Friday, October 28, 2011

Seed Dispersal

How do seeds move from one place to another?  This is a follow-up to our seed collection activity from a few weeks ago. If you haven't done a seed collection, this could be done with seeds available commonly in your refrigerator or pantry.  Also, as a note, this is a slightly more complicated activity and I imagine that it would work best with children that are slightly older - my five year old seemed to get it but I think it was a little tough for my little one.  I had a great friend, Amy, and her son, Lucas, join us for this activity and, as she is the plant goddess I mentioned in an earlier post, she was incredibly helpful in brainstorming ideas for this activity.  (She also has some great suggestions for books about seeds and exploring nature with children that I'll post at the very end.)  What follows is an edited version of what we did including some improvements brainstormed by my mother-in-law, a retired elementary teacher, who is spending time with us this week.

Materials Needed:
  • container with potting soil
  • flower head or seed pod with a multitude of seeds on it - we used a dried sunflower head, but you could use many different types of flowers.  If you don't have access to something like that, you could also use an apple, an orange or a handful of dried beans.
  • 4 to 6 seed samples - try for a diversity of seeds that may use a variety of seed dispersal methods.  Some of the ones we used were: maple seeds, pine cones, butterfly weed seed pods, acorns, blue false indigo seed pod, ornamental pear, crab apple, burdock, and dandelion seed heads.
  • stickers to represent the three different dispersal methods that we are going to talk about (wind, animal/human, and water).  I found relevant clip art images that I printed on some labels, but you could use three different color dot or face stickers.  Alternatively, you could write the word, i.e. "wind", on the plastic sample bag.  (But, stickers are fun!!)
  • piece of fabric - fuzzy fleece or anything with a faux animal texture would work really well
  • pan with water
  • sink with sprayer or small watering can (optional)
If you are working with more than one child, I recommend that you have sample bags containing each of the seeds available for each child to make thing move along more efficiently.

Process and Pictures:
Part 1: Why Do Seeds Disperse?
Lucas extracting the sunflower seeds.
Take the dried seed head and ask your child to see if they can find the seeds in it (you may need to help them).  Demonstrate to them how to remove the seeds and then see if they can extract some seeds as well.  Aim for about 10 seeds. If you are using a science journal, you can give your child a few minutes to draw the seed into their journal.  (They could also trace the seed!)  If you don't have a seed head or pod from outside, you could also cut an apple or orange in half and harvest the seeds from it.

The kids focusing on drawing their seed into their notebooks.
Then, take your container of soil and tell them that you want to plant the seeds so that you can have some more sunflowers (or beans, etc.).  Ask them to watch you carefully as you "plant" the seeds in the soil.  Make one small hole in the soil with your fingertip and then put every single seed, one by one, into that same hole.  Put on your acting personae and totally ham it up here; pretend to look into the hole to see if there is any more room, look worried, etc.  Ask your child if they think the seeds will grow well or not and make sure they justify their answer.   

Discuss with your child what plants need in order to grow - make sure they think about water, sunlight, space, nutrients and temperature.   (Note: the requirements for seed germination are different from plant growth - yup, I'm sure we'll be experimenting with that sometime in the near future.)  Ask your child how you could plant the seeds differently so they might have a better chance of surviving?  Talk about the fact that if all the seeds from a plant were to drop straight down in the same spot, then many baby plants wouldn't be able to survive.  So, instead, many seeds are able to move to other places so they have a better chance of survival.  But, how do seeds move?  Here you can ask some silly questions, like, "Do seeds have a car?"  For the next part of the activity, we will be talking about three different types of dispersal methods: wind, animal/human and water.
Part 2: How Do Seeds Disperse?
For each of the 4 to 6 seed samples collected, you are going to test whether you think they will be dispersed by wind, animal/human and/or water.

"1, 2, 3... Blow!"
To test for wind dispersal, have your child place the seed onto your hand.  Then have them blow onto the seed to mimic the wind and see if the seed will float through the air.  If it does, have them place one of the "wind" stickers onto the specimen bag holding the other seeds, or write the word "wind" on the bag.  They may want to hold the seed themselves to try to blow on it, which is great but try to encourage them to keep their hand steady so that it doesn't roll off.  Observe how the seed moves through the air - if you have a variety of seeds then you should be able to see a few different types of movement through the air from the floating of dandelion seeds to the helicopter motion of maple seeds.  Repeat the process for the rest of the seeds samples you have collected. 

Amy and Lucas examining a crab apple.
There are a couple of things you can do to explore the connection between animals (including humans) and seed dispersal.  The first is to take the piece of fabric and lay it on the table.  Ask your child to take the seed and gently throw it onto the fabric.  Pick up the fabric from one side and observe whether the seed "sticks" to the fabric or rolls off.  If it sticks to the fabric, like a burdock seed might, then animals might be responsible for its dispersal.  

The second thing you can do is examine the seeds and have a conversation with your child in regards to whether they've ever seen an animal eating that type of seed.  Squirrels and acorns are a commonly associated pair, but you could also talk about horses and apples or birds and berries.  Some children may also like talking about the idea of animals helping to provide the seed with a built-in fertilizer after the seed goes through the animal's digestive system! 

Put "animal/human" stickers onto the specimen bags that contain seeds that might be dispersed in this manner.  Note that at this point, some seeds may have tested positive for both wind and animal/human dispersal and will have two stickers; that is totally fine! 

Testing for water dispersal: sink or swim and rain simulation.
Water is maybe the trickiest to test of these three seed dispersal methods.  One thing you can do is to test to see if the seed floats in water.  Note that this isn't necessarily the most accurate method as some seeds, like acorns, only float when they are no longer viable.  (So, if you want to grow an oak tree, dump a handful of acorns in water and only use the ones that sink!)  But, as we're really working on the process of science here, the floating technique is a decent test.

Another idea that Amy had is to place the seed on a pan or plate in the sink and then turn on the water and use the sprayer to see if they can spray the seed across the pan or plate.  Make sure that the water flow is at a fairly low pressure so that the force is reasonably similar to rain.  At higher pressures, you can talk about how maybe  that represents a seed falling into a river while at lower pressures it is more like rain run-off.  If you don't have a sprayer as part of your sink, you could also use a small watering can. 

Again, repeat for each of the seed samples and then mark each bag.

Help your child summarize their experience at the end by asking them to indicate which seed sample(s) represent each of the three types of seed dispersal mechanisms that we talked about.  Also ask if any of the types of seeds seem like they have more than one way that they can move.  (This is one of the reasons that the stickers work well; it makes it easy for the child to quickly identify the results of their tests.)

What's Happening?
Many plants utilize seed dispersal methods so that their seeds, their "offspring" have a better chance of survival.  In general, seeds need both appropriate temperature and moisture in order to germinate.  Seedlings, or young plants, need those two things as well as sunlight, nutrients and appropriate space.  We explored wind, animals/humans and water as three common dispersal methods.  In addition, both gravity and force are often cited methods but we skipped over them to simplify the activity.  The thought of explaining the concept of gravity to my preschoolers was a little daunting to me - not to mention the fact that everything is subject to gravity (thank you, Mr. Newton) so we wouldn't really be distinguishing our samples.  As an example of force dispersal, think of touch-me-not or jewel weed flowers whose ripe seed pod bursts open to spread their seeds.

If you tested all three dispersal methods, you probably found that some of you seed samples tested positively for more than one method.  This roughly approximates nature as some seeds may have a dominant method of dispersal whereas others may disperse by multiple means.  An example is the apple, which is a very commonly dispersed as animals eat it and then take the seeds to new locations.  However, an apple is also able to float (think: bobbing for apples) and is also capable of being moved by water.

For older kids: As I mentioned earlier, this activity is probably more suited to older kids (early elementary) that the really young ones.  For slightly older kids, you can increase the number of samples, have them make a data table that shows their results and incorporate measurement into some of the tests (i.e., measure how far they can blow different seeds).

Books: We found a couple of books at the library that were great supplemental material for this activity.  The first is Eric Carle's "The Tiny Seed", about a tiny seed that is blown from a flower in autumn and all the challenges that it must face to grow into a seed-producing flower.  We also enjoyed "Flip, Float, Fly: Seeds on the Move" by JoAnn Early Macken, which gave lots of examples of movements by different seeds. Amy recommends, "A Seed is Sleepy" by Diann Hutts Aston and Sylvia Long, which contains absolutely beautiful illustrations!

Exploring Nature with Kids: Amy also recommends a couple of other books that are great for teaching kids about nature.  They include: "Sharing Nature with Children" by Joseph Cornell, "Sunflower Houses: Inspiration from the Garden" by Sharon Lovejoy and "Hands-On Nature: Information and Activities for Exploring the Environment with Children" by Jenepher Lingelbach.

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