IOWA 4-9 SCIENCE PROJECT

Teacher Guide for: "Nature's Great Humidifiers" Steve Bartlett
ECOLOGY.693 Grades 7-9

CONCEPT OBJECTIVE:

Students working in groups will collect water vapor from the
leaves of a green plant and design a method for estimating the
amount of water lost by the entire plant


PROCESS OBJECTIVE:

Thinking skills developed in this cycle are measuring, recording,
and investigating.


MATERIALS:

plastic baggies and twisties, small pebbles, pan balances


EXPLORATION:

As a demonstration of water loss from a plant the teacher may
set up a potted plant wrapped in a plastic bag. This should be
done several days in advance so that water vapor condensation
will be easily visible on the sides of the bag. As a comparison,
another potted plant may be used such as a succulent (like a jade
plant). While the students are observing the teacher can ask
individual students the following questions:
"Where did the water in the bag come from?"
"Why is there a difference in the amount of water lost by the two
plants?"
"What variables might affect the amount of water lost by a green
plant?"
The students are divided into groups of 2 or 3 and pick up the
materials. Each group records the weight of the plastic bag and
the pebble. Students go outside and select 3 plants for
experimentation and place the plastic bags around one leaf of
each plant. The pebble is placed in the bag to help the water
vapor drain downwards. After 24-72 hours the students bring the
leaves back to the classroom and weigh the bags. The amount of
water collected in each bag is recorded in a chart or table.


CONCEPT DEVELOPMENT:

Students prepare wet mount slides of both the upper and lower
epidermis of the leaf and observe under both low and high power
making drawings of each. Students should be helped to notice the
pores or stomates especially on the lower epidermis. They are
asked to make a count of the stomates on the lower and upper
epidermis and record in a chart. Students are asked to compare
the amount of water collected in their bags with the number of
stomates they counted.


APPLICATION:

Find a way to actually calculate the amount of water your plant
would give off in 1 day, 1 week, 1 month, 1 growing season.
Investigate some variables which might affect the rate of
transpiration such as time of year, temperature, amount of wind
blowing over the leaves. Compare the amount of water loss of a
broadleafed tree to an evergreen.


EVALUATION:

The teacher's observations of the student toward attaining the
process and concept objectives during the phase (s) of the
learning cycle is a valid evaluation tool.


STUDENT ACTIVITY SHEET: NATURE'S GREAT HUMIDIFIERS
MATERIALS: microscope, slides, leaves saved from the activity
Make a wet mount slide of both the upper and lower epidermis of
each kind of leaf you collected. Peel the epidermis off some
leaves by breaking the leaf blade and pull the two pieces apart.
Hold the epidermis away from you and tear slowly. A transparent
layer of epidermis will separate. Remove the lower epidermis in
the same way.
You can also obtain a section of epidermis by sliding a single
edged razor blade across the surface for a short distance.
Observe each slide under both low and high power
What is the shape of these cells? Draw a picture of what they
look like. Do all the cells of the epidermis have the same
general shape?



Make a drawing of those cells that appear to be different from
the epidermal cells. Do these different cells have dark black
areas in the center of them?



This dark place is a pore, or opening, in the leaf epidermis. It
is a stoma. The cells on each side that control the opening and
closing of the stoma are the guard cells. Make a drawing of one
stoma surrounded by 2 guard cells.



Make a table to record the following information: type of leaf
collected, upper epidermis, lower epidermis and the number of
stomata you count in the low power field for each epidermal
layer.




The water that collected in your plastic bag passed through
these tiny openings. How does the amount of water collected in
each bag compare to the number of stomata you found for each
leaf?



Find a way to actually calculate the amount of water your plant
would give off in 1 day, 1 week, 1 month, a growing season



Investigate some variables which might affect the rate of
transpiration such as time of year, temperature, amount of wind
blowing over the leaves


Compare the amount of water loss of a broadleafed tree to an
evergreen.