Thursday, October 25, 2012

Seed dispersal - predictions, estimations, and fractions

Birches students have been closely investigating seeds for the last two weeks.  We made several interesting observations while on nature walks, including many of the different ways that plants have to spread their seeds. Using plants and seeds that we had collected, students learned to categorized their seeds based on the mechanisms of dispersal: wind, water, animals/humans, gravity, and mechanical force. We also tried our hand at designing our own seeds and testing them by gravity dispersal. And Kate H. found an excellent video to share with us as well.

We talked about why plants expend so much energy on making extra seeds, and wondered if size of the plant/fruit determined how may seeds are made.  Peaches, apples, pumpkins, and strawberries were compared and we decided that fruit size is not necessarily a good determinant of how many seeds a plant will produce.

Just before we sliced open a sugar pumpkin, students made predictions about how many seeds we would find inside, estimates ranged from 500 to 50 seeds total.  Bisecting the pumpkin, we scooped out the seeds of one half of the fruit.  Each student was given a fraction of seeds to count by themselves.  Students grouped their seeds on plates in sets of 5 seeds/group and then added all sets of five to give us their totals.  When it came time to estimate how many seeds we would find in the remaining half of the pumpkin, we were much closer to the actual number.  Plotting a bar graph together we noticed that our first seed number guesses were not as accurate as our second predictions were.  We decided that having a little more information and experience, from counting the first half of the pumpkin, provided us with enough confidence to make more accurate estimations about the quantity of seeds inside.

I think we were all surprised to find that half of our small pumpkin contained 399 seeds and once we added the remaining portion we found that the pumpkin contained 470 seeds total!

From seeds we are moving on to the animals who eat them.  Over the winter we will participate in project feeder watch.  Making our own feeders, we will have an opportunity to become citizen scientists, learn to identify species, talk about migration patterns, how weather may effect our count, and to record data.

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