It's Important to Know About Your

STUDENTS' IDEAS ABOUT PLANTS

QUOTES FROM STUDENTS...AND WHAT THEY MEAN

1. Missing Real-World Connections 

  

                 
  Question: Tell what photosynthesis means as best you can. Describe how that tree outside our window gets its food.
  Dick When a plant makes its own food. Minerals, etc.
  Denise The process by which plants make food. Minerals, water help the plants grow tall and healthy.
  Lauren How a plant makes food for itself. Plants need sun and minerals and water for energy and to grow.
  Heidi When a plant uses water, sunlight, and air to make food. Water and minerals and protein.
  What do their answers tell us? These students finished a unit about plants able to define photosynthesis correctly. But when asked about real-world plants, they revert to their entering misconceptions that plants get their food from water and minerals in the soill.

Their understanding of photosynthesis was not connected to their "real-world" knowledge about plants.
  2. Food is stuff you eat; a plant's food is everything it takes in from the environment
  Question:

Describe what is food for plants.
  Richard Sun, good soil, water, and the food made during photosynthesis.
 

DDaniel:D

 Glucose, sunlight, and minerals from the ground.
  What do their answers tell us?

 

 

 Richard and Daniel show another common pattern of incomplete learning.

Learning about photosynthesis did change their explanations of how plants get food, but not enough!

They still do not appreciate the crucial difference between the materials that plants take in (minerals from the ground, water) and the food that plants make during photosynthesis.

The materials taken into the plant (minerals, fertilizers, water, air) are very low in energy and cannot provide plants or animals with the food energy they need to live.

Sugars and starches made during photosynthesis are high-energy materials that do provide food energy for living things.
 

3. Black Box View of the Plant versus Plants as "busy little things":

Things like energy and matter don't change once they go inside the plant.

  Jake: "You know, I used to think that plants just kinda sit there. But they're really quite busy little things, aren't they?"
w
       
       
  d is rarely used with precision by either students or biologists. When talking about the food made by plants during photosynthesis, however, biologists are more consistent. In this context, biologists use the word "food" to refer to organic compounds with high-energy molecular bonds that organisms can use for growth and metabolism. Other substances that organisms need, such as water, oxygen, and minerals are inorganic and do not contain high-energy bonds in their molecules. These substances are NOT considered food by this scientific definition. It is this distinction that makes the statement "plants make their own food" meaningful. The process of photosynthesis provides the only bridge by which inorganic matter can be transformed into organic matter.

The biological distinction between energy-supplying substances (food) and nonenergy-supplying substances (not food) is critical to understanding the significance of photosynthesis. Plants and other organisms convert glucose into the millions of other organic compounds (proteins, fats, hormones, enzymes, etc.) that make up the bodies of living things. However, all of those compounds (in other words, all food) are ultimately derived from a single source: glucose make during photosynthesis.

The distinction between plants as producers and animals as consumers in ecosystems cannot be meaningful to students who do not understand that the food made during photosynthesis is different in a very important way from other nutrients such as water and minerals. After all, what is it that plants produce and animals consume?

Students do not think about food in these ways, however. To them, food is whatever plants or animals take in to keep them alive and growing. From this perspective, it is easy to see how they could misunderstand or distort instruction about photosynthesis. Their definition of food is sensible, but it misses the essential distinction between energy-containing and non-energy-containing matter.

4. Plants are like humans versus the amazing uniqueness of the plant

  Question:

Describe what is food for plants.
  Richard Sun, good soil, water, and the food made during photosynthesis.
  Daniel Glucose, sunlight, and minerals from the ground.
  What do their answers tell us?  

The significance of the distinction between energy-containing and nonenergy-containing substances lies primarily in energy relationships. Photosynthesis captures energy from sunlight and converts it to chemical potential energy stored in organic compounds (food).

Energy, however, is an abstract and difficult concept for most students. They tend to think about energy in vague terms, as part of everything that plants or people need. In order to appreciate the significance of energy in photosynthesis, they must learn to follow the path that energy takes and the changes it undergoes. Energy can change form. For example, light energy can be transformed into heat energy (notice the heat near a light bulb or the sun’s light energy being changed into heat energy which warms the earth). Students must appreciate the critical importance photosynthesis plays in changing energy from light energy into another form -- chemically stored energy -- that is usable by living things.

5. Molecules or not?

 

Question: What happens to water

once it goes inside the plant?

  
  Monica: It goes up in the leaves, I think.
  Interviewer: How does it go up?
  Monica: I think it just kind of sucks it up.
  Interviewer: So why does it do that?
  Monica: The plant has to drink it...to stay alive.
  Interviewer: So it drinks the water in the leaves?
  What do their answers

tell us?

  

Biologists’ conceptions of photosynthesis also depend on a chemical understanding of the nature of matter. Biologists make a distinction between energy (light, heat, chemically stored energy, sound, etc.) and matter. Photosynthesis is seen as a process by which light energy is used to change matter chemically -- a chemical change or chemical reaction. The substances involved are characterized as chemical compounds. In these chemical reactions, matter is changed but conserved. Scientists think of these chemical reactions as involving rearrangements of molecules which result in the formation of new compounds. Water molecules and carbon dioxide molecules are rearranged to form sugar molecules and oxygen molecules.

Most students, however, are not used to thinking about molecules, chemical formulas, or chemical reactions. In fact, they do not typically think about things they cannot see -- such as the idea that things are happening inside of plants other than water being sucked into the plant by the roots. These invisible things and processes seem very mysterious to them and only vaguely understandable.

5. The Functional Nature of Scientific Explanations.
  Question: Do plants need food? Why or why not?
  Susan: Yes. They need sun, fertilizer, water, and soil.
  Brooks: Yes. It’s like people, they can’t live without food.
  Ryan: Yes. Because plants have to eat or they would die.
  What do their answers tell us? The students’ explanations of "why" don’t really explain anything. Susan and Ryan’s explanations are essentially circular; they restate in different words that plants need food. Brooks appeals to an analogy between plants and humans.

Scientists, on the other hand, strive for functional explanations (for example, "Plants need food because their cells use food as a source of energy.") Biologists think about the function that each substance plays in the internal workings of the plant. They seek to understand not just whether or not a plant needs a particular substance to stay alive; they want to know what happens to that substance inside a plant. How does the plant use it? Thus, an essential part of learning about photosynthesis is learning to develop appropriate functional explanations and definitions

 

6. Nature of Scientific Discourse and Inquiry

  Question: What kinds of things did you do in science class during this unit?
  Rachel: I don’t know why we kept measuring those plants. I mean it was fun for awhile. But I already knew that plants need light and now I know it again.
  Darla: Ms. Roth, do you like arguing or something?
  Ryan:  
  What do their answers tell us? Students need explicit instruction about how to think in scientific ways. We studied students in hands-on, inquiry-oriented classrooms who were actively engaged in generating hypotheses, doing experiments and collecting data, organizing data into graphs, and drawing conclusions. Rachel was one of these students. She ended the unit viewing science as a rather meaningless process of doing and measuring because it didn't help her learn anything new. Similarly, Darla knew that her teacher liked students to debate ideas using evidence from their experiments. But she thought this was just a personal quirk of her teacher. She did not connect this process or argumentation from evidence as a central part of scientific work.

 

 

7. Connections beyond the unit and Learning over time-- to cells, molecules, chemical change, food chains and plants as producers, human body systems, even dinosaurs!

 

In this class, we don't just study something and forget about it. We keep coming back to it. Like the plants, we didn't just study them and then move on. We kept coming back to them.

 

Hey, Ms. Roth, all those things in science, they all kind of connected in the end, didn't they.

 

They (all the concepts we studied in science this year) all kinda connect because we talked about..

 

I didn't feel comfortable studying about photosynthesis, at first, because I didn't really get it and I felt stupid. But then the second time we did it, I really understand and I felt really good. And now it's the best thing I learned this year. I understand it really well.


To help students understand the central ideas, we have carefully limited the amount of scientific terminology introduced, we have not discussed photosynthesis at a molecular level, and we have omitted discussions of the light and dark phases of photosynthesis. The production of oxygen in photosynthesis is de-emphasized in order to emphasize food production. In earlier research, we found that emphasis on these ideas often served only to distract students from the central issues.


C. Why does this unit provide a central question -- Shouldn’t we use students’ questions instead? : Teaching about Scientific Inquiry and the Nature of Science
Constructivist teachers often worry about the teacher selecting the central question for a unit: Shouldn’t the question come from the students? In this unit, the teacher poses the central question to the students, and the class together wrestles with coming up with a satisfying answer based on empirical evidence as much as possible. Why did we organize instruction this way?
Through our research we have found that students need explicit instruction about how to think in scientific ways. We studied students in hands-on, inquiry-oriented classrooms who were actively engaged in generating hypotheses, doing experiments and collecting data, organizing data into graphs, and drawing conclusions. Unfortunately, many students spent 6 weeks in such a unit which was designed to teach them about plants’ role as food producers and ended the unit with views of science such as Rachel’s:

I don’t know why we kept measuring those plants. I mean it was fun for awhile. But I already knew that plants need light and now I know it again.
--Rachel, 5th grade student


Students like Rachel not only failed to change their concepts about how plants get their food after six weeks of experimenting, graphing, and discussing. They also failed to develop important understandings about the nature of science.
What did Rachel learn about scientific inquiry and thinking? She learned that science involves a lot of activity that does not help you make any better sense of things. She learned that it is important to make careful observations and to record them accurately not because such care helps you develop better understandings, but because "that’s what you do in science." Because Rachel did not develop better conceptual understandings about plants, the processes of science seemed meaningless and not worth the effort.
Thus, it is critical for the scientific processes to help students make important changes in their thinking for students to believe that scientific thinking is worthwhile. BUT it is not enough just to engage students in using scientific processes to develop good understandings. Students like Darla, a fifth grader who received instruction from this Food for Plants unit in its first version, were engaged in using scientific thinking processes and used these processes to develop rather deep understandings about how plants make their food. These students felt really good about how much their ideas had changed and grown. But they did not recognize the process of scientific thinking that helped them get there. They asked questions at the end of the year like Darla’s:

Ms. Roth, do you like arguing or something?
Darla knew that their teacher liked them to debate ideas using evidence from their experiments. But she thought this was just a personal quirk of her teacher. She did not connect this process with the nature of scientific work.
In later implementations of this unit, we have made explicit to the students the ways in which their work in the classroom represents scientific ways of knowing. Our research indicates that this enabled students not only to undergo significant conceptual change about plants, it also enabled them to develop deeper understandings of scientific ways of thinking and knowing.
So why does this unit provide the focus question instead of allowing the students to pursue their own interests? We are certainly in favor of valuing students’ questions and providing opportunities for them to pursue their own questions. But there is also a very important role that work on a shared problem of significance can enhance student learning about plants AND about the nature of science. We point to two important reasons.
First, having students work together as a group toward consensus about a shared question of scientific significance provides a context in which the teacher can provide essential modeling and coaching about scientific ways of thinking. Conceptual change is not easy! Students need a teacher to help them figure out what it means to really understand something by using evidence and scientific ways of thinking. It is impossible for a teacher to provide enough of this kind of scaffolding if students are pursuing different questions.
Second, the group working towards consensus provides an excellent context in which to make explicit scientific ways of thinking, talking, and working. The class community can become a scientific inquiry community, and the teacher can make explicit ways in which this community is a scientific community. The emphasis on using evidence to debate and change ideas is a natural lesson that can be modeled in this group context.
D. Why should students care about how plants get their food?: "Why do I have to learn this?"
WHY is this content important for students and literate adults to understand? Why is this content worth teaching? How would we respond to students who ask, "Why do we have to learn this?" Of course, we can easily respond that this content is in the National Science Education Standards and in the Benchmarks for Science Literacy. But how can we help our students see that it matters?
Students need to understand the concept, the idea of photosynthesis, so that they can develop a deep appreciation for and understanding of the importance of plants in our world, in ecosystems. Their lives to be enriched by a fascination with the inner workings of "everyday" things around them, like trees and grass and plants. Becoming knowledgeable about plants and their food important groundwork to help them become activists in support of ecologically sound practices -- people who will make good personal and political decisions about how to live within our biosphere. I also think a basic understanding of photosynthesis will enable students to be more socially smart about food shortage problems in the world.
So these are the big, long-term reasons for wanting students to understand these concepts. But what about in the here and now? In the here and now, students encounter plants around them, no matter where they live. Taking a closer look at plants and getting engaged with them in first-hand ways will awaken students to seeing their world around them in new ways. Plants provides a great context for "looking beneath the surface" of everyday things around us. And middle school students are fascinated by issues of growth and change. While that interest often focuses primarily on themselves, that interest can be tapped in the context of a study of plants.


E. Student Conceptions and Scientific Conceptions
The chart on the following two pages is one way of stating the main ideas for this unit. Our research indicates that most middle school students begin instruction with beliefs like those in the column labeled, "Naive Conceptions." These materials are designed to help students change to ways of thinking more consistent with scientific thinking as represented in the column labeled "Goal Conceptions."
 
 
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