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Having read the
assigned textbook pages you should recognize that corn and
other plants reproduce differently than humans, but there
are some similarities. In both cases a sperm had to
fertilize an egg to create a zygote. In humans,
the zygote, or fertilized egg, divides into two
cells. The resulting cells will also divide doubling
the number of cells. This process of dividing to
double the number of cells continues for nine months at
which time a human has formed that is capable of surviving
outside the mother's womb.
Corn has a much
different strategy. The zygote develops into a tiny
embryo that is enclosed inside a protective outer
shell. This is a seed. The seed also contains
nutrients for the embryo to use until it can produce its
own through photosynthesis. In many plants,
including corn, one seed per fruit, or modified ovary, is
produced. In the case of corn, every single kernel
on a cob is a fruit with a seed inside. The fruit is
an adaptation for dispersal of the seed. When an animal
eats the fruit the seed is not digested but instead is
deposited away from the site of the parent plant and in
its own little package of fertilizer!
As you read in the
textbook, the flowers of the plant are the reproductive
organs and the plant embryo in the seed is created when
one of the two sperm contained in the pollen from the male
flower fertilize one of the eggs in the ovary of the
female flower. The other sperm also fertilizes an
egg, but instead of becoming an embryo it becomes
endosperm, or nourishment for the embryo. Some
flowers can contain both male and female parts. Some
plants have both male and female flowers on one plant, and
in other species there is a male plant and a female
plant. Clearly, plants have many different
reproductive strategies but in all cases of sexual
reproduction the male parts of the flower are the stamen
and the female part is the pistil.
Now lets take a
close-up look at the anatomy of a corn plant's flowers and
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1. Obtain an
"ear" of corn. What part of the reproductive cycle
of corn do you imagine this to be?
___________________________________________________________________________
2. If
this is the female part, where do you suppose the male
flower is on a corn stalk?
___________________________________________________________________________
Go to the
website below and read about "Sex in the
Cornfield." Be sure to click on the blue
words in the text to see close-up photos to help you
understand what you are reading.
http://www.agry.purdue.edu/ext/corn/pubs/corn-02.htm
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Answer the
following questions:
1. What is
the name for a plant containing both male and female
flowers on the same plant? ____________________________
2. What do
we call the male part of the flower that contains pollen?
_____________________________________
3. Where on
the corn plant would I find this male flower?
___________________________
4. Where
must pollen land for pollination to occur?
_______________________________
5. What
would you find attached to each ovule in the ear?
__________________________
6. Explain
the difference between pollination and fertilization:
______________________________________________________________________
______________________________________________________________________
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3. On
your ear of corn, gently follow one silk to the kernel to
which it belongs. When mature, each of these kernels, or
seeds, will contain a complete corn embryo with five tiny
leaves.
4. Obtain a
razor blade and one of the corn kernels that have been
soaking in water.
5.
Gently cut the kernel through the top center and observe
the embryo.
6. Add
a drop of iodine to each half of the kernel to see where
starch is stored in the seed.
7.
Obtain a picture diagramming a corn seed and use it to
label your drawing.
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