Biology-Mr.Willets
Lab-Dicot Seed
Flowering plants (angiosperms) are of two types- monocots and dicots. They differ in several ways. One obvious difference can be seen in the seeds. The books in the lab have diagrams that can help with this lab (pg. 384)
The Lima bean seed is a good example of a dicot seed. Get a dried seed from the front of the room.
Look at the dried seed. There is a concave side where a scar called the hilum is located. This is where the seed was attached inside the pod (the fruit of beans and peas is the pod). What part of your body corresponds to the hilum?(think!) ___________________________
Above the hilum is a small opening called the micropyle. This is where the pollen tube entered to fertilize the egg cell. (Remember that when pollen lands on the stigma-the top of the pistil- it grows a tube down into the ovary to where the egg is.) Use the hand lenses to locate the micropyle. Draw a diagram as explained below in part A.
Return the dried seed. Get a seed that has been soaking in water overnight. Carefully remove the outer protective coat from this seed. This is called the testa. The seed should now easily separate into two parts. DO THIS CAREFULLY!!! Each part is called a cotyledon which stores the food for the embryonic plant. Plants that have two cotyledons in their seeds are called _____________________ (this is obvious if you think about it) The stored food is called the endosperm. In some seeds, the cotyledons are embryonic leaves that make food in the early stages of growth. If you examined a kernel of corn, it would not separate into two parts. It has only one cotyledon. This tells us that corn is a ___________________
On one of the cotyledons, you will see the embryonic plant. Use the hand lenses to see it clearly. Consult the book for a diagram. There are three basic parts to the embryonic plant- the epicotyl (the embryo's leaves), the hypocotyl (the embryo's stem) and the radicle (the embryo's root). Use the books to help find these parts. Draw a diagram as explained in part B below.
A. Make a diagram of the bean seed's basic shape. Label hilum and micropyle. Make it LARGE.
B. Make a diagram of the side of the seed that contains the embryonic plant. Label cotyledon, epicotyl, hypocotyl, and radicle. Make the diagram LARGE.