microtubules arranged in a circle. Unlike animal cells, plant cells do
not have centrioles, but they form a spindle that is almost identical
to that of an animal cell.Separation of Chromatids
by Attaching Spindle Fibers
Some of the microtubules in the spindle interact with each other.
Others attach to a protein structure found on each side of the centro-
mere. The two sets of microtubules extend out toward opposite poles
of the cell. Once the microtubules attach to the centromeres and
poles, the two chromatids in each chromosome can be separated.
The chromatids are moved to each pole of the cell in a manner
similar to bringing in a fish with a fishing rod and reel. When the
microtubule “fishing line” is “reeled in,” the chromatids are
dragged to opposite poles. The reeling in occurs because the ends
of the spindle fibers are broken down bit by bit at each of the poles.
As the fibers become shorter, the chromatids they are pulling move
closer and closer to the poles.
As soon as the chromatids separate from each other they are
called chromosomes. When the chromosomes finally arrive, each
pole has one complete set of chromosomes.SECTION 3Mitosis and Cytokinesis 129
Analysis- Calculate the number of
cells that would be produced
in 1 hour.
2. Calculate the number of
cells that would be produced
in 1 day.
3.Critical ThinkingPredict-
ing PatternsIdentify factors
that might increase or decrease
the rate of mitosis.Calculating the Number of Cells
Resulting from Mitosis
Background
Scientists investigating cancer might need to know the
number of cells produced in a certain amount of time. In
the human body the rate of mitosis is about 25 million
(2.5 107 ) cells produced every second! You can calculate
the number of cells produced by mitosis in a given amount
of time.x + 6x - 7 - 0^2 <
8
493
0
5
2- Calculate the number of cells produced by mitosis in the given time. For example, to find
the number of cells produced in 3 minutes, determine how many seconds there are in 3 minutes (since
the rate is given in seconds).
3 minutes 180 seconds- Multiply the rate of mitosis by the time (in seconds) asked for in the problem
(180 seconds).
2.5 (^10) 180 seconds 4.5 109 cells (4,500,000,000 cells)
(^7) cells
second
60 seconds
1 minute
4B 6E