Sunday, November 24, 2013

Teaching The Scientific/Experimental Method Part II: Plants


Test 1 (two jars on the left) and Test 2 (the two jars on the right)
TEST 1:  Do you need soil to make seeds grow?

·     With water, soil, and rocks
·     With water, rocks, and NO soil
 
G. predicts that the seeds with only rocks (and no soil) will not grow
N.S. agrees with this prediction, and thinks that the seeds with rock and soil will grow
And E.S. concurs - she expects that the seeds with soil and rock will grow (on the left);the seeds on the rocks will just stay on top and do nothing.
    TEST 2:  Do worms help seeds grow?
·   With water, soil, and worms
·   With water, soil, and NO worms

T. thinks they'll both grow (she uses her x-ray vision to see inside the pods that she thinks will emerge:  inside are more edamame seeds)

J. is unsure...without worms, he predicts that the seeds won't grow at all
TEST 3:  Can seeds covered in fabric grow? 
·    Seeds covered in fabric
·    Seeds NOT covered in fabric
 
L.S. was the one who came up with this intriguing idea: 
 "We should get seeds, put fabric on top of them and then plant them. 
I want to see if the fabric will keep them from growing." 
She predicted that the test with fabric covered seeds would not grow. 

TEST 4:  Do seeds and plants need sun to grow?
We used plants that had already sprouted as well as seeds that had not yet sprouted
 
C.'s prediction (above):  The seeds with sun (on the left) "might stay alive or they might die."  The seeds without sun (on the right):  "When we cover [the seeds] with a trash can, [they] won't get any sun so [they] might die."

N.B.'s prediction (below):  "The one without sun will die.  The one with sun will live. Outside [with sun], it's happy."


A.C.:  In a dark trash can, the seeds probably might not grow...[yet she does draw some sprouts]...

A week passed after the children's initial predictions, and then it was time to make some observational drawings and notes to see how our tests were progressing.  Stephanie and I closely examined the tests in advance of the students and noticed something surprising:  the seedlings we’d started without sun (Test 4) were actually growing – and the ones with sun (sitting in our windowsill) were doing…nothing.  What were we going to do?  We wanted our students to understand that sun was necessary for plants to grow, yet here we were faced with an unexpected situation. 
The conundrum ultimately revealed itself to be a teacher problem – do we show them what we think they should know (reverse the tests and help reinforce the idea that sun is indeed necessary for plant growth) or reveal to them the real results of our test:  that the seedlings deprived of light actually did grow substantially and the ones with natural light were slow to grow?  How could this have happened?  We ourselves were at a loss to explain it, and yet, morally and ethically, we had to let the tests stand as they were.
We let the children take a look at all of the four tests and let them draw their own conclusions - which is exactly how it should be.  Part of the beauty of studying the natural world is its endless surprises... 
 
Scientists hard at work
 Test 1:  It was clearly obvious that the seeds without soil (and just rocks) were not showing any signs of growth.  Seeds need soil as a medium to grow.  P. noticed:  you need dirt to spread your roots. 

The boys sketching their observations of Test 1
Test 2:  The seeds growing with worms were doing better than those without – but even those growing without worms were doing well.

M:  Even in the "no worms" jar [the seeds] grew.

W., I., and G. examining seedling growth in both Test 2 jars
Test 3:  Somehow, some way, the seeds wrapped in fabric found a way to grow.  Did they push through or around the fabric?   We don’t know…but there were seedlings popping through the soil…not as many as those popping through the “no fabric” variable test, but they still found a way to push through. 

J:  The one with fabric didn't grow as much because the seed couldn't breathe. It has to breathe in carbon dioxide to live. 

N.S.:  With fabric, only one seed escaped and grew.  Without fabric, it's growing more. There was nothing covering the seeds. 

C:  If fabric covered the seeds, the fabric might catch [them].

I:  if there is fabric, the seeds and the plant can't get any light...[but] the plant pushed the fabric off to get sun. 

L.S.:  The fabric only sort of made a difference.  Both [of the jars] have live plants. 

P:  Maybe the seed snuck out [of the fabric] if it wasn't tightly wrapped.

R:  The [seeds] grew around the fabric.  The one with fabric didn't do as well [as the seeds without] but it did start growing. 

A.C. and E.K. closely examining Test 3
Test 4:  The sprouted plants without sun were significantly less green than the ones with sun…but the seedling kit that was deprived of sun was doing substantially better than the one that had received sun throughout the week.  That being said, there were some obvious differences:  the seedlings without sun did indeed grow, but they weren’t green, and some were beginning to show signs of decay. 

The Test 4 surprise:  somehow they sprouted! But how???
The children postulated two theories:  maybe there was a crack of light that got in through the garbage can under which the seedlings had been hidden?  Maybe hiding under the garbage can created a warmer environment in which the seeds could grow?  As their teachers, Stephanie and I were unsure of their answers, but like the children, we had to patiently wait a few more days to see what the ultimate results of the tests were. 
After two weeks, tests 1, 2, and 3 gave clear results that were already in evidence after the first week:  you DO need soil to help seeds grow, worms ARE helpful but not necessary to help plants grow, seeds wrapped in fabric CAN grow, but those that are not wrapped in fabric grow better.  Two weeks later, we saw very different results for Test 4:  those seedlings that had (somehow miraculously) grown had now started to die  – they were colorless, wan, drooping, and on their way out, and ultimately, they looked like this:
Dead and moldy
T. and M. offered up this theory:  the seedlings that had sprouted without sun in Test 4 were older than the ones with sun.  They sprouted first and so they died first.  Meanwhile, those seeds in Test 4 that had received sunlight were now (ever so slowly) beginning to sprout...

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