Focus on Evidence (investigating water transport in plants)

We want to explain, solve problems, provide solutions. I see it in my two crazy toddlers. With their different ways of thinking, few problems are outside of their reach to solve. Together, they have learned to untie knots, unstrap buckles, remove latches, climb to amazing heights and more just so they can trash their room instead of going to sleep. By the time a student walks into my Grade 7 class, they have been conditioned to “answer the problem” and “provide a solution”.

What about the evidence? Those beautiful details collected from observation seemed to be noted in passing, processed somewhere in their minds, and rapidly discarded. I am trying to ask my students to slow down, pay attention to their observations and collect data. Moving back and forth between the desire for students to design investigations to the need for serious skill building in working like a scientist, we’ve been doing a series of observational-type labs.


My goal is for students to collect data related to movement of material through a plant. (We’re tackling MS-LS1-6. -Construct a scientific explanation based on evidence for the role of photosynthesis in the cycling of matter and flow of energy into and out of organisms – so please let me know if you have any additional ideas.) Water transport in plants amazes me and I am hoping for my students to collect evidence to begin putting forth a simplistic description of the process moving water up a xylem tube. The focus is on evidence and I know they are sick of me asking what evidence will you collect? What is your evidence? Describe your evidence. Wow! This is difficult.

As a group, my students consistently skip over describing evidence and begin talking about how it can be used to answer a question. I pull them back. Describe your evidence. What type of data are you collecting? They respond, “The red at the top of the celery means that…” Again, slow down describe what you are seeing. Pull apart the celery. Collect evidence.

Science Teacher Doyle often writes on the need for students to work on the processes of our world around them and to make strong connections to our own outside world. Evidence must be collected and students need to construct their meaning from their own observations, not heaps of text. At what point is their enough evidence to then make a leap into the abstract? We pulled apart celery as its xylem tubes filled with red food coloring and were amazed at how much quicker the stalks inside the bunch pulled up the liquid than the older stalks on the outside.


We slowly dropped different liquids on the top of a coin. Students saw a fat bubble form when dropping water and watched vinegar and soapy water slide away. We placed bags around branches on trees in the school yard and saw on a sunny day how quickly water vapor filled them up. Evidence was collected. We worked hard to only describe the evidence and then to put together pieces of the puzzle.

Students drew. Their evidence led them to a common “wall” – water goes up the plant and but now what? Where does the process start? Is there a push or a pull? The sun was brought in. “It must take part in this dance,” the students exclaimed. I think we reached the limit or I was simply not patient enough or did not have the right guiding questions. 







(A few more student examples are located at the bottom of the post)

In the end, we made a line from the door to the classroom and linked arms. I asked which experience collected evidence that as a bunch of water molecules we should have linked arms? “Ooh, the drops on a penny!” Why, explain your evidence. The line was broken into segments all the way down to a someone in the root zone. We laughed at the idea of being water molecules stuck in a xylem tube but then wondered about the starting of the process. Is there a push or a pull? “A push from the roots,” volunteered one. We had the last student in the root pull with all of his might. Nothing happened to the rest of the line. Hmmm….any other possibilities? “The other end could pull.” Make way for silly, middle school exaggeration as a tiny pull led to students falling all over themselves. Point made.

What evidence do we have that water comes out of a leaf? They again made the connection to our observations and slowly teased out evaporation. A leap was made by many students and they appeared to nod and smile of understanding. But, we’re not there. Next steps?

This process took time. Collecting evidence takes time, but the hard work lies in pulling that evidence together. I think my students are starting to appreciate data in a new light and I hear them beginning to refer to specific data.  I find myself struggling to find the balance between doing experimentation (they get excited about this) and making meaning of what we’ve done (bring on the crickets). Large whiteboards and group processing helps a lot but I’m looking for more ideas. Please share!

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