Chapter 8 Connections between cell division and reproduction

Chapter 8 Connections between cell division and reproduction

8.1 Like begets like, more or less
Living organisms reproduce by two methods Asexual reproduction Offspring are identical to the original cell or organism Involves inheritance of all genes from one parent Sexual reproduction Offspring are similar to parents, but show variations in traits Involves inheritance of unique sets of genes from two parents Most eukaryotic organisms are capable of both asexual and sexual reproduction. Students may be surprised to learn that asexual reproduction plays a major role in the life cycles of many organisms. For example, the unicellular algae Chlamydomonas generates an increased population by asexual reproduction when conditions are favorable for cell division. In unfavorable conditions, the organism undergoes sexual reproduction. This has the advantage of producing a new combination of genes and traits that could be advantageous for survival under new environmental conditions. Student Misconceptions and Concerns 1. As the authors note in Module 8.1, biologists use the term daughter to indicate offspring and not gender. Students with little experience in this terminology can easily become confused. 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 is variously restricted and regulated. Teaching Tips 1. Sometimes the most basic questions can challenge students and get them focused on the subject at hand. Consider asking your students why we expect that dogs will produce dogs, cats will produce more cats, and chickens will only produce chickens. Why does like produce like? Copyright © 2009 Pearson Education, Inc.

8.2 Cells arise only from preexisting cells
Cell division perpetuates life Cell division is the reproduction of cells Virchow’s principle states “Every cell from a cell” Student Misconceptions and Concerns 1. 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 is variously restricted and regulated. Teaching Tips 1. Virchow’s principle of “every cell from a cell” is worth thinking through with your class. Students might expect that, like automobiles, computers, and cell phones, parts are constructed and cells are assembled. In our society, few nonliving products are generated only from 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 is a common expectation in biology. 2. Students who think through Virchow’s principle might ask how the first cells formed. They might wonder further whether the same environments that produced these cells are still in existence. The conditions on Earth when life first formed were very different from those we know today. Chapter 15 addresses the origin and early evolution of life on Earth. Copyright © 2009 Pearson Education, Inc.

8.2 Cells arise only from preexisting cells
Roles of cell division Asexual reproduction Reproduction of an entire single-celled organism Growth of a multicellular organism Growth from a fertilized egg into an adult Repair and replacement of cells in an adult Sexual reproduction Sperm and egg production Copyright © 2009 Pearson Education, Inc.

8.3 Prokaryotes reproduce by binary fission
Binary fission means “dividing in half” Occurs in prokaryotic cells Two identical cells arise from one cell Steps in the process A single circular chromosome duplicates, and the copies begin to separate from each other The cell elongates, and the chromosomal copies separate further The plasma membrane grows inward at the midpoint to divide the cells The process of binary fission is very rapid. E. coli cells divide every 20 minutes under optimal environmental conditions. The antibiotic penicillin inhibits the growth of the bacterial cell wall. Cells can duplicate their internal contents, including the chromosome, but will burst when they become too large for the existing cell wall. Student Misconceptions and Concerns 1. 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 is variously restricted and regulated. Teaching Tips Consider contrasting the timing of DNA replication and cytokinesis in prokaryotes and eukaryotes. In prokaryotes, addressed in Module 8.3, these processes are over-lapping. However, as revealed in the next few modules, these events are separate in eukaryotes. Copyright © 2009 Pearson Education, Inc.

Division into two daughter cells
Plasma membrane Prokaryotic chromosome Cell wall Duplication of chromosome and separation of copies 1 Continued elongation of the cell and movement of copies 2 Figure 8.3A Binary fission of a prokaryotic cell. This figure shows the steps in binary fission. 3 Division into two daughter cells

Prokaryotic chromosomes
Prokaryotic chromosomes Figure 8.3B Electron micrograph of a dividing bacterium. The chromosomes of each of the two identical cells are visible in this electron micrograph.

8.4 The large, complex chromosomes of eukaryotes duplicate with each cell division
Eukaryotic chromosomes are composed of chromatin Chromatin = DNA + proteins To prepare for division, the chromatin becomes highly compact, and the chromosomes are visible with a microscope Early in the division process, chromosomes duplicate Each chromosome appears as two sister chromatids, containing identical DNA molecules Sister chromatids are joined at the centromere, a narrow region Chromatin is compacted about 100,000 fold to produce the interphase/metaphase chromosome. If all the DNA in the human chromosomes were aligned, it would stretch for one meter. All of this DNA is condensed to fit into a nucleus that can only be seen with the aid of a microscope. The centromere has a unique DNA sequence involving repeated stretches of nucleotides. In biotechnological applications, artificial chromosomes can be produced that have a centromeric sequence. This chromosome will be properly distributed during cell division because the spindle fibers attach to the artificial centromeric sequence. Student Misconceptions and Concerns 1. Students often seem confused by the difference between a DNA molecule and a chromosome. This is especially problematic when discussing DNA replication. 2. Students are often confused by photographs of chromosomes. Such photographs, such as Figure 8.4B, typically show duplicated chromosomes during some aspect of cell division. It remains unclear to many why (a) chromosome structure is typically different between interphase G1 and the stages of division and (b) why chromosomes are not photographed during interphase (the stage in which chromosomes are typically first discussed) before the chromosomes duplicate. Teaching Tips 1. Figure 8.4C is an important point of reference for some basic terminology. Consider referring to it as you distinguish between a DNA molecule and a chromosome, unreplicated and replicated chromosomes, and the nature of sister chromatids. Copyright © 2009 Pearson Education, Inc.

Sister chromatids Centromere
Sister chromatids Centromere Figure 8.4B Electron micrograph of a duplicated chromosome. This electron micrograph provides a view of sister chromatids.

Chromosome distribution to daughter cells
Chromosome duplication Sister chromatids Centromere Figure 8.4C Chromosome duplication and distribution. The term chromatid is used to describe duplicates that are connected at the centromere. This diagram emphasizes that the structures are called chromosomes when separated. This leads to a brief time when a cell has double the number of chromosomes, as in anaphase and telophase of mitosis, prior to cytokinesis. Chromosome distribution to daughter cells

8.5 The cell cycle multiplies cells
The cell cycle is an ordered sequence of events for cell division It consists of two stages Interphase: duplication of cell contents G1—growth, increase in cytoplasm S—duplication of chromosomes G2—growth, preparation for division Mitotic phase: division Mitosis—division of the nucleus Cytokinesis—division of cytoplasm Differences in the length of the cell cycle can be instructive. Yeast cells have a 2-hour life cycle, while human cells in culture take about 24 hours to divide. Mitosis and cytokinesis represent a shorter section of the cycle, lasting one hour for cultured human cells. Teaching Tips 1.The authors note in Module 8.5 that each of your students consists of about 100 trillion cells. It is likely that this number is beyond comprehension for most of your students. Consider sharing several simple examples of the enormity of that number to try to make it more meaningful. For example, the U.S. population in 2008 is about 310 million people. To give every one of those people about $323,000, we will need a total of $100 trillion. Here is another example. If we give you $31,688 every second of your life, and you lived for 100 years, you would receive $100 trillion dollars. 2.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 (1) a chromosome before DNA replication and (2) 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. We have doubled the DNA, but the molecules remain attached (although not attached in the same way as the wire). You might also want to point out that when sister chromatids are separated, they are considered separate chromosomes. 3. In G1, the chromosomes have not duplicated. 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. Copyright © 2009 Pearson Education, Inc.

INTERPHASE S (DNA synthesis) G1 G2 MITOTIC
INTERPHASE S (DNA synthesis) G1 G2 Cytokinesis Mitosis Figure 8.5 The eukaryotic cell cycle. MITOTIC PHASE (M)

8.6 Cell division is a continuum of dynamic changes
Mitosis progresses through a series of stages Prophase Prometaphase Metaphase Anaphase Telophase Cytokinesis often overlaps telophase Teaching Tips 1. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT: the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase are represented in this acronym. 2. The authors note that animals, but not plants, have a pair of centrioles in their centrosomes. They add that the role of centrioles in cell division is a mystery. Students might not appreciate all that remains to be explained in biology. Sharing the existence of such mysteries with them promotes critical thinking skills and helps them imagine a place for themselves in future research. Copyright © 2009 Pearson Education, Inc.

A mitotic spindle is required to divide the chromosomes The mitotic spindle is composed of microtubules It is produced by centrosomes, structures in the cytoplasm that Organize microtubule arrangement Contain a pair of centrioles in animal cells The role of centrioles in cell division is unclear Centrioles give rise to basal bodies that are the foundations for cilia and flagella. They are found in animal cells but also in plants such as mosses and ferns that have swimming sperm. They are not found in flowering plants, showing that centrioles are not essential for spindle formation. There is other evidence, however, that suggests centrioles may influence progression through alternative stages in the cell cycle, including entry into the S phase and completion of cytokinesis. (Reviewed in A. W. Murray, 2001, “Centrioles at the Checkpoint,” Science, 291:1499–1501.) For the BioFlix Animation Mitosis, go to Animation and Video Files. Teaching Tips 1. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT: the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase are represented in this acronym. 2. The authors note that animals, but not plants, have a pair of centrioles in their centrosomes. They add that the role of centrioles in cell division is a mystery. Students might not appreciate all that remains to be explained in biology. Sharing the existence of such mysteries with them promotes critical thinking skills and helps them imagine a place for themselves in future research. Video: Animal Mitosis Video: Sea Urchin (time lapse) Copyright © 2009 Pearson Education, Inc.

INTERPHASE PROPHASE PROMETAPHASE
INTERPHASE PROPHASE PROMETAPHASE Centrosomes (with centriole pairs) Chromatin Early mitotic spindle Centrosome Fragments of nuclear envelope Kinetochore Figure 8.6 The stages of cell division. Centromere Nuclear envelope Plasma membrane Spindle microtubules Chromosome, consisting of two sister chromatids Nucleolus

Interphase In the cytoplasm Cytoplasmic contents double Two centrosomes form In the nucleus Chromosomes duplicate during the S phase Nucleoli, sites of ribosome assembly, are visible Teaching Tips 1. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT: the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase are represented in this acronym. 2. The authors note that animals, but not plants, have a pair of centrioles in their centrosomes. They add that the role of centrioles in cell division is a mystery. Students might not appreciate all that remains to be explained in biology. Sharing the existence of such mysteries with them promotes critical thinking skills and helps them imagine a place for themselves in future research. Copyright © 2009 Pearson Education, Inc.

Applying Your Knowledge Human cells have 46 chromosomes. By the end of interphase How many chromosomes are present in one cell? How many chromatids are present in one cell? Applying Your Knowledge Human cells have 46 chromosomes. By the end of interphase, How many chromosomes are present in one cell? 46 How many chromatids are present in one cell? 92 (Each chromosome has been duplicated and consists of a pair of chromatids joined at the centromere.) Teaching Tips 1. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT: the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase are represented in this acronym. 2. The authors note that animals, but not plants, have a pair of centrioles in their centrosomes. They add that the role of centrioles in cell division is a mystery. Students might not appreciate all that remains to be explained in biology. Sharing the existence of such mysteries with them promotes critical thinking skills and helps them imagine a place for themselves in future research. Copyright © 2009 Pearson Education, Inc.

Prophase In the cytoplasm Microtubules begin to emerge from centrosomes, forming the spindle In the nucleus Chromosomes coil and become compact Nucleoli disappear Teaching Tips 1. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT: the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase are represented in this acronym. 2. The authors note that animals, but not plants, have a pair of centrioles in their centrosomes. They add that the role of centrioles in cell division is a mystery. Students might not appreciate all that remains to be explained in biology. Sharing the existence of such mysteries with them promotes critical thinking skills and helps them imagine a place for themselves in future research. Copyright © 2009 Pearson Education, Inc.

Prometaphase Spindle microtubules reach chromosomes, where they Attach at kinetochores on the centromeres of sister chromatids Move chromosomes to the center of the cell through associated protein “motors” Other microtubules meet those from the opposite poles The nuclear envelope disappears Teaching Tips 1. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT: the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase are represented in this acronym. 2. The authors note that animals, but not plants, have a pair of centrioles in their centrosomes. They add that the role of centrioles in cell division is a mystery. Students might not appreciate all that remains to be explained in biology. Sharing the existence of such mysteries with them promotes critical thinking skills and helps them imagine a place for themselves in future research. Copyright © 2009 Pearson Education, Inc.

TELOPHASE AND CYTOKINESIS
METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Nucleolus forming Metaphase plate Cleavage furrow Figure 8.6 The stages of cell division. Nuclear envelope forming Daughter chromosomes Spindle

Metaphase Spindle is fully formed Chromosomes align at the cell equator Kinetochores of sister chromatids are facing the opposite poles of the spindle Applying Your Knowledge By the end of metaphase How many chromosomes are present in one human cell? How many chromatids are present in one human cell? Applying Your Knowledge By the end of metaphase, How many chromosomes are present in one human cell? 46 How many chromatids are present in one human cell? 92 Teaching Tips 1. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT: the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase are represented in this acronym. 2. The authors note that animals, but not plants, have a pair of centrioles in their centrosomes. They add that the role of centrioles in cell division is a mystery. Students might not appreciate all that remains to be explained in biology. Sharing the existence of such mysteries with them promotes critical thinking skills and helps them imagine a place for themselves in future research. Copyright © 2009 Pearson Education, Inc.

Anaphase Sister chromatids separate at the centromeres Daughter chromosomes are moved to opposite poles of the cell Motor proteins move the chromosomes along the spindle microtubules Kinetochore microtubules shorten The cell elongates due to lengthening of nonkinetochore microtubules Applying Your Knowledge By the end of anaphase How many chromosomes are present in one human cell? How many chromatids are present in one human cell? Applying Your Knowledge By the end of anaphase, How many chromosomes are present in one cell? 92 (Once the sister chromatids separate, they are considered to be individual chromosomes.) How many chromatids are present in one cell? 0 Teaching Tips 1. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT: the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase are represented in this acronym. 2. The authors note that animals, but not plants, have a pair of centrioles in their centrosomes. They add that the role of centrioles in cell division is a mystery. Students might not appreciate all that remains to be explained in biology. Sharing the existence of such mysteries with them promotes critical thinking skills and helps them imagine a place for themselves in future research. Copyright © 2009 Pearson Education, Inc.

Telophase The cell continues to elongate The nuclear envelope forms around chromosomes at each pole, establishing daughter nuclei Chromatin uncoils Nucleoli reappear The spindle disappears Applying Your Knowledge By the end of telophase How many chromosomes are present in one nucleus within the human cell? Are the nuclei identical or different? Applying Your Knowledge By the end of telophase, How many chromosomes are present in one nucleus within the human cell? 46 Are the nuclei identical or different? Identical Teaching Tips 1. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT: the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase are represented in this acronym. 2. The authors note that animals, but not plants, have a pair of centrioles in their centrosomes. They add that the role of centrioles in cell division is a mystery. Students might not appreciate all that remains to be explained in biology. Sharing the existence of such mysteries with them promotes critical thinking skills and helps them imagine a place for themselves in future research. Copyright © 2009 Pearson Education, Inc.

Cytokinesis Cytoplasm is divided into separate cells Applying Your Knowledge By the end of cytokinesis How many chromosomes are present in one human cell? How many chromatids are present in one human cell? Applying Your Knowledge By the end of cytokinesis, How many chromosomes are present in one human cell? 46 How many chromatids are present in one human cell? 0 (Chromatids will not be present until after the next S phase.) Teaching Tips 1. Students might keep better track of the sequence of events in a cell cycle by simply memorizing the letters IPPMAT: the first letters of interphase, prophase, prometaphase, metaphase, anaphase, and telophase are represented in this acronym. 2. The authors note that animals, but not plants, have a pair of centrioles in their centrosomes. They add that the role of centrioles in cell division is a mystery. Students might not appreciate all that remains to be explained in biology. Sharing the existence of such mysteries with them promotes critical thinking skills and helps them imagine a place for themselves in future research. Copyright © 2009 Pearson Education, Inc.

8.7 Cytokinesis differs for plant and animal cells
Cytokinesis Cleavage in animal cells A cleavage furrow forms from a contracting ring of microfilaments, interacting with myosin The cleavage furrow deepens to separate the contents into two cells Cytokinesis in plant cells A cell plate forms in the middle from vesicles containing cell wall material The cell plate grows outward to reach the edges, dividing the contents into two cells Each cell has a plasma membrane and cell wall This material allows a review of cellular components. Students can be reminded that microtubules are composed of actin molecules and that actin and myosin work in concert for muscle cell contraction. They can also be reminded that vesicles have a lipid boundary that will contribute to the plasma membrane of the new plant cells. For the BLAST Animation Cytokinesis in Plants, go to Animation and Video Files. Teaching Tips 1. 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). This occurs in human development during the formation of the placenta. 2. The authors make an analogy between a drawstring and the mechanism of cytokinesis in animal cells. Students seem to appreciate this association. 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, like the drawstring just beneath the surface of the sweat pants, the microfilaments are just beneath the surface of the cell’s plasma membrane. Animation: Cytokinesis Copyright © 2009 Pearson Education, Inc.

Cleavage furrow Cleavage furrow Contracting ring of microfilaments
Cleavage furrow Cleavage furrow Contracting ring of microfilaments Figure 8.7A Cleavage of an animal cell. Daughter cells

Wall of parent cell Cell plate forming Daughter nucleus Cell wall
Cell wall New cell wall Figure 8.7B Cell plate formation in a plant cell. Vesicles containing cell wall material Cell plate Daughter cells

8.8 Anchorage, cell density, and chemical growth factors affect cell division
Factors that control cell division Presence of essential nutrients Growth factors, proteins that stimulate division Presence of other cells causes density-dependent inhibition Contact with a solid surface; most cells show anchorage dependence There is promising research on the use of growth factors to stimulate the regeneration of nerves by promoting axon growth. For example, the macrophage-derived protein oncomodulin has been shown to increase axon length in the optic nerve nearly twofold in vitro. (Laboratory of L. Benowitz, in Yin, et al., 2006, Nature Neuroscience 9, 843–852.) Teaching Tips 1. Students who closely examine a small abrasion on their skin might notice that the wound tends to heal from the outer edges inward. This space-filling mechanism is a natural example of density-dependant inhibition, which is also seen when cells in a cell culture dish stop dividing when they have formed a complete layer. Copyright © 2009 Pearson Education, Inc.

Culture of cells Addition of growth factor
Culture of cells Addition of growth factor Figure 8.8A An experiment demonstrating the effect of growth factors on the division of cultured animal cells.

stop dividing (density- dependent inhibition).
Cells anchor to dish surface and divide. When cells have formed a complete single layer, they stop dividing (density- dependent inhibition). If some cells are scraped away, the remaining cells divide to fill the dish with a single layer and then stop (density-dependent inhibition). Figure 8.8B An experiment demonstrating density-dependent inhibition, using animal cells grown in culture.

8.9 Growth factors signal the cell cycle control system
Cell cycle control system A set of molecules, including growth factors, that triggers and coordinates events of the cell cycle Checkpoints Control points where signals regulate the cell cycle G1 checkpoint allows entry into the S phase or causes the cell to leave the cycle, entering a nondividing G0 phase G2 checkpoint M checkpoint Student Misconceptions and Concerns 1. 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. Teaching Tips 1. The authors make an analogy between the cell cycle control system and the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, as the authors note, unlike a washing machine, the components of the control system of a cell cycle are not all located in one place. Copyright © 2009 Pearson Education, Inc.

G1 checkpoint G0 Control system S G1 G2 M M checkpoint G2 checkpoint
G1 checkpoint G0 Control system S G1 G2 M Figure 8.9A Mechanical model for the cell cycle control system. M checkpoint G2 checkpoint

8.9 Growth factors signal the cell cycle control system
Effects of a growth factor at the G1 checkpoint A growth factor binds to a receptor in the plasma membrane Within the cell, a signal transduction pathway propagates the signal through a series of relay molecules The signal reaches the cell cycle control system to trigger entry into the S phase Student Misconceptions and Concerns 1. 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. Teaching Tips 1. The authors make an analogy between the cell cycle control system and the control device of an automatic washing machine. Each has a control system that triggers and coordinates key events in the cycle. However, as the authors note, unlike a washing machine, the components of the control system of a cell cycle are not all located in one place. Copyright © 2009 Pearson Education, Inc.

Growth factor Plasma membrane Relay proteins Receptor protein
Growth factor Plasma membrane Relay proteins Receptor protein G1 checkpoint Signal transduction pathway Control system G1 S Figure 8.9B How a growth factor signals the cell cycle control system. M G2

8.10 CONNECTION: Growing out of control, cancer cells produce malignant tumors
Cancer cells escape controls on the cell cycle Cancer cells divide rapidly, often in the absence of growth factors They spread to other tissues through the circulatory system Growth is not inhibited by other cells, and tumors form Benign tumors remain at the original site Malignant tumors spread to other locations by metastasis Teaching Tips 1. 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. Many other approaches are under consideration to attack cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. Copyright © 2009 Pearson Education, Inc.

Cancer treatments Localized tumors can be treated with surgery or radiation Chemotherapy is used for metastatic tumors Teaching Tips 1. 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. Many other approaches are under consideration to attack cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. Copyright © 2009 Pearson Education, Inc.

Classification of cancer by origin Carcinomas arise in external or internal body coverings Sarcomas arise in supportive and connective tissue Leukemias and lymphomas arise from blood-forming tissues Teaching Tips 1. 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. Many other approaches are under consideration to attack cancers. You may wish to explore these as sidelights to your lecture. Good resources include cell biology and development textbooks. Copyright © 2009 Pearson Education, Inc.

Lymph vessels Tumor Blood vessel Glandular tissue A tumor grows from a
Lymph vessels Tumor Blood vessel Glandular tissue A tumor grows from a single cancer cell. Cancer cells invade neighboring tissue. Cancer cells spread through lymph and blood vessels to other parts of the body. Figure 8.10 Growth and metastasis of a malignant (cancerous) tumor of the breast.

8.11 Review: Mitosis provides for growth, cell replacement, and asexual reproduction
Mitosis produces genetically identical cells for Growth Replacement Asexual reproduction Teaching Tips 1. Figure 8.11 visually summarizes key functions of mitosis. It is an important image to introduce mitosis or summarize mitosis after addressing its details. Video: Hydra Budding Copyright © 2009 Pearson Education, Inc.

Figure 8.11A Growth (in an onion root).

Chapter 8 Connections between cell division and reproduction

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