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READING ESSENTIALS Chapter 8 83

◗ Before You ReadIn this section you will learn about the way cells grow and divide. Have you ever watched someonetrim a bush or a tree? What would have happened if the bush or tree had not been trimmed? Writedown a few of your thoughts on the lines below.________________________________________________________________________________________________________________________________

__________________________________________________________________________________________________________________

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◗ Read to LearnCell Size Limitations

As you have learned, the plasma membrane lets nutrients intothe cell and allows wastes to leave. Inside the cell, nutrients andwastes move by diffusion. Because a cell’s size can slow the rate of diffusion, cells have to have a way of limiting their growth.Fortunately, cells divide before they become too big and unable tofunction well. Cell division also has other purposes.

Cell ReproductionWhen cells divide, new cells are produced from one cell. The

two cells that are produced are identical to the original cell. Justbefore cells divide, several short, stringy structures appear in thenucleus. These structures are called chromosomes.

What do chromosomes do?Chromosomes (KROH muh sohmz) contain DNA and are

the carriers of the genetic material that is copied and passed fromgeneration to generation. For most of a cell’s lifetime, chromo-somes exist as something called chromatin (KROH muh tihn).Chromatin is long, stringy strands of DNA. Without the properamount of DNA, the cell cannot survive. Therefore the chromo-somes must be accurately passed on to new cells.

The Cell CycleThe cell cycle is the time of growth and division of a cell. A

cell’s life cycle is divided into two periods. There is a period of

Identify theMain Idea As you read thissection, stop after every paragraph and put what youread into your own words.Highlight the main idea ineach paragraph.

1. What structures appear inthe nucleus shortly beforecell division?

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________________________

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Cell Growth and Reproduction

Name Date Class

Section

8.2Section

SC.F.1.4.8 The student knows that cell behavior can be affected by molecules from otherparts of the organism or even from other organisms. SC.F.2.4.2 The student knows thatevery cell contains a “blueprint” coded in DNA molecules that specify how proteins areassembled to regulate cells.

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Cell Growth and Reproduction, continued

Name Date Class

8.2

84 Chapter 8 READING ESSENTIALS

SectionSection

Analyze theDiagram As you read aboutmitosis, highlight each stagein the diagram below.

growth called interphase. There is also a period of nuclear divi-sion called mitosis.

What is interphase?During interphase a cell grows in size, carries on metabolism,

duplicates chromosomes, and prepares for division. Interphase isthe busiest phase of the cell cycle.

What is mitosis?Mitosis (mi TOH sus) follows interphase. It is the process of

nuclear division in which two daughter cells form. Each of thesedaughter cells contains a complete setof chromosomes that are identical tothose of the parent cell.

What are the phases ofmitosis?

There are four phases of mitosis.Each phase merges into the next phase.The four phases are prophase, meta-phase, anaphase, and telophase asshown in the illustration to the left.

Prophase is the first and longestphase. During prophase the chromatincoils up to form chromosomes. Eachduplicated chromosome is made up of two identical halves, called sisterchromatids. Centromeres(SEN truh meers) hold the sister chromatids together.

During metaphase, the second phaseof mitosis, the doubled chromosomesare pulled to the center of the cell.Anaphase is the third phase of mitosis.During this phase, the centromeres ofthe sister chromatids split apart. Thisseparates the sister chromatids fromeach other. In telophase, the last phaseof mitosis, the chromatids move toopposite sides of the cell. Two nuclei areformed—one on each side of the cell.Finally, a new double membrane beginsto form between the two new nuclei.

Spindle fibers

Disappearingnuclear envelope

Doubled chromosome

Centromere

Sister chromatids

Nuclear envelopereappears

Two daughtercells are formed

A ProphaseThe chromatin coils to formchromosomes.

B MetaphaseThe chromosomesmove to the centerof the cell.

C AnaphaseCentromeres split and sister chromatids are pulled to the opposite sides of the cell.

D TelophaseTwo new nucleiare formed and a double membranebegins to form between them.

Stages of Mitosis

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Cell Growth and Reproduction, continued

Name Date Class

8.2

READING ESSENTIALS Chapter 8 85

SectionSection

2. What do tissues organizeto form?

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CytokinesisFollowing telophase, the cell’s cytoplasm divides and sepa-

rates into two new identical cells. This is called cytokinesis(si toh kih NEE sus).

Results of MitosisWhen mitosis is complete, one-celled organisms remain as

single cells. The organism simply multiplied into two organisms.These daughter cells eventually will repeat the same cell cycle as the parent cell and will grow and divide. In larger organisms,cell growth and reproduction result in groups of cells that worktogether as tissue to perform a certain function. Tissues organizein combinations to form organs. Organs perform specific complextasks within the organism. Multiple organs that work togetherform an organ system, such as the digestive system. The stomachis one organ in the digestive system. It functions to digest food. Itis important to remember that no matter how complex the organsystem or organism becomes, the cell is still the most basic unit ofthat organization.

◗ After You ReadMini Glossary

anaphase: the third phase of mitosis in which thecentromeres split and the sister chromatidsof each chromosome are pulled apart

cell cycle: continuous sequence of growth (inter-phase) and division (mitosis) in a cell

centromere (SEN truh meer): cell structure thatjoins two sister chromatids of a chromosome

chromatin (KROH muh tihn): long strands ofDNA found in the eukaryotic cell nucleus;coils up to form chromosomes

chromosomes (KROH muh sohmz): cell struc-tures that contain DNA and carry thegenetic material that is copied and passedfrom generation to generation of cells

cytokinesis (si toh kih NEE sus): cell process fol-lowing mitosis in which the cell’s cytoplasmdivides and separates into new identical cells

interphase: cell growth period where a cellincreases in size, carries on metabolism, andduplicates chromosomes prior to division

metaphase: short second phase of mitosis wheredoubled chromosomes move to the centerof the cell

mitosis (mi TOH sus): period of nuclear cell divi-sion in which two daughter cells areformed, each containing a complete set of chromosomes

organ: group of two or more tissues organizedto perform complex activities within anorganism

organ system: multiple organs that worktogether to perform a specific life function

prophase: first and longest phase of mitosis wherechromatin coils into visible chromosomes

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Cell Growth and Reproduction, continued

Name Date Class

8.2

86 Chapter 8 READING ESSENTIALS

SectionSection

1. Circle the terms from the Mini Glossary that identify the phases of mitosis. Then, in thespace provided, list them in the order they occur.

1. 3.

2. 4.

2. Use the diagram below to help you review the cell cycle by providing two facts for eachperiod.

3. Fill in the blanks with the following terms: tissues, sister chromatids, cell cycle, mitosis,and chromosomes.

a. Two identical halves of a duplicated parent chromosome are called .

b. The process of cell division is called .

c. are the carriers of genetic material that is copied and passed from

generation to generation.

d. The is the period of growth and division of a cell.

e. are groups of cells that work together to perform specific functions.

Visit the Glencoe Science Web site at science.glencoe.com to findyour biology book and learn more about cell growth and reproduction.

The CellCycle

Mitosis

1. _____________________________

1. _____________________________

1. _____________________________

2. _____________________________

2. _____________________________

2. _____________________________

Interphase

1. _____________________________

1. _____________________________

1. _____________________________

2. _____________________________

2. _____________________________

2. _____________________________

sister chromatid: identical half of duplicatedparent chromosome formed during theprophase stage of mitosis; the halves areheld together by a centromere

telophase: final phase of mitosis during whichnew cells prepare for their own independ-ent existence

tissue: groups of cells that work together to per-form a specific function

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READING ESSENTIALS Chapter 8 87

◗ Before You ReadThis section is about cancer and what happens when cells grow out of control. Experts agree that a healthful diet can reduce the risk of cancer. On the lines below list foods that you think belong in ahealthful diet.________________________________________________________________________________________________________________________________

__________________________________________________________________________________________________________________

__________________________________________________________________________________________________________________

◗ Read to LearnNormal Control of the Cell Cycle

The cell cycle is controlled by conditions both inside the celland in the cell’s environment. When something goes wrong withnormal cell conditions, cells lose control of the cell cycle.

Cancer is a growth that occurs when uncontrolled cell divisiontakes place. This loss of control may be caused by changes inenzyme production inside the cell or by some outside factor, suchas air or water pollution. An enzyme, you will remember, is a type of protein found in all living things that changes the rate ofchemical reactions.

Cancer: A Mistake in the Cell CycleScientists think that cancer is caused by changes to one or more

of the genes that produce the substances that help to control thecell cycle. A gene is a part of DNA that controls the productionof a protein. Cancer occurs when something causes the damagedgenes to go into action. When that happens, cancerous cells formmasses of tissue called tumors. Tumors keep normal cells fromgetting needed nutrients. This causes damage to organs. Cancercells can spread throughout the body to other organs as well.

What are the causes of cancer?Cancer is the second leading cause of death in the United

States. Only heart disease leads to more deaths each year. But the causes of cancer are hard to pinpoint. This is because bothenvironmental and genetic factors play a part. We do know thatmany environmental factors damage the genes that control the

Summarize As you read thissection, highlight the mainpoint in each paragraph.Then, write a short paragraphsummarizing what you havelearned.

1. What occurs when uncon-trolled cell division takesplace?

________________________

________________________

________________________

Control of the Cell Cycle

Name Date Class

Section

8.3Section

SC.F.1.4.5 The student knows that complex interactions among the different kinds of mol-ecules in the cell cause distinct cycles of activity governed by proteins. SC.F.1.4.8 The stu-dent knows that cell behavior can be affected by molecules from other parts of theorganism or even from other organisms. Also covers SC.F.2.4.2

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Control of the Cell Cycle, continued

Name Date Class

8.3

88 Chapter 8 READING ESSENTIALS

SectionSection

2. Infer Which snack is morehealthful? (Circle yourchoice.)a. an appleb. a chocolate candy bar

cell cycle. Environmental factors include cigarette smoke, air andwater pollution, and exposure to ultraviolet radiation from thesun. Cancer may also be caused by genetic factors such as viralinfections that damage the genes.

How can cancer be prevented?A healthful lifestyle reduces the risk of cancer. Experts agree

that diets low in fat and high in fiber content can reduce the riskfor many kinds of cancer. Fruits, vegetables, and grain productsare good food choices because they are low in fat and high infiber. Other healthful choices such as daily exercise and not usingtobacco also are known to lower the risk of cancer.

◗ After You ReadMini Glossary

cancer: uncontrolled cell division that may becaused by environmental factors and/orchanges in enzyme production in the cellcycle

gene: segment of DNA that controls protein pro-duction and the cell cycle

1. Write a sentence using both of the terms in the Mini Glossary above.____________________________________________________________________________________

____________________________________________________________________________________

2. Place the following events in the appropriate box based on the order in which they occur:Uncontrolled cell division occurs.

Cancerous cells form tumors that deprive normal cells of nutrients.

Cancer occurs.

Environmental factors or viral infections damage genes.

Visit the Glencoe Science Web site at science.glencoe.com to findyour biology book and learn more about control of the cell cycle.

1.

3.

2.

4.