Download Try this...It works like a charm. And have fun teaching plants!

Transpiration Made Simple!
http://www.amybrownscience.com/2012/04
/transpiration-made-simple.html
The plants always seem to get left out!
It is nearing the end of the school year, standardized testing is all anyone is
talking about, the students are getting antsy to be out for the summer, and
the biology teachers have to decide "what not to cover this year." This
always happens at the end of the year as we begin to run out of time. For
many biology teachers, a unit on plants is the first to go.
Teaching about plants is actually one of my favorite units, and I always
find that my students are woefully lacking in knowledge about the plants. I
make it a priority each year to leave enough time at the end of the school
year for my plant unit. I like teaching plants at the end of the year because
everything in our area is in full bloom! Among the many activities I do
with plants, I always have students germinate seeds . It is mind-boggling to
me how many of my students have never planted a seed! They love taking
care of them in the lab and they get so excited to watch them grow. Since
the weather is nice, the students then take their seedlings home and plant
them in their yards. Many will report back to me at the start of the
following year with news of their plant.
One of the labs I do that is so very easy to setup and clean up, is a
transpiration lab. Transpiration is the loss of water through the leaves. As
the stomata open to allow carbon dioxide to enter the leaf for
photosynthesis, water vapor escapes the leaf and enters the
atmosphere. For trees and other tall plants, it is tricky business to get the
water up to the top of a very tall tree. The major force in water transport is
provided by the evaporation of water from the leaves during
transpiration. As water is lost, the movement of the water out of the leaf
"pulls" water upward through the xylem all the way down to the roots. This
is called transpiration pull.
Measuring transpiration from the leaf is a very simple thing! I went to Wal
Mart and bought begonia plants. The one tray contained 6 plants. The
begonia is a good choice because it has a thick and fleshy leaf. Once back
in my school lab, I placed plants in small (250 mL) beakers. I watered
them thoroughly. Since I wanted to measure the amount of water lost from
the leaves, I took a plastic sandwich bag and wrapped it very tightly around
the beaker, and around the stem of the plant. It is necessary to insure that
no water evaporates from the dirt itself.
1) Place plant in beaker.
2) Wrap beaker tightly around plant, and tightly around the stem. Only the
leaf should be sticking out of the plastic bag.
The only way water is getting out of this beaker is through the leaves of
this plant!
3) Find the initial mass of the entire set-up and write the mass on a piece
of masking tape which is then placed on the beaker.
Now for the testable variables! What factors will cause an increase or
decrease in the rate of transpiration? We decided to test the following
factors:

One plant will be placed in continuous light for 24 hours.

One plant will be placed in front of a blowing fan for 24 hours.

One plant will be placed inside a plastic bag that had previously been
spritzed with water (high humidity inside the bag).

The fourth plant will serve as a control.
This plant was placed in the beaker, the beaker was covered with a plastic
bag, and the initial mass was written on the outside.
The plant was then placed under a lamp and left for 24 hours.
This plant was placed in front of a blowing fan for the same 24 hour period
of time.
The inside of this bag was misted with water and the plant was then sealed
inside the bag for 24 hours. This simulates a high humidity environment.
This is the control. The plant is still transpiring, but without the additional
influence of light, a blowing fan, and without the added humidity. A true
control would be the absence of transpiration, but w e decided to use a plant
at normal room conditions as our control.
Let the plants sit for 24 hours (or longer if you want!). Each plant is
massed again after a 24 hour period of time. Students will be amazed at
how much water has been lost through the leaves. The results should be as
follows:
Plant in Light: This plant loses a good amount of water. The light causes
the plant to continuously carry on photosynthesis. This requires a lot of
carbon dioxide, so the stomata stay open for a longer period of time to let
in the carbon dioxide. While the stomata are open, the plant will lose
water. The heat from the light also plays a role. The increase in heat will
cause a higher rate of evaporation from the leaf.
Plant in front of fan: The increased air movements across the surface of the
leaf will cause a higher rate of evaporation from the plant.
Humidity: Less water is lost from the plant when the humidity of the air
surrounding the plant is high.
All masses should be compared to the control to see if the factor being
tested causes an increase or decrease in the rate of transpiration.
Here are some ideas of how this might be used at different age levels:
Elementary: It may be enough in the lower grades to just show that water
is taken up by the roots and escapes from the leaf. Students can be asked
before the experiment to make predictions as to what they think the
outcome will be. They can form a hypothesis and go through the steps of
the scientific method.
Middle Grades may add the following: Have students calculate how much
water is lost per minute in each plant. Test an additional factor, such as
complete darkness, or various temperatures. Test different types of plants
to see if the transpiration rate is the same in all types of plants.
High School Grades may add the following: Remove the leaves and
determine the surface area of each leaf. Determine how much water is lost
in a given amount of surface area. Have students research the mechanisms
of transpiration, such as cohesion, adhesion, capillary action, and
transpiration pull.
Try this...It works like a charm. And have
fun teaching plants!
Here are some additional resources:
Look for video segments from "The Private Life of Plants"by David
Attenborough. There are quite a few of these on YouTube. Each is very
short - about 3 to 5 minutes - and my students really enjoy them.
Lab: Leaf Structure and Function
Lab: Living Flowers
Photosynthesis: Complete Unit Plan/Bundle
Lab: Pigment Chromatography
Lab: Stomata - Gateways into the Leaf
Labels: transpiration
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