52 MHR • Unit 1 Cells and...

T he human body is like a wonderful “machine” that can carry out amazingfeats. These acrobats use many parts of this machine, such as muscles and

bones, to help them balance as they move through hoops above the stage.They train for a long time to be able to control their movements so exactly.

There are other parts of the human body that work together without suchconscious control. We continually breathe, our hearts beat, and our nervesmonitor our environment to protect us from danger. From time to time we are aware of these actions taking place in our bodies. We say things like, “I’m out of breath,” “My heart is pounding,” or “I’m scared.”

Our bodies also perform a variety of other functions that we do notcontrol, such as digesting our food, monitoring our blood sugar levels, and fighting off viruses and bacteria. These important activities are all part of the constant work going on inside the human body to keep it healthy.

52 MHR • Unit 1 Cells and Systems

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What You Will Learn

In this chapter, you will• investigate how different human body

systems function independently and together• examine the structure and function of the

digestive system, excretory system,circulatory system, and respiratory system

Why It Is Important

Understanding how different human bodysystems function is important for maintainingyour health.

Skills You Will Use

In this chapter, you will• model organs in the circulatory and respiratory

systems• communicate your understanding about the

structures of the heart• use safe dissection techniques

Chapter 2 Human body systems work independently and together. • MHR 53

FOLDABLES TM

Reading & StudySkills

Make the following Foldable to take notes on

the structure and functions of human systems.

STEP 1 Fold one piece of unlined paperwidthwise into thirds.

STEP 2 Fold down 2.5 cmfrom the top.(Hint: From the tipof your indexfinger to your firstknuckle is about2.5 cm.)

STEP 3 Fold the rest into fifths.

STEP 4 Unfold, lay the paper lengthwise,and draw lines along the folds.Label your table as shown.

Make a Table As you read the chapter,develop a table describing the structures and functions of various human systems.

Systems

Digestive

Excretory

Circulatory

Respiratory

Bones &Muscles

Structure Function

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A system is made of parts that work together as a whole. In the human body, many

different systems work independently, but are also connected to each other. Each

organ system consists of organs that are made from various types of tissue. Tissue

refers to a group of similar cells working together to carry out a specific function.

Have you ever walked into a bicycle repair shop like the one in Figure 2.1 and noticed all the bike parts, such as wheels, chains, cables,and brake pads? To understand what these parts do, it is helpful tothink of the systems that make up a bicycle, such as the gear systemand the brake system. It is the parts of these systems working togetherthat make the bicycle an efficient machine.

The Characteristics of SystemsAll systems have the following characteristics:1. A system is made of individual parts that work together as

a whole.2. A system is usually connected to one or more systems.3. If one part of a system is missing or damaged, the system will not

function well or may not function at all.

The idea of a system is probably not new to you. Think of thehuman-made computer system you use and the electrical system thatpowers it. Scientists use the system idea to study natural systems, too,such the solar system or an ecosystem. For example, scientists studythe interaction of living things and non-living things withinecosystems (see Figure 2.2 on the next page).

Body Systems2.1

Key Termsorganorgan systemtissue


Figure 2.1 The efficiency of a bicycle dependson how well the individual parts of its systemswork together to make the bicycle move.

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Did You Know?

Aristotle, who lived from 384 to 322 B.C.E., was a greatphilosopher. He also closelyobserved natural objects andevents. He dissected animals tocompare their body systems, aform of scientific inquiry thatbecame known as comparativeanatomy. Historians believe hemade such studies to develophypotheses about how humanbody systems might work.


In this activity, you will illustrate what you alreadyunderstand about the parts of your body and your own body systems.

What to Do1. Work with a partner. On a large sheet of paper,

trace the outline of your partner’s body. Whendrawing your line leave enough space so you donot mark your partner’s clothes. Make sure thepaper is big enough so that you can outline theentire body.

2. Sketch and label all the different body parts andbody systems you know on the drawing yourpartner has made of your body.

3. Keep your drawing. As you work through thischapter, refer back to it and add any newinformation you learn.

What Did You Find Out?1. Compare your work with your partner’s. Make a list

for each question below.

(a) Which body parts and systems did you bothidentify?

(b) Which body parts and systems did your partneridentify that were different from the ones youidentified?

(c) Share your list and discuss with your class thedifferent body parts and systems that wereidentified.

Your Body Systems2-1 Find Out ACTIVITY

Figure 2.2 Living things (such as turtles) interact with non-living components (such as water and rocks) in this pond.

Section 12.1 has moreinformation about pondecosystems.

ConnectionYour body has a variety of systems that work together to maintain

your health. For example, your digestive system converts the food youeat into energy that is used when you carry out your daily activities,and your excretory system removes the waste from that process.

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Introducing the Systems of the Human Body

Figure 2.3 Eleven systems of thehuman body

To see an interactive, three-dimensional body, go towww.bcscience8.ca.

internet connect

Digestive System

Takes in food.Breaks down food.Absorbs nutrients.Eliminates solid waste.

Respiratory System

Controls breathing.Exchanges gases in lungsand tissues.

Excretory System

Removes liquid and gaswastes from the body.

Circulatory System

Transports blood, nutrients(chemicals needed forsurvival), gases, and wastes.

Immune System

Defends the body againstinfections.

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Reproductive System

RIGHT: Includes reproductiveorgans for producingoffspring.

Endocrine System

LEFT: Manufactures and releaseshormones.

Skeletal System

Supports, protects, and workswith muscles to move partsof the body.

Muscular System

Has muscles that work withthe bones to move parts ofthe body.

Nervous System

Detects changes in theenvironment and signalsthese changes to the body,which then carries out aresponse.

Integumentary System

Includes skin, hair, and nails.Creates a waterproofprotective barrier aroundthe body.

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Organ Systems: Putting It All TogetherIn Figure 2.3 on pages 56–57, you can see 11 different body systems.Each body system is called an organ system. An organ system has oneor more organs that perform specific body functions. For example,your heart is part of the circulatory system. You may recall that theheart pumps blood to the lungs and out into the rest of your body.

Within each organ system are tissues and cells. Cells of the samestructure and function are grouped into tissues. Groups of tissuesform organs, such as the lungs or the heart. For example, heart cellswork together to form heart tissue. Several types of heart tissue worktogether to form the organ you call your heart. Figure 2.4 shows therelationship between cells, tissues, organs, and organ systems.

Tissues: The Foundation of Body Systems The word “tissue” comes from a Latin word meaning to weave. The cells that make up tissues are often “woven,” or held together by fibres or sticky materials that form between tissue cells. Table 2.1on the next page describes how each type of tissue works in your body.These four types of tissue form the basis for all organs in your body.

Figure 2.4 The cell is the basic unit of life. Cells working together make up tissue. An organconsists of several types of tissues working together to perform a task, such as the pumping ofblood by your heart. Organs working together make up an organ system.

Did You Know?

There are different types of cellsin your heart. One unique typeof cell is called a myocyte. (InGreek, myo means muscle, andcyte means cell.) This cell can dosomething no other cell can do.It can beat on its own just like atiny heart. When a group ofmyocytes are close together,they send chemical signals backand forth, which cause them tobeat together at the same time.

heart cell cardiac tissue organ (heart) organ system organism

(circulatory system)

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Imagine that your group has been asked by a localdoctor’s office to make a model of each type of bodytissue. The models will form part of an exhibit on thehuman body. In this activity, your group will determinewhich material will make the best model of eachtissue.

What to Do1. Your teacher will give your group the following

four materials.

• rubber band

• piece of plastic wrap

• electrical wire

• transparent adhesive tape

2. Using the information on tissues in Table 2.1,determine which material best models one of thefour types of tissue. Develop a chart to comparethe material to the type of tissue.

What Did You Find Out?1. Compare your chart with other groups in your

class. Be prepared to defend your answers if thereis a disagreement between groups.

2. Explain in a paragraph how another material couldbe used to model one of the four types of tissue.

Modelling Four Types of Tissue 2-2 Think About It

Table 2.1 How Tissues Function in the Human Body

Muscle tissue, such as skeletal muscle tissue,assists in body movement. It also helps someorgans carry out specific functions, such as theheart pumping blood.

Nerve tissue transfers signals in the body and its organs to tell the body how to respondto changes in its internal and externalenvironments.

Connective tissue holds together and supports other tissues, such as skeletal connective tissue. Connective tissue connects,protects, and insulates organs.

Epithelial tissue covers the surface of organs and the body. It also lines the inside of body parts, such as the mouth, esophagus(shown here), and the stomach.

Select one of the systems from Figure 2.3 on pages56–57. Research anddescribe the characteristicsof the main structures andtheir functions. Explain howthis system interacts with atleast one other system.Begin your research atwww.bcscience8.ca.

Go to Science Skill 8 for information about usingmodels in science.

Science Skills

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Investigating Bones and Muscles2-3

Safety

• Use care when cutting withscissors.

• Do not eat during thisactivity. Do not put yourhands near your face.

• Wear protective gloves.Follow your teacher’sinstructions for removingand disposing of them.

• Make sure your work areais clean before, during, andafter the dissection.

• Clean all equipment andyour work area with a 10 percent bleach solution.

• Wash your handsthoroughly after doing thisinvestigation.

Materials• dissecting tray• scissors• raw chicken wing • probe• 10 percent bleach solution

Raising your hand to answer a question requires at least three of your bodysystems to work together: the nervous system, the skeletal system, and themuscular system. Your nervous system carries a signal from your brain to yourmuscles. This chemical signal activates the muscles to contract. At the same time,bones in the skeletal system are set in motion because a muscle contraction causesa pulling force on a bone and the bone moves. In this activity, you will investigatethe bones and muscles in a chicken wing to help you better understand how theskeletal and muscular systems are related.

As you work through this activity, remember these key points:

• The ends of bones are covered with a slippery layer called cartilage.

• Where two or more bones are connected together is a joint.

• At the joints, bones are held in place by ligaments.

• Muscles are connected to bones by thick white tissue called tendons.

QuestionWhat are the key parts of the skeletal and muscular systems that work together tomove a chicken wing?

Procedure1. Examine the external structure of the chicken wing. Extend the wing and try to

determine how many bones are in the wing.

2. Draw a diagram of the chicken wing and label the “shoulder,” “upper arm,”“elbow,” and “lower arm.”

3. Using your scissors, carefully cut away the skin from the thickest part of theupper arm. Be careful not to cut the muscle.

4. Find the muscles in the upper arm. Muscles should look like pale pink bundlesaround the bone.

Skill Check

• Observing

• Communicating

• Modelling

• Evaluating information


muscle

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Conduct an INVESTIGATION

Inquiry Focus


5. Hold down the shoulder and pull on one of themuscles with the probe. Repeat this procedurewith the other muscle. Observe and record thedirection the arm moves.

6. Cut away the skin around the lower arm andrepeat Procedure steps 4 and 5. Observe andrecord the direction in which the arm moves.

7. Remove any remaining skin. The elbow jointshould now be exposed.

8. Locate a tendon. Tendons are found at the endof muscles that attach to bone. They are shiny,white tissue.

9. Locate a ligament. Ligaments are shiny, white,and look like a small rubber band.

10. Locate cartilage. Cartilage is slippery, whitetissue that can be found at the end of bones.

11. Draw and label a second diagram showingthe joint, tendons, ligaments, and cartilage.

12. Dispose of the chicken wing according to yourteacher’s instructions.

13. Clean up and put away the equipment youhave used. Dispose of the gloves as yourteacher instructs.

14. Wash your hands thoroughly.

Analyze1. Describe how the muscles move in the upper

arm and lower arm.

2. Why are there upper and lower bands ofmuscles in the upper and lower arm?

3. What is the difference between a tendon anda ligament?

Conclude and Apply1. Using the information you collected in this

activity, summarize the key structures in thechicken wing and how they work together tomove the wing.

2. Athletes sometimes have ligament damage.Write a paragraph to explain why this is aserious injury.

ligament

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Building Bones in Space Have you ever dreamed of being an astronautand rocketing to Mars? Within your lifetime,astronauts may travel to distant planets or livein space for years at a time. But first, scientistshave to solve some tricky problems. One ofthe trickiest is how to keep the crew fromwasting away.

Being in space is something like lying inbed for a long time. Without the normal pullof gravity, muscles become flabby and shrinkrapidly. More seriously, the weight-bearingbones of the lower body lose minerals at anaverage rate of about 2 percent each month.And the longer the time spent in space, theworse the problem gets. Back on Earth,problems continue as astronauts readjust togravity. Crew members who spent fourmonths on the Russian space station Mir tookup to three years to regain their pre-flightstrength. Sometimes, bones never fullyrecover.

Working on Earth and in space, scientistsare tackling the problem from several angles.One is in-flight exercise. Astronauts typicallywork out for two hours a day using treadmills,harnesses, and other contraptions that try tomimic the force of gravity on bones andmuscles. But these devices have not stoppedbone loss.

Another idea is creating artificial gravityinside the spacecraft by spinning the ship. Buta spinning ship would not produce enoughgravity to prevent bone loss. More promising,perhaps, is a vibrating plate that astronautswould stand on for a few minutes a day. Thetheory here is that new bone cells form mainlyas a result of thousands of tiny muscle pullsthat occur in daily activity. Vibrating deviceswould cause these small contractions and haveworked well in animal experiments. Otherresearch focusses on hormone, nutrition, anddrug therapies.

The solution to bone and muscle loss mayturn out to be a combination of approaches.

In any case, research thathelps astronauts get to Marswill benefit people onEarth, too. Bone thinningin space, after all, is aspeeded-up form ofosteoporosis, a disease thataffects many people as theyage. Any treatment thatsaves bones could also helppeople with spinal cordinjuries or other conditionsthat keep them immobilefor long periods.

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Figure 2.3 on pages 56–57 shows 11different body systems. If one of thesesystems no longer functioned, what would bethe impact on the rest of the body? Explainyour answer in a paragraph.

Pause and Reflect


Checking Concepts1. What are the three characteristics of a

system?2. How is a bicycle an example of a human-

made system? 3. Which body system removes liquid and gas

wastes from the body?4. Which system does the heart belong to? 5. Which system controls breathing? 6. Which system defends the body against

infection? 7. Match the following four images of tissue

to the correct function.

(a) holds together and supports other tissues

(b) transfers signals in the body(c) covers the surface of the body(d) assists in body movement

8. If you were given a copper wire from anextension cord and asked which type oftissue this cord best modelled, what wouldbe your answer? Explain.

9. What is the difference between an organand a tissue?

10. Explain the four levels of organizationwithin the human body.

Understanding Key Ideas11. Think of a human-made system not

discussed in this textbook or class. Describethis system and explain how the three characteristics of a system arerepresented in your example.

12. Give an example of how two body systemsinterconnect or rely on each other tofunction.

13. Multiple sclerosis (MS) is a disease thatcauses the breakdown of tissue in thecentral nervous system. Which types oftissue are affected by MS?

14. Select one graphic organizer described inScience Skill 10 and use this organizer toexplain the bolded terms in this section.

A B

C D

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A healthy body requires nutrients from five groups: carbohydrates, proteins, fats,

vitamins, and minerals. There are four stages in digestion: ingesting, digesting,

absorbing, and eliminating. The digestive system is basically a long tube along which

organs perform different functions as the nutrients pass through them. The excretory

system removes liquid and gas wastes from your body. In this system, the process of

excretion removes the liquid wastes through the urinary tract. Eating disorders have

a negative effect on how the digestive system functions.

At birth, the average baby has a body mass of 3 to 4 kg. By age 14, a teenager’s body mass has increased at least 10 times or more. Howdid this happen? To grow, your body needs raw materials or nutrients(see Figure 2.5). Nutrients are substances the body requires for energy,growth, development, repair, or maintenance.

We get nutrients from what we eat and drink, which healthprofessionals call our diet. You probably think that “diet” means to cut out foods so you can use lose weight. But the word “diet” actuallyrefers to the amount and type of food you should eat to maintain your health.

The Digestive and ExcretorySystems

2.2

Key Termsdigestionexcretiongastric juicemucusnutrientsvilli


food

nutrients

energy and materials

carbohydrates, fats, proteins, vitamins,

and minerals

growth, development, and repair

provides

in the form of

used for

which provide

Figure 2.5 We need to eat foodsthat will provide us with the nutrientsour bodies need to stay healthy.

Did You Know?

A blue whale eats for only fourmonths of the year. During thistime, it will eat 4000 kg ofplankton a day.

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Four Food GroupsOne way to make sure your diet is healthy is to eat a variety of foodsfrom four food groups: grain products, vegetables and fruit, milkproducts, meat and alternatives (see Figure 2.6).

Food PyramidAnother way to determine whether your diet is healthy is to compareit to a food pyramid (see Figure 2.7). Each coloured band representsone of six (instead of four) food groups: grains, vegetables, fruits, oils,milk products, and meat and beans. The width of each band tells youhow much you should eat from that group. The wide part of theband means you should choose foods from that group that are low insolid fats and added sugars. The further up the pyramid you move,the more fats and sugars the foods contain. Whole wheat pasta withtomato sauce would be at the bottom of the grains band. Pre-packaged macaroni and cheese would be much higher up.

Food AvailabilityUsually, our diets reflect what we can buy at our local grocery store orfarmer’s market, or what we may grow. Our diets may also reflect thetraditional foods of our families. In some communities, traditionalfoods provide a valuable source of nutrients. Canadians living in theNorth may get their iron from the liver of a Canada goose or seal.Other Canadians, who live near oceans, may eat mussels, clams, andkelp, which are good sources of calcium. Although our food maycome from different places, all Canadians need to make the right foodchoices to maintain healthy bodies.

Figure 2.6 Choose foods fromeach of these four food groups.

d

grains

vegetables

fruitsoils

milk products

meat and

beans

Figure 2.7 Choose foods inmoderation (in appropriate amounts)

from each of the coloured bands in this food pyramid. The person

climbing the stairs on thepyramid means that an active

lifestyle, along with thefoods you eat, is important

to your health.(Based on the USDA’s

MyPyramid.)

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How do you know what kinds of food to eat to makesure your body is getting the nutrients it needs? Oneway is to follow the suggestions in Canada’s FoodGuide to Healthy Eating. In this activity, you will usethis guide to help you become an informed foodshopper.

What to Do1. Your teacher will give you a copy of Canada’s Food

Guide. Prepare a shopping list of foods you wouldneed to purchase to have three meals and twosnacks for one day. (Assume the store you shop athas all the food packaged into single servings.) Youmay also use other information from this textbookand any additional print and electronic resourcesavailable to you.

What Did You Find Out?1. Compare your list with your classmates’ lists.

2. Make a second list of all the foods you ateyesterday. Compare this list with your shopping listand answer the following questions.

(a) For which food groups did you have theappropriate number of suggested servings?

(b) For which food groups did you not have theappropriate number of suggested servings?

(c) What foods should you eat more of?

3. What is one food you enjoy that is not on your listof foods to buy? Could you live without this food?

2-4 Find Out ACTIVITYUsing Canada’s Food Guide toHealthy Eating

For more examples of foodguides from various countriesand cultures go towww.bcscience8.ca.

Types of NutrientsA balanced diet ensures that you take in the correct amount ofnutrients your body needs to function. There are five different types ofnutrients you can obtain from food. These are carbohydrates, proteins,fats, minerals, and vitamins.

Carbohydrates

Carbohydrates are the body’s quickest source of energy. There are two types of carbohydrates: simple and complex. A simplecarbohydrate is a molecule of a sugar. The most common type of sugar is glucose. You can think of glucose as fuel for your body.

Recall that the mitochondria in your body cells change glucoseinto energy through the process of cellular respiration. Your body uses this energy for growth, repair, and maintenance.

A complex carbohydrate is a chain of simple carbohydrates (sugarmolecules) joined together. Foods such as pasta, brown rice, andwhole grain cereals contain complex carbohydrates (see Figure 2.9 onthe next page). When you eat a food containing complexcarbohydrates, your body needs to break down the chain into simplesugars before it can use the energy. This process takes time, and in thelong term is one of the reasons eating complex carbohydrates is betterfor you than eating a diet high in simple sugars. Eating sweet foodsmay make you want to eat more or make you hungry again just ashort time later.

internet connect

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Proteins

Proteins are used to build parts of your body’s muscles, skin, hair,and nails. Your body also manufactures proteins for use in variouschemical reactions within your cells. Foods such as fish, poultry, nuts,soy, and dairy products are rich in proteins (see Figure 2.8).

Fats

Fats are used to build cell membranes and can be stored by the bodyfor future energy uses. Foods such as shortening, butter, oil, cream,and meat contain fat (see Figure 2.10).

Currently, many people consume food with too much fat. Dietitiansand doctors recommend that Canadians reduce the total amount of fatin their diets. You may have heard on the news or read in a magazineabout good and bad fat. Good fat is sometimes called unsaturated fatand comes from fruits, vegetables, and fish. Corn oil, olive oil, andvegetable oil are also examples of unsaturated fats. These fats are liquidat room temperature. Animal fats, such as butter or lard, are saturatedfats. These fats are solid at room temperature.

Research shows that diets rich in saturated fat can lead to anincrease in heart disease. Scientists think that saturated fats promotethe build-up of a material called plaque. Plaque is a fatty material thatis deposited along the walls of blood vessels. As plaque builds up inthe blood vessels, the flow of blood through the heart and body isreduced. This leads to an increased risk of heart attacks and strokes.

Figure 2.9 Carbohydrates are in foodssuch as rice, vegetables, cereal, and bread.

Figure 2.10 Fats are in foods such asbutter, vegetable oil, and meat.

Figure 2.8 Proteins are in foodssuch as fish, meat, poultry, eggs,nuts, and soy products.

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Figure 2.11 Minerals perform many different functions in the body.

Minerals and vitamins

Minerals and vitamins are needed by the body in small amounts toperform various body functions. Figure 2.11 shows some of these minerals.Two common minerals and vitamins are calcium and vitamin D.

Calcium is required to help build strong bones. A lack of calciumcan lead to osteoporosis, which is a disease that weakens your bones.Vitamin D is required by your body to assist it in absorbing calcium.

Fluorine (F)

Function: Dentalcavity reductionSource: Fluoridatedwater

Iron (Fe)

Function:Formation of redblood cell parts;transportation ofoxygen throughoutthe bodySource: Liver, eggyolks, grains,meats, leafyvegetables

Sodium (Na)

Function: NerveactivitySource: Bacon,butter, table salt,vegetables

Magnesium (Mg)

Function: Muscleand nerve activity;bone formationSource: Fruits,vegetables, grains

Calcium (Ca)

Function: Teeth andbone formation;muscle and nerveactivitySource: Milk, grains,calcium-fortifiedorange juice and soymilk

Phosphorus (P)

Function: Teeth andbone formation;muscle and nerveactivitySource: Milk,grains, vegetables

Copper (Cu)

Function:Development ofred blood cellsSource: Grains,liver

Potassium (K)

Function: Muscleand nerve activitySource: Vegetables,bananas

Sulfur (S)

Function: Hair, nails,and skin builderSource: Grains,fruits, eggs, cheese

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Go to www.bcscience8.cafor more examples of mineralsand vitamins and how theyfunction in the human body.

internet connect

Water

Water is not a nutrient, but it is necessary for life. Water transports nutrients and wastes. It is also necessary for many chemical reactionsand for cooling the body through perspiration or sweat. Your bodyrequires 3 to 5 L of water each day.

Table 2.2 summarizes the nutrients you have just read about anddescribes some of their functions in your body.

Table 2.2 How Nutrients Function in the Human Body

Nutrient Function

Carbohydrates Are the body’s quickest source of energy. Carbohydrates come in simple and complex forms. Complex carbohydrates are chains of simple carbohydrates (sugar molecules).

Proteins Are used to build parts of the body, such as muscles, skin,and hair, and are also used for various chemical reactions in your body.

Fats Can be stored by the body for future energy use.

Minerals and Are both needed in small amounts to help your bodyvitamins perform various functions, such as building bone strength.

Reading Check

1. Explain one way to determine if you are eating a healthy diet. 2. What is the difference between a simple carbohydrate and a

complex carbohydrate?3. What are two functions of proteins? 4. Give a food example for each of the five nutrients. 5. What is the role of water?6. State one function of fluorine.7. State two sources of potassium.

A person who lacks vitamin D can develop rickets, which causesthe bones to weaken. Fortunately, one way you can help your bodymake vitamin D is by simply going outside in the sunlight. However,it is difficult for some people to get enough sunlight. For example, ifyou live above 52° north latitude, there is not enough sunlight to makevitamin D between the months of October and March. Drinkingbeverages with added vitamin D, such as milk and soy milk, can helpyou get the vitamin D you need.

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Figure 2.12 The four stages of digestion in the digestive system

Enzymes are important proteins for digestion

In your body, many different chemical reactions are occurring. Manyof these reactions could not normally occur at body temperaturebecause they would happen very slowly. An enzyme is a protein foundin your body that helps speeds up these reactions. There are manydifferent types of enzymes in your body. During the digestion process,one enzyme or more will be present in each organ.

Digestion occurs along a big tube

This may sound strange, but your digestive system is basically one bigtube that starts at your mouth and ends at your anus. The shape ofthe tube changes along its length, getting bigger in some places andsmaller in others. The process of digestion breaks down your foodinto small pieces so that the nutrients can be absorbed into your bodyand used for maintenance, growth, and repair. Any materials thatcannot be absorbed are eliminated in the feces.

The Four Stages of DigestionYou can put any food into your mouth, and your body will be able tobreak down, absorb, and store its nutrients. Any food your body cannotuse will be eliminated. This process is called digestion, and it occurs inan amazing system called the digestive system (see Figure 2.12).

Digestion takes place in four stages: • ingesting • absorbing• digesting • eliminating

salivary glandstongue

esophagus

gall bladder

pancreas

stomach

rectumanus

largeintestine

smallintestine

liver

ingesting

digesting

absorbing

eliminating

Word Connect

In scientific terms, “to ingest”means to take in. “To digest”means to break down.

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incisors

opening of a salivary gland duct

cuspids orcanines

bicuspidsor premolars

molars

Tonsils A pair of tonsils is located at the back of the mouth. They playa role in preventinginfections in the nose and mouth by helping toeliminate foreign bacteria.

The tongue is covered by projections.

TongueThe tongue is attached to thefloor of themouth. It is madeof numerousskeletal musclescovered with amucous membrane.

TeethThe incisors are adaptedfor cutting food. Thecuspids, or canines, tearor shred food. The threesets of molars cancrush and grind food.


To get a better idea of how digestion works, imagine the journeyof a favourite food through the four stages of the digestion process. Asyou read, make an illustration or look back at your body diagram fromsection 2.1, and record the names of the different body structures andorgans that carry out the digestion process.

Stage 1: IngestingIngesting, or ingestion, is the starting point of the digestion process.Figure 2.13 shows that this process begins when you bite off a piece ofapple or take a sip of milk.

Stage 2: DigestingYou start digesting your food the moment you start chewing. Thisprocess involves several body structures along the digestive tube.

Mouth

When food enters your mouth, it undergoes both mechanical andchemical digestion. Mechanical digestion occurs when you use yourteeth and tongue to chew food into pieces small enough for you toswallow. Each small piece of food is called a bolus. Before you swallowthe bolus, it is covered in saliva, which helps it continue its journeydown the digestive tube. Saliva is produced from salivary glands inyour mouth. Saliva also contains an enzyme, called amylase. Chemicaldigestion occurs when amylase begins to break down the food bolusby breaking down complex carbohydrates into simple carbohydrates.

Figure 2.14 shows the tongue and other structures of the mouth.

Did You Know?

Salivary glands produce about 1 L of saliva a day.

Figure 2.13 Ingestion begins withyour first bite of food.

Figure 2.14 The mouth

Conduct an Investigation 2-5on page 78

Suggested Activity

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frommouth

contraction

contractionof musclesbehindbolus

muscle

bolusto stomach

contractionin muscles forces thebolus forward

contraction ofmuscles aheadof bolus

muscle


Figure 2.15 The epiglottis covers the airway tube and prevents food from entering.

Esophagus

As the food moves from your mouth, it passes through thepharynx. The pharynx is where your airway passage and the restof your digestive system meet. Imagine two tubes coming togetherand joining into one. Since each tube has a different function, onefor breathing and one for digesting food, your body has a simplebut effective way of keeping the two tubes separate. A small flap offlesh, called the epiglottis, covers the airway tube (see Figure2.15). When you swallow, the flap covers the airway and your foodcarries on to the esophagus. The esophagus is the part of thedigestive tube that connects the pharynx and stomach. If you haveever choked on some food or a drink, your epiglottis has openedup, and the food or liquid has gone down your airway passageinstead of your esophagus.

The esophagus is long and muscular. The bolus is pushedthrough the esophagus in a process called peristalsis (see Figure2.16). The process of peristalsis is like using your hands to squeezea marble down through a small rubber tube. The action of yourhands squeezing the tube is like the muscles of the esophaguspushing each bolus to the stomach.

Figure 2.16 Peristalsis is a series ofmuscle contractions that move foodthrough the digestive system.

airway tube epiglottis

A

B

C

D

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Stomach

Your stomach is like a stretchable muscular bag. In fact, your stomach can stretch to hold about 2 L of food or liquid. Inside the stomach is gastric juice, which is made from hydrochloric acid, mucus, andenzymes and is secreted by your stomach’s lining. Gastric juice is veryacidic and the stomach walls are lined with mucus that protects thetissue from being damaged by the acid. One of the reasons the gastricjuice must be acidic is that the enzyme pepsin, which breaks downprotein, needs an acidic environment in which to function.

As each bolus drops into the stomach, it is covered by gastric juice and is slowly mixed around by the contractions of the stomachmuscles. The bolus breaks down into a liquid called chyme(see Figure 2.17). This process can take from two to six hours.

In Figure 2.18, you can see a sphincter at each end ofthe stomach. Sphincters are found throughout the bodyand are round muscles that, when open, allow materials tomove through them. In your stomach, there are twosphincters. The first is between the esophagus and thestomach, and it regulates the entry of each bolus into the stomach. When a person vomits or has heartburn, theflow of material is reversed, and gastric juice and partiallybroken-down food moves back up the esophagus. Anyburning sensation the person feels in the throat or mouthis because of the hydrochloric acid in the gastric juice. The second sphincter regulates the flow of chyme out ofthe stomach and into the small intestine.


esophagus

stomach

chyme

small intestine

esophagus

duodenum

end of stomach

entrance to stomach

stomachFigure 2.18 A sphincter at theentrance to the stomach controlsthe entry of food from theesophagus. A sphincter at theend of the stomach controls theflow of chyme into the smallintestine.

Figure 2.17 Muscle contractions churn thestomach’s contents until it becomes a thinliquid called chyme.

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Using print and electronicresources, research a differentanimal’s digestive system.Focus on different organs andstructures that may bepresent. For example, why dosome birds have gizzards orcows have four stomachs?Begin your research atwww.bcscience8.ca.


Small intestine

Once the liquid chyme leaves the stomach, it empties into the smallintestine. This organ is a tube about 6 m long and 2.5 cm in diameter.The first metre of the small intestine is called the duodenum. Thesecond stage of the digestion process is complete once the foodparticles leave the duodenum.

More about chemical digestion in the small intestine

Within the first 30 cm of the small intestine are ducts or tubes thatconnect to other organs, such as the pancreas, liver, and gall bladder(see Figure 2.19).

The pancreas is a small organ that produces digestive enzymes thatpass into the small intestine. These enzymes help in the furtherbreakdown of the carbohydrates, protein, and fat in the chyme.

The liver produces a substance called bile. Bile is stored in the gallbladder. The function of bile is to break the globs of fat into smallerdroplets, similar to how dish detergent breaks up grease. This processhelps the pancreatic enzymes break down the fat into even smallerparticles.

Stage 3: AbsorbingNow the nutrients are ready to be absorbed by the remaining 5 m ofthe small intestine. This process is called absorption.

Figure 2.19 Both the liver andpancreas produce chemicals neededfor digestion in the small intestine.

esophagus

pancreas

pancreaticduct

stomach

duodenum

bile duct

smallintestine

liver

gall bladder

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[CAPHOCAUPYL

[NNOLarge intestine

Your large intestine is 5 cm wide and 1.5 m long. Its main function isto take undigested material from the small intestine and reabsorb thewater and some minerals. Peristalsis continues to move the undigestedfood along the digestive tube. By the time the undigested materialleaves your large intestine, 90 percent of the water that entered yoursmall intestine has been reabsorbed. This process takes about 12 to 24 hours.

The role of bacteria in digestion

Many different types of bacteria live in your digestive system.Beneficial bacteria assist in the breakdown and absorption of food. For example, bacteria in the large intestine use undigested material tomake vitamins, such as vitamin K. Vitamin K helps your blood to clot.At birth, babies do not yet have bacteria in their digestive system.Doctors will give them a shot of vitamin K to last until they haveenough bacteria to begin producing it.

Sometimes we ingest bacteria that are not beneficial, such assalmonella, which cause food poisoning.

Small intestine

To help increase the rate of absorption of nutrients into your body, thesmall intestine is covered in villi (singular: villus). Villi are structuresthat look like folds in the wall of the small intestine (see Figure 2.20).

Each of these folds increases the surface area available to take innutrients. In fact, if you were to calculate the total surface area of thesmall intestine, you would find that it takes up an area about the sizeof a tennis court, or about 250 m2. If the small intestine did not havevilli, the total surface area would be only about 0.5 m2, which wouldmake absorption difficult. Food, typically, takes five to six hours topass through the small intestine by peristalsis.

Did You Know?

For many years, scientiststhought that stomach andintestinal ulcers were caused bystress and lifestyle. But currentscientific research hasdiscovered that some ulcers areholes in the lining of thestomach and intestines causedby the bacterium Helicobacterpylori. This discovery by twoAustralian scientists, RobinWarren and Barry Marshall, wonthem the Nobel Prize formedicine in 2005.

smallintestine

villi close-up of villus

Figure 2.20 The small intestine with magnified villimagnified villi

magnification:360�

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Other organs of the excretorysystem include the lungs, theskin, and the liver. What rolesdo these organs play inremoving wastes from yourbody? Begin your research atwww.bcscience8.ca.


Reading Check

1. Which organs and structures carry out digestion?2. What is a bolus?3. Describe the function of an enzyme and give an example.4. What is the function of a mucous coating on the stomach wall?5. How is the surface area of the small intestine increased?6. What is the main function of the large intestine?

Stage 4: EliminatingAny undigested materials left at this point in the digestion process arecalled feces. Feces are the solid waste products of the digestion processand are stored in the rectum until they are eliminated through theanus. This stage is called elimination, which is the end of thedigestion process. The whole process, from ingesting food toeliminating waste, takes approximately 20 to 30 hours.

ExcretionIn Figure 2.3 on pages 56–57, you learned that your excretorysystem removes liquid and gas wastes from your body. In this system,the process of excretionremoves the liquidwastes through theurinary tract. The mainorgans involved are yourtwo kidneys, two tubesthat carry urine calledthe ureters, the bladder,and the urethra (seeFigure 2.21). Thekidneys filter blood andremove any wastes. Asthe blood is filtered,urine is formed andpassed down the uretersto the bladder where it isstored. When thebladder is full, the urineis flushed from the bodythrough the urethra.

37.13M,

Figure 2.21 The kidneys, ureters,bladder, and urethra are the mainorgans involved in excretion.

aortavena cava

bladder

kidney

ureters

urethra

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Nutritional Disorders—Disrupting the Digestive SystemObesity is an excess in body fat. In Canadian teenagers, obesity isquickly becoming a serious health concern. Research has shown thatthe number of obese teenagers tripled between 1981 and 1996. Lackof exercise and improper eating habits are increasing the number ofpeople who are obese. Most cases of obesity result from taking inmore food than the body requires. Potential negative health effects ofobesity include an increased risk of diabetes, heart disease, stroke, andasthma.

Eating DisordersEating disorders occur when a person does not get the requirednutrients to be healthy. Two examples of eating disorders are anorexianervosa and bulimia nervosa (see Table 2.3).

Anorexia nervosa is a disorder that occurs when a person severelyrestricts what she or he eats. The resulting medical problems couldinclude damage to internal organs and weakening of bones.

Bulimia nervosa is a disorder that occurs when a person eats largeamounts of food and then vomits or takes laxatives to get rid of thefood before it can be completely digested. This eating disorder cancause a variety of health problems, including stomach and esophagusirritation and tooth decay from stomach acid in the vomit.


Table 2.3 Characteristics of Anorexia Nervosa and Bulimia Nervosa

People with anorexia nervosa: People with bulimia nervosa:

• are very afraid of gaining bodymass

• limit the amount of food they eatvery strictly

• have a distorted body image, whichmeans they feel overweight evenwhen they are dangerously thin

• have a body mass that is less than85 percent of normal body mass

• do not menstruate (femaleanorexics)

• are very concerned about theirbody shape and weight

• repeatedly eat a much higher thannormal amount of food at onesitting (binge eating) and feel theyare unable to control their eatingat these times

• have a distorted body image,which means they feel overweighteven when they are normal

• have a body mass that is normalor less than normal

• often have bad breath and gumdisease

People with anorexia nervosa People with bulimia nervosa keep their body mass low by: keep their body mass low by:

• eating very little or eating foodsextremely low in calories

• exercising too much• misusing laxatives

• making themselves vomit (purging)after eating

• exercising too much• misusing laxatives

For more information oneating disorders, go towww.bcscience8.ca.

internet connect

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Does Chemical Digestion Begin in the Mouth? 2-5

Safety

• Wear safety goggles.• Wear protective clothing.• Handle chemicals safely.• Be careful and use

appropriate equipmentwhen handling hot objects.

• Be careful when handlingelectrical equipment.

• Wash your handsthoroughly after doing thisinvestigation.

Materials• 4 test tubes• test tube rack• 100 mL graduated cylinder• 10 mL graduated cylinder• two 250 mL beakers• tap water• oatmeal (not instant)• diastase solution (saliva

substitute)• sugar• measuring spoon• medicine dropper• iodine solution• Benedict’s solution• hot plate• test tube clamp

When food is ingested, mechanical digestion breaks down the food into smallpieces called boli (singular: bolus). Enzymes also start to break down complexcarbohydrates into simple carbohydrates. In this investigation, you will determinetests for simple and complex carbohydrates and use these tests to investigate thechemical digestion of oatmeal.

QuestionWhat is the evidence that chemical digestion begins in the mouth?

Procedure

Part 1 Preparing Your Samples

1. Develop and complete a data table like the one below.

2. Put on your safety equipment before continuing.

3. Fill a beaker with 100 mL of water. Add a handful of oatmeal and allow it tostand for 10 min. Stir once or twice.

4. After 10 min, pour off the milky white liquid into another beaker. This will beyour complex carbohydrate or starch mixture.


Test Tube Contents ObservationsNumber

1

2

3

4

Skill Check

• Measuring

• Controlling variables

• Evaluating information

• Working co-operatively

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Conduct an INVESTIGATION

Inquiry Focus


5. Wash out the beaker you just emptied. Refill thebeaker with water and place it on a hot plate.Heat the water until just below boiling.

6. Measure 10 mL of starch mixture into test tubes1, 2, 3, and 4.

Part 2 Testing for Iodine

7. Add four drops of iodine solution to test tube 1.Record your observations.

Part 3 Testing for Sugar

8. Dissolve 5 g of sugar in 25 mL of water.Measure 10 mL of this sugar solution into testtube 2.

9. Add four drops of Benedict’s solution to testtube 2 and heat it in the hot water in the beakeron the hot plate. Record your observations.

Part 4 Investigating Chemical Digestion

10. Add 10 drops of the diastase solution to testtubes 3 and 4 and gently swirl. Wait 5 min.Diastase is an enzyme similar to the enzymefound in your saliva.

11. Add four drops of iodine solution to test tube 3.Record your observations in your table.

12. Add four drops of Benedict’s solution to testtube 4. Place the test tube in the boilingwater and leave it there for 5 min. Recordyour observations.

13. Allow solutions to cool and dispose of themcarefully as instructed by your teacher.

14. Clean up and put away the equipment youhave used.

Analyze1. Describe how you tested for the presence of

starch.

2. Describe how you tested for the presence ofsugar.

3. What effect did the diastase solution have onthe starch solution?

4. What effect did the diastase solution have onthe sugar solution?

Conclude and Apply1. How did your results provide evidence that

chemical digestion begins in the mouth?Remember, diastase acts in the same way asan enzyme found in saliva.

Go to Science Skill 2 for information aboutcontrolling variables.

Science Skills

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Can your body get too much of a good thing? Themillions of cells in your body need energy to work andthat energy comes from the sugar glucose. So how cantoo much glucose in the body be bad?

For glucose to enter cells, helpers called receptorsare needed. These receptors act as doors to let glucosepass from the blood through the cell membrane. Achemical called insulin unlocks the doors to allowglucose to enter the cells. Special cells in the pancreasmake insulin. If the pancreas cannot make insulinproperly, glucose cannot enter the cells and stays inthe blood. This is known as type 1 diabetes. If there arenot enough receptors, glucose also remains outside thecells and stays in the blood. This condition is calledtype 2 diabetes.

If glucose stays in the blood, a person feels tiredbecause the cells are not getting the energy they needto function. The kidneys have to work harder to get ridof the excess glucose in the blood. This can result inhigh blood pressure and, eventually, kidney failure.Nerve cells do not get enough energy from glucose topass information to the heart, so the heart does notpump efficiently. This could lead to a heart attack.Blood flow drops because nerve cells in the bloodvessels are affected. This could lead to blindness,prevent sores from healing, and cause confusion oreven a coma.

Type 2 diabetes is the most common form of thedisease, and millions of Canadians have it. The numbercontinues to climb, with large increases reported in thenumber of young Canadians having the disease. Type 2diabetes can affect anyone, but some groups are morelikely to develop it. It is much more common inAboriginal Canadians and Hispanic, Asian, South Asian,and African Canadians.

At present, there is no cure for diabetes, but drugs,healthy eating, and regular exercise can control thedisease. Maintaining a healthy weight is an importantfactor in controlling diabetes. In the future, scientistsmay find cures if they can transplant healthypancreatic cells into type 1 diabetics and help cellsproduce more receptors for type 2 diabetics.

Questions

1. What two requirements are necessary forglucose to enter cells?

2. How does type 1 diabetes differ from type 2diabetes?

3. If you were a family doctor, whatrecommendations would you give people whoare at risk for diabetes?


Too Much Sugar—Not So Sweet!

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Checking Concepts 1. List the food groups in Canada’s Food

Guide to Healthy Eating and give anexample for each group.

2. List each type of nutrient and describe itsfunction.

3. What is the role of the epiglottis?4. In humans, where does most of the

chemical digestion process occur?5. Why does your stomach need to be very

acidic?6. Order the following structures in the

correct sequence from ingestion toelimination: rectum stomach esophagusduodenum mouth small intestineanus large intestine

7. In which organ is water absorbed?8. What other organs outside the digestive

tube contribute to digestion? 9. Describe one of the beneficial roles of

bacteria in the digestive system.10. Why are eating disorders harmful to the

human body?11. Copy the following concept map into your

notebook and fill in the blanks.

Understanding Key Ideas12. What foods from the four food groups or

the food pyramid would provide a balancedmeal? Explain.

13. Compare and contrast mechanical digestionand chemical digestion.

14. Explain how the digestive system can becompared to a big tube.

15. Bread contains complex carbohydrates. Ifyou let a piece of bread sit in your mouthfor about five minutes without beingchewed, it starts to taste sweet. Explain whythis happens.

16. A blue whale eats 4000 kg per day, and arat eats about 15 g per day. Both animalsreplace about 5 percent of their body masseach day. What is the approximate mass ofboth animals?

17. How is the function of bile similar to thefunction of soap?

18. Explain the relationship for each set ofterms below.(a) digestion, enzymes(b) surface area, villi(c) digestion, bacteria(d) esophagus, peristalsis(e) gastric juice, pepsin, mucus(f) kidney, bladder, excretion

Develop a flowchart showing the organs and structures of the digestive system. Use a different colour for each stage of thedigestion process. (You will need fourcolours.) Recall that some stages overlap.

Pause and Reflect


Digestion

breaks down starts in

to be used by

by chewing

the food is moved through the system by

by enzymes in saliva

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The circulatory system consists of the heart, arteries, capillaries, and veins. Arteries

carry blood away from the heart, and veins carry blood to the heart. In your

capillaries, oxygen is released into your body and carbon dioxide is collected. In

your lungs, oxygen is collected and carbon dioxide is released into the alveoli.

Emphysema, which is often caused by smoking, and pneumonia are two examples

of respiratory diseases.

After a run or some other type of exercise, place your hand on yourchest. Can you feel your heart beating? For your whole life, this organcontinues to beat, moving blood throughout your body. Your heart isa pump that pushes approximately 4 L of blood per minute throughyour body. If an average heart beats about 70 times per minute, andyou live to be 80 years old, that’s almost three billion beats. Thisamazing feat is accomplished by a muscle about the size of your fist.

Unlike other organs in your body, your heart is more difficult totake a picture of because of its constant beating. Blockages in theblood vessels of the heart, which can cause heart attacks, are notvisible in an X ray. Scientists and physicians continue to search for newways to make images of the heart to help them diagnose heartproblems sooner and prevent the advance of heart disease. One recenttechnology is the 64-Slice CT Scanner. The scanner takes 64 picturesof different sections of the heart. Each image is very thin. The imagesare then combined to form the three-dimensional picture you see inFigure 2.22. The whole process takes place in about five heartbeats.

The Circulatory and RespiratorySystems

2.3

Key Termsalveoliarteriesbloodcapillariescirculatory systemgas exchangerespiratory systemveins


Go to www.bcscience8.ca toobserve a heart simulation.

internet connect

Figure 2.22 This picture of the heart was taken by a type of scannercalled the 64-Slice CT Scanner.

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It is difficult to imagine a harder working organ thanyour heart. In fact, the heart pumps about 4 L of bloodthrough your body every minute. In this activity, youwill model the action of the heart by moving 4 L ofwater in one minute.

Materials• 2 buckets—one filled with 4 L of water

• 125 mL measuring cup

• watch with second hand or timer

What to Do

Part 1 Determining Your Heart Rate

1. Find your pulse. Use one of the methods shownbelow. Take your pulse for 15 s and multiply thenumber of beats by 4. This is your heart rate, or thenumber of times your heart beats per minute.Record your result.

2. Exercise for 1 min. For example, climb stairs or runon the spot. Take your pulse again and record theresult.

Part 2 Modelling the Pumping Action of YourHeart

3. Work in pairs. Decide who will be the “timer” andwho will be the “heart.”

4. The “timer” will time for 1 min as the “heart”transfers water from the full bucket to the emptybucket. The “heart” must use only the measuringcup and must not spill any water. The timer alsocounts the number of times the “heart” transferswater from the full bucket to the empty bucket.

5. When you are finished, change roles and repeatstep 4.

6. Clean up and put away the equipment you haveused.

What Did You Find Out?1. Were you able to transfer all the water from one

bucket to the other?

2. Describe how your arm muscles felt after a minuteof modelling the heart. Were you surprised by thisfeeling?

3. How does the modelling of the heart in Part 2relate to the pulse rate you recorded in Part 1?

4. Sometimes a heart does not function properly whenpumping blood to the body. How could you changethe materials used in this activity to model a heartthat cannot pump enough blood through the body?

Modelling the Heart 2-6 Find Out ACTIVITY

Place your fingers against an arteryon either your wrist or your neck.


Science Skills

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Taking a Closer Look at the HeartYour heart is a muscular organ that pumps blood throughout yourbody. Figure 2.23 shows its four chambers: two upper atriumchambers and two lower ventricle chambers.

The atria allow the blood to move from the body into the heart.The ventricles pump the blood out of the heart. It may seembackward that the atria are labelled “right” and “left” on the diagram.But imagine the heart as it is positioned in your body. The rightatrium refers to the right side of your body, not the right side of thediagram.

Notice in Figure 2.23 that the muscle around the left ventricle islarger than that around the right ventricle. The left ventricle pumpsyour blood out to your body. The right ventricle pumps blood to yourlungs, a much shorter distance. The walls of the atria are much thinnerbecause they only have to pump the blood a short distance into theventricles.

Between the chambers are valves. Each valve allows blood to flowin only one direction. If you have ever listened to your heart through astethoscope, the “lub dub” sound you hear is the opening and closingof the valves.


Word Connect

For many scientific words, theplural form is created byadding “s” or “es,” to the endof a word. You will findexamples of these types ofplural words in this chapter,such as veins (singular: vein),arteries (singular: artery),capillaries (singular: capillary).But the plural form of somewords is created by adding adifferent letter. For example,atrium is the singular form,and atria, which refers tomore than one atrium, is theplural form.

FT

aorta

pulmonaryartery

valve

valve

valve

leftatrium

rightatrium

leftventricleright

ventricle

superior vena cava

inferior vena cava

veins fromlung

valve

arteries

Figure 2.23 The human heart. The arrows show the direction of blood flow through the heart.

Find Out Activity 2-8 on page 93

Suggested Activities

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The Circulatory System The heart is part of the circulatory system, which is like anenormous highway system that moves blood throughout your body.The “roads” that make up the circulatory system are your bloodvessels.

Blood moves along these “roads” from your heart to all parts ofyour body and back again as in Figure 2.24. All your blood vesselslined up end to end would be about 100 000 km in length. That isabout 2.5 times around Earth at the equator.

Figure 2.24 The circulatory system moves blood throughout the body.

C–

WSS

T

veins from the head

veins from the arm

vein from kidney

veins from legs

veins taking bloodto heart

arteries to the head

arteries to the arm

arteries to legs

artery to kidney

right atrium receivesblood from body

left atrium receivesblood from lungs

right ventricle pumps blood to lungs

left ventricle pumps blood out to the rest of the body

BCS_G8_U1C02_J15 5/4/06 4:12 PM Page 85

arteriole

bloodflow

bloodflowartery

capillaries

venule

vein


Types of Blood VesselsBlood is carried from your heart throughout your body in three typesof blood vessels: arteries, capillaries, and veins.

Arteries are blood vessels that carry blood away from your heart.Most arteries carry bright red, oxygenated (oxygen-containing) blood.Your blood is under pressure after it is pumped from your heart. Thepressure keeps it flowing in one direction. Your arteries are thick-walledand elastic and can withstand this pressurized flow.

The largest artery in your body is the aorta. It has a width ofabout 25 mm or the width of a penny. As blood moves farther awayfrom your heart, your arteries branch into smaller and smaller arteries(see Figure 2.25). Eventually, the smallest arteries, the arterioles,which have a diameter of about 0.5 mm, reach the capillaries.

Capillaries are a network of tiny blood vessels that act like ahighway interchange. Here oxygen, nutrients, and glucose diffusethrough the very thin walls of the capillaries into the fluid thatsurrounds tissue cells (see Figure 2.26). In exchange, carbon dioxideand other waste materials that have diffused out of these cells diffuseinto the capillaries.

After leaving the capillaries, your blood no longer contains oxygen.This deoxygenated blood is carried back to your heart through tinyvenules and into your veins. Figure 2.23 on page 84 shows bloodfrom the head and body in the superior vena cava and inferior venacava emptying into the heart.

Deoxygenated blood is thicker than oxygenated blood and is muchdarker in colour. In Figure 2.25, the colour blue is used to show thedeoxygenated blood in veins. Once the deoxygenated blood reachesyour heart, it is pumped into your lungs, where it becomes oxygenatedagain.

Section 9.3 has moreinformation about bloodpressure.

Connection

Figure 2.25 Arteries carry blood away from the heart to thecapillaries. From the capillaries, blood moves through thevenules and into the veins back to the heart.

Figure 2.26 Disk-shaped red blood cells carry oxygen totissue cells through the thin-walled capillaries.

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Visualizing Blood Flow2-7 Think About It


Figure 2.27 shows that veins often have valves that prevent thebackflow of blood as it travels back to the heart. They also havethinner walls because the blood travelling back to the heart is notunder pressure like the blood in the arteries.

In this activity, you will create a flowchart to showblood flow in the body.

What to Do1. Copy this flowchart into your notebook.

2. Starting with the right atrium, place the followingstructures on the flowchart in the order that bloodflows through the body.

left ventricle left atriumbody lungsright atrium right ventricle

3. Add the following terms to the flowchart.

aorta superior vena cavapulmonary vein inferior vena cavapulmonary artery

4. The arrows represent the flow of blood betweenthe structures. In your flowchart, show this bymaking oxygenated blood red and deoxygenatedblood blue.

What Did You Find Out?1. You know that most arteries carry oxygenated

blood and are coloured red. You also know thatmost veins carry deoxygenated blood and arecoloured blue. Where in your diagram is there an exception to this statement?

artery vein

valveinner layer

middle layer

outer layer

arteriolevenule

capillary

rightatrium

Figure 2.27 An artery has much thicker walls than a vein.

BCS_G8_U1C02_J15 5/4/06 4:12 PM Page 87


superior vena cava aorta

pulmonary artery

left atrium

pulmonary vein

left lung

leftventricle

rightventricle

inferiorvena cava

rightlung

rightatrium

pulmonaryvein

pulmonaryartery

capillaries

Figure 2.28 Blood flow through the heart and lungs from a different view

Figure 2.28 shows blood flow through the heart and lungs. In thisdiagram, you can see the blood on the right side of the heart is blueand the blood on the left is red. The deoxygenated blue blood goesout of the heart to the lungs. This is the only artery in the body tocarry deoxygenated blood. The only vein to carry oxygenated redblood comes from the lungs back to the left side of the heart.

The Components of BloodBlood performs several essential functions necessary for your health. Ittransports oxygen, nutrients, and water to your cells and carries carbondioxide and wastes away from your cells. Blood also carries specializedcells to help fight infections and heal wounds.

The human body contains about 5 L of blood. About 55 percentof this volume is a liquid called plasma. Plasma is a clear, yellowishfluid that contains numerous proteins, minerals, and other substances.Figure 2.29 on the next page shows some of the importantcomponents of plasma.

BCS_G8_U1C02_J15 5/4/06 4:12 PM Page 88


Did You Know?

There are about 25 trillion redblood cells in your body.

Scientists are finding newinformation about blood cellsand their functions. Go towww.bcscience8.ca to findout about current research onblood cells.

Figure 2.30 Three of thecomponents in blood: red blood cells(red disks), white blood cells (palepurple spheres), and platelets(irregular shapes)

Red blood cells, white blood cells, and platelets make up the other45 percent of blood components (see Figure 2.30).

Every second your body produces approximately two million redblood cells. Red blood cells carry oxygen from your lungs to the cellsof your body and carbon dioxide from your body cells to your lungs,where it is exhaled. Red blood cells are formed in a fatty tissue calledbone marrow. Bone marrow is found inside bone, such as inside thehollow part of your thigh bone. Red blood cells are also produced inthe liver and spleen.

Within each red blood cell are protein molecules of hemoglobin.This molecule carries oxygen to the capillaries and carbon dioxide tothe lungs.

White blood cells fight infection and prevent the growth ofcancer. They are much larger in size than red blood cells. A drop ofhealthy blood contains about 5000 to 11 000 white blood cells.When you get an infection, the number of your white blood cellsincreases.

Platelets are important for clotting blood. When you get a cut,platelets stop the bleeding and seal the wound by thickening theblood so a scab can form over the cut. There are about 200 000 to400 000 platelets in a drop of blood.

Reading Check

1. What are the four chambers of the heart?2. What causes the “lub dub” sound your heart makes?3. Explain the difference in structure between arteries and veins.4. Do all arteries carry oxygenated blood? Explain.5. What are the components of blood and their functions?

Plasma (55%) water proteins and minerals dissolved salts

OtherComponents (45%) red blood cells white blood cells platelets

Figure 2.29 The components of blood

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Did You Know?

Section 9.3 has moreinformation about how air isbrought into your lungs.

Connection

The Respiratory SystemAs you sit reading, you are carrying out a variety of body processes,but none more important than breathing in oxygen and exhalingcarbon dioxide. This is the main purpose of the respiratory system.Without this exchange of gases, you would be unable to survive.

The respiratory system shown in Figure 2.31 is made up ofstructures and organs that move oxygen into your body and carbondioxide out of your body. Your lungs are important organs in thissystem because they deliver oxygen for cellular respiration and excretecarbon dioxide.

Breathing is the process that brings oxygen into your body.Breathing begins when you inhale air through your nose or mouth.The air is warmed and filtered by tiny hairs, called cilia, and stickymucus in your nose. The cilia and mucus trap dirt and other particlesand either push these particles back out the nostril or down into thedigestive system.

The air continues down into the pharynx, past the epiglottis andthrough your larynx, or voice box. The larynx contains your vocalcords, which vibrate as air passes through them, producing the soundsof your voice. Then the air goes into the airway passage called thetrachea. You can feel your trachea by gently rubbing your hand upand down on your neck. The bumps you feel are C-shaped bands ofcartilage that maintain the tubular shape of the trachea and are similarto the ridges of a vacuum hose.

Humans can travel above 8000 mfor only a brief period of timewithout the support of additionaloxygen. At this altitude, the aircontains very little oxygen.Mountain climbers who attemptto scale very tall peaks, such asMount Everest (8850 m), maydevelop severe altitude sickness.They may suffer extremeheadaches, be unable to breathe, and lose muscle co-ordination.

pharynx

bronchiole

left lung

nasal cavity

epiglottis

larynx

esophagus

trachea

bronchus

right lung

Figure 2.31 The structures of the respiratory system

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At the base of the trachea branch two tubes called the bronchi(singular: bronchus). Air passes through both of these tubes and goesdirectly to your lungs. Air continues down the bronchi, which branchinto smaller air tubes called bronchioles. Finally, the air reaches tiny,thin-walled sacs called alveoli (singular: alveolus). There are millionsof alveoli at the ends of the bronchioles, and this is where gasexchange takes place.

Gas Exchange in the AlveoliYou can see in Figure 2.32 that each alveolus is surrounded bycapillaries. Notice how each alveolus resembles a bunch of grapes on astem. This is where the respiratory structures and circulatorystructures interact. In Figure 2.33, you can see deoxygenated bloodcoming from the capillaries surrounding the alveolus. Carbon dioxidediffuses into the alveolus, and oxygen diffuses the other way into thecapillaries and binds with the red blood cells. The oxygenated bloodreturns to the heart to be pumped to the rest of the body. This wholeprocess is called gas exchange.

alveoli

arterybronchiole

capillaries

veinalveolar sac

alveolus

airred bloodcells

capillary

CO2

CO2

CO2CO2

CO2

O2

O2

O2

O2

O2

Figure 2.32 Enlarged alveoli. Gas exchange occurs wherethe alveoli, capillaries, and blood vessels meet.

Figure 2.33 Gases move back and forthbetween the alveolus and the surroundingblood vessels.

Reading Check

1. Describe the path air must take to reach the lungs.2. What is the difference between bronchi and bronchioles?3. Name the gases exchanged between the alveoli and capillaries. 4. How does the structure of the alveoli speed up gas exchange?5. What structures from the respiratory and circulatory systems are

involved in gas exchange?

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Go to www.bcscience8.cafor more information on theeffects of smoking.

internet connect


SmokingMany respiratory diseases such as lung cancer and emphysema result from smoking tobacco products, such as cigarettes or cigars.Emphysema causes the alveoli walls to lose their elasticity (see Figure 2.34). This makes breathing increasingly difficult as the diseaseprogresses. Smoking is also linked to heart disease. Often people whohave respiratory diseases caused by smoking will also have heart disease.

What is in a cigarette?

Smoking is the number one cause of lung cancer. There are over 4000 chemicals in a cigarette. Fifty of these chemicals are carcinogenic.This means research has shown that exposure to these chemicals canpotentially cause cancer. The top six most harmful chemicals incigarettes and tobacco products are nicotine, tar, carbon monoxide,formaldehyde, hydrogen cynanide, and benzene.

Smoking also destroys the cilia lining your respiratory system sothat dirt and other particles trapped in the mucus cannot be removedeasily.

Figure 2.34 A healthy lung (left) and a diseased lung showing the effects of smoking (right)

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Between the upper and lower parts of the heart arecheck valves that allow the blood to flow in only onedirection. When you listen to the sound of the heartbeating, the “lub dub” sound you hear is the openingand closing of the valves. In this activity, you will builda model heart valve.

Safety

• Use care when cutting with scissors.

Materials • film canister with a 3 mm hole in lid and bottom• scissors• paper• tape• pushpin

What to Do1. Your teacher will drill holes in a film canister for

you. Place the cap on the film canister.

2. Hold one of the ends of canister up to your mouthand exhale into it. What does it sound like? Inhaleair through the same hole. What does it sound like?

3. Cut a 1.5 cm-square piece of paper. Place the pieceof paper over the hole on the outside of the lid ofthe canister. Tape it on one edge so that the papercan flap outward but still lie flat against the hole.

4. Exhale air through the bottom of the canisteragain. What does it sound like?

5. Inhale air from the same hole with enough force toclose the paper flap. Now repeatedly exhale andinhale through the hole. What does it sound like?Watch the paper flap as another student performsthe same exhaling and inhaling air on his or hercanister. How does the paper flap react?

6. Use a pushpin to make a pinhole in the middle ofthe paper flap. Repeat step 5. How is the sounddifferent when you inhale and exhale? How doesthe paper flap react? Gradually make the pinholebigger and bigger, while continuing to repeat step5 every time you make the hole a bit bigger.

What Did You Find Out?1. Describe the sound you heard while exhaling and

inhaling air through the canister with the paperflap. How is your canister model similar to thefunction of the human heart?

2. Describe how the piece of paper acts as a valve.

3. How did poking holes in the paper affect the valvefunction of the piece of paper?

4. If someone had a heart valve with a hole in it, howmight it affect the flow of blood in the heart?

5. Where are valves located in your body? (Name twodifferent locations.)

Lub dub!2-8 Find Out ACTIVITY


Science Skills

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POTPIECETO


Help for Broken HeartsThe first human heart transplant created a sensationaround the world in 1967. Although the patient died18 days later, the operation had opened a door. Sincethen, heart transplant technology has improved somuch that now 60 percent of transplant patients liveat least five years and some much longer.

The problem is that there are never enough donorhearts available for the thousands of patients whoneed them. So scientists have come up with artificialdevices to help fill the gap. So far, these have beentemporary bridges to keep patients alive until naturalhearts become available. But the dream of researchershas always been to build a fully functional, permanentdevice.

An artificial heart must be reliably powerful,practical, and biologically harmless. Early designscaused infections and strokes or were rejected by thebody. A big challenge has been dealing with a powersupply. In 1982, the first real mechanical heart wasimplanted in a gravely ill Seattle man. The implant wasconnected to a refrigerator-sized external power unitby wires stuck through his body. The patient survived112 days before dying of machine-causedcomplications.

More successful have been implants that helprather than replace the heart. With these ventricularassist devices (VADs), the diseased heart is left inplace. The VAD is implanted in the abdomen to takeover the job of the faulty ventricle (usually the left).The early VADs were also connected to cumbersomeexternal power supplies. Newer models are thumb-sized with much smaller battery packs. They transferpower through the skin without wires piercing thebody. Eventually, VADs may be developed that can beleft in place permanently.

But the closest thing to the researchers’ dreamhappened in 2001 in Louisville, Kentucky, when a manreceived the world’s first complete, self-containedmechanical heart. Made of plastic and titanium, theAbioCorTM heart replaces the ventricles, and isattached to the atria and pulmonary artery. It has asmall external battery pack that can recharge an

internal battery with no wires going throughthe skin. This experimental device has so

far extended the lives of severalpatients an average of five months.

As scientists learn more about theheart and new technologies continue

to evolve, a completely artificial heartcould well become a reality in this

century.

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Checking Concepts1. Describe the pathway blood follows

through the heart.2. What is the difference between an artery

and a vein?3. Describe three components of blood.4. What materials are found in plasma?5. How are the functions of the atria and

ventricles different?6. Describe the two blood vessel networks in

the circulatory system.7. Describe the structure and function of the

trachea.8. What process occurs in the alveoli?9. Describe two consequences of smoking.

10. Why can pneumonia lead to serious illness?11. Fill in the blanks with the correct term.

Blood is made up of:(a) _______, which is a clear, yellowish

________.(b) _______, which carry ________from

the lungs to the body.(c) _______, which fight bacteria and

viruses.(d) _______, which help prevent serious

bleeding by helping blood _______.

Understanding Key Ideas12. How are the circulatory system and

respiratory system interrelated?13. What volume of blood does your body

pump in a day or 24 hours?14. If your body had a disease that reduced the

number of your red blood cells, how wouldyour body be affected?

15. Explain how the pulmonary artery and thepulmonary vein differ from all other bloodvessels.

16. Explain the relationship for each set ofterms below.(a) superior vena cava, inferior vena cava (b) heart, blood, blood vessels(c) red blood cells, hemoglobin

(d) arterioles, capillaries, venules (e) carbon dioxide, oxygen, alveoli

17. At altitudes of 5500 m above sea level, the body has more difficulty functioningbecause the concentration of oxygen islower. The highest city in the world isWenzhuan, in the Himalayas, at anelevation of 5099 m above sea level. Howdoes your knowledge of the circulatory andrespiratory systems help you make aconnection between these two facts?

18. The following diagram is another way toillustrate the circulatory system. Whichterms below match the letter labels on thediagram?

Imagine there is a red blood cell in your bodythat has just been produced. Write a shortstory about the voyage of this red blood cellthrough the body.

Pause and Reflect


A

B

C

DE

F

G

H

(a) aorta(b) capillary(c) inferior vena

cava(d) kidney(e) lungs(f) pulmonary artery(g) pulmonary vein(h) superior vena

cava

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Prepare Your Own SummaryIn this chapter, you studied how human bodysystems work independently and together.Create your own summary of the key ideas fromthis chapter. You may include graphic organizersor illustrations with your notes. (See ScienceSkill 10 for help with using graphic organizers.)Use the following headings to organize yournotes:1. Organization of Human Body Systems2. The Digestive and Excretory Systems3. The Circulatory System4. The Respiratory System

Checking Concepts1. Match the statements with the correct terms

below.(a) A tissue is made from ______.(b) The lung is an example of ______.(c) ______ tissue works with bones to move

the body.

2. Draw a flowchart illustrating the followingterms in the correct order: organs, cells,tissues, living things, organ systems.

3. What structure prevents food from enteringthe respiratory tract?

4. Is the following statement true or false? If the statement is false, rewrite it so that itis true. “One of the functions of thestomach is the absorption of nutrients.”

5. What is the function of enzymes in the body?

6. What is the function of bile in thedigestion process?

7. What is the function of villi in the smallintestine?

8. What happens when a person takes in morefood energy than his or her body needs?

9. What is the difference between a vein and acapillary?

10. What are the components of blood? 11. Use the figure below to answer the

following questions.

(a) Which heart chamber pumps blood tothe lungs?

(b) Where does the blood go after leavingchamber 4?

(c) From which vein does chamber 3receive blood?

(d) Does the vein in part (c) carryoxygenated or deoxygenated blood?

12. What role does oxygen play in the body?13. What is the percentage of different types of

blood cells in the human body?14. What body system exchanges oxygen and

carbon dioxide?15. What material is passed through the body

at the end of the elimination stage?16. Approximately how long does the whole

digestion process take?

C h a p t e r

2

muscle organtissue nervecells

1

3

42

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17. What are the structures in the excretorysystem involved in removing waste fromthe body?

Understanding Key Ideas18. Below are nutritional labels from two

different food items. (a) Create two bar graphs that compare the

different amounts and the percentagedaily value of nutrients, vitamins, andminerals in both food items.

(b) Which nutritional table represents a glass of pop? Which nutritional table represents a serving of frozen vegetables? Explain your answer.

19. Why are nerve cells made of long fibres,but red blood cells are thick and diskshaped? Explain how their differences arerelated to the function of each type of cell.

20. In patients with cystic fibrosis, the duct(tube) joining the pancreas to the smallintestine is often blocked. What effectmight this have on digestion?

21. A diet low in saturated fat helps maintainthe elasticity of your blood vessels andhelps prevent them from clogging up. Whyis this type of diet considered to be healthyfor your heart?

22. What defence mechanisms does the bodyhave to prevent dust and other particlesfrom entering the lungs?

23. Use words and diagrams to explain howoxygen and carbon dioxide are exchangedin the lungs.

Using what you have learned in this chapter,write a paragraph describing one of thesetwo situations.

(a) Describe what happens in your digestivesystem to a hamburger you eat for dinner.

(b) Describe what happens to a molecule ofoxygen you have just breathed into yourbody.

Pause and Reflect

Nutritional Facts—Food Item Afor 250 mL

Amount % Daily Value

Calories 110

Fat 0 g 0%

Sodium 30 mg 1%

Carbohydrate 30 g 10%

Sugar 30 g

Protein 0 g

Not a significant source of saturated fat,trans fat, cholesterol, fibre, vitamin A, C,calcium, or iron

Nutritional Facts—Food Item Bfor 250 mL

Amount % Daily Value

Calories 140

Fat 0.5 g 2%

Sodium 120 mg 4%

Carbohydrate 24 g 8%

Sugar 10 g

Protein 6 g

Vitamin A 40% Vitamin C 30% Calcium 4% Iron 12%

BCS_G8_U1C02_J15 5/4/06 4:12 PM Page 97

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