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.

8.6 Cell division is a continuum of dynamic changes A mitotic spindle is required to divide the chromosomes Composed of microtubules produced by centrosomes, structures in the cytoplasm that Organize microtubule arrangement Contain a pair of centrioles in animal cells 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 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

Figure 8.6 The stages of cell division. INTERPHASE

Figure 8.6 The stages of cell division. PROPHASE

Figure 8.6 The stages of cell division. PROMETAPHASE

8.6 Cell division is a continuum of dynamic changes Interphase In the cytoplasm Cytoplasmic contents double Two centrosomes form In the nucleus Chromosomes duplicate during the S phase Nucleoli 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.

8.6 Cell division is a continuum of dynamic changes 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.

8.6 Cell division is a continuum of dynamic changes Prophase Cytoplasm: Microtubules form spindle Nucleus: Chromosomes 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.

8.6 Cell division is a continuum of dynamic changes 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

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

Figure 8.6 The stages of cell division. METAPHASE

Figure 8.6 The stages of cell division. ANAPHASE

TELOPHASE AND CYTOKINESIS Figure 8.6 The stages of cell division. TELOPHASE AND CYTOKINESIS

8.6 Cell division is a continuum of dynamic changes 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.

8.6 Cell division is a continuum of dynamic changes Anaphase Sister chromatids separate at the centromeres Daughter chromosomes are moved to opposite poles of the cell 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.

8.6 Cell division is a continuum of dynamic changes 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.

8.6 Cell division is a continuum of dynamic changes 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

Figure 8.7A Cleavage of an animal cell. furrow

Cleavage furrow Contracting ring of microfilaments Daughter cells 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

Wall of parent cell Cell plate forming Daughter nucleus Wall of parent cell Cell plate forming Daughter nucleus Figure 8.7B Cell plate formation in a plant cell.

Cell wall New cell wall Vesicles containing cell wall material Cell wall New cell wall Figure 8.7B Cell plate formation in a plant cell. Vesicles containing cell wall material Cell plate Daughter cells