THE NSES PLANT-IN-A-JAR AS A CATALYST FOR LEARNING

Stephen T= hompson, University of South Carolina

Abstract

This article presents and discusses activities that use a phenomena first, guided inquiry approach to teach important concepts related to plant function, and the history and nat= ure of scientific inquiry. These activities are intended for use with students = in grades 3-8 as well as in elementary science methods courses. The activities= are consistent with inquiry-based instruction as advocated by the National Scie= nce Education Standards, are inexpensive, and address common misconceptions rel= ated to the water cycle, transpiration, photosynthesis, and cellular respiration= .

= The NSES Plant-in-a-jar as a Catalyst for Learning

Many students hold misconceptions related to plant functions (Hershey, 2004). At the same time, most elementary and middle level teachers receive little training in botany, making it difficult for them to even identify students’ misconceptions about plants (Ami= r and Tamir, 1994). The literature on teaching about plants also contains frequent errors, misconceptions, and overgeneralizations, leaving classroom teachers with few reliable resources to inform their teaching practices (Hershey). It is against this backdrop that the National Research Council (= NRC) encourages science teachers, including those in the life sciences, to adopt inquiry-based teaching practices (1996; 2000; 2001). However, this effort is hampered by limited background knowledge about plants and a lack of appropr= iate inquiry-based instructional resources that focus on concepts related to pla= nt functions.

In this article I p= resent and discuss several activities that respond to each of these issues. These activities have been used extensively with grades 3-8 students as well as in elementary science methods courses and are presented as activities for these grades. Work samples from students are also provided as examples of typical student thinking about the concepts presented in the article. These activit= ies focus on the three major learning outcomes of inquiry-based teaching identi= fied by the NRC, conceptual understandings in science, abilities to perform scientific inquiries, and understandings about inquiry (1996; 2000). These activities also provide opportunities to develop student understandings of = the History and Nature of Science, one of the eight National Science Education Content Standards (NRC, 1996). Developing student understanding of these outcomes requires direct experiences and continued practice with the proces= ses of inquiry. Teachers must first introduce students to the fundamental eleme= nts of inquiry and then assist students to reflect on the processes in which th= ey engage (NRC, 2000).

The instructional s= equence presented here starts with students speculating about the fate of a plant sealed in a jar (terrarium) and then making observations over several month= s to determine the accuracy of their speculations. Student observations, and the discussions that stem from them, allow teachers to expose various science m= isconceptions held by students. These same observations and discussions also form the bas= is for a series of guided-inquiry activities that address important Life and E= arth Science concepts. As students work to answer relevant content questions they take part in customs and routines similar to those engaged in by practicing scientists. Following these engagements, teachers tie classroom practices to both the work of scientists and the history of scientific inquiry. This provides students with a robust model of scientific practices that connects their work in the classroom to the work of scientists engaged in inquiry. T= hese activities cost very little and can be used to address concepts related to = the water cycle, transpiration, photosynthesis, and cellular respiration among others.

Materials

For each student= group:

<= span style=3D'mso-list:Ignore'>o&nb= sp; A small Ivy (Hedera), fern or other low-growing, dense plant

<= span style=3D'mso-list:Ignore'>o&nb= sp; Potting soil from a local nursery

<= span style=3D'mso-list:Ignore'>o&nb= sp; A small amount of activated charcoal may be added to the soil to absorb excess moisture and reduce likelihood of mold developing in the jar

<= span style=3D'mso-list:Ignore'>o&nb= sp; Large (at least a gallon) clear jar (glass or plastic) with an airtight lid

<= span style=3D'mso-list:Ignore'>o&nb= sp; Duct Tape

<= span style=3D'mso-list:Ignore'>o&nb= sp; Indirect sunlight so terrarium does not over= heat

<= span style=3D'mso-list:Ignore'>o&nb= sp; Small amount of water (just enough to make t= he soil slightly moist)

o&nb= sp; Optional: 1) A small non-mercury thermometer with large, easy to read numbers to monitor temperature inside the jar

2) A ruler used to measure plant height

o = Plastic sandwich bag

When conducting th= ese activities, I try to use a small (doesn’t push against the sides or t= op of the jar) plant that can thrive under adverse conditions (See Figure 1 fo= r an example of a typical plant-in-a-jar set-up). I place the soil and plant in = the jar, making sure the soil is slightly moist but not overly wet. Soil that is too wet will promote the growth of mold in the jar, resulting in a shortened plant lifespan (For information on how to reduce the development of mold in terrariums, see Van Arsdale, 2004). You may want to place a small thermomet= er in each jar so students can monitor the temperature inside the jar. Additionally, it may be useful to provide students with rulers to measure p= lant height and width.

= Procedure

Introducing the Plant-in-a-Jar

When I introduce the plant-in-a-jar to my

students I provide each small group of student= s with their own plant to observe over several months. I then read and discuss this National Science Education Standards (NSES) assessment vignette with them, which forms the prompt and basis for the activities presented in this artic= le. When introducing the prompt, I substitute the word estimate for predict to avoid confusion about how

Figure 1. Ivy-(Hedera helix) Plant-in-a-jar the word predict is used in the NSES prompt.

Some moist soil is placed inside a clear glass jar. A healthy green plant is pla= nted in the soil. The cover is screwed on tightly. The jar is located in a window where it receives sunlight. I= ts temperature is maintained between 60^oand 80^oF. How = long do you predict the plant will live? Write a justification supporting your p= rediction. Use relevant ideas from the life, physical and earth sciences to make a prediction and justification. If you are unsure of a prediction, your justification should state that, and tell what information you would need to make a better prediction. You should know that there is not a single correct prediction (Page 92, NRC, 1996).

Prior to sealing th= e jar I allow all students to inspect the plant and the jar. We then decide on an observation schedule and determine which factors to observe. Observations a= re typically made every second or third day with students, while preservice teachers usually make weekly observations due to limited class meetings. Generally we make two types of observations, qualitative and quantitative, providing me with opportunities to discuss and reinforce the benefits and drawbacks of using each. Quantitative observations focus on things s= uch as the number of leaves on the plant (if it is possible to count them), the number of healthy and/or dead or dying leaves (often easier to count), plant height, plant width (which may be a rough measurement due to plant location= ), the number of flowers (if any), and the temperature inside the jar. Qualita= tive observations focus on descriptions of the plant, soil and jar. I encourage students to write thick descriptions here, for example I encourage them to record and describe in detail specific observations such as leaves beginnin= g to curl or brown spots appearing. I find it is helpful here to have students t= ake digital pictures of the plant at each observation so that qualitative observations can be recorded and discrepancies resolved (e.g., “There= is more moisture on the jar this time.”).

When sealing the jar, I have a sing= le student place duct tape over the lid, sign and date the tape using an ink p= en, thereby ensuring it will remain sealed. I then instruct students to write in their science journals a detailed description of what they think is going to happen to the plant and why. I also request that their justifications inclu= de a specific timeline for the plant’s lifespan. If students have no idea I ask them to state what other information they would need in order to make an estimate. With younger students I allow them to draw a picture and write captions describing what they think will happen to the plant, when they thi= nk it will happen, and why they think it will happen. Typically students belie= ve the plant will die in a short period of time, when in reality a plant can survive in a jar for several months under the right conditions and have been known to survive for years (Plant Explorers, 2006).

Discussing In= itial Estimates

After students have recorded their individual estimates and justifications we discuss them as a class. I make no judgments about initial ideas; instead I allow students ti= me to share ideas. I also encourage them to search for relevant information fr= om other sources and to look for evidence to support or refute ideas when they make future observations. I point out that by making detailed observations = over time the class may be able to determine which estimates and ideas are most accurate.

Initial estimates and justifications usually focus on resources in the jar being us= ed up or becoming depleted. Figure 2 is a third graders’ drawing that is representative of those typically encountered when the plant activity is introduced. Older students have similar misconceptions about the fate of the plant. The important point here though, is to record and publicly discuss students’ initial estimates and justifications. During these conversations, I highlight that public idea sharing is consistent wi= th the way new knowledge is created in science. I also encourage students to revise ideas at any time during the activities, but require a written justification (or revised drawing) explaining the changes. Here I point out that revision of ideas based on new evidence is another key aspect of the nature of scientific inquiry.

Figure 2. Third-graders drawing predic= ting

what will happen to a = plant sealed in a jar,

“I think that the plant will = soak up all of

the water and then when the plant soaks <= o:p>

up all the water it will die”. =

Initial Obser= vations

During subsequent c= lasses I continue to have students record observations and possible explanati= ons for their observations in their science journals. I also encourage them to revise plant lifespan estimates and write about troubling issues. We then share, discuss, and publicly record student observations, revised estimates= and troubling issues. Again, I don’t pass judgment on student ideas, inst= ead I use questioning to help students clarify ideas and make connections betwe= en observations, evidence and assertions. The first observations and discussio= ns generally center on the moisture that accumulates on the inside of the jar.= I encourage students to discuss and explain the origins of the moisture. Alth= ough I lead these conversations, I encourage students to co-construct their understandings of the observations and related concepts, in this case the w= ater on the side of the jar and the water cycle. If not offered by students, I use = their observations and ideas to introduce concepts and the related scientific vocabulary.

Over time class conversations about observations and the possible explanations for them beg= in to model a form of scientific discourse, argumentation based on evidence= . As students discuss and debate their ideas and observations I encourage the= m to take positions that are supported by evidence. I emphasize that it is acceptable to disagree, as long as the disagreement is grounded in evidence= and not emotion. I explicitly point out that scientists often disagree and challenge conclusions of other scientists. However, they usually do so in a manner that relies on evidence to support beliefs or ideas. I also point out that the degree of accumulated evidence determines what is accepted as usef= ul information within a given scientific community (in this case the scientific community of the classroom).

I also use these st= udent observations to make connections to the History and Nature of Science. Here= I share the story of Nathaniel Bagshaw Ward (1791-1868) and his “accide= ntal invention” of the first terrarium. Ward makes observations of the wat= er cycle occurring inside a glass jar that are very similar to those of my students when he describes his invention of the terrarium,

I had buried the chrysalis (cocoon) of a sphinx (moth) in some moist mould (decomposed leaves) contained in a wide-mouth glass bottle, covered with a = lid. In watching the bottle from day to day, I observed that the moisture which, during the heat of the day arose from the mould, condensed on the surface of the glass, and returned whence it came; thus keeping the earth always in the same degree of humidity. About a week prior to the final change of the inse= ct, a seedling fern and a grass made their appearance on the surface of the mould. (Ward, 1852; Quoted on page 276 in Hershey, 1996)

Transpiration Activities, Conversations and Historical Connections

A common student misconception that typically surfaces here has to do with the water that en= ters the plant roots. Some students believe water entering the plants roots is “used up” by the pla= nt and will eventually reduce the overall amount of water within the jar (See Figure 2). This provides an important segue to activities that address this misconception. If not mentioned by the students, I focus their attention on this topic by asking, “What happens to the water that goes into the p= lant roots?”

During the ensuing discussion I share the story of Stephen Hales, a British scientist who conducted several experiments examining this very question during the 1700s (Hershey, 1991). I also suggest that by conducting one of those experiments= , we may be able to gain some insight into the question. At this point I have st= udent groups find a plant outside and cover any plant part with a plastic sandwich bag, seal it as tightly as possible (See Figure 3), and make detailed observations for fifteen minutes. &nb= sp;

Prior to the activity, we discuss details that each group needs to record when th= ey make observations. Depending on the age of the students this data might inc= lude a plant description, the surface area of covered leaves (determined by trac= ing leaves on graph paper Fig= ure 3. Covered Plant Part = and counting the total number of squares covered), leaf or plant typ= es, or plant location (emphasizing factors such the amount of sun and water available). We also decide on a common observation schedule (every minute or two), and I remind students to return with whatever they collect in their sealed sandwich bags.

When the students return I have them share observations and their explanations f= or them. Students will have varying amounts of moisture in their sandwich bags= and initial class discussion revolves around the origins of the moisture. To determine which bags have the most moisture we mass an empty sandwich bag a= nd all students’ bags. We then subtract the mass of the empty bag from t= he mass of each student’s bag, rank them from heaviest to lightest, and = add this to our data.

To reinfo= rce the processes of transpiration we set up and grow a plant in a hydroponics syst= em (See Figure 4). I use this demonstration to promote student understanding t= hat nutrients are Figure 4. Plant growing in hydroponics system transported via water through roots as opposed to roots eating minerals in the soil.

It is also helpful to have students observe cut pieces of celery, some soaking in a mixture of 1 cup water and 4 drops red food coloring and others soaking in plain water. By observing these over a day or two students are a= ble to see veins in the celery leaf blades change color as the colored water mo= ves through the plant veins and into the leaves. When the colored water reaches= the leaves I am also able to cut the celery stalk to show students how the colo= red water moved through the veins from base to top and into the leaf blades. He= re I am sure to let students know that colored water is not taken up by intact r= oots of plants and that this demonstration works because the plant xylem has been cut open, allowing the celery petioles to take up the colored water

Collective= ly, I use these examples to demonstrate how moisture enters the plant at the root, travels through the stem and reaches leaves (and flowers) where it is relea= sed through the stomata (as evidenced by the moisture in students’ sandwi= ch bags). Invariably = some student will make an inference about the differing amounts of moisture such= as, “Mine has more water because my plant was in the sun”. At this point I ask the student how he/she knows this and how we could prove this statement true or false. Duri= ng this dialogue I frame questions that prompt students to think about how scientists support their claims and what tools they use when trying to info= rm others. The idea that scientists construct tables and graphs from data to organize and identify patterns that support their ideas is introduced. We also discuss that we have “data” which may be able to provide some direction in our think= ing about the moisture in the sandwich bags.&n= bsp;

I then have the class construct one common da= ta table that includes all of the variables and data from our transpiration activity (see Table 1). After the data is entered into the table I asked students to look for patterns and we decide which variables appear to have = some influence on the amount of water collected.

Table 1

Example Common Data= Table

=	Plant	Leaf	Location	Water
=	Type	Simple or Compoun= d	Surface Area (in = squares)	Water (Nearby)	Sun or Shade	Amount collected = (rank by mass)
Student 1	Bush	Compound	14	No	Shade	2
Student 2	Tree	Simple	22	Yes	Sun	1

Several ideas gener= ally emerge and I encourage students to select one idea they wish to investigate. The students then develop procedures to investigate one of the variables th= ey believe influences the rate of transpiration. Finally, we conduct the investigations and share findings to determine factors that affect the rate of transpirati= on in plants.

To make ad= ditional connections to the history of science I also share the story of John Woodward’s 1699 transpiration measurement experiments. Woodward grew spearmint plants in glass vials and measured how much water the plants used during transpiration. He concluded that most water used by the plants evaporated into the air (Hershey, 2003). At this point students are general= ly satisfied that the plants have sufficient water to survive in the jar.

Carbon Cycle Activities, Conversations and Historical Connections

In the fol= lowing classes I return students’ attention to the plant-in-a-jar and repeat= an instructional pattern similar to the original one. Students make observatio= ns, revise estimates, and record troubling issues. We then discuss their thinki= ng. At this point most students have developed a genuine interest in the plants= and want to find answers to the plant-in-a-jar dilemma.

By now students are generally convinced that even though the plant has suffici= ent water, it is still going to die soon. Younger students tend to focus on the air in the jar being “us= ed up” and the plant suffocating. Figure 5 is a fourth grader’s drawing that captures this idea. Older students generally believe that all = of the carbon dioxide in the jar

is used up during photosynthesis le= aving the plant in an oxygen rich environment that will eventually kill it. Again I encourage students to shar= e what they already know using terms and ideas they introduce or that we have developed together.

Figure 5. Fourth-graders drawing predicting what will

happen to a plant sealed in a jar, “I think that in about =

2 weeks it is going to die because it doesn’t get enough

air because it is closed with a lid”.

With younger studen= ts I focus on the terms oxygen, carbon dioxide, photosynthesis, and cellular respiration. If not brought up by the students I introduce and/or review photosynthesis and respiration. I also reinforce the idea that all cells breathe and that plants are made of cells.

To supplement these conversations and enhance student understandings of cellular respiration and photosynthesis a variety= of hands-on exercises can be used. These include an activity that uses Fast Pl= ant seedlings to demonstrate the production and consumption of oxygen by plants (Williams, 1991). This activity also shows students the importance of carbo= n in photosynthetic reactions and how the amount of sunlight influences the rate= of photosynthesis. Another effective activity that can be employed here provid= es a dramatic demonstration that plants require carbon dioxide for photosynthesis (Hershey, 1992). Students grow plants under “normal” conditions= and in an environment free of carbon dioxide. This allows students to experience the effects of carbon dioxide deprivation on plant growth first hand.

To make additional connections to the history= and nature of science I share the story of Theodor Englemann, who in 1882 recor= ded the first visual demonstration of light wavelengths absorbed by photosynthe= tic pigments (Hangarter and Gest, 2004). This conversation allows me to reinfor= ce the serendipitous nature of scientific advancement. The invention of photography resulted in significant advancement in the understanding of photosynthesis. This occurred as botanist sought to capture properties of objects not previously recorded by using photographic techniques and while doing so found ways to create “living images” that revealed properties of photosynthesis (Hangarter and Gest). Here I am also able to introduce and discuss the reciprocal relationship between new technologies = and scientific advancement.

After the activities and related conversations we then take time to construct individ= ual diagrams of the carbon cycle, using our understanding that cells, both plant and animal, are producers of carbon dioxide and consumers of oxygen during respiration. With older students I have similar conversations but introduce= the chemical equations for photosynthesis (6CO₂+6H_{2O
+ energy -> 6O₂+C₆H₁₂O_=
6)
and cellular respiration (6O₂+C₆H_{12<=
/sub>O₆->6H₂O+6CO₂+ energy) to the class. I ask
students to make observations about the two equations. As students recognize
that the products of one reaction are the reactants of the other and vice
versa, they see a simple solution to the dilemma about the health of the pl=
ant.
At this point I ask students to consider the rate at which each of these
processes is occurring. We then discuss that while photosynthesis occurs du=
ring
the day, cellular respiration occurs both during the day and at night. This
raises new student questions about the amount and types of gases in the jar.
These conversations allow me to discuss that like animals, plants can adapt=
to
changes in the environment. As the level of carbon dioxide increases in the
air, a plant is able to increase its rate of photosynthesis. Thus the
plant-in-the-jar is able to generate more oxygen and restore balance to the=
ratio
of gases in the jar.}}

Finally, student observations provide me with the opportunity to disc= uss the role decomposition plays in the carbon cycle. As students notice and discuss dead leaves and the impact they have on our closed ecosystem I introduce and reinforce concepts related to conservation of mass and energy. Here we discuss that nothing enters or leaves our jar and that as plant par= ts die and decay some carbon dioxide gas is returned to the atmosphere. <= /o:p>

Extensions

Although I chose to embed the study of the history and nature of scie= nce into these activities, it would be very easy to use the plant-in-the-jar as= the focal point for a unit of study on the history and nature of science. Many = of the current experiment done by students are reenactments of experiments don= e by scientists centuries ago (Hershey, 1991). Through the study of these experiments and the context within which the works were completed, students= can develop a better understanding and appreciation of both the history and nat= ure of science. Here students can examine the story of Dr. Nathaniel Ward and t= he first terrarium (Hershey, 1996) to learn that some scientific discoveries happen by mistake. To show the tentative nature of scientific knowledge students can learn about Johannes Baptista van Helmont’s Willow experiments and the resulting de= bate that led to his ideas eventually being disproved (Hershey, 2003). This is n= ot an exhaustive list, but it begins to capture the potential of using histori= cal science experiments for this purpose.

The plant-in-a-jar also provides opportunities to demonstrate more contemporary connections to the tentative nature of scientific knowledge, as scientists struggle to agree on the impact that high levels of atmospheric carbon associated with global warming will have on plants in the less controlled environment called Earth (Oak Ridge National Laboratory, 2005; Shwartz, 2002). These conversations allow me to introduce current scientific research in this area such as the Biosphere 2, the airtight replica of Earth’s environment used by scientists to study how changes in carbon dioxide levels and moisture, among other factors, influence environmental systems on Earth (David, 2000).

Summary=

The activi= ties I’ve presented here provide a fun, engaging way to get students interested in important concepts related to plant functions. The trick is t= hat all of this conversation about important science concepts originates from student observations. It is through students’ observations and their attempts to explain what they are seeing, that a high-level of interest is generated that is otherwise difficult to produce. Following the approach outlined above, I am also able to make student misconceptions public and th= en address them over time through concrete experiences, demonstrations, and discussions.

At the same time the instructional strategies presented here help students better understand the history and nature of the work of scientists engaged in inquiry. By examini= ng the history of scientific inquiry, engaging in aspects of these inquiries, = and then reflecting upon the practices under the guidance of teachers, students develop a better understanding of the nature of scientific work. As a resul= t of these activities I also find that students better appreciate and understand those factors that influence the nature of this work.

References

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Hangarter, R. P., Gest, H. 2004. Pictorial demonstrations of photosynthesis. Photosynthesis Research 80: 421-425.=

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Shwartz, Mark. Dec. 5, 2002. High Carbon Dioxide le= vel can retard plant growth, study reveals.” Stanford Report. http://= news-service.stanford.edu/news/2002/december11/jasperplots-124.html<= /a> (accessed January 3, 2006).

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