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
I. Content Background
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.
A. 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.
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.
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.
B. 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.
2. Metaphase
During Metaphase, the chromosomes line up along the middle of the cell and are attached to the spindle fibers by the centromeres.
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.
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.
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.
C. 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.
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.
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.
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.
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 II. mMisconceptions associated with this benchmark:
(found at http://www.biologylessons.sdsu.edu/classes/lab8/altern.html)
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
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
III. Sample Test Questions
1. The following list describes some of the events associated with normal cell division
IA. A Nuclear membrane forms around each of set of new of chromosomes
IIB. Separation of centromeres
IIIC. Replication of each chromosome
IVD. Movement of single-stranded chromosomes toward opposite ends of cell.
Which series of events is chronologically correct?
a). III, II, IV, ICBDA b). I, II, III, IVABCD c). CDBAIII, IV, II, I d). DCABIV, III, I, II
2. Which diagram correctly represents mitosis?
a. b. c. d.
3. The two cells below are undergoing cytokinesis. Which statement best describes these cells?
a. Division A could be in a maple tree and division B could be in a grasshopper.
b. Division A could be in a grasshopper and division B could be in a cat.
c. Both divisions could be in a human
d. 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.
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
6. in meiosis most closely resembles events of mitosis except that the cells
are ______.
a. interphase, diploid b. meiosis II, diploid
c. interphase, haploid d. meiosis II, haploid
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
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
(a)
(a)
(d)
(a)
(ba)
(b)
(d)
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
IV. 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 Mitosishttp://www.cellsalive.com/mitosis.htm
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 http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/main.html
“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 Tutorialhttp://www.biology.arizona.edu/cell_bio/tutorials/meiosis/main.html
“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. http://wise.berkeley.edu/welcome.phpWeb-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 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 plant-based 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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