
It should appear the same way throughout this investigation.]
5. Save your graph(s) as Trial I – Bagged Air – 24 hr.
Trial II
24-hour cycle of bagged leaves
1. Again, select a healthy potted plant with broad leaves.
2. Remember the stomata openings. In a way, this is how the plant breathes
and exchanges gases like we do. In light guard cells around the opening
swell, causing the pore to be at its widest, and CO2 (carbon dioxide gas)
spreads into the leaf and into the cells to be used in photosynthesis. In the
dark or under drought conditions the guard cells are closed and no
photosynthesis takes place. Opening of the stomata not only allows CO 2
to diffuse into the leaf, but allows water vapor to diffuse out of the leaf. The
release of water from leaves through their stomata is called transpiration.
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[stomadrawing.jpg – do redraw and try to make it very similar in tilt and
shape to the real picture from the high-powered microscope view.]
What different conditions will cause the stomata to open or change size?
[The alteration in the size of the stomata occur in response to a variety of
the external stimuli such as light, thermal energy, CO2 concentration and
water.]
3. Think about the differences you would see on your graphs if you bagged a
living leaf with a relative humidity sensor and light sensor for 24 hours.
Would the graph show signs of moisture changes with the varying
amounts of light? Record your thoughts in Notes.
[Water molecules evaporate from a leaf during transpiration.
Transpiration is the evaporation of water from plants when the stomata is
open. The amount of light will provide changes in the thermal energy
changing the size of the stomata. The graph will show changes in both the
amount of moisture and light in the bag over a 24-hour period. See
Analysis for the explanation of the changes of the relative humidity due to
the change in light and thermal energy.]
3. Divide your class in two different groups for testing. One type of testers
will bag a paper leaf with a relative humidity sensor and a light sensor for
24 hours. The other type of testers will bag a living leaf with a relative
humidity sensor and a light sensor for 24 hours.
4. Refer to Technical Hints to run the relative humidity sensor software.
5. Refer to Technical Hints to run the light sensor software.
6. If you are one of the paper leaf testers, bag your paper leaf from Trial I
with a relative humidity sensor and a light sensor. Make sure the slots on
the relative humidity sensor are not blocked and are open to the air in the
bag by standing the sensor on one end. Also, make sure the tip of the light
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sensor is not blocked. Seal the bag and start both sensors. Stop recording
after 24 hours.
[lightrelativehumiditypaper.jpg]
7. Save your graph(s) as Trial II – Bagged Paper Leaf – 24 hr.
8. If you are one of the living leaf testers, place your plant near a window.
Bag a living leaf while it is still on the plant with a relative humidity sensor
and a light sensor. Make sure the slots on the relative humidity sensor are
not blocked and are open to the air in the bag by standing the sensor on
one end. Also, make sure the tip of the light sensor is not blocked. Seal
the bag and start both sensors. Stop recording after 24 hours.
[lightandrelativehumiditylive.jpg]
9. Save your graph(s) as Trial II – Bagged Living Leaf – 24 hr.
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Technical Hints
• Choosing the relative humidity sensor
• Choosing the light sensor
• Running relative humidity sensor
• Running light sensor
• Saving graph
• Overlaying graphs
• Creating a drawing
Analysis
1. Observe the light graph from Trial I. How did you impression of a 24-hour
day/night cycle compare to your graph?
[Answer: Student answers will vary. Ask the students to adjust their
original drawing or list to reflect the data from the graph. Explain to the
students that some light probes have a limited range. They may top out
(shown by the flat line at 5000 lx) if the sun is too bright.
[[lightbaggedair.jpg] Please do not draw this graph. It is just a place
holder.]
2. Overlay the bagged air relative humidity and light graphs from Trial II for
both the paper leaf and the living leaf. Refer to Technical Hints to see
how to overlay graphs. How were the two graphs similar?
[Answer: Both graphs showed a variation of light for the day/night cycle.
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[[lightrelativehumidityairgraph.jpg] Please do not draw this graph. It is just
a place holder.]
[[lightrelativehumiditygraphlive.jpg] Please do not draw this graph. It is just
a place holder.]
3. Overlay the paper leaf graphs in Trial II for both relative humidity and light.
Refer to Technical Hints to see how to overlay graphs. Which graph
showed a greater amount of humidity? Can you explain the difference in
relative humidity?
[Answer: The living leaf showed a greater amount of moisture, especially
during daytime. When it is light during the day, the stomata is open
releasing more moisture.
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[[relativehumiditygraph.jpg] Please do not draw this graph. It is just a place
holder.]
4. How does the amount of light relate to the thermal energy within the bag?
[The amount of light will provide changes in the thermal energy on the
bag. As the light level increases, the thermal energy increases. As the
light level decreases, the thermal energy decreases.]
5. Transpiration is really the evaporation of water from a leaf from the
stomato. Draw a picture of the process of evaporation of water from your
leaf. Refer to Technical Hints to see how to create a drawing. Label any
important parts of your drawing.
[This picture should include the sun above the
leaf. The water, sun, and the stomata should be labeled.
transpiringleaf.jpg]
[Student drawings will vary. Stomata are generally on the underside of the
leaf, away from the direct sunlight. The drawings should include a source
of energy, water, and the stomata.]
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6. How does transpiration of a plant leaf compare to respiration of a human?
[Student answers will vary. Regardless of the description provided, the
student should relate the process of transpiration to that of breathing? In
both cases gases are exchanged between the living system and its
surroundings. In both cases, this exchange is necessary for life.]
Further Investigations
• Try Trial II again, but this time smear a small amount of oil on the leaves
before you bag them. Do you think the leaves will still transpire?
• Do all leaves transpire as much as other leaves? Select another type of
plant or tree and bag a leaf. Was the result the same as the previous test?
How did the leaves change in the amount of water transpired? Did the
leaves respond to change in light the same?
Performance Assessment – use the motion sensor to produce a motion graph.
Position (0-4 meters) versus Time (0-60 seconds)
Written Assessment – verbalize in mathematical terms the motion that was
produced.