Limits to Cell Growth • There Are Two Reasons Why the Cell Divides: 1. The

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Interest Grabber Section Outline

Section 10-1 Section 10-1

Getting Through

Materials move through cells by diffusion. Oxygen and food move into 10–1 Cell Growth cells, while waste products move out of cells. How does the size of a cell A. Limits to Cell Growth affect how efficiently materials get to all parts of a cell? 1. DNA “Overload” Work with a partner to complete this activity. 2. Exchanging Materials 3. Ratio of Surface Area to Volume 1. On a sheet of paper, make a drawing of a cell that has the following dimensions: 5 cm x 5 cm x 5 cm. Your partner should draw another cell 4. Cell Division about one half the size of your cell on a separate sheet of paper. 2. Compare your drawings. How much longer do you think it would take to get from the cell membrane to the center of the big cell than from the cell membrane to the center of the smaller cell? 3. What is the advantage of cells being small?

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Limits to Cell Growth DNA “Overload” • DNA contains all the information to control the cell. • There are two reasons why the cell divides: • There is only a certain amount of DNA within a cell. • As the cell gets larger, there are more demands on the 1. The larger the cell, the more demands the cell DNA and it won’t be able to keep up. places on its DNA. 2. The cell has trouble moving enough nutrients and wastes across the cell membrane.

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Exchanging Materials Ratio of Surface Area to Volume • Materials such as food, oxygen, water and wastes, • As the cell grows, its volume grows much more rapidly enter and leave the cell through the cell membrane. than its surface area. • Some things pass through by diffusion, but other must • Take a look at the chart to understand. use the protein channels or pumps. • Only a certain amount can pass through within a given time. As the cells gets larger, more and more materials are going to have to pass through the membrane which may become too much for the channels.

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Ratio of Surface Area to Volume in Cells Interest Grabber

Section 10-1 Section 10-2

Cell Cycle

Cell Size The cell cycle represents recurring events that take place in the period of time from the beginning of one cell division to the beginning of the next. In addition to cell division, the cell cycle includes periods when the cell is growing and actively producing materials it needs for the next division.

Surface Area (length x width x 1. Why is the cell cycle called a cycle? 6) Volume (length x width x height) 2. Why do you think that it is important for a cell to grow in size during its Ratio of Surface Area cell cycle? to Volume 3. What might happen to a cell if all events leading up to cell division took place as they should, but the cell did not divide?

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Section Outline

Section 10-2

Chromosomes 10–2 Cell Division • Chromosomes carry the information that is passed on from one A. Chromosomes generation to the next. B. The Cell Cycle • They are made up of DNA and proteins. C. Events of the Cell Cycle • Every organism has a specific number of chromosomes in each cell. D. Mitosis 1. Prophase – Fruit flies have 8 2. Metaphase – Humans have 46 3. Anaphase – Carrots have 18 4. Telophase • Chromosomes are only visible E. Cytokinesis during cell division. • DNA is copied just before cell division. • They consist of two sister chromatids.

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Figure 10–4 The Cell Cycle

Section 10-2

Three Stages of the Cell Cycle Introductions 1. Interphase 2. Mitosis 3. Cytokinesis • What is the Cell Cycle? G1 phase – Cell reproduction in which two identical cells are made from one cell

• Why do cells need to reproduce? M phase – So organisms can grow and replace old, worn out cells • What types of cells reproduce using mitosis? S phase – Body cells - Any cells except the sex cells.

G2 phase

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Interphase Mitosis • G1 phase: – Cell grows in size. • Scientists divide the events of mitosis into four phases: – Cell synthesizes new proteins – Prophase and organelles. – Metaphase • S phase: – Anaphase – DNA is replicated. – Telophase

• G2 phase: – Organelles and molecules for cell division are produced. – Cell grows a little more.

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Prophase Metaphase • DNA coils to form chromosomes. • Nuclear membrane and nucleolus disappear. • Chromosomes are moved to the • Centrioles move to opposite side middle of the cell by the of the cell. microtubules of the spindle. • Spindle fibers begin to develop.

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Anaphase Telophase • Centromeres split. • Sister chromatids move • Chromosomes begin to apart to opposite side of the uncoil. cell becoming individual • Nuclear membrane and chromosomes. nucleolus reappear. • Spindle fibers and centrioles begin to disappear. • Cytoplasm begins to pinch inward.

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Figure 10–5 Mitosis and Cytokinesis

Section 10-2

Cytokinesis Spindle forming Centrioles • In animals, the cytoplasm pinches in the middle until it Nuclear Chromatin Centromere Centriole becomes two equal parts. Chromosomes envelope (paired chromatids) • In plants, a cell plate forms Interphase Prophase Spindle half way between the two nuclei. It continues to go Cytokinesis Centriole until the cell is split. Individual Metaphase Telophase chromosomes

Nuclear Anaphase envelope reforming

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Figure 10–5 Mitosis and Cytokinesis Figure 10–5 Mitosis and Cytokinesis

Section 10-2 Section 10-2

Spindle Spindle forming forming Centrioles Centrioles

Nuclear Chromatin Centromere Centriole Nuclear Chromatin Centromere Centriole Chromosomes Chromosomes envelope envelope (paired chromatids) (paired chromatids) Interphase Interphase Prophase Spindle Prophase Spindle

Cytokinesis Centriole Cytokinesis Centriole

Individual Metaphase Individual Metaphase Telophase chromosomes Telophase chromosomes

Nuclear Anaphase Nuclear Anaphase envelope envelope reforming reforming

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Figure 10–5 Mitosis and Cytokinesis Figure 10–5 Mitosis and Cytokinesis

Section 10-2 Section 10-2

Spindle Spindle forming forming Centrioles Centrioles

Cytokinesis Centriole Cytokinesis Centriole

Individual Metaphase Individual Metaphase Telophase chromosomes Telophase chromosomes

Nuclear Anaphase Nuclear Anaphase envelope envelope reforming reforming

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Figure 10–5 Mitosis and Cytokinesis Concept Map

Section 10-2 Section 10-2

Spindle forming Cell Cycle Centrioles

includes Nuclear Chromatin Centromere Centriole Chromosomes envelope (paired chromatids) Interphase Prophase Spindle Interphase M phase (Mitosis) Cytokinesis Cytokinesis Centriole

Individual Metaphase is divided into is divided into Telophase chromosomes

Nuclear Anaphase envelope reforming G1 phase S phase G2 phase Prophase Metaphase Anaphase Telophase

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Interest Grabber Section Outline

Section 10-3 Section 10-3

Knowing When to Stop 10–3 Regulating the Cell Cycle Suppose you had a paper cut on your finger. Although the cut may have A. Controls on Cell Division bled and stung a little, after a few days, it will have disappeared, and your B. Cell Cycle Regulators finger would be as good as new. 1. Internal Regulators 2. External Regulators 1. How do you think the body repairs an injury, such as a cut on a C. Uncontrolled Cell Growth finger? 2. How long do you think this repair process continues? 3. What do you think causes the cells to stop the repair process?

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Control of Cell Division

Section 10-3

Controls on Cell Division

• When an injury such as a cut in the skin or a break in a bone, cells alone the edges are stimulated to divide rapidly. • This action produces new cells to start the process of healing. • When the healing process is complete, the rate of cell division slows.

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Uncontrolled Cell Growth Cell Cycle Regulators • The consequences of uncontrolled • Tim Hunt and Mark Kirschner cell growth in multicellular discovered that cells in mitosis organisms are very severe. contained a protein called cyclin. • Cancer is a disorder in which • If this protein is injected into a come of the body’s own cells lose non-dividing cell, it causes the the ability to control growth. formation of the spindle. • Cancer cells do not respond to the signals that regulate the growth of • It was decided that cyclins most cells. regulate the timing of the cell • They form masses called tumors cycle in eukaryotic cells. that can damage surrounding • There are internal and external tissues. regulators.

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Figure 10–8 Effect of Cyclins Videos

Section 10-3

The sample is injected into a second cell in G2 of interphase. Click a hyperlink to choose a video. Animal Cell Mitosis

A sample of Animal Cell Cytokinesis cytoplasm is removed from a cell in mitosis.

As a result, the second cell enters mitosis.

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Video 1 Video 2

Animal Cell Mitosis Animal Cell Cytokinesis

Click the image to play the video segment. Click the image to play the video segment.

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Go Online Interest Grabber Answers

1. On a sheet of paper, make a drawing of a cell that has the following Links on cell growth dimensions: 5 cm x 5 cm x 5 cm. Your partner should draw another cell Links from the authors on stem cells about one half the size of your cell on a separate sheet of paper. Share cell cycle lab data 2. Compare your drawings. How much longer do you think it would take to get from the cell membrane to the center of the big cell than from the Interactive test cell membrane to the center of the smaller cell? It would take twice the amount of time. For links on cell division, go to www.SciLinks.org and enter the Web 3. What is the advantage of cells being small? Code as follows: cbn-3102. If cells are small, materials can be distributed to all parts of the cell quickly. For links on the cell cycle, go to www.SciLinks.org and enter the Web Code as follows: cbn-3103.

Interest Grabber Answers Interest Grabber Answers

1. Why is the cell cycle called a cycle? 1. How do you think the body repairs an injury, such as a cut on a finger? It represents recurring events. The cut is repaired by the production of new cells through cell division. 2. Why do you think that it is important for a cell to grow in size during its cell 2. How long do you think this repair process continues? cycle? Cell division continues until the cut is repaired. If a cell did not grow in size, each cell division would produce progressively 3. What do you think causes the cells to stop the repair process? smaller cells. Students will likely say that when the cut is filled in, there is no room for 3. What might happen to a cell if all events leading up to cell division took more cells to grow. place as they should, but the cell did not divide? Students may infer that a cell that undergoes all sequences of the cell cycle would grow increasingly larger—to a point at which the cell could no longer exchange materials with the environment efficiently enough to live.

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