Focus on California Life Science 7th Grade Unit 1 - Chapter 4 Cell Processes and Energy

A Chapter Cell Processes and Energy ' A Standards Preview All living organisms are composed of cells , from just one to many trillions , whose details usually are visible only through a microscope . As a basis for understanding this concept Students know that liberate energy for the work that cells do and that capture sunlight energy for photosynthesis . Students know cells divide to increase their numbers through a process of mitosis , which results in two daughter cells with identical sets of chromosomes . Student know that as cellular organisms develop , their cells differentiate . A typical cell of any ism contains genetic instructions that specify its traits . Those traits may be modified by tal influences . As a basis for understanding this concept Students know DNA ( acid ) is the genetic material of living organisms and is located in the somes of each cell Sunlight on these maple leaves powers the process of photosynthesis . 112

. Cell Processes and Energy , the BIG Idea How do cells obtain the energy they need to carry out all their functions ?

Check What You Know Hummingbirds feed on the nectar produced by flowers . Nectar is a sweet liquid composed largely of carbohydrates . What does nectar provide for the cells of the hummingbird ?

chapter 113 The images shown here represent some of the key terms in this chapter . You can use this vocabulary skill to help you understand the meaning of some key terms in this chapter . Greek Word Origins Many English science words come from ancient Greek words . one example is the word photograph . The first part of photograph comes from the Greek word photos , which means light . The second part comes from , which means written or recorded . A photograph is a picture recorded by using light . The table below shows three Greek words that are sources of some key terms in this chapter . Recall from Chapter that prefixes are word parts placed at the beginning of a root word to change its meaning . Greek Word Meaning of Greek Word I Key Term self autotroph An organism that makes food for itself other , different heterotroph An organism that depends on other organisms for food kinesis motion cytokinesis During cell division , the process in which a cell cytoplasm divides and move into the two new cells that form Apply It ! food .

I Chapter Vocabulary ( photosynthesis ' autotroph I ' heterotroph pigment chlorophyll stomata Section ( respiration fermentation Section ( page cell cycle interphase replication mitosis chromosome . chromosome cytokinesis Section ( page 138 ) differentiation stem cell stem cells , Build Science Vocabulary Online Web Code Chapter 115

Create Outlines in an outline , you show the relationship between main ideas and supporting ideas . An outline is usually set up like the example shown below . Roman numerals show the main topics . Capital letters and regular numerals show the . Use the headings , Key Concepts , and Key Terms to help you decide what to include in your outline . Look at the outline for the first part of Section in this chapter . Respiration I . What In Respiration ?

by which celle get energy from glucose . During respiration , cells . Breakdown food molecules such no sugar . Release the energy in the molecules and Releasing Energy . capture sunlight energy . score as . use stored energy by breaking down carbohydrates Apply It ! What is the one main topic in the partial outline above ?

How do you indicate main topics in an outline ?

How many appear under in the outline above ?

What are these ?

when you read Section , complete the outline above . Also make an outline of Section .

Standards Investigation Shine On ! Every morning when the sun rises , tiny living factories starta manufacturing process called photosynthesis . The power they use is sunlight . In this investigation , you will study how light affects one familiar group of . Your Goal To determine how different lighting conditions affect the health and growth of plants To complete the investigation , you will write up a plan to grow plants under different lighting conditions care for your plants daily , and keep careful records of their health and growth for three weeks graph your data , and draw conclusions about the effect of light on plant growth follow the safety guidelines in Appendix A Plan It ! Brainstorm with classmates to answer these questions What different light conditions might you test ?

What plants will you use ?

How will you measure health and growth ?

How can you be sure your results are due to the light conditions ?

Write up your plan and submit it to your teacher . 117 ( Standards Focus Students know that mitochondria liberate energy for the work that cells do and that capture sunlight energy for photosynthesis . How does the sun supply living things with the energy they need ?

What happens during the process of photosynthesis ?

Key Terms photosynthesis autotroph heterotroph pigment chlorophyll stomata Photosynthesis Standards Where Does the Energy Come From ?

Obtain a calculator that does not use batteries . Place the calculator in direct light . Cover the solar cells with your finger . Note how your action affects the number display . Uncover the solar cells . What happens to the number display ?

Now cover all but one of the solar cells . How does that affect the number display ?

Think It Over Inferring From your observations , what can you infer about the energy that powers the calculator ?

On a plain in Africa , a herd of zebras peacefully eat the grass . But watch grazing will soon be harshly inter . A group of lions is about to attack the herd . The lions will kill one of the zebras and eat it . Both the zebras and the lions use the food they eat to obtain energy . Every living thing needs energy . All cells need energy to carry out their functions , such as making proteins and porting substances into and out of the cell . The meat supplies the lion cells with the energy they need . just as the grass provides the cells with energy . But plants and tain other organisms , such as algae and some bacteria , obtain their energy in a different way . These organisms use the energy in sunlight to make their own food .

at if The sun is the source of energy for most FIGURE Energy From the Sun The sun supplies energy for most living things , directly or indirectly . Relating Cause and Effect How does sunlight provide food for the zebra ?

Sources of Energy The process by which a cell captures energy in sunlight and uses it to make food is called photosynthesis ( toh SIN sis ) The term photosynthesis comes from the Greek words photo , which means light , and synthesis . which means putting Nearly all living things obtain energy either directly or indirectly from the energy of sunlight captured during photosynthesis . Grass obtains energy directly from sunlight , because it makes its own food during photosynthesis . When the zebra eats the grass , it gets energy that has been stored in the grass . Similarly , the lion obtains energy stored in the zebra . The zebra and lion both obtain the sun energy indirectly , from the energy that the grass obtained through photosynthesis . Plants manufacture their own food through the process of photosynthesis . An organism that makes its own food is called an autotroph ( oh ) An organism that can not make its mu own food , including animals such as the and the lion , is and called a heterotroph ( HET ur oh ) Many which make , its own food obtain food by eating other organisms . Some , such during photosynthesis , is an as fungi , absorb their food from other organisms . aU 29595 and ' because they can not make their own food . what are

Go For The Photosynthesis Process Visit Web Code Two Stages of Photosynthesis Photosynthesis has two stages . as shown in the diagram . Interpreting Diagrams Which stage requires light ?

120 Stage Chloroplast in plant cells capture energy from sunlight . The Two Stages of Photosynthesis Photosynthesis is a complex process . During photosynthesis , plants and some other organisms use energy from the sun to convert carbon dioxide and water into oxygen and sugars . The process of photosynthesis is shown in Figure . You can think of photosynthesis as taking place in two stages capturing the sun energy and producing sugars . You re probably familiar with many processes . To make a cake , for example , the first stage is to combine the ingredients to make the batter . The second stage is to bake the batter . To get the desired stages must occur in the correct order . Stage Capturing the Sun Energy The stage of photosynthesis involves capturing the energy in sunlight . In plants , this process occurs mostly in the leaves . Recall that are green inside plant cells . The green color comes from pigments , colored chemical compounds that absorb light . The main photosynthetic ment in is chlorophyll ( uh ) Chlorophyll functions in a manner similar to that of the solar cells in a calculator . Solar cells capture the energy in light and use it to power the calculator . Similarly , chlorophyll captures light energy and uses it to power the ond stage of photosynthesis . Stage The captured light energy is used to produce sugars and oxygen from water and carbon dioxide . Carbon dioxide enters the leaf through openings called stomata . Water enters the plant through roots and moves upward to the leaf .

stage Using Energy to Make Food In the next stage . of photosynthesis , the cell uses the captured energy to produce sugars . The cell needs two raw materials for this stage water ( and carbon dioxide ( In plants , the roots absorb at water from the soil . The water then moves up through the a plant stem to the leaves . Carbon dioxide is one of the gases in . Cut a strip by 20 the air . Carbon dioxide enters the plan . through small ings on the undersides of the leaves called stomata ( muh tuh ) singular stoma ) Once in the leaves , the water and carbon dioxide move into the . Inside the , the water and carbon dioxide undergo a complex series of chemical reactions . The reactions are powered by the energy captured in the first stage . These reactions produce chemicals as products . One product is a sugar that has six carbon atoms . sugars have the chemical formula . Recall that sugars are a type of carbohydrate . Cells can use the energy in the sugar to carry out important cell functions . The other product of photosynthesis is oxygen ( 02 ) which exits the leaf through the stomata . In fact , almost all the oxygen in atmosphere was produced by living things through the process of photosynthesis . I What makes plants green ?

a leaf on top of . Roll the edge of a dime ' After 10 minutes . remove out of a paper coffee filter . the paper strip , about from the bottom . over a section of the leaf , leaving a narrow band of color on the paper strip . plastic cup to a depth of . Stand the paper Strip in the cup so the color band is about above the alcohol . Hook the other end of the strip over the top of the cup . the paper strip and let it dry . Observe the strip . Wash your hands . Inferring What does the paper strip appearance reveal about leaf pigments ?

Sugars are used by me . for er er Oxygen exits through stomata on the underside of the leaf . Chapter 121 The Photosynthesis Equation The events of thesis can be summed up by the following chemical equation light energy sco , 61420 . 60 , carbon dioxide water oxygen Notice that the raw materia molecules of carbon dioxide and six molecules of on the left side of the equation . The molecule of a sugar and six of on the right side of the equation . An arrow , which you can read as yields , connects the raw als to the products . Light energy , which is necessary for the chemical reaction to occur , is written above the arrow . What happens to the sugar produced in photosynthesis ?

Plant cells use some of the sugar for food . The cells break down the sugar molecules to release the energy they contain . This energy can then be used to carry out the plants functions . noun . stem , Enemy Some sugar mo ec es are into other compounds , when you ea ( mot , you such as cellulose . Other sugar molecules may be stored in the obtain energy stored during plant cells for later use . When you eat food from plants , such photosynthesis . as potatoes or carrots , you are eating the plant stored energy . Reading In the photosynthesis equation . what does the Checkpoint ) arrow mean ?

Reading , 59330 Assessment Build Science Vocabulary Greek Word Origins What clue in the Key Term photosynthesis lets you 19 ( know that the term has something to do with light ?

Reviewing Key Concepts a . Reviewing Why do living things need energy ?

Explaining How do plants obtain energy ?

um Applying Concepts An insect eats a leaf . Explain ' hug how the insect depends on the sun for energy . In a a . Reviewing What chemical equation sums up the ta . events of photosynthesis ?

an i is . Comparing and Contrasting What are the substances lob needed for photosynthesis ?

What substances are . produced during photosynthesis ' words chlorophyll , Making Generalizations Would you expect a plant to um ! carbon . produce more oxygen on a cloudy day or a sunny day ?

Hamid . Explain . ind 1129 Section I , Standards Focus Students know that mitochondria liberate energy for Vigorous exercise , such as hiking , requires a lot of energy . All the energy your body uses comes the work that cells do and that capture sunlight energy for photosynthesis . What events occur during respiration ?

What is fermentation ?

Key Terms respiration fermentation A , I noun Energy from food . it Respiration Standards What Is a Product of Respiration ?

Put on your goggles . Fill two test tubes half full of warm water . Add of sugar to one of the test tubes . Put the tubes in a rack . Add of dried yeast ( a organism ) to each tube . Stir the contents of each tube with a straw . Place a stopper snugly in the top of each tube . Observe any changes that occur in the two test tubes over the next 10 to 15 minutes . Think It Over Observing What changes occurred in each test tube ?

How can you account for any differences that you observed ?

You and your friend have been hiking all morning . You look for a flat rock to sit on , so you can eat lunch . The steepest part of the trail is ahead . You need a lot of energy to get to the top of the mountain . That energy will come from food . Before food can provide your body with energy , it must pass through your digestive system . There . the food is broken down into small molecules These molecules can then pass into your bloodstream . Next , the molecules travel through the bloodstream to the cells of your body . Inside the cells , the energy in the molecules is released . In this section , you learn how your body cells obtain energy from the food you eat .

Hook Energy From Respiration All organisms need energy to live . The leopard frog uses energy to leap great distances . Although the mushrooms do move , they still need energy to grow and reproduce . Predicting During the winter months , some animals go into a state called hibernation . During hibernation , an animal does not eat , and its body activities are greatly reduced . Predict what will happen to an animal rate of cellular respiration when the animal goes into hibernation . Explain your prediction . 124 I What Is Respiration ?

After you eat a meal , your body converts some of the food into glucose , a type of sugar . Respiration is the process by which cells obtain energy from glucose . During break down simple food molecules such as sugar and release the energy they contain . Because living things need a continuous supply of energy , the cells of all living things carry out respiration continuously . Plant cells , as well as animal cells , respire . Storing and Releasing Energy Energy stored in cells is something like money you put in a savings account in a bank . When you want to buy something , you withdraw some of the money . Cells store and use energy in a similar way . During photosynthesis , plants capture the energy from sunlight and save it in the form of carbohydrates , including sugars and starches . Similarly , when you eat a meal , you add to your body energy savings account . When cells need energy , they withdraw it by breaking down the carbohydrates in the cess of respiration . Breathing and Respiration The term has two meanings . You have probably used it to mean breathing , that is , moving air in and out of your lungs . To avoid confusion , the respiration process that takes place inside cells is sometimes called cellular respiration . The two meanings of the term respiration do point out a connection , however . Breathing brings oxygen , which is usually necessary for cellular tion , into your lungs . What is respiration ?

stage in the cytoplasm , The Mo stages of Respiration Like photosynthesis , is a process . Figure shows these two stages . The stage takes place in the cytoplasm . There . molecules of glucose are broken down into smaller molecules . Oxygen is not involved , and only a small amount of energy is released . The second stage of respiration takes place in the . There , the small molecules are broken down into even smaller molecules . These chemical reactions require gen , and they release a great deal of energy . This is why the mitochondria are sometimes called the powerhouses of the cell . The energy liberated , or released , by mitochondria is still stored in the form of chemical energy . But now it is stored in molecules that are readily used by the cell . Two other products of respiration are carbon dioxide and water . The carbon dioxide diffuses out of the cell . In most mals , the carbon dioxide and some water leave the body during exhalation . Thus , when you breathe in , you take in raw material for respiration . When you breathe out , you release carbon dioxide and of respiration . The Respiration Equation Although respiration occurs in a series of complex steps , the overall process can be in the following equation sugar oxygen carbon dioxide waur Notice that the raw materials for respiration are sugar and oxygen . Plants and other organisms that undergo thesis make their own sugar . The glucose in the cells of animals and other organisms comm from food they eat . The oxygen comes from the air or water surrounding the organism . glucose is broken down into smaller molecules . A small amount of energy is released . Forms Mo Stages of Respiration Respiration . like photosynthesis , takes place in two stages . Note that energy is released in both stages . Interpreting Diagrams In which stage of respiration is oxygen used ?

stage in the mitochondria . the smaller molecules combine with oxygen to produce water and carbon dioxide . This reaction releases a large amount of energy . Chapter 125 Chloroplast I Photosynthesis During photosynthesis , plants use carbon dioxide and release oxygen . 50 Home Photosynthesis and Respiration You can think of photosynthesis and respiration as opposite processes . Comparing and Contrasting which process uses oxygen ?

Which uses carbon dioxide ?

For Links on cellular respiration Web Code 126 Respiration During respiration , organisms use oxygen and release carbon dioxide . Mitochondrion Comparing Photosynthesis and Respiration Can you notice anything familiar about the equation for respiration ?

You are quite right if you said it is the opposite of the equation for photosynthesis . This is an important point . During synthesis , carbon dioxide and water are used to produce sugars and oxygen . During respiration , the sugar glucose and oxygen are used to produce carbon dioxide and water . Photosynthesis and respiration can be thought of as opposite processes . Together , these two processes form a cycle that keeps the levels of oxygen and carbon dioxide fairly constant in atmosphere . As you can see in Figure , living things use both gases over and over again . which or ) produces water ?

Fermentation Some cells are able to obtain energy from food without using oxygen . For example , some organisms live where there is no oxygen , such as deep in the ocean or in the mud of lakes or swamps . These organisms obtain their energy through fermentation , an process that does not require oxygen . Fermentation provides energy for cells without using oxygen . The amount of energy released from each sugar molecule during fermentation , however , is much lower than the amount released during respiration .

when yeast and some other organisms break down sugars . This process is sometimes called alcoholic mentation because alcohol is one of the products . The other products are carbon dioxide and a small amount of energy . The products of alcoholic fermentation are important to bakers and brewers . The carbon dioxide produced by yeast creates air pockets in bread dough , causing it to rise . Carbon dioxide is also the source of bubbles in alcoholic drinks such as , beer and sparkling wine . Alcoholic Fermentation One type of fermentation occurs Lactic Acid Fermentation Another type of fermentation takes place at times in your body . You probably felt its effects . Think of a time when you ran as fast as you could for as long as you could . Your leg muscles were pushing hard against the ground . and you were breathing quickly . No matter how hard you breathed . your muscle cells used up the oxygen faster than it could be replaced . Because your , cells lacked oxygen , fermentation occurred . The fermentation Lactic Acid Fermentation supplied your cells with energy . One product of this type of When ' mentation is an acid known as lactic acid . When lactic acid a i en ' i ' ens builds up , you feel a painful sensation in your muscles . Your with energy muscles feel weak and sore . Which kind of fermentation is important to Checkpoint ) bakers ?

section Assessment ix ' Target Reading Skill Create Outlines Identifying What is the process in which cells Use your completed outline to help answer obtain energy without using oxygen ?

the questions below . inferring How would athletes be affected if this process could not take place ?

Predicting Is this process more likely to occur during a short run or a long walk ?

Explain your Reviewing Key Concepts a . Reviewing What happens during respiration ?

answer . Reviewing What is the equation for respiration ?

Comparing and Contrasting Compare the equations for respiration and IN photosynthesis . Relating Cause and men Explain why Make Bread With an adult family member . Cellular adds carbon dioxide to the follow a recipe in a cookbook to make a loaf of atmosphere , but does not bread using yeast . Explain to your family the cellular process that causes the dough to rise . After you bake the bread , observe a slice and look for evidence that fermentation occurred . 127

me Own Lab Exhaling Carbon Dioxide Problem is there a relationship between exercise and the amount of carbon dioxide you exhale ?

Skills Focus predicting , controlling variables Materials beakers bromthymol blue solution ( solution ) 30 straws I stopwatch or watch with second hand graduated cylinder , 25 paper towels Procedure El Testing for Carbon Dioxide . Label one beaker Beaker and the other beaker Beaker . Beaker will be the trol in the experiment . Bromthymol blue can be used to test for the presence of carbon dioxide . To see how this works , fill each beaker with 15 of thymol solution . CAUTION Bromthymol blue can stain skin and clothing . Avoid ing or splashing it on yourself . Note and record the color of the solution in both beakers . Place a straw in Beaker . Gently blow through the straw into the solution until the solution changes color . CAUTION Use the straw to breathe out only . Do not suck the solution back through the straw . Your ner should begin timing when you first blow through the straw and stop as soon as the solution changes color . Record the time that has elapsed . 128 . PART Exercise and Carbon Dioxide . In Part you timed the change of color out exercising first . Predict how long it will take the solution to change color if you duct the test after you exercise . Design an experiment to test your prediction . Be sure to include a plan for recording your results and steps to review your results . Write down the steps of your experiment and get your teacher approval . Then , duct your experiment . CAUTION Do not yourself . If you have a medical condition that limits your ability to exercise , do not take part in the exercise portion of this experiment . Analyze and Conclude . Measuring How long did it take for the tion to change color the first time you did the test ( without exercising ) Drawing Conclusions How did exercising affect the amount of time it took for the solution to change color ?

Predicting What was your prediction in Step based upon ?

Was your prediction accurate ?

Controlling Variables in Part , what did you need to control ?

Explain how you controlled those variables . Communicating Write a paragraph that relates the results of your experiment to the process of cellular respiration . Be sure to explain how increased cellular activity affects carbon dioxide output . More to Explore Some plants grow in water . If you added bromthymol blue to the water , do you think it would turn color ?

Hint What might happen to the carbon dioxide that the plants produce during respiration ?

Standards Focus Students know cells divide to increase their numbers through a process of mitosis , which results in two daughter cells with identical sets of chromosomes . Students know DNA ( acid ) is the genetic material of living organisms and is located in the chromosomes of each cell . What events take place during the three stages of the cell cycle ?

How does the structure of DNA help account for the way in which DNA copies itself ?

Key Terms A cell cycle I interphase replication mitosis chromosome I Cell Division What Are the Yeast Cells Doing ?

Use a plastic dropper to transfer some yeast cells from a yeast culture to a microscope slide . Your teacher has prepared the slide by drying methylene blue stain onto it . Add a and place the slide under a microscope . Examine the cells on the slide . Use low power first , then high power . Look for what appears to be two cells attached to each other . One cell may be larger than the other . Draw what you see . Think It Over Developing Hypotheses What process do you think the double cells are undergoing ?

Develop a hypothesis that might explain what you see . In the early autumn , many local fairs run pumpkin contests . Proud growers enter their largest pumpkins , hoping to win a prize . The pumpkin below has a mass greater than 600 grams ! This giant pumpkin began as a structure inside a small . How did the pumpkin grow so big ?

body are dividing as you read this page . pumpkin chapters 9129 A pumpkin grows in size by increasing both the size and the number of its cells . A single cell grows and then divides , forming two cells . Then two cells grow and divide , forming four , and so on . This cess of cell growth and division does not occur only in pumpkins , though . In fact , many cells in your

' Cell Processes and Energy Modeling Mitosis Refer to Figure 12 as you carry out this activity . Construct a model of a cell that has four chromosomes . Use a piece of construction paper to represent the cell . Use pipe cleaners to represent the chromosomes . Make sure that the chromosomes look like double rods . Position the chromosomes in the cell where they would be during prophase . Repeat Step for metaphase , anaphase , and telophase . Making Models How did the model help you understand the events of mitosis ?

130 Stage How do little pigs get to be big pigs ?

Their cells grow and divide . over and over . The regular sequence of growth and division that cells undergo is known as the . During the cell cycle . a cell grows . prepares for division , and divides into two new cells , which are called daughter Each of the daughter cells then begins the cell cycle again . You can see details of the cell cycle in Figure 12 . Notice that the cell cycle is divided into three main stages interphase , mitosis , and cytokinesis . The first stage of the cell cycle is called interphase . is the period before cell division . During interphase , the cell grows , makes a copy of its DNA , and prepares to divide into two cells . Growing During the first part of interphase . the cell grows to its full size and produces structures it needs . For example . the cell makes new ribosomes and produces enzymes . Copies are made of both mitochondria and . Copying DNA in the next part of interphase . the cell makes an exact copy of the DNA in its nucleus in a process called replication . Recall that DNA is found in the thin strands of chromatin in the nucleus . During interphase , the , chromatin appears as a dense mass within a clearly defined nucleus . DNA holds all the information that the cell needs to carry out its functions . Replication of DNA is veryimportant , since each daughter cell must have a complete set of DNA to survive . At the end of DNA replication . the cell contains two identical sets of DNA . You will learn the details of DNA replication later in this section . Preparing for Division Once the DNA has replicated , preparation for cell division begins . The cell produces that it will use to divide into two new cells . At the end of interphase , the cell is ready to divide .

Stage Mitosis Once interphase is complete , the second stage of the cell cycle begins . Mitosis ( my TOH sis ) is the stage during which the cell nucleus divides into two new nuclei . During mitosis , one copy of the DNA is distributed into each of the two daughter cells . Scientists divide mitosis into four parts , or phases phase . metaphase . anaphase , and telophase . During prophase , the threadlike chromatin in the nucleus condenses to form structures called chromosomes ( Each chromosome has two rods because the cell DNA has replicated . and each rod in a chromosome is an exact copy of the other . Each identical rod in a chromosome is called a . Notice in Figure 11 that the two are held together by a structure called a centromere . As the cell progresses through metaphase , anaphase , and telophase , the separate from each other and move to opposite ends of the cell . Then two nuclear envelopes form around the new chromosomes at the two ends of the cell . Chromosomes Centromere FIGURE 10 Bigger Pig , More Cells The mother pig has more cells in her body than her small piglets . 11 Chromosomes During mitosis , the chromatin condenses to form chromosomes . Each chromosome consists of two identical rods , or . Applying Concepts During which phase of mitosis do the chromosomes form ?

9131 12 The Cell Cycle Cells undergo an orderly sequence of events as they grow and divide . The shown here is a typical cell cycle i an animal cell . Comparing and Contrasting Compare the location of the chromosomes during metaphase and anaphase . 1320 an Mitosis Telophase A Interphase The cell grows to its mature size . makes a copy of its DNA . and prepares to divide into two cells . Two cylindrical structures called are also copied . Cytokinesis A The cell membrane pinches in around the middle of the cell . The cell splits in two . Each daughter cell ends up with an identical set of chromosomes and about half the . The chromosomes begin to stretch out and lose their rodlike appearance . A new nuclear envelope forms around each region of chromosomes . The DNA is once again separated from the cytoplasm by a membrane .

For . The Cell Cycle Web Code Spindle fiber a A Mitosis Prophase Chromatin in the nucleus condenses to form chromosomes . The pairs of move to opposite sides of the nucleus . Spindle form a bridge between the ends of the cell . The nuclear envelope breaks down . a Mitosis Metaphase The chromosomes line up across the center of the cell . Each chromosome attaches to a fiber at its centromere . Anaphase The split . The two separate , and each becomes a new chromosome . The new chromosomes move to opposite ends of the cell . The cell stretches out as the opposite ends are pushed apart .

. How long does it take for a cell to go through one cell cycle ?

it all depends on the cell . A human liver cell , for example , completes one cell cycle in about 22 hours . as shown in the graph . Study the graph and then answer the following questions . Reading Graphs What do the three curved arrows outside the circle represent ?

Reading Graphs in what stage of the cell cycle is the wedge representing growth ?

Interpreting Data In human liver cells , how long does it take DNA replication to occur ?

Drawing Conclusions In human liver cells , what stage in the cell cycle takes the longest time ?

FIGURE 13 Cytokinesis in Plant Cells During cytokinesis in plant cells , a cell plate forms between the two new nuclei . Applying Concepts What is the function of the cell plate ?

Stage Cytokinesis The stage of the cell cycle , which is called Cytokinesis ( sy toh NEE sis ) completes the process of cell division . During cytokinesis . the cytoplasm divides . The are distributed into each of the two new cells . Cytokinesis ally starts at about the same time as telophase . When is complete , two new cells , or daughter cells , have formed . Each daughter cell has the saute number of somes as the original parent cell . At the end of Cytokinesis , each cell enters interphase , and the cycle begins again . Cytokinesis in Animal Cells During Cytokinesis in mal cells , the cell membrane squeezes together around the middle of the cell . The cytoplasm pinches into two cells . Each daughter cell gets about half of the . Cytokinesis In Plant Cells Cytokinesis is somewhat ferent in plant cells . A plant cell rigid cell wall can not squeeze together in the same way that a cell membrane can . Instead , a structure called a cell plate forms across the middle of the cell . The cell plate gradually develops into new cell membranes between the two daughter cells . New cell walls then form around the cell membranes . landing During what phase of mitosis do begin ?

Structure and Replication of DNA DNA replication ensures that each daughter cell will have the genetic information it needs to carry out its activities . Before scientists could understand how DNA replicates , they had to know its structure . In 1952 , Rosalind Franklin used an method to photograph DNA molecules . Her photographs helped James Watson and Francis Crick out the ture of DNA in 1953 . The Structure of DNA If you were to unravel a some , you would that the DNA strands are wound tightly around proteins . The proteins help support the some structure . Notice in Figure 14 that the strands of the DNA molecule look like a twisted ladder . The two sides of the DNA ladder are made up of molecules of a sugar called , alternating with molecules known as phosphates . Each rung is made up of a pair of molecules called nitrogen bases . Nitrogen bases are molecules that contain the element nitrogen and other elements . DNA has four kinds of nitrogen bases adenine ( AD uh neen ) thymine ( THY meen ) guanine ( neen ) and cytosine ( SY tuh seen ) The capital letters A , and are used to represent the four bases . The bases on one side of the ladder pair with the bases on the other side . Adenine ( A ) only pairs with thymine ( while guanine ( only pairs with cytosine ( This pairing pattern is the key how DNA replication occurs . FIGURE 14 The Structure of DNA The DNA molecule , supported by proteins , is shaped like a twisted ladder . Nitrogen bases ' Thymine Guanine cytosine Adenine Guanine Adenine Cytosine Thymine Proteins ( a sugar ) Phosphate Chapter 135

Old strand FIGURE 15 DNA Replication During DNA replication , a DNA New strand molecule unzips between its paired bases . New bases pair . the ham on each old strand . The Replication Process DNA replication begins when A a result , two DNA the two sides of the DNA molecule unwind and separate , Strands form somewhat like a zipper unzipping . As you can see in Figure 15 , the molecule separates between the paired nitrogen bases . Next , nitrogen bases that are in the nucleus pair up with the bases on each half of the DNA molecule . Because of the way in the nitrogen bases pair with one another , the order of the bases in each new DNA molecule exactly matches the order in the original DNA molecule . Adenine always pairs with thymine , while guanine always pairs with cytosine . Once the new bases are attached , two new DNA molecules are formed . During DNA replication , which base pairs with ) guanine ?

loading Assessment Build Science Vocabulary Greek Word a . Listing List the nitrogen bases in DNA . Origins The Greek word kinesis means , Describe how the nitrogen base During , what motion occurs ?

pair in a DNA molecule . Reviewing Key concepts Inferring One section of a strand of DNA , has the base se . What is the a . Reviewing What are the three stages of base sequence the other strand ?

the cell cycle ?

Summarizing Summarize what happens to ' chromosomes during the stage of the cell In I cycle in which the nucleus divides . include i it It I the terms prophase , metaphase , I I and . I ! Interpreting Diagrams Look at Figure . mu What is the role of spindle during I i cell division ?

135 Multiplying by . Fill in the column labeled Total Number by be How long do the stages of the cell cycle take ?

ata um ' across ea row your ski Focus . Add the totals for the five stages to find the observing . total number of cells counted . Materials Analyze and Conclude microscope on your observations , did . colored pencils root tissue lave aNl ' rate or low . optional ) stage of the ce prepared slides of onion root tip cells Cy ' you serve most en division . Calculating The cell cycle for onion root tips takes about 720 minutes ( 12 hours ) Use your procedure data and the formula below to find the ' Place the slide on the stage of a microscope . her of each stage a es Use low power to locate a cell in interphase . Numb Then switch to high power , and make a me ' 120 min labeled drawing of the cell . CAUTION Slides 5139 ?

i umber and break easily . Do not allow the Ce objective to touch the slide . If the slide Communicating use the data to comp , 2791 Wu the amount of time spent in mitosis with the ' 355 ' total time for the whole cell cycle . Write your , Repeat Step to find cells in prophase , answer in the form of a paragraph . metaphase , anaphase , and telophase . Then copy the data table into your notebook . More to . Return to low power . Find an area of the Examine prepared slides of animal cells slide with many cells undergoing cell going cell division . Use drawings and descriptions sion . Switch to the magnification that lets to compare plant and animal mitosis . I you see about 50 cells at once ( for example , 100 ) Examine the cells row by row . and count the cells that are in interphase . Record that number in the data table under First Sample . Examine the cells row by row four more times to count the cells in prophase , metaphase , anaphase , and telophase . Record the results . Move to a new area on the slide . Repeat Steps and record your counts in the column labeled Second Sample .

Standards Focus Students know that as multicellular organisms op , their cells differentiate . What is differentiation What factors influence how and when cells differentiate within different organisms ?

00 Key Terms differentiation ' stem cell A skin cell undergoes mitosis . 138 Differentiation Standards How Is It Different ?

Study the photos above of a growing bean plant . Write your observations about how the plant changes in structure in each stage of its development . Think It Over Forming Operational Definitions As the plant grows , its cells divide and undergo a process called differentiation . Based on your observations , what does differentiation mean ?

You have learned that the cell theory states that living things are made of cells . Some living things are , or cellular . organisms . Other living things are multicellular . They consist of many kinds that differ from one ano her . The i cell theory also says that cells are produced from other cells . When a cell divides by mitosis , it produces two daughter cells with identical sets . So how do cells in cellular organisms different from one another ?

Differentiation Cell division alone can not explain the development of new structures . If cells only divided . the result would merely be a big ball of identical cells . instead , cells differentiate . Differentiation is the process by which ells change in ture and become capable of carrying out specialized functions . cells differentiate , they become different from one another . They also form groups made of other , similarly cells . These groups then form tissues and organs .

Undifferentiated plant cell Differences in Structure Multicellular organisms begin their lives as one cell . Through mitosis and , the single cell becomes an organism with specialized structures . For example , Figure 16 shows an undifferentiated plant cell and the kinds of cells that can arise from this cell . Notice how different they look . Differences in Function As cells differentiate in structure , a division of labor results . That is , they begin to carry out ferent functions . For example , plant leaves contain cells that carry out photosynthesis . Root cells , which are underground , do not carry out photosynthesis . So it shouldn surprise you that some in leaf cells and root cells differ , too . Leaf cells have plenty of for capturing sunlight , while root cells have none . Instead , many root cells have projections that reach into the soil . These structures increase the amount of water the root cells can absorb from the soil . Tissues . Organs , and Systems When cells differentiate , they also become organized . At first , they group into tissues . Such cells work together , carrying out functions . For example , muscle cells in animals become organized into long strands of muscle tissue that can move legs or arms . Groups of tissues can combine to form organs , such as the roots of a plant or the ach of an animal . Systems , such as the digestive system , begin to function as organs and tissues work together . Increasingly Specialized Cells As development continues , more differentiation occurs . For example , the ina in your eye consists of two types of cells that are sensitive to light . Rod cells function in dim light but can not detect color . Cone cells detect color , but require brighter light to function . The cells of your retina differentiated early in your ment . Rods and cones differentiated ) What Is the result of cell differentiation ?

Leaf cell Transport cell ' Root cell Specialized Cells Plants have undifferentiated cells in their stems and roots that can give rise to different kinds of cells . Inferring Can photosynthesis take place In a root cell ?

Why or why not ?

chapters 139 FIGURE 17 A Source of Blood Cells Different types of blood cells can form when stem cells undergo differentiation . Observing How do the structures of red blood cells and white blood cells differ ?

1400 Undifferentiated Stem Cell How Cells Differentiate During development , cells become how they will differentiate . The instructions that determine what will pen to a cell are coded in the DNA in its nucleus . Differentiation occurs when certain sections of DNA are turned off . The active DNA then guides how the cell develops . Once a cell future has been determined , when and how much it changes depends on its DNA , its function , and the type of organism . Some cells differentiate completely during development . Others do not change until later in the life of an organism . Cell Differentiation Among Animals Did you know that a lizard that loses its tail can grow a new one ?

Many adult animals , such as insects and some crustaceans and reptiles , can grow a limb or a tail to replace a lost one . Cells at the point of injury can differentiate , forming new muscle , bone , blood , and nerves . The replacement of lost body parts in lizards and some other animals does not occur in humans . Once human cells , they usually lose the ability to become other types of cells . A blood cell can not change into a skin cell , for instance . However , humans do produce certain stem can differentiate throughout life . Stem cells exist all around the body . These cells can respond to specific needs in the body by becoming specialized . For example , your body needs a constant supply of new blood cells to replace older cells . Every day , stem cells produce a steady supply of blood cells . These include red cells that carry oxygen , white cells that infection , and other cells needed in the blood . loading What kind of cells can stem cells produce in the ) human body ?

White Blood Cell . African violet plant The leaf is cut and cell differentiation leads transferred to soil . to new root and leaf tissues . Cell Differentiation in Plants Cells differentiate in FIGURE 18 plants much the same way they do in animals . A New Plant ated cells become grouped into the tissues that make up the The stem ofa leaf from an roots , stems , and leaves . Cells also continue to differentiate Alma Plan 59 ther within each kind of organ . For example , some cells in the the a new stem become specialized as the tubes that transport food and water through the plant . Many plants have the ability to grow throughout their lives This growth happens because certain cells in the roots and stems of plants are not in their development . These cells can undergo rapid cell division and differentiation , increasing the size of the roots and stems . It can also lead to the growth of new roots , stems , and leaves . For example , if a leaf of an African violet plant is cut and put into soil or water , its stem will begin to grow roots ! Eventually , more cells will differentiate into root cells and stem cells , and a new plant grows . Gardeners use this technique to ate many plants from one original plant . Section Assessment Target Reading Skill Create Outlines Comparing and Contrasting How does the Use your completed outline to help answer ability of cells to differentiate in humans the questions below . compare to the ability in plants ?

Reviewing Key Concepts a . Describing What happens to cells when they undergo differentiation ?

Explaining How does differentiation lead to Use a ball of clay to tissues and organs in a developing organism ?

represent a single cell . Divide the cell into Applying How does the phrase two smaller ones , and then again into four . division of labor relate to differentiation ?

Fashion each cell into a different shape . Identifying Name two factors that affect Then divide each shape in two , and reshape how and when cells differentiate . the new pieces to look like the shape they , Relating cause and Effect what came from . Explain to a family member how human stem cells to differentiate into ' 59 ' specialized blood cells ?

in a developing organism . 141 Chapter Study Guide BIG Idea Photosynthesis Key Concepts Nearly all living things obtain energy either directly or indirectly from the energy of sunlight captured during photosynthesis . During photosynthesis , plants and some other organisms use energy from the sun to convert carbon dioxide and water into oxygen and sugars . The equation for photosynthesis is light energy ( 602 Key Terms photosynthesis pigment autotroph chlorophyll heterotroph stomata Respiration Key Concepts During respiration , cells break down simple food molecules such as sugar and release the energy they contain . The respiration equation is 602 energy Fermentation provides energy for cells without using oxygen . Key Terms respiration fermentation 1426 Cells obtain through the processes of photosynthesis and Inspiration , whi are carried out by and mitochondria . Cell Division ( Key Concepts , During interphase . the cell grows , makes a copy of its DNA , and prepares to divide into two cells . During mitosis . one copy of the DNA is distributed into each of the two daughter cells . During cytokinesis , the cytoplasm divides . The are distributed into each of the two new cells . Because of the way in which the nitrogen bases pair with one another , the order of the bases in each new DNA molecule exactly matches the order in the original DNA molecule . Key Terms cell cycle interphase replication mitosis chromosome cytokinesis Cell Differentiation Key Concepts As cells differentiate , they become different from one another . They also form groups made of other , similarly specialized cells . These groups then form tissues and organs . Once a cell future has been determined , when and how much it changes depends on the cell function and the type of organism . Key Terms differentiation stem cell

Go . For . Visit Web Code Reading Skill Create Outlines To help review the structure and Wham DNA replication of DNA . in details under A and DNA in the partially completed outline at right . Replication of DNA Reviewing Key Terms Choose the letter of the best answer . Complete the following sentences so that . The in which photosynthesis takes a ' key te ?

Chlorophyll is a type . which is on non . A lion is a heterotroph , a type of organism ' gal We in the mud of . What process produces carbon dioxide ?

their energy through fermentation , I is replication mum , Cytokinesis IS the stage of the cell cycle in respiration ' The process in which a cell ( an exact 10 ' rod 0031 Cells and blood Ca ?

can copy of its DNA is Called be produced in the body by stem cells because . respiration . replication . reproduction . The stage ofthe cell cycle when a spindle forms is called interphase . prophase . metaphase . Which of the following is a result of differentiation ?

a . An organism grows larger . Cells in an embryo increase in number . Cells in an embryo become different from one another . I . An organism reproduces . 143 Review and Assessment Checking Concepts Applying Skills 11 . explain what happens to energy from Use the table below to answer Questions the sun during photosynthesis . Percentages of Nitrogen Bases 12 . Why do organisms need to carry out the in the DNA of Various , process of respiration ?

13 . How are respiration and fermentation similar ?

How are these processes different ?

14 . Explain why cell division is a vital process for organisms . 15 . Describe what happens during . Cytosine 20 23 23 . Graphing For each organism , draw a bar 17 . How are stem cells different from other cells graph to show the percentages of each in an adult animal ?

nitrogen base in its DNA . 16 . How do the events in the cell cycle ensure that the genetic information in the daughter cells will be identical to that of the parent cell ?

24 . Interpreting Data What is the relationship Th ink i rig Critically between the amounts of adenine and thymine in the DNA of each organism ?

What is the 18 ' th much relationship between the amounts of guanine ash into the air that it most of the and sunlight that usually strikes Earth . How might this affect the of io the 25 . Inferring Based on your answer to Question energy they need io live ?

24 , what can you infer about the structure of DNA in these three organisms ?

19 . Comparing and Contrasting Explain the , ihe processes of 26 . Applying Concepts Suppose cytosine made and up 28 of the nitrogen bases in an organism . What percentage of the organism nitrogen 20 . Relating Cause and Effect Do plant cells bases be thymine ?

Explain . need to carry out respiration ?

Explain . 21 . Inferring The diagram below shows part of one strand of a DNA molecule . What would the bases on the other strand be ?

Standards ' 93 Performance Assessment Bring in your plants , recorded observations . and graphs to share with the class . Be prepared to describe your mental plan and explain your results . How well 22 . Making Generalizations is cell did you follow your experimental plan ?

What did differentiation a necessary process in a you learn about photosynthesis and light from the developing organism ?

experiment you performed ?

1440 Standards Practice Choose the letter of the best answer . Which of the following statements is true ?

A Plants can not respire because they have no mitochondria . Photosynthesis produces carbon dioxide . Animals can not photosynthesize . Only plants and only animals respire . Which of the following nitrogen base pairs can be found in DNA ?

A . Which stage of mitosis is represented by the following cell ?

A interphase anaphase telophase metaphase . Which of the following statements about differentiated cells is false ?

A They look different but have the same functions . They look different and have different functions . They become grouped with similar cells , forming tissues . They make up the tissues and organs of multicellular organisms . Which statement best describes chromosomes ?

A They carry out respiration . They consist mostly of the pigment chlorophyll . They consist of tightly coiled strands of DNA and proteins . Their structure is only visible during interphase . Success Tracker at Use the table below to answer Questions and . Effect of Temperature on Length of Onion Cell Cycle . A scientist performed an experiment to determine the effect of temperature on the length of the cell cycle . On the basis of the data in the table above , how long would the cell cycle last at a temperature of ?

A less than hours more than hours between and hours about 20 hours . The data in the table above show that A cells divide faster when the temperature is decreased . cells divide faster when the temperature is increased . the length of the cell cycle is not affected by temperature . the length of the cell cycle is inherited . idea . Compare and contrast the raw materials and products of photosynthesis with those of respiration . Then explain how the two processes are connected . 145

troT ( 33 ) Elm Chapter I What Is Life Science ?

scientific progress is made by asking meaningful questions and conducting careful investigations . What skills do scientists use to learn about the world ?

What are some big ideas in life science ?

What is scientific inquiry ?

Why is preparation important when carrying out scientific investigations in the lab and in the field ?

Chapter Using Light . Ught entering the eye is bent by the cornea and lens to form an image on the retina . What are the basic properties of waves ?

How does visible light help you see ?

What determines the color of an opaque object ?

What determines the types of images formed by convex and concave lenses ?

Chapter Cell Structure and Function Cells are the basic building blocks of all living things . All cells have similar structures and carry out similar functions . What is the cell theory ?

What are found in the cytoplasm , and what are their functions ?

How is water important to the function of cells ?

How do most small molecules cross the cell membrane ?

Chapter Cell Processes and Energy cells obtain energy through the processes of respiration and photosynthesis , which are carried out by mitochondria and . What happens during the process of photosynthesis ?

What events take place during the three stages of the cell cycle ?

What factors influence how and when cells differentiate within different organisms ?

i Emily wanted to learn more about cells . She cut a leaf from a freshwater plant and used it to prepare a microscope slide . Then she used a cotton swab to get some cells from the inside of her cheek . She used the cheek cells to prepare another slide . Next , she used a chemical to stain the cells so they would be easier to see . Unfortunately , the slides got mixed up before they could be labeled . Emily used a microscope to see if she could determine which slide held plant cells and which held cheek cells . She observed the structures in cells from each slide and drew diagrams to show what she observed . She noted that the cells on one slide had cell walls , while the cells on the other . did not . She observed mitochondria in both samples and in one sample . She also noted that some of the cells with cell walls had chromosomes in their nuclei . Drawing of Drawing of slide A slide . Which is an example of a scientific model ?

which of the following would be found in ( Chapter ) plant cells but not in cheek cells ?

Chapter ) microscope slides cell walls chromosomes the microscope mitochondria nuclei ' Where in plant cells does photosynthesis mitochondria occur ?

theme , What forms the enlarged images produced cell wall by a microscope ?

Chapter ) mitochondria nuclei I . Summary Does the Slide A drawing ' the Pup the Ye represent plant or cheek cells ?

How do you ' know ?

What process do Emily tions of chromosomes provide evidence for ?

Explain why chromosomes were not visible in all the cells on that slide . 147