Sunday, April 15, 2012

Dissecting Bean Seeds

Spring has definitely arrived here and I am itching to get outside in the garden.  We have big, maybe too big given our newborn, plans for the garden this year including a square foot gardening project for the older girls.  (That particular project involves power tools - hooray!)  We just received some seeds we ordered in the mail this week from Seeds of Change (a great source for organic seeds - we got some San Marzano tomato seeds this year because I hear they make an amazing sauce!) and I made the comment about every seed having a baby plant inside.  The girls, as you can imagine with a new baby in the house, are fascinated by babies right now and wanted to see the baby plant so we decided to dissect some beans!
Materials Needed:
  • variety of dried beans - we used a bag of mixed dried beans intended for soup
  • water
  • paper towels
  • 5 plastic containers
  • magnifying glass
  • markers - I recommend permanent (for adult use!)
  • science journal


What You Do:
The first step is to sort the mixture of beans.  Select 4-5 different types of beans that you want to examine from your mixture.  Try to pick the larger, meatier beans.  We used lima, pinto, northern, kidney and pink beans.  You can do this with just one bean type, but since we wanted to compare the different beans and it is also good practice with the skill of classification, we decided to use a mixture of beans.


Once the beans have been sorted, carefully pour water to cover them and leave for 24 hours.  If you are limited on time, you can also try using hot water and leaving the beans for an hour or two to soften.  Have your child make a prediction about the seeds - maybe how big the baby plant is inside or whether the baby plants will look the same or different between the variety of beans.




When the beans have softened (you should see the seed coat starting to peel off a bit of its own accord), remove it from the water and carefully remove the seed coat then split the seed in half.  You may need to use your thumbnail to help split the bean.


Examine the baby plant inside the bean with the help of a magnifying glass.  Your child should be able to see the embryonic leaves and a structure that looks like a miniature root.  (See below for an explanation of the parts of the seed.)  


You can use the markers to very gently color the different parts so they are easier to identify.  I tried using both washable and permanent markers and the permanent (or, in the words of Robert Munsch in Purple, Green and Yellow "super-indelible-never-come-off-til-your-dead-and-maybe-even-later" markers) were much better at transferring color to the structures, but you may want to have the adult do it!  

Ask them to evaluate their prediction.  We were looking at whether the baby plants would look similar or different and the girls decided that all the bean seeds looked pretty similar to each other, although some were larger than others.  As a side note, if you are only going to choose one type of bean to do this with, don't be tempted to choose the lima bean because of its large size - the embryonic plant was not much bigger than the others and we found that the radicle (root structure) kept breaking when we tried to open each of the beans.  Have your child draw what they see in their science journal.

What's Happening?
A seed contains all of the materials necessary for the early life of a plant, including the seed coat for protection, the endoderm and the embryonic ("baby") plant.  The seed coat is also called the testa.  On beans, you can often see the hilium, or scar tisssue, that marks where the seed was connected to the mother plant.  In addition, above the hilium you may be able to see the micropyle, a small hole that the pollen tube entered during fertilization and through which water can enter to aid in the early growth of the seed.

The endosperm serves as the food source until the plant is big enough to make food on its own.  The majority of the human diet consists of plant endosperm - from starchy popcorn to the wheat seeds that are milled to make flour.  The endosperm is made up of two cotyledons in bean plants, which are considered dicots.  Other plants like corn, which are monocots, contain only one cotyledon.  (di = two, and mono = one)  The cotyledons are often called the seed leaves when they emerge from the soil - all the rest of the leaves develop above the seed leaves and the seed leaves eventually wither away when the food has been used up and the plant is able to produce its own food.

The plant embryo consists of different tissues including the epicotyl, hypocotyl and the radicle.  The radicle emerges first during germination and travels down into the soil forming a long tap root.  The epicotyl is the part of the plant embryo above where the cotyledons are attached (epi = over or on top of) and it eventually forms the leaves of the plant.  The hypocotyl is the part of the plant embryo below which the cotyledons are attached (hypo = low or below).  The epicotyl will eventually form the stem of the plants.

The picture below is of a pinto bean with the parts of the plant embryo color coded (very generally).  (The pic was taken with my iPhone using the easy macro cell lens band from photojojo.com - the best $15 I've ever spent!) 



Extensions
We used some awesome parts of a seed cards that are a free download on the Walk Beside Me blog.  (She also has parts of a flower, parts of a leaf and parts of a plant cards!)  They are in a Montessori style and, as both my older girls are in Montessori this year, they immediately grasped the idea behind them.  We printed out two copies, cut off the title in one of the copies and had them match all the cards of the same structure together.  


A great book to teach about the nature of seeds is "A Seed is Sleepy".  It talks about different types of seeds, and it might be really fun to try this experiment again but with different types of seeds.  Try to get fairly large seeds that are a variety of monocots and dicots - so, maybe corn, bean and pea.  Because some seeds have much tougher seed coats (if you've ever planted morning glories you know you are supposed to nick them before you plant them) you may have to experiment with how long the seeds need to be soaked. 

Check out this time lapse video from YouTube of radish seeds growing.  You will notice the radicle (root) emerging first, followed by the stem and seed leaves (or cotyledons) emerging later.  Radish seeds are a great seed to experiment with because they sprout fairly quickly (3-5 days).
 
Science Process Skills Used In This Activity:

Observing Communicating Classifying Measuring Inferring Predicting
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Visit the science process skills page for more information on the different skills.  I hope you enjoy this activity!   If you try it, please leave me a comment to let me know how it goes!  You can also post any pictures you take to the Momma Owl group on Flickr.  Have fun with science!



2 comments:

  1. Thank you so much! We're doing this is our Classical Conversations Homeschool Group tomorrow and I needed to read your post. Following you now in Pinterest too!

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  2. This is just what I was looking for! We'll be doing this in my science Co-op tomorrow, and your pages offers more information than many that I have seen. Thanks!

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