Plant Transpiration Lab
In
this online lab, I compared the rates of transpiration on nine different plant
species undergoing varying environmental conditions. We used a potometer
to determine the mL of water of each plant in the experiment. I tested and
recorded data, observing the effect of environmental factors (wind, heat and
light) on the plants transpiration rate for an hour. My control was the plants
transpiration rate without any environmental factors interfering. All of these
influences and environmental factors increased the transpiration rate of the
plants.
Here are my results of the nine plants in the lab
Amount of water transpired in 1 hour (mL)
Plant Control Fan Heat Light
Arrowhead
|
3.6
|
7.5
|
6.6
|
4.0
|
Coleus
|
0.9
|
6.0
|
3.9
|
3.0
|
Devil’s Ivy
|
2.9
|
4.4
|
4.1
|
3.6
|
Dieffenbachia
|
4.1
|
7.7
|
6.0
|
3.9
|
English Ivy
|
1.8
|
5.1
|
3.2
|
2.1
|
Geranium
|
1.2
|
4.7
|
5.8
|
2.4
|
Rubber Plant
|
4.9
|
8.4
|
6.8
|
4.3
|
Weeping fig
|
3.3
|
6.1
|
4.9
|
2.5
|
Zebra Plant
|
4.2
|
7.6
|
6.1
|
3.2
|
About Plant Transpiration
"What factors affect the transpiration rate in
plants?
In vascular plants, water is absorbed through the
roots and carried upward through the stem to the leaves. The force behind this
upward movement is called capillary action, a force of attraction between
molecules that causes liquids to move up narrow tubes, such as those inside a
plant's stem.
Some of the water absorbed by a plant's roots is
used for photosynthesis, but much is lost to the environment through a process
called transpiration. During photosynthesis, tiny pores on the surface of the
leaves, called stomata, open to permit the intake of carbon dioxide and the
release of oxygen. Because the stomata must remain open for the exchange of
gases, large amounts of water are lost to the environment through
evaporation.
Water that evaporates from the leaves is
continually replaced with water that is absorbed through the roots. Therefore a
plant's rate of transpiration can be measured by observing the amount of water
taken up through a plant's roots over a period of time. The transpiration rate
can be approximated by measuring the amount of water taken up in a short time
through the plant's stem.
In a laboratory, a plant's transpiration rate can
be measured using a potometer. A potometer can be assembled from standard
laboratory materials including: a ring stand, clamps, a 10mL pipette, a 100mL
burette, a T-tube, glass tubing, and rubber tubing.
To measure
transpiration rate, a plant sprig is mounted on the potometer and the burette
and pipette are filled with water. Over time the plant will transpire and
absorb water through its stem. The potometer is constructed in such a way that
the plant's water source is the pipette, therefore the amount of water
transpired over time can be determined by reading the water level in the
pipette after time has passed. The water supply in the pipette can be
replenished from the water supply in the burette by releasing the pinch
clamp." (Online Plant Transpiration Lab )
Journal Questions
1. Describe the process of transpiration in
vascular plants
Transpiration is a process
like sweating for plants. Leaf and stem surfaces are dotted with stomata (small
openings like pores) that are more numerous on the underside of the leaf. The
purpose of transpiration is to cool the plant and enable the flow of minerals
and nutrients from the root to shoot. All plants
continuously absorb water through their roots. This water is conducted upward
through the stem and is distributed to all the aerial parts including the
leaves. Only a small quantity of this water (about 2%) is used by the plant in
photosynthesis and other activities. The rest of it is almost lost to the
atmosphere as water vapor. Transpiration is a very useful process for
the plants for two reasons: first, to get rid of the excess water absorbed and
second, for cooling the plant in hot weather.
2. Describe any experimental controls used in the
investigation.
The control for this experiment was
recording each plants rate of transpiration without any environmental factors
influencing the test.
3. What were environmental factors that you
tested increased the rate of transpiration? Was the rate of transpiration
increased for all plants tested?
All the factors that were used (wind,
heat, light) influenced the rate of transpiration by increasing it. The data
table shows that all plants had an increase in their rate of transpiration with
every factor tested.
4. Did any of the environmental
factors (heat, light, or wind) increase the transpiration rate more than the
others? Why?
Yes. Plants
transpire in light with a more rapid rate than in the dark. This is a legal
factor because in the light the stimulation of opening of the stomata is larger
than in the dark. Due to light, the cells vibrate against each
other, warming the leaf making the temperature increase, speeding up the
process. Heat and the rate of the temperature also affect the rate of
transpiration. They transpire more rapidly when the temperature is high because
at high temperature water evaporates more rapidly.
5. Which species of plants that you
tested had the highest transpiration rates? Why do you think different species
of plants transpire at different rates?
According to the data collected,
the rubber plant had the highest transpiration rates. There are a number of
reasons why different species of plants transpire at different rates. For
example, the origin of the plant - plants originally from
sub-tropical or tropical areas will transpire at a higher rate than those
originally from arid or semi-arid areas. The size of the plant (larger
leaf surface area = more transpiration). The metabolic rate of the plant =
plants with a higher metabolism have a higher transpiration rate. The
amount of water in the soil - plants that have access to more soil water will
transpire at a higher rate than those which don't. Availability of
nutrients - plants which have adequate nutrient supplies have higher metabolic
rates than those which don't, and therefore transpire at a higher rate.
6. Suppose
you coated the leaves of a plant with petroleum jelly. How would the plant's
rate of transpiration be affected?
If I coated the leaves of the plant
with petroleum jelly, the act of transpiration would completely stop. By
covering the entire leaf with petroleum jelly the plants gard cell would be unable
to obtain co2 from the atmosphere thus making the rate of photosynthesis stop
and if photosynthesis stops the plant will not be able to produce glucose and
in doubt will not be able to produce ATP and will die.
7. Of what
value to a plant is the ability to lose water through transpiration?
Because water
has cohesion between molecules it is drawn up through the xylem when the water
evaporates from the top of the column. This creates the transpiration flow
through the xylem and carries any dissolved nutrients upwards with the
water. Having the ability to draw water and nutrients upwards to a
branching leaf canopy allows plants to spread the leaves to intercept more
sunlight. Transpiration raises the air humidity and moderates the daily change
in temperature. Evaporation cools the leaves just as sweat evaporating
from skin is cooling.
