Adaptations
Purpose
To test a leaf’s adaptation of opening or closing
its pores in response to its environment.
Process Skills
Observe, Measure, Collect data, Interpret data,
Identify and control variables, Draw conclusions
Background
Controlling Water Loss
from Leaves
Materials
(per group)
q data sheets
q 3 sandwich-sized zipper bags
q masking tape
q3 identical sponges
(same size and material)
q scale (grams or ounces)
q liquid measure (mL or tsp.)
q water
q plate or tray
q short pencil
Leaves are a crucial part of a plant. One of
their most important functions is to make food.
They do this by combining water and sunlight.
As part of this process, leaves release water
vapor into the surrounding air. On leaves,
small holes called stomata allow water vapor
and other gases to pass into and out of the leaf.
These stomata open and close to control the amount
of water vapor and other gases that enter and leave a leaf.
Stomata are one of the most important adaptations on a leaf, because they help each plant
adjust to changes in its own climate. Plants in dry areas with a lot of sunlight keep their
stomata closed during most of the day to retain water. The stomata open at night, when
it is cooler and water loss will not be as great. Plants in shaded, humid areas can keep
their stomata open longer during the day to keep from getting waterlogged. Stomata are
an adaptation that helps a plant survive in its environment.
Time –
stoma
tty,
Dr. Dennis Kunk
el
©
Ge
Grouping – Pairs or small groups
©
Set-up day: about 30 minutes
First observation day: about 10 minutes
Second observation day: about 20 minutes
Whole experiment: three days within a
one-week span
He
m
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Experiment
Adaptations—Controlling Water Loss from Leaves
Procedure
Preparation
3.Carefully poke the pencil through both
sides of Bag B 20 times. This will make
a total of 40 holes. Push the pencil far
enough to make a hole as wide as the
pencil. Spread the holes apart evenly.
1.Read the procedures below. Then
record a hypothesis on the data sheet.
2.Use the three zipper bags to represent
the outer layer of three leaves. Use
masking tape to label the bags A, B,
and C. Also write your name(s) on
the tape. Prepare the bags as follows:
4.Place one dry sponge inside each of the
bags. Weigh each of the dry sponges
with its bag on the scale. Be sure Bags
A, B, and C all weigh exactly the same.
Record this dry weight on the data
sheet, along with the starting date
and time.
5.Ask your partner to hold Bag A open
so you can slowly pour water onto the
sponge, adding 5 mL (1 tsp.) of water
at a time. Add as much water to the
sponge as you can before it begins
to drip.
Bag A:
no holes and sealed
represents a leaf with
its stomata closed,
like a desert leaf in
dry conditions
Bag B:
40 holes and sealed
represents a leaf
with some stomata
open, like a leaf in a
forest with light rain
6.Pour the same amount of water as you
used in step 5 onto the sponges in Bags
B and C. Record on your data sheet the
total amount of water you poured onto
each sponge.
Bag C:
no holes and
propped open
represents a leaf
with many stomata
open, like a tropical
rainforest leaf
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Experiment
Adaptations—Controlling Water Loss from Leaves
7.Weigh each wet sponge and bag
together. They should all weigh the
same. Record this weight on your
data sheet.
then use it to prop the bag open again
when done.] Record the weights in the
First Observation table. Also record the
date and time of your observations.
8.Seal bags A and B firmly. Use the short
pencil or another object to prop open
Bag C, so the zipper seal stays wide
open. Lay the bags flat on the plates
or the tray.
Second Observation
After two more days have passed, at
about the same time of day as the Set-up
Day, repeat the steps from the First
Observation. Record the weights in
the Second Observation table.
9.Place all three bags in a spot where
they will not be disturbed for several
days. All the bags should receive
similar light and temperature.
Measure Water Loss
For each bag, subtract its final weight
from the weight of the bag with the wet
sponge on the Set-up Day. This will tell
you the weight of the water it lost. Record
these amounts in the final table of your
data sheet.
First Observation
After two days have passed, at about the
same time of day as the Set-up Day, weigh
each sponge in its bag. [Note: Remove the
pencil from Bag C during weighing, and
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Experiment
Adaptations—Controlling Water Loss from Leaves Data Sheet
Name________________________________________ Date_____________
Hypothesis: Which sponge will lose the most water, and why?
Collect Data
Set-up
Date:
Weight of each
dry sponge in bag
Volume of water
poured onto each sponge
First Observation
Time:
Weight of each
wet sponge in bag
Date:
Time:
Date:
Time:
Weight of sponge in Bag A
Weight of sponge in Bag B
Weight of sponge in Bag C
Second Observation
Weight of sponge in Bag A
Weight of sponge in Bag B
Weight of sponge in Bag C
Weight of Water Lost Since Set-up
Bag A
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Bag B
4
Bag C
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Experiment
Adaptations—Controlling Water Loss from Leaves Questions
Name________________________________________ Date_____________
Analyze Data
1. How did having openings in the bags affect the amount of water that was lost? Why?
2. Where did the water go after it left the sponge?
3. Which part of a plant did each of the following represent?
sponge:
bag:
holes in bags:
4. If a normally dry area goes through a rainy period, what would likely happen to the
stomata on the leaves of plants in the area? Why?
5. Why might stomata open and close throughout the day?
Draw Conclusions
Summarize in your own words why the opening of stomata is an effective adaptation
for plants.
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Adaptations
Controlling Water Loss
from Leaves
Teaching Tips
These process activities will help students understand that all living things adapt
to changes in their environments. This is true of humans, animals, and plants.
Students will also gain an appreciation for the vast diversity in the natural world.
Set-up and
procedures
materials
extensions and
variations
lan to start the experiment on a Monday, with follow-up observations on
P
Wednesday and Friday. However, if weight differences are not significant
by Friday, carry over the observations into the following week. The sponges
in bags B and C may dry completely within several days, so running the
experiment too long will make it hard to discern differences between
the two.
The sponges used by each group must have an equal starting weight when
wet. If the sponges and the amount of water used are identical, this should
be the case. If need be, help students adjust the starting weight by adding
or squeezing out water.
Each group will need counter or table space to set three zipper bags near
each other. The bags will need to be undisturbed between observations.
A warm, sunny place will speed up evaporation, but groups need not
place their bags in the same spot as other groups. In fact, if some groups
place their bags in warmer spots than others, this can promote discussion
and comparisons of the results.
Poke the pencil far enough through the sides of Bag B so the full diameter
creates the holes, not just the tip. This will allow airflow.
is essential that students use a scale sensitive enough to measure slight
It
weight differences between the sponges in ounces or grams. Be sure
students know how to use it properly.
If using a balance scale, you can use common items as weights. For
example, A U.S. penny weighs about 3 grams, and a small paper clip
weighs about 0.5 grams.
Discount stores sell multi-packs of sponges at low cost. Parents may be
willing to provide them. If you can’t get three full-size sponges for each
group, cut larger sponges into pieces of equal size and weight.
It will be easier to observe weight differences among larger sponges.
ariation: To best simulate real leaves, have students extend a string
V
between two chairs and clip the bags so they hang from the string. This
will allow more air circulation than setting the bags on a plate or tray.
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EXPERIMENT
Adaptations—Controlling Water Loss from Leaves
Variation:
Another transpiration experiment consists of wrapping plastic
bags around live leaves on a plant to capture released water. Close the
bag snugly around the branch with string or a rubber band. After a day
or more, carefully remove the bags and compare the amount of water
released from different plant types, including native and non-native.
Inquiry Science: Try the tests in bright sunlight and in the dark to model
and investigate how stomata may function differently in day and night.
Inquiry Science/Technology: If you have a good microscope available, invite
students to investigate whether leaves they bring into the class have
visible stomata. If not, you can find photos and diagrams by searching
for stomate or stomata images on the Internet.
Math: This experiment calls for students to determine the weight of the
water lost from each sponge. Using logic and math, guide students to
figure the volume of water lost in each bag. Recall that students measured
the volume of water they put into each sponge, as well as the weight of
the water that was lost.
Research/Home Connection: Guide student research into which plants
at the school or in their community are native and which are not.
Discuss how the non-native plants may have had to adapt to survive
in the local climate.
Research: See Using the Internet in the Unit Guide for suggested websites
to extend the learning.
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EXPERIMENT
Adaptations—Controlling Water Loss from Leaves Data Sheet
Answer key
Hypotheses should be supported with logical reasoning. Data will vary. Proper units should accompany
all volumes and weights.
Weight of Water Lost Since Set-up should be computed by subtracting the weight of each bag after the
final observation from the initial weight of the bag with the wet sponge.
Experiment
Adaptations—Controlling Water Loss from Leaves Data Sheet
Name________________________________________ Date_____________
Hypothesis: Which sponge will lose the most water, and why?
Collect Data
Set-up
Date:
Weight of each
dry sponge in bag
Volume of water
poured onto each sponge
First Observation
Time:
Weight of each
wet sponge in bag
Date:
Time:
Date:
Time:
Weight of sponge in Bag A
Weight of sponge in Bag B
Weight of sponge in Bag C
Second Observation
Weight of sponge in Bag A
Weight of sponge in Bag B
Weight of sponge in Bag C
Weight of Water Lost Since Set-up
Bag A
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Bag B
Bag C
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EXPERIMENT
Adaptations—Controlling Water Loss from Leaves Questions
Answer key And Explanations
Analyze Data
1.How did having openings in the bags affect the amount of water that was lost? Why?
The more openings there were, the greater the amount of water that was lost. This happens because
the increased airflow allows water to escape the bag, rather than remaining trapped inside it.
2.Where did the water go after it left the sponge?
The water evaporated into the air.
3.Which part of a plant did each of the following represent?
sponge: inside of the leaf
bag: outer layer of the leaf (epidermis or skin)
holes in bags: stomata
4.If a normally dry area goes through a rainy period, what would likely happen to the stomata
on the leaves of plants in the area? Why?
The stomata would open more to release the excess water. Desert plants are adapted to survive with
less water, so their stomata are generally closed during dry conditions and open during wet periods.
5.Why might stomata open and close throughout the day?
Stomata are more likely to open when conditions are cooler and more humid. These pores can open
without risking great water loss. During warmer, drier times, many plants’ stomata remain closed to
conserve water.
Draw Conclusions
Summarize in your own words why the opening of stomata is an effective adaptation
for plants.
Plants have stomata on their leaves to control how much water and oxygen the plant releases. Stomata
also control how much carbon dioxide the plant takes in. The stomata of plants in different climates
open more or less in response to natural conditions. The stomata are an important adaptation because
they help keep a healthy amount of water in the plant. Too much water can rot the plant, and too little
water can dry the plant out. Either outcome can slow growth and eventually kill the plant.
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