Performance Benchmark L.12.A.3
Students know all body cells in an organism develop from a single cell and contain essentially
identical genetic instructions. E/S
One idea from the Cell Theory is that all cells must arise from pre-existing cells through a
process of cellular division (mitosis or meiosis). In a one-celled organism, a mitotic cell division
results in the creation of another individual of that species with identical DNA. In multicellular
organisms, mitotic cell division results in new body cells for growth and repair. Some rare
multicellular organisms reproduce asexually through mitosis to produce a complete, independent
offspring with identical DNA. However, most multicellular organisms reproduce sexually which
involves the production of cells with half the compliment of DNA (a haploid cell) that recombine
with another haploid cell, usually from another organism, to produce a genetically unique cell
with a full compliment of DNA that can now grow and develop into a new individual.
Cell Cycle
All cells progress through the cell cycle at some part of their lives. The cell cycle starts right
after the successful division of two daughter cells. Cells that cease cell division, like nerve cells,
are not considered to be in the cell cycle. The cell cycle consists of four distinct stages, G1, S,
G2 and M (Figure 1). G1, S, G2 are collectively called Interphase. Interphase is the period
between cell division where the cell will grow, duplicate its DNA, and fulfill the role of the cell.
The time that a cell remains in Interphase depends on the role of the cell. For example, human
skin cells divide about once a day. Therefore, the cells will remain in Interphase approximately
22 hours. Conversely, a liver cell may go years without dividing.
Figure 1. The cell cycle.
http://www.biology.arizona.edu/Cell_bio/
tutorials/cell_cycle/cells2.html
Figure 2. The cell in Interphase.
http://staff.jccc.net/pdecell/celldivision/m
itosis1.html
The G1 (Gap 1) phase is the first part of Interphase. Most of the cell’s growth takes place in this
phase. The cell will increase in size and synthesize new organelles. A cell may progress
quickly to the S-phase or remain in the G1 phase near indefinitely.
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The S (synthesis) phase follows the G1. Chromosomes are replicated in this phase. At the
beginning of the S phase, each chromosome consists of a single double-helix strand of DNA,
called a chromatid. At the end of the S phase, a chromosome consists of two sister chromatids.
Lastly, the cell enters the G2 (Gap 2) phase of Interphase. The cell will make final preparations
for mitosis. This phase can be seen as a safety check point, where the DNA can be checked for
errors.
Mitosis
After Interphase, the cell is ready to divide. Mitosis is divided into 4 major phases: Prophase,
Metaphase, Anaphase, and Telophase.
1. Prophase
Prophase is the first phase of mitosis. Several processes take place during this phase. First, the
chromatic material condenses into visible chromosomes and the sister chromatids are joined
together at the centromere. The nuclear membrane disappears. In the cytoplasm, a pair of
centrioles begins to separate and migrate to opposite poles of the cell. A network of
microtubules begins to form between the centrioles called the spindle. The spindle fibers will be
instrumental in guiding the chromatids to opposite ends of the cell.
a.
Chromatin
b.
Figure 3. This figure shows the relationship
between DNA, chromatin, chromatids, and
chromosomes.
Figure 4. a.) The photograph shows two cells in Prophase.
(http://www.bio.txstate.edu/)
b.)The diagram shows the important steps in Prophase.
(http://staff.jccc.net/pdecell/celldivision/mitosis1.html)
2. Metaphase
During Metaphase, the chromosomes line up along the middle of the cell and are attached to the
spindle fibers by the centromeres.
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a.
b.
Figure 5. a.) The diagram shows the important steps in Metaphase.
(http://staff.jccc.net/pdecell/celldivision/mitosis1.html) b.) The photograph shows a
cell in Metaphase. (http://www.bio.txstate.edu/)
3. Anaphase
Anaphase begins when the centromeres holding the sister chromatids together split and the
spindle fibers shorten, pulling one chromatid toward each end of the cell.
a.
b.
Figure 6. a.) The photograph shows a cell in Anaphase.
(http://www.bio.txstate.edu/)
b.)The diagram shows the important steps in Anaphase.
(http://staff.jccc.net/pdecell/celldivision/mitosis1.html)
4. Telophase
Telophase is essentially the reverse of Prophase. The spindle fibers disappear, the chromosomes
unravel back to chromatin, and two new nuclear membranes form.
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b.
Figure 7. a.)The diagram shows the important steps in Telophase. http://staff.jccc.net/pdecell/celldivision/mitosis1.html)
b.) The photograph shows a cell in Telophase. (http://www.bio.txstate.edu/
5. Cytokinesis
Occurring concurrently with Telophase is cytokinesis. Cytokinesis is the division of the
cytoplasm. Cytokinesis is different in animal and plant cells. In plant cells, a cell plate forms a
new cell wall divider between the two nuclei and grows outward until it fully separates the two
daughter cells. In animal cells, the cell membrane is pulled inward by a ring of filaments. This
make the cell appear to “pinch in” from the sides. This process continues until two new daughter
cells result.
Figure 9. Cytokinesis in a plant cell.
http://www.bio.txstate.edu
Figure 8. A comparison of cytokinesis in plant and animal
cells. From (http://www.trentu.ca/biology/101/4.html)
Figure 10. Cytokinesis in a animal cell.
http://trc.ucdavis.edu/biosci10v
/bis10v/week3/06cytokinesis.html
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Meiosis
Meiosis is a second type of cellular division. In meiosis, the result is 4 cells with half the
complement of DNA instead of two identical cells. Therefore, the purpose of meiosis is to
convert a diploid cell to a haploid gamete that would be involved in sexual reproduction to
increase diversity in the offspring. The cells going through meiosis split twice, but the
chromosome material is replicated only once. These two divisions are denoted as Meiosis I and
Meiosis II.
1. Meiosis I
In Meiosis I, the number of chromosome sets is reduced by half (2n to n). The separation of
each homologous chromosome pair is a random event which results in gametes containing a
random combination of chromosomes. The phases of meiosis I are Prophase I, Metaphase I, and
Anaphase I.
Prophase I – The chromosomes enter Prophase I already
replicated forming a pair of sister chromatids connected at their
centromeres. The homologous chromosomes do not move
independently as they did in mitosis. The homologous
chromosomes pair up forming a tetrad (maternal and paternal
homologous chromosomes each made up of two sister
chromatids). Crossing over (or transfer) of genetic material may
occur between homologous chromosomes, thereby increasing
genetic variability. Other events of Prophase I are very much like
mitosis’ Prophase. The chromatin material coils up into
chromosomes becoming visible, the nuclear membrane
disappears, spindle fibers form, and centromeres separate.
Tetrad
Figure 11. Prophase I
Metaphase I – Just as in mitosis, the chromosomes line up on the middle of the cell. However, in
meiosis the chromosomes line up with their homologous partner and attach themselves to the
spindle fibers.
Figure 12. Anaphase I.
http://www.biologycorner.com/w
orksheets/meiosis.html
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Anaphase I – Again Anaphase I looks very similar to Anaphase in mitosis. The chromosomes
separate and travel toward the poles. The difference is that it is not the sister chromatids that are
separating but the homologous chromosomes that separate resulting in half the number of
chromosomes at each pole but each chromosome is double stranded. The separation of
homologous chromosomes is called disjunction.
Telophase I – Telophase I ends with the first meiotic division and cytokinesis. Some cells
deconsolidate the chromosomes and form a simple nuclear membrane others do not and proceed
directly into Prophase II. The result of Meiosis I is two haploid daughter cells.
Figure 13. An overview of Meiosis I ending with
Telophase I.
http://homepages.ius.edu/GKIRCHNE/Mitosis.htm
2. Meiosis II
Meiosis II is simply the mitotic division of the two haploid cells resulting from meiosis I.
Prophase II – A new set of spindle fibers form.
Metaphase II – The chromosomes line up on the middle of each cell and attach to the
spindle fibers.
Anaphase II – The sister chromatids separate and travel towards the pole.
Telophase II and cytokinesis – the chromatids unravel into chromatin, nuclear
membranes reform and the cell physically divided into two.
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Figure 14. An overview of Meiosis
http://www.ksu.edu/biology/pob/genetics/defi
n.htm
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Performance Benchmark L.12.A.3
Students know all body cells in an organism develop from a single cell and contain essentially
identical genetic instructions. E/S
Common misconceptions associated with this benchmark:
1. Students see the familiar X-shaped structure seen in a light microscope is a “basic”
single (unreplicated) chromosome.
The X-shaped structures seen in a light microscope are condensed, replicated chromosomes
containing two identical DNA double helices.
2. A chromosome is a chromosome - there is little differentiation between replicated and
unreplicated states.
In late anaphase and G1 of interphase, a chromosome is unreplicated and consists of a single
DNA double helix.
3. The X-shaped chromosomes are homologous chromosome pairs.
The X-shaped structures are unpaired, replicated chromosomes. Pairing of homologous
chromosomes does not occur during mitosis.
4. Unreplicated chromosomes seen in anaphase are unpaired chromosomes.
These are simply unreplicated chromosomes, and this is the only time they are condensed and
therefore visible.
5. The two non-identical homologous chromosomes in a parent cell go to separate daughter
cells.
In anaphase, the identical chromatids of a replicated chromosome go to separate daughter cells.
Each daughter cell gets a complete copy of the chromosomes in the parent cell.
For more information on common misconceptions associated with this benchmark, go to
http://www.biologylessons.sdsu.edu/classes/lab8/altern.html
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Performance Benchmark L.12.A.3
Students know all body cells in an organism develop from a single cell and contain essentially
identical genetic instructions. E/S
Sample Test Questions
1. The following list describes some of the events associated with normal cell division
I A Nuclear membrane forms around each of set of new of chromosomes
II Separation of centromeres
III Replication of each chromosome
IV Movement of single-stranded chromosomes toward opposite ends of cell.
Which series of events is chronologically correct?
a) III, II, IV, I
b) I, II, III, IV
c) III, IV, II, I
d) IV, III, I, II
2. Which diagram correctly represents mitosis?
n
2n
a.
b.
2n
2n
2n
c.
2n
n
d.
2n
n
2n
3. The two cells below are undergoing cytokinesis. Which statement best describes these cells?
A
a.
b.
c.
d.
B
Division A could be in a maple tree and division B could be in a grasshopper.
Division A could be in a grasshopper and division B could be in a cat.
Both divisions could be in a human
Division A could be in a grasshopper and division B could be in a maple tree.
4. Normal mitotic division results in
a. Two daughter cells with the same number and kinds of chromosomes as the parent
cell.
b. Four daughter cells with half the number and kinds of chromosomes as the parent cell.
c. Two daughter cells with half the number and kinds of chromosomes as the parent cell.
d. Four daughter cells with the same number and kinds of chromosomes as the parent
cell.
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5. If the diploid number of chromosomes is 20, what would be the chromosome count in the egg
cells of this species?
a. 5
b. 10
c. 20
d. 40
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Performance Benchmark L.12.A.3
Students know all body cells in an organism develop from a single cell and contain essentially
identical genetic instructions. E/S
Answers to Sample Test Questions
1. (a)
2. (a)
3. (d)
4. (a)
5. (b)
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Performance Benchmark L.12.A.3
Students know all body cells in an organism develop from a single cell and contain essentially
identical genetic instructions. E/S
Intervention Strategies and Resources
The following is a list of intervention strategies and resources that will facilitate student
understanding of this benchmark.
1. Cells Alive – Animal Cell Mitosis
This website has many well done animations about mitosis, meiosis, and cell
cycle. It is a good resource for visual learners. It also has many links for students
under “homework links”.
To access this simulation, go to
http://www.cellsalive.com/mitosis.htm
2. The Biology Project - The Cell Cycle & Mitosis Tutorial
“This exercise is designed to introduce you to the events that occur in the cell
cycle and the process of mitosis that divides the duplicated genetic material
creating two identical daughter cells.” This website activity has several pages of
reading about the cell cycle and the phases of mitosis. It even has another
animation of mitosis. It ends with a 11 question self quiz about what was read.
Once done with the quiz, choose the “Online Onion Root Tips” activity to
conduct a virtual lab to “Determining time spent in different phases of the cell
cycle”. Students will be presented with 36 pictures of cells and have to identify
the phase of each and then calculate what percentage of time spent in each phase
of the cell cycle.
To access this exercise, go to
http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/main.html
3. The Biology Project – Meiosis Tutorial
“This exercise is designed to help you understand the events that occur in process
of meiosis, which takes place to produce our gametes”. This is the partner site to
the one above on mitosis.
To access this exercise, go to
http://www.biology.arizona.edu/cell_bio/tutorials/meiosis/main.html
4. Web-based Inquiry - Using real world evidence
You will have to open an account for this project as will your students. It is also
recommended that the teacher walk through each project before presenting to
students. “WISE (Web-Based Inquiry Science Environment) is a simple yet
powerful learning environment where students examine real world evidence and
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analyze current scientific controversies. Our curriculum projects are designed to
meet standards and complement your current science curriculum, and your grade
5-12 students will find them exciting and engaging. A web browser is all they
need to take notes, discuss theories, and organize their arguments... they can even
work from home! Our Teacher Area lets you explore new projects and grade your
students' work on the Web. Best of all, everything in WISE is completely free.”
There is a WISE project entitled TELS: Mitosis and Meiosis that examines the
“two processes that cells use when they reproduce-mitosis and meiosis. They will
learn when and where these kinds of cell reproduction happen in their body, and
also what happens when something goes wrong.” There is another WISE project
entitled Mitosis & Cell Processes that helps “students understand the stages of
mitosis and associated cell structures within the context of learning about cancer.
The students actively explore mitosis by investigating three hypothetical plantbased medicines. Each plant interferes with mitosis in a different way. The
students will recommend a plant for further research based on what they discover
through their inquiry.”
To access this project, go to
http://wise.berkeley.edu/welcome.php
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