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Interest Grabber

Getting Through

Materials move through cells by diffusion. Oxygen and food move into cells, while waste products move out of cells. How does the size of a cell affect how efficiently materials get to all parts of a cell? Work with a partner to complete this activity.

Section 10-1

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 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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Section Outline

10–1 Cell Growth A. Limits to Cell Growth

1. DNA “Overload” 2. Exchanging Materials 3. Ratio of Surface Area to Volume 4. Cell Division

Section 10-1

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Limits to Cell Growth

•  There are two reasons why the cell divides:

1. The larger the cell, the more demands the cell places on its DNA. 2. The cell has trouble moving enough nutrients and wastes across the cell membrane.

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DNA “Overload”

• DNA contains all the information to control the cell. • There is only a certain amount of DNA within a cell. • As the cell gets larger, there are more demands on the DNA and it won’t be able to keep up.

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Exchanging Materials • Materials such as food, oxygen, water and wastes, enter and leave the cell through the cell membrane. • Some things pass through by diffusion, but other must 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

• As the cell grows, its volume grows much more rapidly than its surface area. • Take a look at the chart to understand.

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Cell Size

Surface Area (length x width x 6) Volume (length x width x height)

Ratio of Surface Area to Volume

Ratio of Surface Area to Volume in Cells

Section 10-1

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Interest Grabber

Cell Cycle

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.

Section 10-2

1. Why is the cell cycle called a cycle? 2. Why do you think that it is important for a cell to grow in size during its

cell cycle? 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

10–2 Cell Division A. Chromosomes B. The Cell Cycle C. Events of the Cell Cycle D. Mitosis

1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

E. Cytokinesis

Section 10-2

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Chromosomes • Chromosomes carry the information that is passed on from one generation to the next. • They are made up of DNA and proteins. • Every organism has a specific number of chromosomes in each cell.

–  Fruit flies have 8 –  Humans have 46 –  Carrots have 18

• Chromosomes are only visible during cell division. • DNA is copied just before cell division. • They consist of two sister chromatids.

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Introductions

• What is the Cell Cycle? –  Cell reproduction in which two identical cells are made from one

cell • Why do cells need to reproduce?

–  So organisms can grow and replace old, worn out cells • What types of cells reproduce using mitosis?

–  Body cells - Any cells except the sex cells.

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M phase

G2 phase

S phase

G1 phase

Figure 10–4 The Cell Cycle

Section 10-2

Three Stages of the Cell Cycle

1.  Interphase 2.  Mitosis

3.  Cytokinesis

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Interphase • G1 phase:

–  Cell grows in size. –  Cell synthesizes new proteins

and organelles. • S phase:

–  DNA is replicated. • G2 phase:

–  Organelles and molecules for cell division are produced.

–  Cell grows a little more.

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Mitosis

• Scientists divide the events of mitosis into four phases: –  Prophase –  Metaphase –  Anaphase –  Telophase

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Prophase

• DNA coils to form chromosomes. • Nuclear membrane and nucleolus disappear. • Centrioles move to opposite side of the cell. • Spindle fibers begin to develop.

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Metaphase

• Chromosomes are moved to the middle of the cell by the microtubules of the spindle.

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Anaphase

• Centromeres split. • Sister chromatids move apart to opposite side of the cell becoming individual chromosomes.

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Telophase

• Chromosomes begin to uncoil. • Nuclear membrane and nucleolus reappear. • Spindle fibers and centrioles begin to disappear. • Cytoplasm begins to pinch inward.

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Cytokinesis

• In animals, the cytoplasm pinches in the middle until it becomes two equal parts. • In plants, a cell plate forms half way between the two nuclei. It continues to go until the cell is split.

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Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

Centriole Chromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Section 10-2

Figure 10–5 Mitosis and Cytokinesis

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Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

Centriole Chromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Section 10-2

Figure 10–5 Mitosis and Cytokinesis

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Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

Centriole Chromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Section 10-2

Figure 10–5 Mitosis and Cytokinesis

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Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

Centriole Chromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Section 10-2

Figure 10–5 Mitosis and Cytokinesis

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Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

Centriole Chromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Section 10-2

Figure 10–5 Mitosis and Cytokinesis

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Centrioles

Chromatin

Interphase

Nuclear envelope

Cytokinesis

Nuclear envelope reforming

Telophase

Anaphase

Individual chromosomes

Metaphase

Centriole

Spindle

Centriole Chromosomes

(paired chromatids)

Prophase

Centromere

Spindle forming

Section 10-2

Figure 10–5 Mitosis and Cytokinesis

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includes

is divided into is divided into

Concept Map

Section 10-2

Cell Cycle

M phase (Mitosis) Interphase

G1 phase S phase Prophase G2 phase Metaphase Telophase Anaphase

Cytokinesis

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Interest Grabber

Knowing When to Stop

Suppose you had a paper cut on your finger. Although the cut may have bled and stung a little, after a few days, it will have disappeared, and your finger would be as good as new.

Section 10-3

1. How do you think the body repairs an injury, such as a cut on a 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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Section Outline

10–3 Regulating the Cell Cycle A. Controls on Cell Division B. Cell Cycle Regulators

1. Internal Regulators 2. External Regulators

C. Uncontrolled Cell Growth

Section 10-3

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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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Control of Cell Division

Section 10-3

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Cell Cycle Regulators • Tim Hunt and Mark Kirschner discovered that cells in mitosis contained a protein called cyclin. • If this protein is injected into a non-dividing cell, it causes the formation of the spindle. • It was decided that cyclins regulate the timing of the cell cycle in eukaryotic cells. • There are internal and external regulators.

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Uncontrolled Cell Growth

• The consequences of uncontrolled cell growth in multicellular organisms are very severe. • Cancer is a disorder in which come of the body’s own cells lose the ability to control growth. • Cancer cells do not respond to the signals that regulate the growth of most cells. • They form masses called tumors that can damage surrounding tissues.

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

The sample is injected into a second cell in G2

of interphase.

As a result, the second cell enters mitosis.

Figure 10–8 Effect of Cyclins

Section 10-3

Videos

Click a hyperlink to choose a video. Animal Cell Mitosis Animal Cell Cytokinesis

Click the image to play the video segment.

Video 1

Animal Cell Mitosis

Click the image to play the video segment.

Video 2

Animal Cell Cytokinesis

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Links on cell growth Links from the authors on stem cells Share cell cycle lab data Interactive test

For links on cell division, go to www.SciLinks.org and enter the Web Code as follows: cbn-3102. For links on the cell cycle, go to www.SciLinks.org and enter the Web Code as follows: cbn-3103.

Go Online Interest Grabber Answers

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 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? It would take twice the amount of time.

3. What is the advantage of cells being small? If cells are small, materials can be distributed to all parts of the cell quickly.

Interest Grabber Answers

1. Why is the cell cycle called a cycle? It represents recurring events.

2. Why do you think that it is important for a cell to grow in size during its cell cycle? If a cell did not grow in size, each cell division would produce progressively smaller cells.

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? 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.

Interest Grabber Answers

1. How do you think the body repairs an injury, such as a cut on a finger? The cut is repaired by the production of new cells through cell division.

2. How long do you think this repair process continues? Cell division continues until the cut is repaired.

3. What do you think causes the cells to stop the repair process? Students will likely say that when the cut is filled in, there is no room for more cells to grow.

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