Beth Richards
C&T 852
November 18, 2008
Student Interview
DecompositionAdapted from Rotting Apple, Probe #18, Uncovering Student Ideas In Science, Another 25 Formative Assessment Probes, Vol. 3, 2008, NSTA Press.
Purpose: The purpose of this assessment is to determine if 8th grade students perceive that biological agents (living organisms) are involved in decomposition.
Main Ideas:
- Decomposition- the process of breaking down organic material; a reduction of the net energy level and change in the physical and chemical composition of organic material.
- Decomposers- (also detritivores) organisms that consume dead organisms.
- Decomposition is an important part of nutrient cycling in ecosystems.
- Living organisms are involved in the process of decomposition.
Exercise 1: Apple Prop / Exercise 2: Check-list of decomposers / Exercise 3: Time-lapse video of decaying apple
General & Probing Questions
- Would you describe this as a “living’, “once living”, or a “never living” object?
- Why did the tree produce the apple? Does is have a purpose?
- What happens to the apple after it falls off? What happens to the apple if it is left undisturbed on the ground?
- Check the items that you believe are involved in the process of decomposition (decay).
- How do you know that these are decomposers? (Choose a few checked items and question why they believe they are decomposers.)
- What is happening in the video? What is the process called?
- What “things” are causing the decay/decomposition (student term)?
- Is there more than one “thing” (decomposer, organism) decomposing the apple?
- What would you predict the apple to look like much later, after the video ends?
- Where does the matter, the stuff the apple is made of, go?
- Is decomposition important? Why?
Student Descriptions
My daughter and two of her friends were interviewed. They are in the 4th month of 8th grade. They have been classmates since early elementary school and have been exposed to the same science curriculum that included lessons on decomposition in elementary and middle school. All three students are high academic achievers, participate in sports, and are socially active. The students were cooperative and attentive during the interview.
I am acquainted with the students and their families and the interviews were conducted in my home with parental permission.
Interview Transcript
Exercise 1: Apple Prop
Would you describe this apple as “living”, “once living” or a “never living” object?
Student 1: Once living because there was an apple tree and apple trees are living and it was on that apple tree. All of the nutrients come from the apple tree. Once it is off the tree I don’t think it is living anymore.
Student 2: A living thing. It hasn’t died and it is not disintegrated yet.
Student 3: It is living because it is a fruit and it has to grow somehow and nonliving things can’t grow.
Why did the apple tree produce the apple?
Student 1: Because the apple has seeds in it. It produces seeds so that there can be more apple trees.
Student 2: Cuz of the seeds? (nervous laugh) For food to eat and farming.
Student 3: Uhm, good question. Because it is what it does. It gets nutrients from the apple.
What happens to the apple after it falls off the tree? What if it landed on the ground and was left there undisturbed, what happens to the apple?
Student 1: It would break down into the soil and decay.
Student 2: It begins to ripen and then it begins to rot.
Student 3: It will decompose.
Results
These questions probe for understanding of the life cycle of a tree and decomposition. The life cycle of organisms is an important concept for a comprehensive understanding of the interdependence of organisms in an ecosystem. Students 1 and 2 have an incomplete conception of the life cycle of the tree. Decompose, rot, and decay are terms used by the students indicating that the students have an apparent precursor factual understanding of decomposition. However, decomposers only decompose dead organic matter indicating there are gaps in their conceptual knowledge of decomposition.
Exercise 2: Checklist of Decomposers
The checklist used in this exercise is attached.
Students checked the following items:
Student 1: Soil, bacteria, mold, isopod, worms, and a ? next to air
What makes you think that the items you checked are involvedin decay?
Well, soil is the ground and the apple is on the ground and it decays and goes into the soil.
Well, bacteria is everywhere and so if the apple falls on the ground it is going to have bacteria on it. We have to wash our apples when we get it from the store anyway because there is probably bacteria on it. Mold because anything, like fruit, and stuff like that can get molded when they are there too long and they are bad.
What do you mean by “bad”? Like how milk can sour, things can like sour and be bad.
What is the role of mold? Why is the mold there? Mold is on it when…let me think… I don’t know how to explain it but…
What is the mold for? Does it have a job or purpose? I know like something has to like, I forget what, but I know some living thing breaks down things into soil. Composition (student is referring to compost piles) piles have things to break down.
Student 2: Soil, bacteria, water, ants, fly, isopod, air, worms.
Why did you pick soil?
Well the soil, it like holds like the worms, it is kind of like where they fall, the soil will get colder or warmer and change the apple’s outer thing,… I don’t know.
Why did you pick air?
Because the air could, when it rains, it will start to grow mold on it. When it is hot out it will like start to go bad.
You picked some organisms like worms, rolly-polly, and bacteria; why did you pick those?
Because they could eat away the apple.
Student 3: Soil, bacteria, water, air.
Why is the soil and air involved?
The soil takes the moisture, bacteria eat it, and like gets inside of it and ruins it, and the water erodes it away, and the air can erode it too.
Results
These questions probe specifically for student understanding of decomposition.
It is apparent that 2 and 3 do not have a clear understanding that decomposers are living organisms. However, it was difficult to design the question without hinting that decomposers are living organisms and the wording of the question may have influenced their choices. I also think the students are using their prior knowledge, and even trying to actively remember prior lessons on decomposition. For example, student 3 is trying to incorporate her knowledge about climate into her reasoning.
Student 3 has a conceptual misunderstanding that water and air play a physical role in decomposition. Although she indicates that organisms “eat” the apple, she has a factual misconception that water and air also work to decompose the apple through a mechanism of erosion. Although the abiotic factors, water and air, may play a part in dispersing the organic matter, the matter doesn’t just disappear without living organisms to break it down.
Exercise 3: Time-lapse Video
Students were encouraged to think out loud while watching the video. I reassured the students that I was not looking for “right answers”.
Student 1:
The apples get that brown stuff on it when it sits there too long.
What is the brown?
Becoming bad.
What does it mean to become bad?
Like, like it is not good anymore. Is that mold then?
Did it shrink? What is the white? Eew, is that mold?
That part must be mold, the other part I’m not so sure.
But it didn’t absorb, it didn’t totally break down.
(Video ends)
Yes, the video could have gone on longer.
OK, good I thought, was I wrong?
Yes, they had to stop somewhere; it didn’t say how long they recorded.
So, what is happening on the video?
It is breaking down, and I think the white stuff is mold.
OK, what is the process called?
Oh, I know, decomposing into the soil, breaking down. Ah, I know it. (trying to recall a term)
OK, what things are causing the decay or the decomposition? Like, what was the white stuff?
I think it was mold.
What would you predict the apple to look like much later, after the video ends?
It would probably, the mold would spread and it would look really ugly. And eventually it would break down into the soil.
Where does the matter, the stuff the apple is made of, where does that go?
Into the soil.
Do you think decomposition, the process is important?
Yes I think it is important.
Why?
Because if things don’t decompose the earth would be filled with like, what litter is, except like worse. And things need to break down into the soil so we can have a healthy environment.
Ok, we are done.
Can you tell me the right answers now?
Student 2:
What do you think?
What do you think is happening in the video?
Um- The apple is like decomposing, rotting, turning into soil.
And the process is called…
I don’t know.
What things do you think are involved in the decomposing?
The climate, and the living things around it that could…
(video ends)
Did you see anything in the video that was causing the rot?
Like there is like, I thought it would be like, like something was living because there was white on the outside (of the apple).
Was there just one thing breaking down the apple, or more than one thing?
I think there are multiple.
What would you predict the apple to look like much, much later if that video had gone on?
I think it would have turned into like little, tiny, organisms, or little tiny pieces of dirt.
Where do you think all that matter goes when the apple is fully decomposed? Where does all the matter go?
I think it evaporates.
Do you think decomposition, this process, is important? And Why?
Because it plays a major role in our food pyramid. When it decomposes other things can eat it. If things didn’t decompose other animals couldn’t eat it and it would ruin the whole food chain thing.
Student 3:
Mold! The part not covered by the skin is the main part that gets attacked.
Pretty gross!
(video ends)
What do you think is happening in the video?
The air and the bacteria in the air are decomposing the apple.
What is this process called?
Decomposing?
What things are causing the decay or decomposition?
Air and the bacteria in the air.
Do you think there are other things beside the bacteria and air causing the decay?
Well, it looks like a pretty clean environment. Age.
Age?
Well, it ends up taking a long time and living things can’t live forever.
What do you mean when you say age?
Well like it is going through its life cycle.
The apple?
Yah, it has to go back into the earth.
What would you predict the apple to look like much later, if that video went on and on?
Eventually there would be nothing left but bacteria. And then there wouldn’t even be bacteria because it doesn’t have anything to feed on so it would die too.
Where does the matter that makes up the apple go when the whole process is done?
Well, the bacteria ate it (laughs).
Do you think the decomposition process is important?
Yah, because otherwise the earth would be really cluttered. And the soil wouldn’t have anything to feed on.
Results
Student 1 has a consistent conception that organisms decompose “into the soil”. The apple is not sitting on the soil in the video; the apple appears to be in a relatively clean, indoor environment. The student may be using prior knowledge or the image I created with the apple prop, the apple sitting on the ground undisturbed after falling off the tree, which may be influencing her interpretation.
Student 3, in contrast, analyzes exactly what she is viewing, attributing the decay to bacteria and air.
Student 2 perceives that the process is “making soil”. The video doesn’t demonstrate this, the apple is not fully decomposed when the video ends, but the student is apparently applying prior knowledge.
Students appear to have an understanding that the decomposers, identified by the students as mold or bacteria, “eats” the apple. However, a consistent conceptual misunderstanding is that abiotic factors, air and climate, are decomposing the apple. Students do not have a factual understanding of the role of abiotic and biotic factors in an ecosystem. The “soil feeds on”, the organic matter “evaporates” and the concept of “erosion” may be vernacular misconceptions.
All students understand the general importance of decomposition as it relates to the health of ecosystems. The role of decomposition in the food chain is a little fuzzy, an incomplete understanding.
Conclusion
Although the students attempt to apply prior knowledge to the concepts and visual demonstration of decomposition, there are gaps in their conceptual knowledge regarding the life cycle of plants, the food chain, definition of a decomposer, and the role of abiotic and biotic factors in an ecosystem.
The interrelatedness of abiotic and biotic factors in an ecosystem can be visually represented for students using concept maps, an example of which is attached. Research supports student construction of concept maps to aid them in constructing knowledge of complex systems, such as an ecosystem and the biosphere. Constructing the concept map as the unit progresses and revisiting them frequently help students connect discrete facts to the broader concepts.
Students also need other methods of construct knowledge for themselves. More meaningful learning is achieved through inquiry-based instruction (NRC 2000). Composting projects or experiments can easily be done in the classroom using worms, garbage items (carrots, apples, etc), soil, and see-through plastic containers.
Using multiple instructional strategies, including demonstrations and questioning, help students construct deeper conceptual knowledge of complex systems (Treagust). The time-lapse video provided an excellent visual demonstration of the process of decomposition.
Reflecting on the interview process, the most challenging part was designing questions that did not lead the student’s thought process. It was hard not to put words in their mouths and hint about what I was looking for. At one point I designated the mold as the decomposer for one student.
However, I think the tools I used were effective. Having a real apple on the table for exercise 1 may have helped students visualize the tree and its life cycle. The checklist of decomposers uncovered factual knowledge, although I was unable to write a question that was unambiguous without hinting that decomposers are living organisms. I started with “Check the items involved in the rotting and decay of dead plants and animals” and changed it to “Check the items that cause the rotting or decay of dead plants and animals”. These instructions may have led to selecting abiotic factors, which 2 of the 3 students chose. The time-lapse video was especially effective, one that I would use in the classroom to provide a visual representation of the process of decomposition. I think it was engaging and thought provoking.
Overall, I think the probe uncovered important gaps in the students’ conceptual knowledge of decomposition and the broader concepts of ecology. With a little refinement of the tools, and improved questioning techniques, this probe can be effective for instructional purposes.
Works cited
NRC (2000). Inquiry and the National Science Education Standards. Washington, D.C., National Academy Press.
Treagust, D. F. General Instructional Methods and Strategies. Science Teaching