Download Bean plants: A growth experience

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Bean plants: A growth experience
Teaching plant growth to seventh-grade life science students
has been interesting for me because I grew up in a rural area
and always had to help in the
garden. I made many assumptions about what my rural and
suburban students knew.
One year I decided to have
them grow plants to observe the
roots, stems, leaves, flowers, and
fruit as we studied these parts.
To keep it simple, I bought
nine-bean soup mix from the
grocery store and allowed the
students to choose anything from the mix except the split
peas. This way they had a variety of seeds to choose from
and it was inexpensive for me. One bag provides more than
enough seeds for each of my 125 students to chose four beans.
Materials for this lab include a bag of topsoil or potting
soil; a bag of small stones or gravel; 125 clear, colorless, plastic cups; plastic wrap; and rubber bands. Students are given
the following directions verbally or on paper:
1. Put one layer of stones in the bottom of your cup.
2. Add soil, leaving 1 cm of space at the top.
3. Pick four beans—either four of the same type or four different types.
4. Place the beans halfway down the side of the cup at the
3, 6, 9, and 12 o’clock positions, making sure they are
visible (see Figure 1).
5. On the outside of
the cup, number each
FIGURE 1 Setup
bean 1 through 4 with
a grease pencil or permanent marker. Write
your name on the bottom of the cup.
6. Find the mass of
the total system before
you add water. Record
this in your data table.
7. Decide how much
water to add using a
graduated cylinder.
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April 2004
Base this on any past experiences with houseplants and
what you observe as you add the water. Does it still look
dry? If so, add more, keeping track of the total amount
added. Record this in your data table. Slowly pour the
water into the cup.
Data table A
Date
Bean plant observations
Mass
Location Observations
Mass
before
of water
adding (1 mL = 1 g)
water
8. Seal the cup with plastic wrap and a rubber band to
keep the system from drying out until the seeds have
germinated.
9. Decide where you will store your system out of the
way of other classes. Record the location in your data
table. (I allow them to put their cups anywhere, such
as in the cupboards, on the windowsill, in a drawer,
or on the top of the cupboards. Students are not told
how to do several parts because they learn much more
from trying different things [inquiry], observing what
their classmates are doing, and drawing conclusions.
This is not a controlled experiment in the “only one
variable” sense. I’m amazed at where they put them!)
At the end of the first day, after the bean plantings have
been set up and stored, we discuss
• why the rocks needed to be in first (drainage),
• why water wasn’t added before massing (this information
will be useful at the end),
Donna West is a science teacher at Bay Trail Middle School in
Penfield, New York.
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FIGURE 2
Bean research and lab analysis
You have 30 minutes to complete this assignment.
1. On your own paper, in your neatest handwriting, and
using all you have learned and observed about plants,
summarize each bean plant structure. Devote one
paragraph to each structure and one paragraph for a
conclusion. Also include an introduction that explains
what you did to set up this experiment and conclusion.
Include anything else that you observed as well.
a. Seeds:
• Monocot or dicot? How do you know?
• How long did germination take? If a seed didn’t germinate,
what are some possible reasons why it didn’t?
• Does the direction the seed is planted (right side up or
upside down) affect the direction the roots and stems
grow? How do you know?
• Where did the cotyledons go? What are they for?
• What appeared first—root, stem, or leaves? How do you
know?
b. Roots:
• What kind were they—tap or fibrous? How do you know?
• What direction did they grow?
• What affects the direction the roots grow?
c. Stems:
• What kind were they? Herbaceous or woody?
• How tall did they grow compared to other bean plants
you observe in the room? Why?
• If a stem broke, what happened?
d. Leaves:
• How many per plant?
• How big was your biggest leaf? Compared to other bean
plants in the room, were yours smaller, the same, or
larger? Why?
• What kind—broad or needle-like?
• why we covered the cups with plastic wrap (keep moisture in for germination),
• how much water they added and why they chose that
amount (so they can share their reasoning with the class),
• why they chose the locations they did to store their plants
(so they can hear what others are thinking and rethink
their misconceptions), and
• what types of observations would be appropriate for the
data table (for example, bean #4 germinated and roots
are visible, bean #2 looks moldy, or the soil has settled).
• Parallel or net veins in the leaves?
• Color—dark green or lighter than most? Why?
• How did they feel—smooth, fuzzy, sticky, powdery?
e. Flowers:
• How many days from germination until flowers formed?
• Location of flowers—top of stem or near leaves?
• How many flowers per plant?
• Numbers of pistils, stamen, petals, and sepals?
• Color?
f. Fruit:
• What will the fruit of this plant be?
• Where will the fruit be located?
2. Conduct an analysis of your numerical data. Use
sentences that restate the question to make your
answers clear.
a. Calculate the amount of mass your whole system (cup,
soil, plants, and stones) gained or lost. (Assume that
the soil is completely dry and the mass of the soil
remains constant.) To do this, subtract the mass today
from the mass on the first day. If the answer is a positive
number, your system gained. If the mass is a negative
number, your system lost. Explain the gain or loss.
b. What is the total amount of water you added to your
system? How does this compare to any weight gain of
your system? Where is that mass now?
c. What else, besides the water, did the plant take in?
d. Where did all the root, stem, and leaf tissue come from?
3. Graphing the height of the bean plants.
a. Create a line graph of the change in the heights of your
four plants using four separate, different-colored lines.
Be sure to title your graph, label the x and y axes, and
make a key.
When students arrive the next day, they remass the cup
and its contents before adding water, then add more water,
discard the plastic wrap if they see signs of germination, and
return the plant to its storage spot or choose a new storage
location. Students discuss things such as “My plant is yellow
(after being kept in the cupboard) because I must have
planted yellow beans,” or “My plants are tall (after being
kept in the cupboard) because they grow best in the dark,”
or “My plants are short (after being kept on the windowsill)
because they are getting too much Sun.”
April 2004
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FIGURE 3
Rubric
Needs improvement
Topic and
possible points
Excellent
Experiment (5)
data tables complete and neat, data tables mostly complete
show good observation skills
data tables and observations
need more thorough work
Part 1 (18)
complete and thorough,
shows learning occurred
each question was answered,
but could be more thorough or
correct
most answers are incorrect,
short, vague, or absent
Part 2 (6)
mass difference calculated,
labeled, and explained
thoroughly
mass difference calculated,
explanation could be more
thorough
mass not calculated or
explanation missing
Writing mechanics (5)
spelling, capitalization, and
word selection are good
spelling, capitalization, and
word selection have errors
many spelling, capitalization,
and word choice errors
Numbers (3)
assigned to lines, not spaces
between
assigned to lines, not spaces between; starting numbers incorrect
assigned to spaces or missing
Dates (2)
consecutive and continuous
not consecutive or not continuous
not consecutive and not
continuous
Labels (2)
both bottom and side labels
are present and accurate
one label accurate
missing one or both, or both
inaccurate
Key to lines (1)
present
present but inaccurate
no key
Sensible (1)
graph shows growth that is
accurate
graph shows questionable
plant growth
graph shows inaccurate plant
growth
Neatness (2)
neat
mostly neat
messy, illegible in parts
Satisfactory
Data analysis
Graph
In their journals, students must list four observations about
their systems and complete data table B once the plants are
growing above the soil.
Data table B
Date
Bean #1
Height of bean plants in cm
Bean #2
Bean #3
Bean #4
This project should be done at a time in the curriculum that
will allow students to make uninterrupted observations for a num46
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April 2004
ber of weeks, so don’t start it before any long vacations. I let this
activity run about five weeks, which is usually long enough for
the plants to develop flowers and even some beans. The time of
year and latitude of your location may affect this timetable.
I have been amazed to hear the reasoning students come
up with to explain their observations. We address and correct misconceptions in class, which are recorded in students’ journals so I can check for comprehension. We have
a five-minute discussion each time students take a daily
measurement, during which they share their observations
and try to explain what they have observed.
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After the plants have gone full cycle (from seed to producing seeds), students are given a copy of the Bean Research and Lab Analysis worksheet (Figure 2) and asked to
work alone to analyze what they have learned about plants
based on their journal information and what we have studied in class. I also provide them with a copy of the grading
rubric (Figure 3).
Common misconceptions that changed are:
• All seeds need sunlight to germinate.
• The plant’s increase in mass comes from the plant taking
in the soil.
• The fruit of the plant is its beans.
• Roots grow down due to the Sun.
Students who held these misconcepExplore plant growth at
tions prior to the activity usually www.scilinks.org.
have them corrected when they hear Enter code SS040403
what others think during class discussions, learn about plant parts and growth during the plant
unit, and observe firsthand how the plants change as they
grow. In most cases, students have identified and corrected
their misconceptions by the time they start to work on the
Bean Research and Lab Analysis worksheet.
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CIRCLE NO. 11 ON READERS SERVICE CARD
April 2004
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