Mitosis
WHAT IS MITOSIS?
Copyright 2007, Micro Bus
There are various structures within the cell, but many are too difficult
to see. For example, within the nucleus lie the chromosomes. These are important
for heredity and reproduction. When a cell splits and becomes two, certain
processes occur within the nucleus first. One of these processes involves
the splitting of the chromosomes. This process is called Mitosis and
there are four distinct stages.
In the drawings below, you can see the
chromosomes in the nucleus going through the process of mitosis, or division.
If you have a microscope (400X) and a properly stained slide of the onion
root tip (or allium root tip), you can see
the phases in different cells, frozen in time. You will be looking at strands of DNA inside the cell!
PHASES OF MITOSIS
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First Phase
is called Prophase,
the DNA molecules of the chromosomes condense. The outer boundary
of the cell is the faint circle just inside the box.
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Second
Phase is called Metaphase. The chromosomes line up in the center of the cell, separate and become a
pair of identical chromosomes
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Third Phase is
called Anaphase.
Each set of chromosomes moves toward the opposite end of the cell.
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Fourth
Phase is called Telophase. Here, the spindle fibers disappear, the nuclear membrane appears and the cell
divides into two daughter cells. Notice the indentation starting on the
outer cell wall. Eventually these two indentations will touch and
the cell will become two.
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Summary: When a cell divides, first the chromosomes split and become two. Each new one
looks exactly like the original old one. Then the chromosomes move away from
each other and become two similar nuclei. Finally, the cell splits in two,
making two new identical cells, each with an identical nucleus.
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With your stained onion
root tip slide, look down near the pointed end (tip). You should
be able to identify all the stages of mitosis. At left is an actual
picture of an onion root tip specimen. Can you identify the phase
of the chromosomes in the center that look like a spider? (Answer
below)
Memory Aid:
An easy way to learn the names of the phases in order is to remember the
"word" PMAT. Visualize a floor mat with a big letter
"P" inscribed on it.
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Other interesting information
about cells: Many cells of the same kind are called tissue. Blood is a tissue. When many
different kinds of cells work together, we get an organ, like a heart. Finally,
when many organs work together, they form a complex living thing, like a flower,
a flea, or a human. Think of all the different types of cells and organs working
together to keep you alive!
Answer to question above: metaphase
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