CHAPTER 8 Zygotes and...

230 Chapter 8

Zygotes and DevelopmentC H A P T E R

Getting Started

C H A P T E R

88

1 Only one egg cell and one sperm cell areneeded to form a zygote. In fact, as soon asthe egg is fertilized, it forms a barrier to keepall other sperm out. But both plant andanimal males produce millions of sperm cells.Why are so many produced if only a singlesperm is required?

2 Organisms develop in so many different ways.Look at the photographs and list some of thestrategies for development that arerepresented. What are the advantages of eachstrategy? Can you identify any possibledisadvantages? What are they?

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Zygotes and Development 231

Observing the Growth and Development of Brine Shrimp

Brine shrimp, related to shrimps andlobsters, have a simple life cycle. Eggs hatchinto larvae. As they develop to adults, theyshed their outer skeleton approximately 12times. With each shedding, the brineshrimp not only get larger but also addbody segments. Close examination willreveal that the number of hairs on theirlegs increases as they age.

Place 100 mL of a 4% salt solution into a250-mL beaker. Add approximately 0.1 g ofshrimp eggs to the water. Using a hand lens,examine the water for brine shrimp eggseach day until they hatch.

1. Describe the appearance of the eggs.

2. Construct a data table. How many daysdid it take for the eggs to hatch?

3. Describe the appearance of the brineshrimp as they develop.

3 The female seaturtle comes ashoreonce every two or threeyears to nest and lay her eggs.Some species travel as much as3000 km from their birthplace totheir feeding grounds. Then, theyreturn to the beach where they wereborn. They dig holes, lay their eggs, cover themup with sand, and return to the ocean, abandoningthe eggs. Why do the turtles travel so far toreproduce? Why do they lay so many eggs? The seaturtle produces many eggs, while humans usuallyproduce a single offspring. What are theadvantages of each strategy?

ReflectingThink about the questions in , , .

What ideas do you already have? What

other questions do you have about

zygotes and how they develop? Think

about your answers and questions as you

read the chapter.

1 2 3

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232 Chapter 8

For a species to survive, its offspring must survive. Different organismsuse very different strategies and combinations of strategies to ensurethe survival of their offspring (Figure 1). Nevertheless, some generalcategories can be identified.

Key Strategies for the Survival of Offspring

• Some organisms producea zygote that remains insuspended animation(i.e., does not develop)until environmentalconditions becomefavourable. Water, food,and/or warmth canactivate growth and development.

• Some organisms wrap their developing zygote—calledan embryo—in a food package. This food supportsimmediate development, making theorganisms less dependent uponenvironmental factors.

• In some organisms, the embryos developwithin the adult organism, protected fromunfavourable environmental conditions.

• The adults of some organisms protect andnourish their offspring after birth.

Spores

A spore is a reproductive body encased within a protective shell. If environmental conditionsbecome unfavourable for life, the organismmay produce spores that enter a state ofsuspended animation. Once conditions becomefavourable again, the spores germinate, and theorganisms enter a growth phase.

Many different bacteria form spores, asshown in Figures 2 and 3, with each cellforming a single spore. The spore containsgenetic material surrounded by a tough cellwall, which is resistant to heat, drying, boiling,and radiation. When conditions improve, thewall breaks down and an active bacteriumemerges.

Survival and Development of Organisms

8.18.1

Figure 3

Anthrax is a disease caused bythe spore-forming bacteria,Bacillus anthracis. Each of therodlike filaments is a separateorganism. The white, oval disksthat appear in each of thefilaments is a spore. The deadlydisease affects sheep, cattle, andpeople. Spores can lie on theground for many years,becoming active only when theyenter an animal.

Figure 1

Figure 2

An electron microscope photo of a spore inside a bacterial cell

Fungi reproduce by way of tiny spores that are easily dispersed bywind. Once environmental conditions become favourable, cells in thespore begin to divide and grow.

A spore from the fungus that grows into bread mould can sit on acounter for months. If the spore finally lands on a food source, such asa sandwich, it germinates. If the sandwich sits in a locker for a fewweeks, the conditions are ideal for growth. The warmth and moisturecause the fungus to grow into thousands of threadlike structures. Eachthread develops a spore case, which can release thousands of spores(Figure 4).

Moss and fern plants also reproduce by way of spores (Figures 5and 6). The spores grow into structures that produce male or femalesex cells.

Figure 6

Spore cases are the brownstructures found under theleaves (fronds) of fern plants.

Seeds

A seed contains the plant embryo wrapped in a protective package thatcontains food. Unlike spores, which must wait until environmentalconditions become favourable, seeds bring nutrients to theirenvironment and can get a head start on growth.

Needle-producing trees,such as pine, spruce, and fir,have exposed seeds in aconelike structure, as seen inFigure 7. Because the seedsare not protected, they areoften described as “nakedseed coats.” Flowering plantseeds are enclosed andprotected inside a fruit,formed by the ovary of theflower (Figure 8).

Figure 5

The orange structure is a ripe sporecase of a moss plant.

Figure 4

The black spots on the bread mouldare spore cases.


Figure 8

The apple seeds are protectedwithin the fruit.

Figure 7

These pine seeds are not protected.

234 Chapter 8

Eggs

The vast majority of animals lay eggs. An eggincludes a zygote and some food, plus somemechanism for protection (e.g., a shell or ajellylike substance). Some organisms fertilizetheir eggs internally (e.g., insects, birds) beforea tough shell is secreted. Others, usuallyaquatic animals (e.g., fish, frogs), fertilize theeggs externally.

The tapeworm, a parasite that lives in theintestines, produces thousands of eggs in eachegg case (Figure 9). As an infected animaldefecates, some of the egg cases break and eggsare released. A resistant coating prevents theeggs from drying up and sticks to blades ofgrass or other plant material. If another animaleats the grass, it swallows the eggs. In theintestines, they develop into adult tapewormsthat can grow up to 20 m long.

For the tapeworm, the strategy of laying alarge number of eggs is important, becauseonly a few of the eggs will actually find theirway into the body of another animal. Manyother animals produce thousands of eggs forthis same reason: few of their offspring surviveto adulthood. Most of the others are eaten.

Reptile and bird eggs are especially welladapted for surviving on land. Their“amniotic” egg, shown in Figure 10, provides aself-contained environment for the developingembryo.

The spiny anteater and duckbill platypusare the only mammals that lay eggs (Figure 11).Like birds, they incubate the eggsoutside the body. However, they nourishthe young from mammary glands thatsecrete milk directly onto the fur.

Figure 11

The spiny anteater (left) and the duckbill platypus (right) are mammals that lay eggs.

allantois: Holds wastesproduced by the embryo

amnion: Fluid-filled sac thatcushions the embryo

chorion: Linesthe egg shell

albumen (eggwhite): Containsproteinyolk sac: Contains

stored food

air space

Figure 10

The amniotic egg is a protective, self-contained environment.

Figure 9

Each egg case produced by this tapeworm willcontain thousands of eggs.


MarsupialMammals

Marsupials (e.g.,kangaroos, koalas,and opossums) areborn tiny andimmature (Figure 12). Afteremerging from theuterus, they crawlinto a pouch andattach to the nippleof a mammary gland. Once they have grown too big to be carried, the offspring leave the pouch but may returnfor additional milk as long as the mother allows.

Placental Mammals

Most mammals, including humans, belong to a groupcalled placentals (Figure 13). Their young develop in the uterus or womb. After the embryo implants in theendometrium, blood vessels from the mother and embryogrow side-by-side and form an organ called the placenta.Although the two blood supplies remain separate, oxygenand nutrients diffuse from the mother’s blood into theembryo’s blood. Wastes from the embryo diffuse into themother’s blood and are carried away to be excreted. Theumbilical cord connects the embryo and the placenta.

In general, the offspring of placental mammals developmore slowly than the young of other animals and requiregreater long-term care. The mother provides the youngwith milk and protects them from danger.

Research SkillsSKILLS HANDBOOK: 3A

Understanding Concepts1. Identify an organism that uses

each of the following strategies toensure survival of their offspring.Describe the strategy more fullyand explain why it is used.

(a) The zygote remains insuspended animation untilenvironmental conditionsbecome favourable.

(b) The zygote is wrapped in afood package.

(c) The young develop within theadult organism.

(d) The adult protects andnourishes the offspring afterbirth.

2. Identify three organisms each thatproduce spores, seeds, and eggs.

3. Compare reproduction by sporesand seeds by listing theadvantages and disadvantages ofeach strategy.

4. Compare the development of thezygotes of a bird, a frog, and ahuman, by listing the advantagesand disadvantages of eachstrategy.

Making Connections5. In Australia, the introduction of

placental mammals has oftencaused problems for residentmarsupial mammals. Research theimpact on the ecosystem andhypothesize about why marsupialmammals aren’t able to competewith placental mammals that havesimilar needs.

3A

How does changing the wayanimals reproduce affect theother species in theecosystem? Consider thisquestion as you think aboutyour Challenge.

Figure 12

Opossums are marsupial mammals.Inside their mother’s pouch, each ofthe young has its own nipple.

Figure 13

Wildebeest are placental mammals. A young wildebeest must begin runningshortly after it is born. If it doesn’t, it might fall prey to hyenas.

One successful strategy for reproduction is theproduction of seeds. A seed is actually anembryo with packaged food. The food, usuallyin the form of starch, provides nourishmentfor the early growth of the young plant until itbegins to manufacture its own food. The foodin seeds also feeds humans around the world.Half the world’s food comes from the seeds ofjust three plants—wheat, rice, and corn.

In this investigation iodine is used toidentify starch. Starch turns a blue-blackcolour when iodine is added.

QuestionDo seeds carry food?

Hypothesis

Write a hypothesis for this experiment.

Materials

Procedure

Obtain a dry bean seed and one soaked inwater for 24 h. Use Figure 1 to help youidentify the various parts of the seed.

(a) Compare the appearance of thesoaked and dry bean seeds.

2

1

(b) Suggest a reason for at least onedifference you observe.

Use your fingers to gently remove the seedcoat from the soaked bean seed. Using adissecting needle, pry the two sections ofthe seed apart. Locate the embryo andexamine it with a hand lens or dissectingmicroscope.

(a) Draw a diagram of the embryo. Labelthe cotyledon, the hypocotyl, theepicotyl, and the radicle.

Caution: Exercise care when using the sharp dissecting needle.

Devise a test to determine which parts ofthe embryo contain starch. Test theembryo for the presence of starch.

(a) Describe the test you used for starch.

(b)On your diagram, use a colouredpencil to mark any areas where youobtained a positive test for starch.

(c) What function does the starch serve?Caution: Iodine irritates eyes and skin and may stain.

Obtain a corn seed (kernel of corn) thathas been soaked in water for 24 h. Lay thecorn seed down with the embryo facingupward. Use Figure 2 to help you identifythe various parts of the seed. Carefullyexamine the seed.

(a) How does the corn seed differ fromthe bean seed?

(b)One side of the corn seed is lighter.This is the location of the embryo.Draw the embryo and label yourdiagram.

5

4

3

Examining Plant Embryos

8.2 Investigation8.2 Investigation

236 Chapter 8

SKILLS MENUQuestioning Conducting AnalyzingHypothesizing Recording CommunicatingPlanning

6C

4B

Scientific DrawingSKILLS HANDBOOK: 6C Designing a Procedure4B

Figure 1

A bean seed

• safety goggles• gloves• apron • dry bean seeds• bean seeds soaked in

water for 24 h• dissecting needle• hand lens or dissecting

microscope

• iodine solution• paper towels• coloured pencils• corn seeds soaked in

water for 24 h• single-edged razor blade

Figure 2

A corn seed


Using a razor blade, cut the seed in halflengthwise to expose the interior.

Use caution when using the razor blade.

Test various areas of the corn seed forstarch using the same technique you usedin step 4.

(a) Which areas have the greatest amountof starch? Use a coloured pencil toindicate these areas on your diagram.

Analysis and Communication

Analyze your observations by answeringthe following questions:

(a) Bean seeds are classified as“dicotyledons” and the corn seeds areclassified as “monocotyledons.” On thebasis of your observations explain themeaning of the prefixes “mono” and“di.”

(b)Your teacher will supply you with adiagram of a germinating bean seed,similar to Figure 3. Using a redcoloured pencil, colour the radicle ineach of the successive pictures. Repeatthe procedure by colouring thehypocotyl with a blue pencil and theepicotyl with a green pencil.

8

7

6

Exploring1. Find out more about the importance of a

cotyledon by doing this experiment. In a trayof potting soil, plant three rows of beanseeds. In row 1, plant the entire seed. In row2, remove one of the cotyledons and thenplant the seeds. In row 3, remove bothcotyledons and plant the embryos only.Measure and compare the growth rates ofthe plants.

(c) Your teacher will supply you with adiagram of a germinating corn kernel,similar to Figure 4. Using a redcoloured pencil, colour the radicle ineach of the successive pictures. Repeatthe procedure by colouring thehypocotyl with a blue pencil and theepicotyl with a green pencil.

(d)Examine the diagram of thegerminating bean seedling anddescribe what happens to thecotyledon as the seedling grows.

(e)Why does the bean plant no longerneed the cotyledon?

(f) Examine the diagram of thegerminating corn seedling. Explainwhy the endosperm gets smaller as theplant grows.

Step 6

2A

Controlled Experiments2A

Figure 3

A germinating bean seed

Figure 4

A germinating corn seed

238 Chapter 8

Everything a new plant needs is foundinside the seed: the embryo and apackaged food supply. Its protective coatresists the cold and prevents drying formany months or maybe even years. Eachseed is specially adapted for specificenvironmental influences. Each embryo“knows” when it is time to start growing(germinating).

Most of the world’s food crops areannual plants. Harvesting crops meanstaking the seeds and growing themanew each year (Figure 1). Knowledgeof factors affecting seed germination isvital to food production.

In this investigation, you will designan experiment to determine howvarious environmental factors affectseed germination. Because not all seeds are the same, your conclusionsmust be restricted to the seeds you are studying.

Question

Write an overall question for thisinvestigation.

Hypothesis

Write a hypothesis for your group’sresearch project.

Materials

Experimental Design

You will work in research teams. Eachteam will work on one of the questions inTable 1. Pairs of teams working on thesame question will use either radish andtomato seeds or bean and lettuce seeds,and then share data.

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2

1

Germinating Seeds

8.3 Investigation8.3 InvestigationSKILLS MENU

Questioning Conducting AnalyzingHypothesizing Recording CommunicatingPlanning

Table 1 The Research QuestionsA How does temperature affect the germination and growth of

seeds? Consider testing a warm environment, room temperature,and a low temperature.

B Does light affect germination and growth of seeds? Considerusing different light sources (artificial and natural) and a darkarea.

C How do plants grow in acidic conditions? Use differentconcentrations of acetic acid (vinegar) in water.

D How do plants grow in basic conditions? Use differentconcentrations of dilute sodium hydroxide in water as the base.

2A

Controlled ExperimentsSKILLS HANDBOOK: 2A Designing a Procedure4B

Figure 1

Seeds, like this wheat grain, are one of Canada’s most important products.

Work with your team to design anexperiment to investigate your problem.Work with other teams to ensure that youwill be able to exchange data later. Readthe following suggestions before youbegin:

• Make sure that your seeds do not dry out.• Check your seeds for mould that will slow

growth and eventually kill the seeds.Remove seeds that show signs of mould.Always use clean tweezers to handle seeds,to reduce the risk of introducing mould.

4

• safety goggles• apron• gloves• radish and tomato seeds

• bean and lettuce seeds• other materials as

required

Caution: Sodium hydroxide is corrosive. Wear gloves andsafety goggles when using; avoid contact with skin.

4B


Your design must include a complete listof materials and equipment and describeany safety precautions needed.Wear safety goggles and a lab apron for the entire procedure.Even if your procedure does not require you to work with anacid or base, other people in the class will be. The entirework area must be safe.

You must identify your independent anddependent variables and describe how youwill control other variables.

Your design must include a description ofhow you will measure your variables.Include sample tables for recording data.

Present your design to your teacher forapproval.

Procedure

Conduct your investigation.

Analysis and Communication

Analyze your results by answering thefollowing questions:

(a) What conclusions can you draw fromyour experiment?

(b)What other experiments might youneed to perform to test yourconclusions?

(c) If possible, present your data in graphform.

(d)How did your results compare withthose of the other groups with yourresearch problem? with your types ofseeds?

(e)Can you draw any conclusions from theclass data?

Prepare a complete written report.11

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6

5 Making Connections1. Did you notice the different lengths of the

seedlings? With enough data, you candetermine the range of growth for a particularplant at a particular time. Construct a graph torepresent the data in Table 2. Whatconclusions can you draw from the data?Why aren’t all of the seedlings the samelength if the environmental conditions are thesame?

2. Why might scientists be interested in theanswers to the questions your classresearched?

Reflecting3. If your team repeated the experiment, what

would you do differently? Why would youchange your approach?

Length of shoot Number (mm) after day 2 of plants

10 1

12 3

14 6

16 14

18 22

20 15

22 7

24 3

26 1

Table 2

8A

7B

In this investigation you had to work in ateam to design and conduct aninvestigation. What have you learned fromthis experience that might help you whenyou are working on your challenge?

Reporting Your Work8A Constructing Graphs7B

240 Chapter 8

Life begins as a single unfertilized egg which,when fertilized, becomes a zygote. As thezygote becomes an embryo, it undergoesmany cell divisions by mitosis. Specific genesare turned “on” and others are turned “off” asthe number of cells increases. Cells begin todifferentiate into various tissues, and organsbegin to develop.

Although animals vary greatly as adults,their initial stages of development aresurprisingly similar. By observing thedevelopment of a frog embryo, you can beginto appreciate how a human embryo develops.

Materials• small bowl• unfertilized chicken egg• pencil• fertilized frog eggs (if available—spring only)• microscope slide• tweezers• prepared slides: frog embryology set• light microscope

Procedure

Fill a small bowl halfway with water. Gentlycrack the shell of an unfertilized chickenegg around its centre. Place the egg in thesmall bowl and gently break open the shellto release the contents.

1

What you see is a single, large cell (theyolk) surrounded by the egg white.Carefully examine the egg cell. UseFigure 1 to help you identify and locatethe structures. You may have to gently turnthe egg yolk to see the blastodisc. Also,examine the shell to find the eggmembranes and air space.

(a) Often, the appearance of a structureprovides clues to its function. Create asummary table similar to Table 1.Record the appearance and predict afunction for each structure.

2

Eggs and Embryo Development

8.4 Activity8.4 Activity

Structure Appearance Predicted function

shell ? ?

shell membranes ? ?

air space ? ?

yolk ? ?

albumen ? ?

blastodisc ? ?

Table 1

albumen (eggwhite): Contains pro-tein secreted by thewalls of the oviduct

blastodisc: Smallwhite spot under the cell membrane,contains the nucleus of the egg cell

shell: Hard, butpermeable toatmospheric gases and variouschemicals

chalaza: Two cordlikestructures of thickened protein ateither end of yolk

air space

shell membranesyolk: Contains protein and fat

Step 1

Figure 1

The egg shell is fused to two cell membranes all aroundthe egg. At the airspace at the blunt end, the twomembranes are separated. Note the chalaza that connectthe egg cell with the two ends of the egg. They probablyact as shock absorbers.

Figure 3

After fertilization, the zygote undergoes several cell divisions,called cleavages, during which all the cells divide at the sametime. The first cleavage divides the zygote into two cells.

The next cleavage occurs perpendicular to the first anddivides the zygote into four cells. The third cleavage dividesthe mass into eight cells.

a

b


Using the tweezers, gently touch the yolk.Note the thin membrane that surrounds it.

(a) Gently puncture the membrane anddescribe what happens.

If living frog eggs are available (Figure 2),place a single egg on a microscope slideand observe it with a microscope using lowpower.

(a) Describe the appearance of the frog egg.

Obtain prepared slides of developing frogembryos and examine them using the lowpower of the microscope. Use Figures 3, 4,and 5 to help you identify what you see.

(a) Make sketches of the slides you viewed.Make sure to label your diagrams.

5

4

3

Understanding Concepts1. Unlike human mothers, chickens and frogs

supply no food or oxygen to developingembryos after their eggs are laid.

(a) How do these embryos get food?

(b) How do they get oxygen?

2. How is the chicken egg different from thefrog egg?

3. Why do frogs lay so many more eggs thanchickens?

Exploring4. The chalaza may help rotate the blastodisc to

the top of the yolk. What is the advantage ofhaving the blastodisc on the top of the egg?

animal pole

vegetal pole

tail bud

heart region

head region external gills

mouth

Figure 4

About 8 h after fertilization, thezygote, now called an embryo,resembles a raspberry. The 64-cellstage is a hollow ball of cells. Inthe next stage, some cells migratetoward the inside of the hollow mass.

A round structure called a yolk plugcan now be seen protruding from theinner layer. After 48 h, a groovecalled the neural fold appears alongthe outer surface of the embryo. Cellsin this area will develop into the spinalcord and brain.

neural folds

Figure 5

By the fourth day after fertilization theembryo begins to look like a tadpole.

On day 4 beating of the heart isvisible. After 6 days, blood can beseen moving through the developinggills.

5B

Figure 2

The fertilized frog egg canbe divided into two regions.The lighter vegetal polecontains the yolk. Thedarker animal pole developsinto the embryo.

6C

Using the MicroscopeSKILLS HANDBOOK: 5B Scientific Drawing6C

firstcleavage,2.5 h

a

a

secondcleavage,3.5 h

b

b

a

b

eight-cellstage, 4.5 h

c

c

heartbeat, 4 days

a circulation in gills,6 days

b

blastula,12 h

a gastrula,about 20 h

b yolk plugstage, 32 h

c embryo,48 h

d

d

242 Chapter 8

During human intercourse,about 150 to 300 millionsperm cells travel through thevagina into the uterus.However, only a few hundredactually reach the oviductsand the egg (Figure 1).

During fertilization(Figure 2), also calledconception, the head of thesperm cell penetrates the cellmembrane of the egg. Eventhough several sperm becomeattached to this membrane,only a single sperm cellpenetrates the egg.

Human Conception and Pregnancy

8.58.5

Did You Know

Sperm cells cansurvive as long as

five days in the oviduct ofthe female. The egg cell iscapable of surviving only48 h after ovulation if it isnot fertilized.

Figure 1

Human sperm cell and egg cell

Sperm cells attach tothe egg cell. A singlesperm cell penetratesthe cell membrane.

a The mitochondria andflagellum of thesperm cell arepinched off by thecell membrane of theegg cell.

b The nucleus of the spermcell finds the nucleus ofthe egg cell, and the23 chromosomes from thesperm cell combine withthe 23 chromosomes fromthe egg cell.

cFigure 2

Fertilization


That sperm cell’s nucleus combines withthe egg’s nucleus. The mitochondria andflagellum of the sperm cell are pinched off bythe egg’s cell membrane.

Within hours after fertilization, tiny hairlikecilia that line the oviduct move the zygote intothe uterus. As it travels, it undergoes mitosis(Figure 3). Around the fourth day, a 16-cellmass enters the uterus where it floats freely forabout two days (Figure 4). The dividing cellmass, which now has more than 100 cells and isa hollow sphere, implants in the wall of theendometrium. It is now called an embryo.

Embryonic blood vessels and maternalblood vessels in the endometrium combine toform the placenta. Through the placenta,nutrients and oxygen diffuse from bloodvessels of the mother into blood vessels of the embryo,while wastes diffuse from the embryo’s blood into themother’s. The mother disposes of the wastes.

After about three months of pregnancy, the placentabegins producing estrogen and progesterone. High levelsof progesterone, first from the corpus luteum and laterfrom the placenta, prevent further ovulation. This meansthat once a woman is pregnant, she cannot conceive againuntil after the birth.

Understanding Concepts1. Describe the journey of the egg

from ovary to uterus. How longdoes it take the fertilized egg totravel to the uterus?

2. How does the placenta form?What is its function?

3. The placenta begins secretingprogesterone and estrogen afterthree months of pregnancy.Progesterone is responsible forthe following functions:• maintains the glandular tissue

of the endometrium;• inhibits ovulation;• inhibits contractions of

the uterus.

(a) Predict what would happenduring pregnancy if theplacenta became damagedand could not maintainprogesterone levels. Providereasons for your prediction.

(b) Why don’t pregnant womenconceive again later in theirpregnancy?

Figure 3

After conception, the zygote begins to dividerapidly. Here it has completed the first division.

Figure 4

Cell division continues through the six days fromconception to implantation.

244 Chapter 8

Technology has a long history of medical inventions that have enabledpeople to live fuller lives. Crutches and splints were likely the first suchinventions, allowing more mobility. Eyeglasses, developed in the mid-1600s, were one of the first technologies to assist a faulty organ.However, no technology has raised the interest and concern of peoplethe way that reproductive technology has. Reproductive technology isnot only changing the way that babies are born but the very laws thatdetermine parenthood and responsibility. As research related toreproductive technologies continues to develop, controversial issueswill arise. These issues will require us to debate how issues and personalbeliefs relate to their use.

Many people are unable to have a baby. There are many reasons forthis: a man may not produce enough sperm, a woman’s oviducts maybe blocked, the person’s brain may not secrete enough hormones, awoman’s follicles may not function properly. Some of these people goto fertility doctors in order to conceive a child.

Using Reproductive Technology

Fertility DrugsFertility drugs simulate the action of hormones from the pituitary(Figure 1). The drugs stimulate follicle development in the ovary,which makes it more probable that one or more egg cells may bereleased. Because fertility drugs increase the probability that multipleeggs will be released, the chance of having a multiple birth alsoincreases.

Cytoplasmic TransferIn cytoplasmic transfer, thecytoplasm from an egg from ayounger woman is transferredinto the egg cell of an olderwoman. It is believed that thetransfer reduces theprobability of genetic defectsfollowing fertilization.

Human Reproductive Technology

8.68.6

brain

Fertility drugs stimulate hormones from thepituitary gland toincrease follicledevelopment andstimulate ovulation.pituitary

increased follicle development

ovulation of multiple egg cells

Figure 1

Fertility drugs


Genetic mother(donor)

egg removed Birth mother

Father

fertilization ofdonor’s egg and father’s spermin vitro

embryotransferred

sperm collected

a

b

c

d

IntrauterineInseminationSperm cells are transferreddirectly into the oviducts ofthe woman followingovulation in intrauterineinsemination (Figure 2).Normally, most sperm cellsdie as they travel through theuterus to the oviduct.Insemination ensures thatsperm cells reach the egg ingreater numbers.

Gamete IntrafallopianTransferGamete intrafallopiantransfer involves the spermand egg being inserted in theoviduct (or Fallopian tube). The technique is believed to increase the chances of successfulfertilization by bringing sperm and egg cells together.

In Vitro FertilizationThe first step of in vitro fertilization (Figure 3) is the use of hormonesto prepare the ovaries for ovulation. During ovulation, a physicianinserts an instrument, called a laparoscope, into the woman’sabdomen. A light in the laparoscope enables the physician to locate theovary. A suction apparatus extracts mature eggs from the ovary. Theeggs are placed in a glass petri dish and fertilized by the partner’ssperm. Following a brief incubation period, one or more embryos aretransferred into the uterus by a small catheter. If at least one of theembryos implants, a baby will be born nine months later.

sperm cells collectedin petri dish

sperm cells collectedin syringe

catheter placed inoviduct, and spermcells injected intothe oviduct

egg cell

egg cells fertilizedby sperm cells in oviduct

ovary

a

b

c

d

Figure 3

In vitro fertilization. In this example the egg istaken from a donor, but the genetic mother andbirth mother can be the same person.

Figure 2

Intrauterine insemination

Understanding Concepts1. Explain why the name “test-tube

baby” is not accurate.

2. Why might in vitro fertilization beused?

3. Identify one disadvantage of usingfertility drugs.

4. Reorder the random list ofstatements to illustrate the correctsequence of steps performedduring in vitro fertilization.• Eggs are placed in a petri dish.• Eggs are extracted from the

ovary.• Eggs are fertilized by sperm.• Hormone fertility drugs are

given to the woman.• Embryo is transferred to the

uterus.• Embryos are incubated.

Making Connections5. A baby could have “five different

parents” if some of thesereproductive technologies wereused. What legal and moral issueswould this raise?

6. Reproductive technologies createcontroversy because of the ethicalquestions involved. Discuss issuesrelated to each of the reproductivetechnologies described in thissection. Prepare a summaryparagraph outlining your point ofview.

246 Chapter 8

Egg Freezing and Egg DonationsFertility drugs are employed to initiate multipleovulations. Although a single egg may be fertilized, excesseggs are frozen. At a later date these eggs can be thawedand fertilized. Sometimes zygotes are frozen afterfertilization. Some of the eggs or zygotes could beimplanted into the same mother at a later date, ordonated to another woman who either had no eggs in herovary or was unable to ovulate.

Embryo TransferA woman with a defective cervix or uterus may askanother woman to give birth to her genetic child throughembryo transfer (Figure 4). In this case, the egg from thefirst woman is combined with the sperm of her partner.Fertilization occurs in vitro. The zygote is transferred to a“surrogate” mother who carries the baby to term and thenreturns it to the genetic parents. This technology raiseslegal and ethical questions.

Genetic mother

Father

egg removed

sperm collected embryotransferred

Birth mother(surrogate)

fertilization of genetic mother’segg and the father’s spermin vitro

a

b

c

d

You may want to create a scenario (a short “real-world” story) for each issue in yoursurvey. This will allow the person being interviewed to better understand the meaning ofthe questions. If you chose to address issues involving the technologies in this section,what scenarios could you write?

For your display, you will need a central issue. What issues can you see in thetechnologies presented in this section?

The future technology in your story or play may be one of the technologies in this section.How will the characters in your story or play address the issues that relate to it?

Figure 4

Embryo transfer


Madeline Boscoe wears many hats: she is both the executivedirector of the Canadian

Women’s Health Network and thedirector of the Women’s Health Clinic in Winnipeg.

Boscoe started her career in community-based healtheducation programs geared toward women, particularly aroundfamily planning and prenatal care. This experience led her to adecision to become a registered nurse, training at the VancouverGeneral Hospital School of Nursing. Although today she useslittle of her nursing training (“I learned most of my work on thejob”), she feels that some background in nursing or a relatedarea of medicine is important for a job in the health care field.

In order to do her job, Boscoe draws on her communicationskills: writing, conflict resolution, policy analysis, and strong “peopleskills, including networking.” She advocates for better public policies inwomen’s health care, ensuring that women have enough information tomake informed choices with respect to their health. This informationmight include counselling or participating in experimental treatments.

Health advocacy, Boscoe believes, starts with looking at the health of the whole person, including economic health.

Exploring

1. Research the background and trainingrequired to become a registered nurse.

2. Research which careers require anursing training.

3. Might poverty be the enemy of goodhealth? Write a report describing yourviews.

4. Choose one type of medical treatmentthat might be suggested by a doctor,and imagine that it is being offered toyou. What kinds of information wouldyou need to know before you decidedwhether or not to give consent for thetreatment? What ethical issues wouldyou need to consider?

Working to ImproveWomen’s Health

”“My work is about making a contribution to

a better future.

Career ProfileCareer Profile

3A


248 Chapter 8

Embryology is the study of the developmentof an organism before hatching or birth.During the late 1800s, scientists noted astriking similarity between the embryos ofdifferent groups of vertebrate animals.Embryologist K. E. von Baer once wrote thatbecause he had not labelled two similarembryos when he received them, he could

not identify whether they were the embryos oflizards, birds, or mammals. Later, biologistssuggested that embryos are similar because allvertebrates have a common ancestor. Thisdoes not mean that birds evolved from lizards,or mammals from birds; it means that theyoung forms of these organisms resemble theyoung of related species.

Comparing Embryo Development

8.78.7 Case Study

chicken

Stage 1 Stage 2 Stage 3 Stage 4 Stage 5

human

pig

salamander

Figure 1

Embryo development in four species


Examine the embryonic development ofthe chicken, human, pig, and salamandershown in Figure 1.

The first stage of embryonic developmentis the fertilized egg, or zygote. The eggs of thedifferent animals are very similar in shapeand appearance. Small differences can bedetected in the size of the eggs and thevolume ratio of nucleus to cytoplasm. Thesecond stage shown follows cell division of thezygote. This stage illustrates how a single cellis now a ball containing several cells.

(a) Which cell mass is most similar to that ofthe salamander?

(b)In what way does the cell mass of thehuman embryo differ from that of thechicken?

Embryos that develop in a uterus have asmall yolk sac early in their development, butlose it later.

(c) Identify the yolk sacs of each embryo instage 3 of Figure 1.

During stage 3, tiny gill slits can be seen inthe sides of the neck. In fish, gill slits developinto gills. In mammals, they develop intoparts of the ear. The backbone and tailbonecan also be seen. The yolk sac in the egg-laying animals has shrunk as the animalgrows. An umbilical cord is now visible inmammal embryos.

(d)Identify the gill slits, backbone, andtailbone in each embryo.

Understanding Concepts1. At which stage of development can you

differentiate between the embryos of thechicken and the human? Explain your answer.

2. At which stage of development can youdifferentiate between the embryos of the pigand the human? Explain your answer.

3. Suggest an animal whose embryo wouldresemble a human embryo even more thanthe pig embryo. Provide reasons for yourselection.

During stage 4, more differences can beidentified among the organisms. Limb budsand a primitive brain and eyes can be seen.

(e)Identify the brain and eye for eachembryo.

(f) Identify changes in the yolk sac of thesalamander from stages 3 to 4. What hascaused the change?

(g)Identify the limb buds in each embryo.

During stage 5, the embryos begin to looklike the adult form. An ear can be seen inmost of the embryos. Specialized structuressuch as the chicken’s beak and wings, and thehuman’s fingers, can now be seen. At thisstage, a mammalian embryo is called a fetus.

(h)Which of the organisms spends time in alarva form?

(i) Which organism loses its tailbone?

250 Chapter 8

Your life began as a single cell about the sizeof the dot on an “i.” In a mere 280 days (ninemonths), you grew into a baby about 50 cmlong and with a mass of about 3 kg,composed of trillions of cells. Never againwill you experience growth at such a rate, northe number and diversity of developmentalchanges.

After the embryo implants in theendometrium of the uterus, it grows rapidly.By the fourth week of pregnancy the yolk sac,which has no nutrient value in humans,develops beside the embryo (Figure 1). A membrane, called the amnion, developsinto a fluid-filled sac that insulates theembryo, protecting it from infection,dehydration, impact, and changes intemperature.

Blood vessels from the embryo and themother’s endometrium form the placenta.Nutrients and oxygen diffuse from themother’s blood into the blood of the embryo.Wastes diffuse in the opposite direction,moving from the embryo to the mother. The umbilical cord connects the embryo with the placenta.

First Trimester

Human pregnancy can be divided into three trimesters,or three-month stages. The first trimester lasts fromfertilization to the end of the third month (Figure 2).By the end of the first month, the embryo is 7 mm long,500 times larger than the fertilized egg. The four-chambered heart has formed, a large anterior brain isvisible, and limb buds with tiny fingers and toes havedeveloped. A tail and gill arches, characteristics of allvertebrates, can be seen.

By the end of the second month, the cartilage of theembryo’s skeleton begins to be replaced by bone andthe embryo is now called a fetus. Most of the body partshave formed. The facial features continueto develop as the fetus now goes into agrowth phase. Arms and legs begin to move and a sucking reflex can be seen.

The Human Embryo

8.88.8

Figure 1

Formation of the membranes that protect the embryo

Figure 2

First trimester: Alimb bud and thebeginnings of theeye can be seen.


Second Trimester

By the second trimester (Figure 3), the 57-mm fetus movesenough to be felt by the mother. All the organs haveformed and, like other mammals, soft hair covers theentire body.

Early in the fourth month the fetus begins to swallowamniotic fluid and hiccup. A month later, it may suck itsthumb. By the sixth month, eyelids and eyelashes form.Most of the cartilage in the skeleton has been replaced bybone.

If the mother goes into labour at the end of the second trimester,there is a chance thatthe 350-mm, 680-g fetuswill survive.

Third Trimester

During the third trimester (Figure 4), from the seventhmonth until birth, the fetus grows rapidly. The organsystems, established during the first two trimesters, beginto function properly. All that remains is to increase bodymass. The average baby is approximately 530 mm long andhas a mass of 3400 g at birth.

Understanding Concepts1. Explain why some people claim

that you have to swim before youlearn to walk.

2. What function does the followingserve?

(a) the placenta

(b) the umbilical cord

3. Differentiate between an embryoand a fetus.

4. Make a chart of the changes thatoccur during each trimester.

5. What is the function of theamnion?

Making Connections6. The circulatory system is the first

system to function in the embryo.Why do you think this happens?

Exploring7. What are some of the early signs

of pregnancy? Researchpregnancy tests and how theywork.

Figure 4

Third trimester: The fetus grows rapidly.

3A


Did You Know

When a mothersmokes, the

embryo receives many ofthe harmful chemicalsthrough the placenta.Nicotine can constrict theblood vessels to theplacenta, reducing thesupply of oxygen to theembryo. This may explainwhy mothers who smokegive birth to small babies.

Figure 3

Second trimester: All of the organs andfacial features are present, but the organsmay not be fully functional.

252 Chapter 8

The placenta acts as a barrier, preventing themother’s blood cells and large molecules fromentering the circulatory system of the fetus.Smaller molecules, such as nutrients andoxygen, do move across the placenta(Figure 1). Unfortunately, some harmfulagents, such as alcohol, are also small enoughto cross the placenta. When a mother drinksalcohol, it crosses the placenta and enters theblood of the embryo.

The effects on the embryo are the same asthose on the mother: alcohol depresses thefunctioning of the nervous system. Alcohol isalso a poison. Like other poisons, it is brokendown by the liver. Unfortunately, the liver ofan embryo is not fully developed until the lastfew months of pregnancy, so alcohol cannotbe broken down quickly. This means thatalcohol remains harmful much longer in theembryo than it does in the mother. Not only

can alcohol kill many embryonic cells, it mayalso change the genetic information in somecells, which can produce a mutation.

Fetal alcohol syndrome (FAS) is a host ofbirth defects associated with alcoholconsumption by the mother. Symptoms offetal alcohol syndrome include mentaldisability, abnormal facial features, centralnervous system problems, behaviouraldifficulties, and growth deficiencies. It causesfacial deformities such as a small head, thinupper lip, and small jaw bone. FAS can bemild or serious, depending on the amount ofalcohol consumed by the mother.

It has been estimated that 60% to 70% ofalcoholic women who become pregnant givebirth to babies suffering from FAS. Andevidence suggests that the problem is gettingworse. A woman need not be an alcoholic tohave an FAS child.

Fetal Alcohol Syndrome

8.98.9 Explore an Issue

Figure 1

Alcohol and other drugs can pass from the mother’s bloodacross the placenta into the embryo.

Point

• FAS is the third most commonreason for babies being bornwith mental disability inCanada and the United States.(The most common reasonsfor mental disability aregenetic defects, which are notpreventable.) Heart defectsand defects of the nervoussystem are most common inFAS children. Any measure wecan take to reduce this toll isacceptable.

• Despite a growing awarenessthat avoiding alcohol preventsFAS, about one-fifth ofpregnant women continued todrink even after they learnedthey were pregnant. Educationis not enough.

Counterpoint

• Most birth defects occurduring the first three monthsof pregnancy, when the organsare forming. Should womenalso be monitored to ensurethat they have a well-balanceddiet, don’t gain too muchweight, or don’t becomedepressed? Scientific studieshave also linked many otherfactors to birth problems.

• The suspension of rights forany individual is a seriousmatter. All people would hopethat mothers would recognizetheir responsibility, butlegislation is not the answer.Changes in attitudes are bestaccomplished througheducation.

What do you think?

• In your group, discuss the statement and the points andcounterpoints above. Write down additional points andcounterpoints that your group considered.

• Decide whether your group agrees or disagrees with the statement.• Search newspapers, a library periodical index, a CD-ROM directory,

and, if available, the Internet for information on FAS and otherpreventable birth defects.

• Prepare to defend your group’s position in a class discussion.

Statement

Pregnant women should be required to have blood tests on a regularbasis to monitor drinking problems.

FAS: A Preventable Problem?


One study indicated that four times asmany pregnant women admitted to “frequent”drinking in 1995 than in a similar 1991 study.Among 1313 pregnant women, 3.5% said theyhad an average of seven or more drinks aweek or had consumed five or more drinks on

at least one occasion in the previous month.According to the March of Dimes, alcohol isthe most common cause of fetal damage inthe country and the leading cause ofpreventable mental disability.

8B

3A

3B

Exploring an IssueSKILLS HANDBOOK: 8B Research Skills3A Critical Thinking3B

254 Chapter 8

About nine months after the embryo was implanted, contractions ofthe muscles of the uterus signal the beginning of parturition, theprocess of birth (Figure 1). The cervix begins to dilate, or open up.The membrane surrounding the baby is forced into the vagina (alsocalled the birth canal). Usually, the amniotic membrane breaks andamniotic fluid lubricates the canal. This event is often referred to asthe “breaking of the water.” Once the cervix has dilated enough,uterine contractions push the head into the birth canal followed bythe rest of the body. In human babies, the head and shoulders arewidest. Once they are free of the birth canal, the baby slips out easily.The baby is born. A short while later, the placenta is expelled fromthe uterus.

Immediately after birth, the baby still remains attached to themother by the umbilical cord. Once the blood flow through theumbilical cord becomes restricted, the baby must begin breathing onits own. The umbilical cord is cut and tied off to prevent bleeding(Figure 2). Within a few weeks, the dead tissue from the umbilicalcord dries and falls off the baby’s abdomen, leaving the navel.

Hormones play a vital role in the birthing process. Prior to labour,the hormone relaxin is produced by the placenta. Relaxin causes theligaments in the pelvis to loosen. This provides a more flexiblepassageway for the baby during birth. As labour starts, the hormoneoxytocin is secreted by the pituitary gland. Oxytocin causes stronguterine contractions, which push the baby into the birth canal.

After the placenta is expelled, secretion of estrogen andprogesterone stops. The levels of these two hormones in the mother’sblood drop. If the mother does not breast feed, her menstrual cyclebegins again within a few months after birth.

Hormones and Lactation

At the beginning of puberty,estrogen stimulates breastdevelopment. During pregnancy,high levels of estrogen andprogesterone prepare the breastsfor milk production. Each breastcontains about twenty lobes ofglandular tissue, each suppliedwith a tiny duct that carries fluidstoward the nipple (Figure 3).

Birth

8.108.10

Figure 1

cervical opening startsto enlarge

a

amniotic sac breaks andfluid flows out

b

uterine muscles contractto push the baby out

c

baby emerges from thebirth canal

d

Figure 2

The umbilical cord no longer functionsafter birth. It dries up and falls off.


At birth, the mother’s pituitary gland in the brainsecretes prolactin, another hormone (Figure 4). Prolactinstimulates the glands in the breast to begin producingfluids. Initially, the fluid produced is called colostrum.Colostrum contains sugar and proteins but lacks the fatsfound in breast milk. It also helps develop the baby’simmune system. A day or two after birth, the prolactinstimulates the production of milk.

Milk production is stimulated by the baby’s suckingaction and the removal of milk. Many North Americanmothers who breast-feed prefer to end breast-feeding oncetheir youngster begins developing teeth. In somecountries, especially those with few available sources ofprotein, breast-feeding may continue for four or even fiveyears.

Milk and the Mother

Milk production greatly increases the energy and nutrientrequirements of the mother. Human milk contains about50% more lactose (milk sugar) than cow’s milk does. Atthe height of lactation, a woman can produce as much as1.5 L of milk each day. A mother producing that muchmilk would need about 50 g of fat and 100 g of lactoseeach day to replace her losses. In addition, a breast-feeding mother needs 3 g of calcium phosphate each day.In order to have enough calcium and phosphate in hermilk, the woman’s body can start to take those mineralsfrom her bones. Failure to replace the needed mineralsresults in a progressive deterioration of the mother’sskeleton and teeth.

Understanding Concepts1. Summarize the four stages of

labour shown in Figure 1.

2. Explain the functions of relaxinand oxytocin.

3. How does a sucking actionstimulate the production ofbreast milk?

4. Occasionally a physician gives apregnant woman who is pasther delivery date an injection ofoxytocin. What is the injectionexpected to do?

Making Connections5. Why is it important for nursing

mothers to eat a well-balanceddiet?

Exploring6. What is colostrum and why is it

important for the newborn babyto drink it?

milk duct

chest muscles

rib

rib muscle

fat

milk gland

nipple

Figure 3

The mother’s breast contains glands thatbegin producing milk shortly after the baby’sbirth.

Pituitaryreleasesprolactin.

Pituitaryreleasesoxytocin.

Oxytocin causes musclecontractions that forcemilk into milk ducts, so

baby can nurse.

Suckling of babystimulates pituitary.

Prolactinstimulates

milkproduction.

pituitary

Figure 4

Milk glands, the baby, and hormones work together to ensurethere is milk when the baby is hungry.

256 Chapter 8

Chapter 8 ReviewChapter 8 Review

Key ExpectationsThroughout this chapter, you have hadopportunities to do the following things:

• Identify advantages and disadvantages of variousstrategies for the development of a zygote. (8.1)

• Describe the events of fertilization, the stages ofembryo development, and the stages of birth.(8.4, 8.5, 8.7, 8.8, 8.10)

• Examine the structures within a seed and anegg that enable adaptation to a variety ofenvironments, and organize, record, analyze,and communicate results. (8.2, 8.3, 8.4)

• Formulate and research questions related toreproductive technologies, and communicateresults. (8.8, 8.9)

• Provide examples of technologies that helpproduce a baby, and discuss the ethicalimplications of using such technologies. (8.6)

• Explore careers that require an understandingof reproductive biology. (Career Profile)

KEY TERMS

amnion placentaconception sporeembryo trimesterparturition umbilical cord

Reflecting• “Different organisms use very different strategies, and

combinations of strategies, to ensure the survival of

their offspring.” Reflect on this idea. How does it

connect with what you’ve done in this chapter? (To

review, check the sections indicated above.)

• Revise your answers to the questions raised in

Getting Started. How has your thinking changed?

• What new questions do you have? How will you

answer them?

Understanding Concepts1. Make a concept map to summarize the

material you have studied in this chapter. Startwith the word “zygote.”

2. Provide examples of organisms that reproduceby way of(a) spores(b) seeds(c) eggs(d) zygotes developing within the parent

3. In plant reproduction, what advantages doseeds have over spores?

4. Draw and label the following diagram of aseed and indicate the function of the labelledparts.

5. Where is the food found in a seed? How is thatfood used by the plant? by the humanpopulation?

6. In the human female reproductive system,identify the(a) organ that is the site of implantation of the

embryo(b) tissue that provides nourishment for

embryo(c) tissue that secretes estrogen after ovulation(d) site of egg development and estrogen

secretion

7. Trace the path of an egg from the ovarythrough fertilization to implantation. Whathappens to the egg if it is not fertilized?

8. Explain why pregnancy is not possible once awoman reaches menopause.


9. Draw and label adiagram of an egg andexplain the function ofeach of the structures.

10. What causes fetal alcohol syndrome, and whatare some of its symptoms?

11. Explain the functions of the hormonesoxytocin and relaxin during birth.

Applying Skills12. A group of science students decided to test

different nutrients to determine which wouldspeed the growth of brine shrimp. Thefollowing procedure was followed.

(a) Identify the independent and dependentvariables.

(b) Write a hypothesis for the investigation.(c) Identify any problems with the

experimental design.(d) How would you correct the problems you

identified in (c)?

13. Some students decided to do an experiment todetermine the effect of temperature on seedgermination. The four groups, called A, B, C,and D, proposed different procedures, shownin Figure 1.(a) Identify the question being investigated.(b) Which procedure was the best

experimental design to test the question?(c) Identify any errors in the other

procedures.(d) Identify the independent and dependent

variables in procedure C.(e) What question is being investigated in

procedure D?(f) Identify the variables that have been

controlled in procedure D.

Making Connections14. Compare in vitro fertilization with the normal

course of events in human reproduction.

15. Indicate the advantages for each of thefollowing reproductive strategies:(a) A bacterium forms a spore with a resistant

coating.(b) An opossum produces eight embryos, but

only six find their way into the pouch andattach to a nipple.

(c) The wildebeest gives birth to young thatbegin running next to the mother a fewminutes after birth.

(d) The whooping crane lays two eggs. Thefirst chick to hatch breaks the other egg.Only the first chick will survive.

(e) A parasitic worm produces hundreds ofthousands of eggs. The eggs are releasedwith the solid wastes of the host animal.

16. When the rabbit was introduced into Australiait quickly took over much of the habitat of thewombat (a marsupial). What makes the rabbitmore successful than the wombat?

Figure 1

ChallengeChallenge

258 Unit 2

When Dolly the cloned sheep was born(Figure 1),it set off an explosion of debate about the ethicsof reproductive technology.

Scientists are making rapid advances in theirunderstanding of reproduction, both in animalsand plants. Out of those discoveries are risingnew technologies that allow infertile people tohave children, that allow genetic material fromone organism to be transplanted into another,that allow doctors, drug designers, and seedmakers to probe into reproductive cells andchange them. Advances in science and technologyare happening so rapidly that many people donot have access to the most recent information.Can an individual make a responsible decisionabout using these technologies without fullyunderstanding their impact?

A Survey on ReproductiveTechnology

What do people believe about reproductive technology? What do they find acceptable and unacceptable? You will conduct a survey to determine public opinion on two or three issues surrounding reproductive technology, and then analyze and report your results. Are there differences in opinion based on age or genderbeliefs? What other factors are involved?

Design and conduct a survey that includes:• Brief descriptions of two or three issues around reproductive

technology that you have chosen for study. The issues may berelated to human reproduction or reproduction of food plants.

• A set of questions for each issue that probes the beliefs of thepeople you will survey.

• Completed questionnaires.• A report that analyzes the data you have collected.

1

Society and Reproductive Technology

Figure 1

Dolly was the first mammal to be clonedusing non-reproductive cells.

Reproduction 259

A Public Information Display

Before individuals can make responsible decisions aboutreproductive technology, they must have a clearunderstanding of the issues. You will prepare aninformation display that clearly presents an issue inreproductive technology in a way that is informative. Yourdisplay should also deal with any misconceptions thatmay exist in the minds of the public.

Design a display about an issue in reproductivetechnology in video, audio, or multimedia thatincludes:• Basic information about a reproductive technology,

presented in a way that is easy to understand. Thedisplay may deal with a technology used in humans or other animals or plants.

• Some of the misconceptions around the technology,and ways that help individuals deal with them.

• Different perspectives on the issue that involves thetechnology.

• A report explaining how you decided what informationto include and why you chose to present it as you did.

A Futuristic Short Story or Play

The pace of development of new technology isincreasing. Will the incredible rate of discovery anddevelopment continue? If it does, what kinds ofreproductive choices and decisions will futuregenerations face?

Write a short story or play related to the use ofreproductive technology in the future thatincludes:• A description, using scientific terms, of how the

future technology works.• Characters or situations that illustrate different

perpectives on the issues related to the reproductivetechnology chosen.

3

2

Your completed challenge willbe assessed according to howwell you:

Process• understand the specific

challenge• develop a plan• choose and safely use

appropriate tools,equipment, and materialswhen necessary

• conduct the plan applyingtechnical skills andprocedures when necessary

• analyze the results

Communication• prepare an appropriate

presentation of the task• use correct terms, symbols,

and SI units• incorporate information

technology

Product• meet established criteria• show understanding of

concepts, principles, laws, and theories

• make effective use of materials

• consider legal and ethicalissues

• address the identifiedsituation/problem

Unit 2 ReviewUnit 2 Review

260 Unit 2

Understanding Concepts1. In your notebook, write the following

sentences, filling in the blanks with the wordor phrase that correctly completes thesentence. Use the words from this list: meiosis,mitosis, placenta, hermaphroditic, mutation,clone, interphase, metaphase, andconjugation.(a) This phase of mitosis, called _____, is

identified by chromosomes lining up inthe middle of a cell.

(b) The stage between divisions, called _____,is marked by rapid growth, the duplicationof genetic material, followed by anotherperiod of growth.

(c) The division process in which sex cells areformed is referred to as _____.

(d) The division process in which a single celldivides into two identical daughter cells isreferred to as _____.

(e) If the nucleus is removed from one eggcell and replaced with the nucleus from anembryo, the offspring is a(n) _____ of thecell that donates the nucleus.

(f) A change in a cell’s genetic information isa(n) _____.

(g) Animals that contain both male andfemale sex organs are said to be _____.

(h) Bacteria exchange genetic information byway of plasmids in a process called _____.

(i) The organ responsible for nutrientexchange between a human mother andfetus is said to be the _____.

2. Indicate whether each of the statements (a) to(j) is TRUE or FALSE. If you think thestatement is FALSE, rewrite it to make it true.(a) The larger the organism, the larger is the

size of its cells.(b) If a fertilized egg from a mouse has 22

chromosomes, you should expect 22chromosomes in the muscle cell of thesame mouse.

(c) When plants such as strawberriesreproduce by sending out runners, theyreproduce without sex cells.

(d) If a sheep were cloned you would expectthe offspring to be the same sex as theparent or original.

(e) All of the cells in the human body divide atthe same rate.

(f) Human sperm cells have half as manychromosomes as unfertilized egg cells.

(g) Multiple human sperm cells fertilize asingle egg cell simultaneously.

(h) Cancer cells divide at a faster rate thannormal cells.

(i) Female aphids can give birth to maleaphids through asexual reproduction.

(j) Fertilization of the human egg takes placein the ovary and the baby develops in theoviduct.

For questions 3 to 6, write the letter of the bestanswer in your notebook. Write only one answerfor each question.

3. The purpose of meiosis is to(a) produce offspring(b) duplicate DNA(c) produce daughter cells with the same

chromosome number as the mother cell(d) produce sex cells with half the

chromosome number as the mother cell

4. A human sperm cell contains(a) 23 chromosomes of which two are X

chromosomes(b) 46 chromosomes of which two are Y

chromosomes(c) 23 chromosomes of which one is X or Y(d) 46 chromosomes of which one is X or Y

5. Normal chimpanzee cells have 48chromosomes. Which one of the followingstatements about chimpanzee cells is correct?(a) muscle cells have 24 chromosomes(b) a zygote would have 96 chromosomes(c) a cell following meiosis I would have 24

chromosomes(d) a cell following meiosis I would have 48

chromosomes

?

?

?

?

?

?

?

?

?

Reproduction 261

6. The process in Figure 1 would occur in the(a) brain(b) heart(c) liver(d) ovary

Use the information below to answer questions 7and 8.

A science class decides to design anexperiment to test the effect of pH on seedgermination.

Problem: How does pH (acidity) affect thegrowth of germinating seeds?

Materials:

• various pH buffer solutions

• 4 petri dishes

• 40 seeds per group

• ruler

Design: Germinating seeds were placed inpetri dishes. Different pH solutions wereprovided. The length of the seedling wasmeasured daily.

Three groups submitted different proposals, as shown in Figure 2.

7. The best proposal was provided by (a) group 1, because a wide range of pH was

used and various amounts of solution wereadded.

(b) group 2, because everything was keptconstant.

(c) group 3, because only pH was changed.(d) group 1 and group 3 are equally good,

because a wide range of pH was used.

8. The appropriate independent and dependentvariables for the problem stated above wouldbe:(a) independent variable = amount of solution

used, dependent variable = type of seeds.

(b) independent variable = number of petridishes used, dependent variable = pH solutions used.

(c) independent variable = different pHsolutions used, dependent variable = length of seedlings.

(d) independent variable = same pH solutionsused, dependent variable = length of seedlings.

9. The nutrient starch would be found, in greatest quantity, in the area of Figure 3labelled

(a) 1 (d)4(b)2 (e)5(c) 3

Figure 3

Figure 2

Figure 1

262 Unit 2

Use Figure 4 below to answer questions 10 and 11.

10. The male parts of the flower can be identifiedas structures(a) 1 and 6(b) 1 and 2(c) 2 and 4(d) 5 and 6(e) 2 and 3

11. The female structure that receives pollen froman insect during cross-pollination is labelled(a) 1(b) 2(c) 4(d) 5(e) 6

Applying Skills12. John Needham boiled flasks containing

nutrient meat broth for a few minutes in orderto kill the microbes. The broth appeared clearafter boiling. The flasks were then tightlysealed and left for a few days and the murkycontents were examined under a microscope.The broth was teeming with microorganisms.(a) Does this mean that the broth had

spontaneously created microorganisms?Give your reasons.

(b) What changes would you make toNeedham’s experimental procedurebefore accepting his data?

13. A scientist wanted to determine if age affectsbody mass. The scientist hypothesized thatbody mass increases with age. To test thishypothesis, five people from each age groupwere selected at random. Their body mass wasrecorded. The results are provided in Table 1below.

The scientist concluded that the older aperson becomes, the greater their body mass.Critique the experimental design used by thescientist. What additional information wouldyou want to collect before accepting theconclusion?

14. Use Figure 5 to answer the followingquestions.(a) In which phase of the cell cycle does

growth occur?(b) In which phase of the cell cycle do double-

stranded chromosomes become single-stranded chromosomes?

(c) In which phases of the cell cycle is the cellundergoing cell division?

(d) In which phase of the cell cycle is the cellduplicating genetic information?

Table 1

Age group Average body mass (kg)

20 - 29 60 kg

30 - 39 65 kg

40 - 49 72 kg

50 - 59 75 kg

60 - 69 68 kg

Figure 5

3

6

1

2

4

5

Figure 4

Reproduction 263

15. Figure 6 compares mitosis and meiosis in a cellthat contains 28 chromosomes.(a) How many chromosomes would be found

in cell 1?(b) How many chromosomes would be found

in cell 3?(c) If nondisjunction did not occur, how many

chromosomes would be found in cell 3?(d) How many chromosomes would be found

in cell 4?(e) Which cells shown in the diagram above

would have a haploid chromosome number?

16. Figure 7 outlines the events that take placeduring the female menstrual cycle.(a) Use Figure 7 to describe the events of the

female menstrual cycle during the flowphase, follicular phase, and luteal phase.

(b) If a woman wanted to become pregnant,which time during the cycle would be bestfor fertilization?

(c) Which hormone is produced by follicle cells?(d) Which hormone(s) is produced by the

corpus luteum?(e) How would the diagram differ if a woman

reached menopause?

Making Connections17. Describe the effects of both parents using

drugs and alcohol on the conception anddevelopment of their fetus.

18. Many people exposed to nuclear radiationfrom the Chernobyl nuclear disasterdeveloped tumors. Some of these cancers arethe result of chromosomal damage. Highintensity radiation causes chromosomes tobreak apart, and small fragments becomescattered throughout the nucleus.(a) Why would the fragmentation of

chromosomes affect cell division?(b) Suggest a method that can be used to

detect these changes in chromosomes.

19. In intrauterine insemination, sperm cells fromthe donor or partner are transferred by way ofa catheter into the oviducts of the womanfollowing ovulation. (a) Suggest one reason why this technique

might be employed.(b) Provide one reason why someone might

object to this technology.

20. Fertility drugs can be employed to initiatemultiple ovulations, and excess eggs can befrozen. At a later date these eggs can bethawed and fertilized. Some of the eggs couldbe implanted back into the same mother at alater date or given to another woman whoeither had no eggs in the ovary or was unableto ovulate.(a) Suggest one reason why this technique

might be employed.(b) Provide one reason why someone might

object to this technology.

Figure 6

ovulation

endometrium

follicle development corpus luteum

Figure 7

CHAPTER 8 Zygotes and...

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