Transpiration lab
In this activity, your
students will observe the process of transpiration. They will determine the
rate of transpiration for one plant branch.
As plants moved to the land from a
water environment, desiccation (drying out) became a problem to overcome. The cuticle,
which is a thick, waxy layer on a plant's surface helps to prevent water loss.
The cuticle however, also prevents the
exchange of oxygen and carbon dioxide with the environment. Because
photosynthesis requires the exchange of these two gases, the plant needs a way
to allow for this exchange. Small pores con the leaves,
called stomata enable the intake of carbon dioxide and the release of
oxygen during photosynthesis.
Most plants loose 90% of the water
taken into the roots as a result of the process of transpiration. Transpiration
is the movement of water molecules from the plant into the air. Most water loss
is through the stomata when they are open for photosynthesis.
Environmental conditions can cause changes in the
opening and closing of the stomata. Some environmental conditions will increase
the rate of transpiration, while others will slow it down.
Materials/resources
Materials:
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Demo
set up |
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two
test tubes (same size) |
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Pre-activities
Students should
understand transpiration.
Activities
Teacher hints:
1.
You
can cut stems of plants yourself. However, if you use grown plants, you must
plant the seeds (I use beans) two to three weeks prior to the lab activity.
2.
Make
all measurements in millimeters.
3.
You
may want to remind students of controlled lab setups to help with the question
about the test tube in which evaporation occurs.
4.
Review
the concept of slope to determine rate.
5.
Cut the plants
with scissors and place them quickly into the test tube.
Student
procedures:
Day One:
1.
Obtain
two test tubes. Fill each test tube three-quarters full with water. Place both
test tubes in a test tube rack.
2.
Follow
the teacher's instructions to obtain your plant stem.
3.
Place
the plant stem so that it stands upright in one of your test tubes. Use the lab
sheet to continue with activity.
4.
Use
the glass marking pencil to mark the water level in each of the test tubes.
5.
Use
a ruler to measure the height of the water in each test tube. Record these
initial amounts in the lab table.
6.
Check
the water height every ten minutes. Record the height of the water in each tube
until the end of class.
7.
Follow
the teacher's instructions for clean up and where to place lab set up
overnight.
Day Two:
1.
Obtain
the lab set up.
2.
Measure
the height of water in each tube. Record height of each in the lab sheet from
yesterday.
3.
.Follow
the teacher's instructions for final clean up of material.
4.
Graph
your results.
5.
Answer
the lab questions. (Answers)
6.
Determine
the rate of transpiration.
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Diagram
1:
Results:
height of water (in mm) in test tubes
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Construct
a line graph from our results from day one. Rate
of transpiration: 1. Subtract the over night height from the
initial height for each test tube: initial
height tube (a)_____ - overnight height (a)______= difference(a) _______mm initial
height tube (b)_____ - overnight height (b)______= difference(b) _______mm 2. To find the water difference due to
transpiration subtract difference (b) from difference(a). difference(a)_____ - difference(b)______ = ______mm
of water due to transpiration. 3.
To determine the rate of transpiration per hour divide the mm of water change
by 24 (24 hours per day). ______mm
of water 24 hours = ______mm of water transpired
/hour. |
