Students need to discover why all cells cannot produce
babies. Mitosis is the process whereby cells exactly duplicate themselves.
Both old and new human cells contain 46 chromosomes. During meiosis,
which involves the sperm and egg cells, each cell has 23 chromosomes.
When the sperm and egg unite, the fertilized egg will have the normal number
of 46 chromosomes, half from the mother and half from the father.
In the worksheet we have the students trace the stages of mitosis
and meiosis. Before mitosis begins, the nucleus contains chromatin
(protein + DNA). As the cell begins to divide, the chromatin begins
to condense into 23 pairs of x-shaped structures called chromosomes.
The centrioles (whose function is not fully defined) move and spindle fibers
begin to develop around them. Each of the chromosomes become a pair
of identical chromosomes. The centrioles are at opposite sides.
The spindle fibers stretch from one side of the cell to the other.
The chromosomes pair across the center of the spindle. The two halves
of each chromosome pair separate and move to opposite sides of the cell.
Two new nuclear membranes develop. The cell begins to break.
The two new cells are complete.
During meiosis the story is a little different. There are
different avenues for the female and male sex cells. Meiosis is the
process that produces 23 chromosomes (haploid) from 46 chromosomes (diploid).
Meiosis is long and complicated and frequently takes days to complete instead
of hours or minutes as does mitosis.
- Go over the information on the worksheet emphasizing
mitosis and meiosis. Mitosis is just the dividing of a cell into equal
parts. The two types of meiosis one involving the sperm and one involving
the egg. Meiosis is characterized by going through two phases of
cell division. The first phase closely resembles mitosis. One
sex cell produces two sex cells in the first phase. The two sex cells
will then divide again to produce 4 sex cells. In females, however,
only one egg is produced (the remaining 3 cells are called "polar bodies"
and their function is not positively known.) The resulting sex cell
will have one half of the normal number of chromosomes (23). Meiosis
only occurs in sex cells, not in other cells.
- Instruct students to using coloring pencils to make the
worksheet more readable.
- Use the Internet if students are unfamiliar with cell
structure. Search under “cells” or “genes” to look for information.