1. Chapter 8
Cell Cycle - Mitosis

2. WHAT CELL REPRODUCTION ACCOMPLISHES
may result in the birth of new organisms
more commonly involves the production of new cells
When a cell undergoes reproduction, or cell division, two “daughter” cells are produced that are genetically identical
to each other
to the “parent” cell.
Cell Theory – Cells Come From Cells
Student Misconceptions and Concerns
1. Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling can be prevented if each gamete has only half the genetic material of the adult cells.
2. Some basic familiarity or faint memory of mitosis and meiosis might result in a lack of enthusiasm for mitosis and meiosis in some of your students. Consider beginning such lectures with important topics related to cellular reproduction. For example, cancer cells reproduce uncontrollably, stem cells have the capacity to regenerate lost or damaged tissues, and the study of embryonic stem cells holds great potential but is variously restricted and regulated.
3. As the authors note, biologists use the term daughter to indicate offspring and not gender. Students with little experience in this terminology can easily become confused.
Teaching Tips
1. The authors do not use the word clone in this chapter. You might wish to point out to your students that asexual reproduction produces clones.
2. Consider pointing out that asexual reproduction is common in prokaryotes and single-celled organisms.
3. You might want to get your students thinking by asking them why eggs and sperm are different. (This depends on the species, but within vertebrates, eggs and sperm are specialized for different tasks. Sperm are adapted to move to an egg, donate a nucleus, and activate development of the egg. Eggs contain a nucleus and most of the cytoplasm of the future zygote. Thus, eggs are typically larger, nonmotile, and full of cellular resources to sustain cell division and support growth.)
4. Virchow’s principle of “Every cell from a cell” (not specifically addressed in this chapter) is worth thinking through with your class. Students might expect that like automobiles, computers, and cell phones, cell parts are constructed de novo and cells are assembled. In our society, few nonliving products are generated from only existing products (try to think of such examples). For example, you do not need a painting to paint or a house to construct a house. Yet, this common expectation exists in biology. 2

3. WHAT CELL REPRODUCTION ACCOMPLISHES
Cell division plays important roles in the lives of organisms.
Cell division
replaces damaged or lost cells
permits growth
allows for reproduction
Student Misconceptions and Concerns
1. Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling can be prevented if each gamete has only half the genetic material of the adult cells.
2. Some basic familiarity or faint memory of mitosis and meiosis might result in a lack of enthusiasm for mitosis and meiosis in some of your students. Consider beginning such lectures with important topics related to cellular reproduction. For example, cancer cells reproduce uncontrollably, stem cells have the capacity to regenerate lost or damaged tissues, and the study of embryonic stem cells holds great potential but is variously restricted and regulated.
3. As the authors note, biologists use the term daughter to indicate offspring and not gender. Students with little experience in this terminology can easily become confused.
Teaching Tips
1. The authors do not use the word clone in this chapter. You might wish to point out to your students that asexual reproduction produces clones.
2. Consider pointing out that asexual reproduction is common in prokaryotes and single-celled organisms.
3. You might want to get your students thinking by asking them why eggs and sperm are different. (This depends on the species, but within vertebrates, eggs and sperm are specialized for different tasks. Sperm are adapted to move to an egg, donate a nucleus, and activate development of the egg. Eggs contain a nucleus and most of the cytoplasm of the future zygote. Thus, eggs are typically larger, nonmotile, and full of cellular resources to sustain cell division and support growth.)
4. Virchow’s principle of “Every cell from a cell” (not specifically addressed in this chapter) is worth thinking through with your class. Students might expect that like automobiles, computers, and cell phones, cell parts are constructed de novo and cells are assembled. In our society, few nonliving products are generated from only existing products (try to think of such examples). For example, you do not need a painting to paint or a house to construct a house. Yet, this common expectation exists in biology. 3

4. Eukaryotic Chromosomes
Before a cell divides, it duplicates all of its chromosomes through the process of replication, resulting in two copies called sister chromatids containing identical genes.
Two sister chromatids are joined together tightly at a narrow “waist” called the centromere.
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 4

6. Eukaryotic Chromosomes
When the cell divides, the sister chromatids of a duplicated chromosome separate from each other.
Once separated, each chromatid is
considered a full-fledged chromosome
identical to the original chromosome.
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 6

7. 7 Distribution via mitosis Duplication of all chromosomes Genetically
Figure 8.UN01
Distribution via
mitosis
Duplication
of all
chromosomes
Genetically
identical
daughter cells
Figure 8.UN01 Summary of Key Concepts: What Cell Reproduction Accomplishes 7

8. WHAT CELL REPRODUCTION ACCOMPLISHES
In asexual reproduction,
single-celled organisms reproduce by simple cell division in which the parent cell and daughter cells have identical DNA
there is no fertilization of an egg by a sperm.
Some multicellular organisms, such as sea stars, can grow new individuals from fragmented pieces.
Growing a new plant from a clipping is another example of asexual reproduction.
Producing more skin cells is yet another example of asexual reproduction.
Student Misconceptions and Concerns
1. Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling can be prevented if each gamete has only half the genetic material of the adult cells.
2. Some basic familiarity or faint memory of mitosis and meiosis might result in a lack of enthusiasm for mitosis and meiosis in some of your students. Consider beginning such lectures with important topics related to cellular reproduction. For example, cancer cells reproduce uncontrollably, stem cells have the capacity to regenerate lost or damaged tissues, and the study of embryonic stem cells holds great potential but is variously restricted and regulated.
3. As the authors note, biologists use the term daughter to indicate offspring and not gender. Students with little experience in this terminology can easily become confused.
Teaching Tips
1. The authors do not use the word clone in this chapter. You might wish to point out to your students that asexual reproduction produces clones.
2. Consider pointing out that asexual reproduction is common in prokaryotes and single-celled organisms.
3. You might want to get your students thinking by asking them why eggs and sperm are different. (This depends on the species, but within vertebrates, eggs and sperm are specialized for different tasks. Sperm are adapted to move to an egg, donate a nucleus, and activate development of the egg. Eggs contain a nucleus and most of the cytoplasm of the future zygote. Thus, eggs are typically larger, nonmotile, and full of cellular resources to sustain cell division and support growth.)
4. Virchow’s principle of “Every cell from a cell” (not specifically addressed in this chapter) is worth thinking through with your class. Students might expect that like automobiles, computers, and cell phones, cell parts are constructed de novo and cells are assembled. In our society, few nonliving products are generated from only existing products (try to think of such examples). For example, you do not need a painting to paint or a house to construct a house. Yet, this common expectation exists in biology. 8

9. WHAT CELL REPRODUCTION ACCOMPLISHES
Sexual reproduction requires fertilization of an egg by a sperm using a special type of cell division called meiosis.
Thus, sexually reproducing organisms use
meiosis for reproduction
mitosis for growth and maintenance.
Student Misconceptions and Concerns
1. Students might not immediately see the need for meiosis in sexual reproduction. Consider an example of what would happen over many generations if gametes were produced by mitosis. The resulting genetic doubling can be prevented if each gamete has only half the genetic material of the adult cells.
2. Some basic familiarity or faint memory of mitosis and meiosis might result in a lack of enthusiasm for mitosis and meiosis in some of your students. Consider beginning such lectures with important topics related to cellular reproduction. For example, cancer cells reproduce uncontrollably, stem cells have the capacity to regenerate lost or damaged tissues, and the study of embryonic stem cells holds great potential but is variously restricted and regulated.
3. As the authors note, biologists use the term daughter to indicate offspring and not gender. Students with little experience in this terminology can easily become confused.
Teaching Tips
1. The authors do not use the word clone in this chapter. You might wish to point out to your students that asexual reproduction produces clones.
2. Consider pointing out that asexual reproduction is common in prokaryotes and single-celled organisms.
3. You might want to get your students thinking by asking them why eggs and sperm are different. (This depends on the species, but within vertebrates, eggs and sperm are specialized for different tasks. Sperm are adapted to move to an egg, donate a nucleus, and activate development of the egg. Eggs contain a nucleus and most of the cytoplasm of the future zygote. Thus, eggs are typically larger, nonmotile, and full of cellular resources to sustain cell division and support growth.)
4. Virchow’s principle of “Every cell from a cell” (not specifically addressed in this chapter) is worth thinking through with your class. Students might expect that like automobiles, computers, and cell phones, cell parts are constructed de novo and cells are assembled. In our society, few nonliving products are generated from only existing products (try to think of such examples). For example, you do not need a painting to paint or a house to construct a house. Yet, this common expectation exists in biology. 9

10. Eukaryotic Chromosomes
Chromosomes are
made of chromatin, fibers composed of roughly equal amounts of DNA and protein molecules
not visible in a cell until cell division occurs.
Each eukaryotic chromosome contains one very long DNA molecule, typically bearing thousands of genes.
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 10

11. Figure 8.3 LM
Chromosomes
Figure 8.3 A plant cell just before division (colored by stains) 11

12. The DNA in a cell is packed into an elaborate, multilevel system of coiling and folding.
Histones are proteins used to package DNA in eukaryotes.
Nucleosomes consist of DNA wound around histone molecules.
DNA double helix
Histones
“Beads on a string”
TEM
Nucleosome
Tight helical fiber
Thick supercoil
Duplicated chromosomes
(sister chromatids)
TEM
Centromere
Figure 8.4 DNA packing in a eukaryotic chromosome 12

13. 13 DNA double helix Histones “Beads on a string” Nucleosome TEM
Figure 8.4 DNA packing in a eukaryotic chromosome (part 1) 13

14. 14 Species Number of chromosomes in body cells Indian muntjac deer
Figure 8.2
Species
Number of chromosomes in body cells
Indian muntjac deer 6
Koala 16
Opossum 22
Giraffe 30
Mouse 40
Human 46
Duck-billed platypus 54
Buffalo 60
Dog 78
Red viscacha rat
102
Figure 8.2 The number of chromosomes in the cells of selected mammals 14

15. The Cell Cycle
A cell cycle is the ordered sequence of events that extends
from the time a cell is first formed from a dividing parent cell to its own division into two cells.
The cell cycle consists of two distinct phases:
interphase
the mitotic phase.
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 15

16. DNA synthesis; chromosome duplication chromosome duplication
Figure 8.UN03
S phase
DNA synthesis; chromosome duplication
Interphase
Cell growth and
chromosome duplication G1 G2
Mitotic
(M) phase
Genetically
identical
“daughter”
cells
Cytokinesis
(division of
cytoplasm)
Mitosis
(division of
nucleus)
Figure 8.UN03 Summary of Key Concepts: The Cell Cycle 16

17. The Cell Cycle Most of a cell cycle is spent in interphase.
During interphase a cell
performs its normal functions
Replicates all of its DNA – sister chromatids
doubles everything in its cytoplasm
grows in size
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 17

18. The Cell Cycle - Interphase
Interphase can be broken down into 3 distinct phases
G1 phase – cells increase in size, make new proteins and organelles
S phase – chromosomes replicate, DNA synthesis
G2 phase – completion of organelle production
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 18

19. The Cell Cycle
The mitotic (M) phase includes two overlapping processes:
mitosis, in which the nucleus and its contents divide evenly into two daughter nuclei
cytokinesis, in which the cytoplasm is divided in two
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 19

20. Mitosis and Cytokinesis
During mitosis the mitotic spindle, a football-shaped structure of microtubules, guides the separation of two sets of sister chromatids.
Spindle microtubules grow from structures within the cytoplasm called centrosomes.
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 20

21. Mitosis and Cytokinesis
Mitosis consists of four distinct phases:
Prophase
Metaphase
Anaphase
Telophase
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 21

22. 22 Bioflix Animation: Mitosis Student Misconceptions and Concerns
© 2013 Pearson Education, Inc.
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 22

23. Mitosis and Cytokinesis
Prophase
Changes occur in nucleus and cytoplasm
Chromatin fibers coil in the nucleus into visible chromosomes
Each chromosome exists as 2 identical sister chromatids connected at the centromere
Microtubules start to grow from each centrosome and the centrosomes move away from each other
Nuclear envelope breaks into pieces
Spindle microtubules attach to the centromeres of the chromosomes and move them toward the center of the cell.
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 23

24. 24 INTERPHASE PROPHASE Centrosomes (with centriole pairs)
Figure 8.7a
INTERPHASE
PROPHASE
Centrosomes
(with centriole pairs)
Early mitotic
spindle
Fragments of
nuclear envelope
Centrosome
Chromatin
Centromere
Nuclear
envelope
Plasma
membrane
Chromosome
(two sister chromatids)
Spindle microtubules
Figure 8.7 Cell reproduction: A dance of the chromosomes (part 1) 24

25. Mitosis and Cytokinesis
Metaphase
Mitotic spindle is fully formed
Chromosomes line up between the two poles of the spindle (between the two centrosomes)
Microtubules attached to the centromeres play tug of war keeping the chromosomes in the middle of the cell.
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 25

26. Mitosis and Cytokinesis
Anaphase
Sister chromatids separate and move toward opposite poles of the cell as the spindle microtubules shorten
Microtubules not attached to chromosomes get longer and elongate the cell.
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 26

27. 27 METAPHASE ANAPHASE Nuclear Cleavage envelope furrow forming Spindle
Figure 8.7b
METAPHASE
ANAPHASE
TELOPHASE AND CYTOKINESIS
Nuclear
envelope
forming
Cleavage
furrow
Spindle
Daughter
chromosomes
Figure 8.7 Cell reproduction: A dance of the chromosomes (part 2) 27

28. Mitosis and Cytokinesis
Telophase and Cytokinesis
Chromosomes have reached the opposite ends of the cell
Nuclear envelope forms
Chromosomes uncoil
Spindle dissapears
Cytoplasm divides
Cell pinches in two (cleavage furrow in animals)
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 28

29. Mitosis and Cytokinesis
Cytokinesis usually
begins during telophase,
divides the cytoplasm
is different in plant and animal cells.
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 29

30. Mitosis and Cytokinesis
In animal cells, cytokinesis
is known as cleavage
begins with the appearance of a cleavage furrow, an indentation at the equator of the cell.
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 30

31. 31 Cleavage furrow Contracting ring of microfilaments Daughter cells
Figure 8.8aa
Cleavage furrow
Contracting ring of
microfilaments
Daughter cells
Figure 8.8 Cytokinesis in animal cells (part 1a) 31

32. Mitosis and Cytokinesis
In plant cells, cytokinesis begins when vesicles containing cell wall material collect at the middle of the cell and then fuse, forming a membranous disk called the cell plate.
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 32

33. 33 Cell plate forming Wall of parent cell Daughter nucleus LM
Figure 8.8ba
Cell plate
forming
Wall of parent cell
Daughter nucleus LM
Figure 8.8 Cytokinesis in plant cells (part 2a) 33

34. Cancer Cells: Growing Out of Control
Normal plant and animal cells have a cell cycle control system that consists of specialized proteins called cyclins, which send “stop” and “go-ahead” signals at certain key points during the cell cycle.
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 34

35. What Is Cancer? Cancer is a disease of the cell cycle.
Cancer cells do not respond normally to the cell cycle control system.
Cancer begins when a normal cell undergoes transformation in which a mutation in the genetic code (DNA) occurs. This mutation interferes with the production of proteins vital in the cell cycle control system.
Cancer cells can form tumors, abnormally growing masses of body cells.
If the abnormal cells remain at the original site, the lump is called a benign tumor.
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 35

36. A person with a malignant tumor is said to have cancer.
What Is Cancer?
The spread of cancer cells beyond their original site of origin is metastasis.
Malignant tumors can
spread to other parts of the body and
interrupt normal body functions.
A person with a malignant tumor is said to have cancer.
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 36

37. 37 A tumor grows from a single cancer cell. Cancer cells invade
Figure 8.9
Lymph
vessels
Tumor
Blood
vessel
Glandular
tissue
A tumor grows
from a single
cancer cell.
Cancer cells invade
neighboring tissue.
Metastasis: Cancer
cells spread through
lymph and blood
vessels to other parts
of the body.
Figure 8.9 Growth and metastasis of a malignant tumor of the breast 37

38. Cancer treatment can involve
radiation therapy, which damages DNA and disrupts cell division, and
chemotherapy, the use of drugs to disrupt cell division.
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 38

39. Cancer Prevention and Survival
Certain behaviors can decrease the risk of cancer:
not smoking
exercising adequately
avoiding exposure to the sun
eating a high-fiber, low-fat diet
performing self-exams
regularly visiting a doctor to identify tumors early
Student Misconceptions and Concerns
1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic in this chapter when discussing DNA replication.
2. Students are often confused by photographs of chromosomes. A chromosome is often described as a single strand, yet photographs typically show duplicated chromosomes appearing like the letter “X.” It remains unclear to many students why (a) chromosome structure is typically different between interphase G1 and stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes replicate.
3. Students do not typically know that all cancers are genetically based. Consider making this clear early in your discussions. Challenge your students to explain how certain viruses can lead to cancer (such as HPV, human papillomavirus associated with genital warts and cervical cancer).
Teaching Tips
1. Mitochondrial DNA is widely used to analyze evolutionary relationships. Students might be challenged to search the Internet for examples of its use in tracing human evolutionary history.
2. Consider this additional analogy between histones and DNA. DNA is like a very long piece of thread wrapped around a series of spools (histones). The DNA wraps one spool, then extends to another spool, repeating this many hundreds of times—all with one continuous strand of thread.
3. The concepts of DNA replication and sister chromatids are often obstacles for many students. If you can find twist ties or other bendable wire, you can demonstrate or have students model the difference between (a) a chromosome before DNA replication and (b) sister chromatids after DNA replication. One piece of wire will represent a chromosome before replication. Two twist ties twisted about each other can represent sister chromatids (even though this is not the actual physical relationship between sister chromatids). In the model, we have doubled the DNA, but the molecules remain attached. (You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes.)
4. In G1, the chromosomes have not replicated. But by G2, chromosomes consist of sister chromatids. If you have created a demonstration of sister chromatids, relate DNA replication and sister chromatids to the cell cycle.
5. The cell cycle control system is somewhat like the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, the components of the control system of a cell cycle are not located in one place, like a washing machine.
6. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPMAT. The first letters of interphase, prophase, metaphase, anaphase, and telophase are represented in this made-up word.
7. Many students think of mitosis and cytokinesis as one process. In some situations, mitosis occurs without subsequent cytokinesis. Challenge your students to predict the outcome of mitosis without cytokinesis (multinuclear cells called a syncytium). One place this occurs is in human development during the formation of the placenta.
8. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this analogy. Have your students think of a person tightening the drawstring of sweatpants so tight that they pinch themselves in two, or perhaps nearly so! The analogy is especially good because the drawstring is just beneath the surface of the sweatpants, and the microfilaments are just beneath the surface of the cell’s plasma membrane.
9. Chemotherapy has some disastrous side effects. The drugs used to fight cancer attack rapidly dividing cells. Unfortunately for men, the cells that make sperm are also rapidly dividing. In some circumstances, chemotherapy can leave a man infertile (unable to produce viable sperm) but still able to produce an erection.
10.Many other approaches (such as cancer vaccines) are under consideration to fight cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. 39

40. THE END