Download WHAT IS THE PURPOSE OF A SEED LEAF?

WHAT IS THE PURPOSE
OF A SEED LEAF?
Introduction
Plants can reproduce in several ways depending on the species. Most of
the best-known plants—like those that provide us with vegetables, trees,
and flowers—grow from seeds. A seed is a reproductive structure that
keeps the developing embryo inside a protective outer coating. Once
the coating softens, germination occurs and the embryo starts to grow.
Roots appear first, followed quickly by tiny shoots and leaves. The first
set of leaves that appear on a young plant are called the cotyledons, or
seed leaves. There are two big groups of seeds plants: monocotyledons
and dicotyledons. Monocotyledons—like corn, wheat, and grass—
produce only one seed leaf, and dicotyledons—such as tomatoes, pecan
trees, and roses—produce two seed leaves. In this experiment, you will
investigate the roles of seed leaves in developing plants.
Time Needed
30 minutes on day 1
5 minutes on days 2 and 3
15 minutes on days 4 to 7
5 minutes on days 8 to 13
15 minutes on day 14
What You Need
F 6 seedlings
F aluminum roasting pan (medium size) with aluminum lid
F ruler
F labels
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WHAT IS THE PURPOSE OF A SEED LEAF?
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F small beaker
F sharpened pencil
F small bag of potting soil
F scissors
F graph paper (2 or 3 sheets)
F permanent marker
F access to water
F access to window or a plant grow light
F science notebook
Safety Precautions
Take care when working with scissors. Please review and
follow the safety guidelines.
What You Do: Day 1
1. Obtain an aluminum roasting pan with lid. Label one end of the loaf
pan as “Exp” and the other end as “Cont.”
2. Use the pencil to punch six large holes into the bottom of the pan.
Place the aluminum pan on the turned-over lid to use it as a tray.
3. Fill the pan three quarters full with potting soil, and pat it down.
4. Use the pencil to make six 2.5-centimeter (cm; 1-inch) holes in the
soil, three on the “Exp” end of the pan and three on the “Cont” end.
5. Gently transfer one seedling into each of the six holes. Cover the
seedlings with soil. See Figure 1 for reference.
6. Use a beaker of water to dampen the soil evenly. Do not add so
much water that puddles begin to form.
7. Place the aluminum pan of pea plants under the light source.
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WHAT IS THE PURPOSE OF A SEED LEAF?
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light source
seedlings
Cont
Exp
aluminum
roasting pan
lid
Figure 1
Figure 1
What You Do: Days 2 and 3
Check to see if the soil around the seedlings is dry. If so, use a beaker of
water to evenly water the soil.
What You Do: Days 4 to 7
1. Check to see if the soil around the seedlings is dry. If so, use a
beaker of water to evenly water the soil.
2. Examine each seedling to see if seeds leaves have appeared and
matured. Seed leaves, or cotyledons, shown in Figure 2, typically
appear between days 4 and 7.
3. Once seed leaves on all seedlings have developed, modify the size
of the seed leaves on the “Exp” plants. To do so, use scissors to trim
off half of the leaf. Be sure to remove the same amount of seed leaf
for each plant. Do not make any cuts on the “Cont” plants.
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WHAT IS THE PURPOSE OF A SEED LEAF?
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Figure
Figure 22
What You Do: Days 8 to 13
Check to see if the soil is dry around the pea seedlings. If so, use a
beaker of water to evenly water the soil.
What You Do: Day 14
1. Compare the surface area of the leaves in the “Exp” and
“Cont”groups. To do so:
a. Use scissors to cut each leaf from one of the seedlings in the
“Exp” end of the tray. Place the leaves on a piece of graph paper
and trace around them. Count the squares on the graph paper
that covered “Exp” leaves, and record the number in your
notebook. Discard the leaves. Do the same for the leaves of the
other two “Exp” seedlings.
b. Use scissors to cut each leaf from one of the seedlings in the
“Cont” end of the tray. Place the leaves on a piece of graph
paper and trace around them. Count the squares on the graph
paper that covered “Cont” leaves, and record the number in
your notebook. Discard the leaves. Do the same for the leaves of
the other two “Cont” seedlings.
c. Compare the total number of squares covered by “Exp” leaves
to the total number of squares covered by “Cont” leaves. Circle
the total that is the largest.
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WHAT IS THE PURPOSE OF A SEED LEAF?
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Observations
1. In which group of plants is leaf surface area the greatest?
Why do you think this is so?
2. Based on the results of your experiment, what is the role
of the seed leaves of a seedling?
3. What would you expect to happen to a seedling if cold
weather partially damaged its seed leaves? Explain your
answer.
4. What would you expect to happen to a seedling if insects
ate its seed leaves? Explain your answer?
Want to Know More?
See Our Findings.
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SAFETY PRECAUTIONS
Review Before Starting Any Experiment
GENERAL
• Always obtain your teacher’s permission for experiments performed
at school, and your parent’s permission for experiments performed
at home, before attempting any experiment.
• Read all instructions for an experiment before starting the
experiment, and follow the directions exactly as they appear in
this volume.
• If an experiment requires adult supervision, do not perform the
experiment unless you have an adult supervising you the entire
time you are performing the experiment.
• Wash your hands before the start of and after each experiment
you perform.
• Keep your work area clean.
• Never eat or drink while performing an experiment. Never taste a
substance used in an experiment unless you are told that it is safe
to do so.
• Be aware of the location of safety equipment you may need in an
emergency, such as running water, an eyewash if you are at school,
and a fire extinguisher.
• If you are going outside, make sure you have permission to go
from your teacher and parent. Take a buddy with you, and dress
appropriately for the weather. Make sure you or someone who
accompanies you is familiar with the area, and bring along a firstaid kit in case of emergency.
• Never look directly into the Sun.
CHEMICAL SAFETY
• Always wear goggles when working with chemicals, such as acids
and bases, and near heat sources like flames. If at all possible,
avoid wearing contact lenses when working with chemicals.
• If any substance gets into your eyes, notify an adult (e.g., your
teacher or parent) immediately, and flush your eyes with running
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SAFETY PRECAUTIONS
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water for at least 15 minutes. Do not mix chemicals unless you are
told to do so by a teacher or parent.
• Never touch, taste, or smell chemicals unless instructed to do so.
• Keep chemicals in closed containers when they are not in use.
• Dispose of all chemicals properly. Do not pour any chemicals or
solids down the drain unless instructed to do so.
• Use safety gloves and a plastic apron when handling chemicals. If
any chemicals spill on your skin, rinse the affected area with
running water for at least 10 minutes, and notify your teacher or
parent immediately.
• Take precautions to avoid spilling chemicals. If a chemical spills on
any surface, notify your teacher or parent immediately to assist
with clean-up.
• Exercise caution when using sharp instruments such as knives or
scissors. Always cut away from yourself, not toward yourself. If you
cut yourself, notify your teacher or parent immediately.
GLASSWARE
• Clean glassware when you are finished with the experiment.
• Be careful when using glassware. If a piece of glassware breaks,
have an adult assist you in clean-up to avoid injuries from broken
glass. Never use broken or damaged glassware.
FIRE SAFETY
• Do not heat glassware that is not completely dry. Do not pick up
hot glassware without heat-resistant gloves or tongs.
• When heating glassware, keep it away from yourself and from
others.
• Do not heat anything unless instructed to do so by a teacher or
parent.
• Do not heat substances in a closed container.
• After an experiment, make sure that all heating sources are off
and that all flames have been put out.
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SAFETY PRECAUTIONS
• Do not reach across such heating sources as flames.
• If you have long hair, tie it back, out of the way. Do not wear
clothing with loose sleeves, scarves, bows, ties, or anything else
that may hang into a fire. Do not wear long earrings.
ELECTRICAL SAFETY
• Do not touch electrical equipment when your hands are wet.
• Do not plug several electrical devices into one outlet or use an
extension cord.
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