Corn

=Corn Dissection= toc

Purpose
Examine the structure of the fruiting body of corn. Identify the key structures and their functions. Compare and contrast corn seeds to other seeds that students have dissected.

Materials

 * Notebooks
 * Pencils/Colored Pencils
 * Rulers
 * Hand Lenses
 * Microscopes
 * Scalpels
 * Probes
 * [[file:corndissection.notebook]]

[[image:CornPlantCBSM.jpg width="160" height="317" align="right" caption="Corn Plant"]]Introduction

 * Corn is a grass. The ear of corn that we are familiar with is the female fruiting body of the plant.
 * The silk and ear make up the female flower and ovary.
 * The tassel is the male flower and contains the anthers which produce the pollen.
 * As a grass, corn has separate male and female flowers. It is wind pollinated.
 * Leaves attach to the stalk (stem) at nodes. This is also the point where the ears will branch off.

Documentation
Children should draw, measure, and describe in their notebooks each section of the dissection. Any interesting specimens should be shared with the class via the ProScope.

[[image:corn04small.jpg width="240" height="192" align="left" caption="Ear of corn showing silks attached to the kernels."]]Step 1: Remove Husk
Carefully remove each leaf of the husk one at a time, uncovering the ear of corn. Try not to break off the silks. Notice how each silk leads to an individual kernel.

Corn is a very complicated fruit. The female flower is the silk. Each thread of silk is attached to one individual ovule. After the pollen fertilizes the ovule, the embryo will begin to develop, forming what we know as an individual kernel of corn. Think about how many pollen grains must land on the silks to fertilize each and every ovule! You my have seen ears of corn with unformed kernels. These are ovules that were not fertilized. When the kernels dry out and harden, the embryo is protected until conditions are right for germination.

[[image:corn03small.jpg width="240" height="192" align="left" caption="Cross-section of ear of corn."]]Step 2: Cross-Section of Ear
Break the ear of corn in half to reveal the attachment of the kernels and the cob.

Notice that each kernel of corn is attached to the cob by a pedicel. This structure acts like an umbilical cord and supplies the developing embryo with nutrients. The nutrients flow from the plant through the cob.

[[image:corn01small.jpg width="240" height="192" align="left" caption="Individual Kernel showing pedicel"]]Step 3: Individual Kernel
Carefully remove an individual kernel of corn, making sure the pedicel remains attached. Examine it closely. Notice the familiar yellow, waxy outer covering of the seed. Unlike many other seeds, this is not just a testa or seed coat. On cereal grains, this is referred to as the bran and is made up of several layers. The deepest layer is the testa. The outer layer is the epidermis.

[[image:corn02small.jpg width="240" height="192" align="left" caption="Cross-section of corn kernel."]]Step 4: Kernel Cross-Section
Using a scalpel, slice an individual kernel in cross-section to reveal the internal structures of the seed. The first thing you will notice is that the embryo is different than those of beans and other dicots. Corn is an example of a monocot. When the seed germinates, only one leaf or cotyledon will emerge. In grains, the embryo is referred to as the germ. You will notice the germ as more dense tissue at the base of the kernel near the pedicel. Surrounding the germ is the spongy, starchy endosperm. This is the stored energy for germination. In this view one can better appreciate how thick the cuticle of the kernel is the covers and protects the seed.

//I believe that if one were to put a small drop of iodine on the exposed endosperm, it would turn a dark purple, while the germ would remain lighter. Iodine reacts with starch. -mw//



Resources

 * [|Corn Genetics]
 * [|Corn Development]