Critical Thinking/Problem Solving - Life ScienceCritical Thinking/Problem Solving worksheets in this...
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Life Science
Transcript of Critical Thinking/Problem Solving - Life ScienceCritical Thinking/Problem Solving worksheets in this...
Life Science
To the TeacherCritical Thinking/Problem Solving worksheets in this booklet exercise the students’ abilities to applythinking skills to situations related to concepts presented in the student edition. Students will applytheir knowledge to a new situation, analyze the new information, and synthesize in order to respondin a creative way. A series of responses that students might give are provided for you at the end ofthis booklet.
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CriticalThinking
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Table of Contents
To the Teacher . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
Skills Correlation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
Activities 1 New Status for an Old Life-Form . . . . . . . . . . . . . . . . . . . . . . 1
2 The Mechanics of Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3 Cloning the Woolly Mammoth . . . . . . . . . . . . . . . . . . . . . . . . 3
4 New Hope After a Long Search . . . . . . . . . . . . . . . . . . . . . . . . 4
5 Saving Tropical Rain Forests . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6 Waste-Eating Bacteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
7 Dying Frogs Give Ecological Clues . . . . . . . . . . . . . . . . . . . . . 7
8 Using Photosynthesis to Reduce World Hunger . . . . . . . . . . 8
9 Rescuing Endangered Plants . . . . . . . . . . . . . . . . . . . . . . . . . . 9
10 Coral Reefs at Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
11 Afraid of Snakes? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
12 Global Warming and Migration Patterns . . . . . . . . . . . . . . 12
13 The Everglades—Protecting a Delicate Balance . . . . . . . . . 13
14 The Human Body in Space . . . . . . . . . . . . . . . . . . . . . . . . . . 14
15 Are sports drinks beneficial? . . . . . . . . . . . . . . . . . . . . . . . . . 15
16 More Is Not Always Better . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
17 The High Risks of Smoking . . . . . . . . . . . . . . . . . . . . . . . . . . 17
18 New Hope for Treating Spinal Cord Injuries . . . . . . . . . . . 18
19 More than Skin Deep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
20 Fighting Disease Through Immunization . . . . . . . . . . . . . . . 20
21 Invasive Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
22 Nitrogen Fertilizers—Too Much of a Good Thing? . . . . . . . 22
23 The High Cost of Wetlands Destruction . . . . . . . . . . . . . . . . 23
Answer Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
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1ActivityNew Status for an Old Life-FormProblem
Solving
When early scientists first began to classify life,they divided it into two kingdoms—the animalkingdom and the plant kingdom. Later, whenthey began looking at objects under micro-scopes, they discovered another category oflife—one-celled organisms or protists.
Adding a New DomainUntil recently, all three of those kingdoms fellunder just two domains: prokarya and eukarya.Prokaryotes are bacteria or simple-celled organ-isms that do not have a true nucleus. Eukaryotesare plants, humans, animals, and other cells witha nucleus. However, in 1977, scientists made adiscovery that prompted them to add a newdomain to the classification system. The life-form that brought about that change is a single-celled organism called archaeabacteria.
For many years, archaea were considered tobe bacteria, so they were placed in the prokaryadomain. But scientists are discovering there’smuch more to prokarya than previouslythought. For that reason, prokarya is nowdivided into two separate categories: bacteriaand archaea. Instead of two domains, life-formsnow are classified into three domains: bacteria,archaea, and eukarya.
Surviving the ExtremesMicroscopically, archaea may look similar to bacte-ria but they are different. Archaea can thrive inmany types of environments but are especiallysuited to survival in extreme habitats. They can live
in hot water and in cold water. They have beenfound near thermal vents on the ocean floor, 500m to 600 m below ground, and in icy cold oceanwaters around Antarctica. Archaea can adapt toextremely salty water and live in environmentswith little oxygen. Because of their adaptability toextreme conditions, scientists are considering thefact that similar organisms could be present belowthe surface of Mars and other planets.
Although scientists’ understanding of archaea isstill limited, the life processes of these organismsare of interest to more than just scientists. Manu-facturers are hoping archaea can lead to improvedcold-water laundry detergents, longer-lasting fra-grances, and low-spoilage food processing.
Applying Problem Solving Skills1. Write at least two questions a scientist would want to ask before creating a new domain for an
organism.
2. Researchers think that archaea’s ability to withstand extreme conditions will make them useful inmedicines and other products, such as cold-water detergents. Describe a medicine or product thatcould benefit from archaea’s adaptability to extremes.
EUKARYABACTERIA
ARCHAEA
flagellates
basal protists
fungi
animals
plants
chromists
alveolates
rhodophytes
halophiles
cyanobacteria
heterotrophicbacteria
Name Date Class
Life-form Domains
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The Mechanics of Memory
A concert violinist plays a difficult piece ofmusic. A scientist forms a hypothesis. A toddlertakes a few shaky steps and, a week later, iswalking steadily. All of these processes—learn-ing, reasoning, and thought—would not bepossible without memory.
Getting the MessageScientists who want to understand how memoryworks study the brain, nerve cells, and synapses,the pathways between nerve cells. Nerve cells,called neurons, transmit and receive messagesthroughout the body.
A neuron has three parts: a cell body, den-drites, and an axon. The star-shaped cell body isthe part of the cell that contains the nucleus.Branchlike fibers, called dendrites, extend fromthe cell body and form the dendritic field. Thedendritic field receives messages from other neu-rons and carries them back to the cell body. Theaxon is a tubelike structure extending from thenerve cell. It is the only part of the neuron thatcarries information away from the cell body, inthe form of chemical signals, to the dendriticfields of other cells.
Fine-Tuning ConnectionsSome research shows that when thoughts orphysical actions are repeated over and over, theshapes of neurons change. Axons have tiny fin-gers that spread out to cover a wide area. Onetheory is that when a particular message isrepeated, these fingers come together. Thischange in the shape of the axon allows the neu-ron to work better. Therefore, the more a person
practices hitting a baseball or studies for a test,the more efficiently the information flows.
Synapses also change with learning. Synapsesare structures that form junctions between neu-rons. The messages they transfer cause neurons tobecome either active or inactive. Neurons take ininformation from the synapses and then sendmessages to other nerve cells or to muscles in thebody. Early in life, people have many moresynapses than they do in adulthood. As peoplelearn, the body prunes, or gets rid of, unnecessarysynapses. The ones that remain become strongerand more focused. Throughout our lives, newsynapses form as we learn from new experiences.
Most researchers agree that memory is part ofa system. For example, if you use your memoryto learn the lyrics of a song, more than one setof neurons is involved. One set might help yourecall the words, another the tune, and anotheryour feelings about the song. The combinationof these messages form your memory.
2Activity
CriticalThinking
Applying Critical Thinking Skills1. How would you explain to a younger student the parts of neurons and how they transmit infor-
mation? How would you explain the physical changes that take place in a neuron as a result oflearning? Form an explanation in your own words.
2. One scientific theory suggests that the shapes of axons change as someone practices or learnsmore about a particular subject. Give an example of a situation that has occurred in your own lifethat supports this theory.
Name Date Class
Synapse
Cell body
Dendrite
Neuron
Axon from another neuron
Axon
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3ActivityCloning the Woolly Mammoth Problem
Solving
In 1999, scientists watched as a helicopterpulled a huge block of ice and soil from the ground in northern Siberia. Inside the 20-metric-ton frozen block was an animal thatdied 23,000 years ago—a woolly mammoth.
More than a FossilMany other mammoths have been discoveredaround the world, but this was the first time thatthe remains were nearly complete. This particu-lar mammoth, known as the Zharkov mam-moth, had been preserved with its skin, hair, andsoft tissue—not just fossilized bones and tusks. Itwas airlifted to the Russian city of Khatanga,where it was stored in an ice cellar to maintain atemperature of –12°C.
Research teams hope that studying thewoolly mammoth’s remains would give themclues to explain why the animal became extinct.It is possible the woolly mammoth was huntedto extinction, or it might have been killed off bydramatic climate changes, malnutrition, or evena deadly virus.
Secrets Locked in DNAWhile these discoveries are important to the sci-entific community, the real excitement lies withthe possibility that scientists might be able toclone the male mammoth. Cloning is the processof producing a genetically identical organism. IfDNA can be found in the body cells of the car-cass, scientists could try to create a living versionof the extinct woolly mammoth.
Because the body is so well-preserved, scien-tists hope the woolly mammoth’s DNA still
exists. DNA has never been taken from the cellnuclei of an extinct species. Scientists don’t even know if the DNA could survive more than afew thousand years. The same extreme tempera-tures that preserved the remains also might havedamaged any chromosomes in the mammoth’sbody cells.
Fragments of mammoth DNA 50,000 to100,000 years old have been found in otherwoolly mammoths. These findings allowed sci-entists to establish the close relationshipbetween mammoths and elephants. The frag-ments also showed that there were once threesubspecies of woolly mammoths.
A New ProcessCloning is unpredictable and has only been donesuccessfully at the cellular level. When a sheepnamed Dolly was cloned in 1996, it was the world’sfirst clone of a living adult female sheep. Dolly wascloned by taking an egg cell from one adult female,removing its nucleus, and then replacing it withthe nucleus from a mammary gland cell from adifferent sheep.
Some scientists say that this type of cloningcould not work on the mammoth without having some of the mammoth’s living cells.Still others hope they can retrieve a cellnucleus from the woolly mammoth. If so,they will try to clone it using an elephant egg and an elephant as a substitute mother. Ifthat doesn’t work, they might be able to takefrozen sperm chromosomes from the woollymammoth and use them to create an elephant-mammoth hybrid.
Applying Problem Solving Skills1. If scientists are able to create an elephant-mammoth embryo, what major obstacle might they
face in successfully producing a mammoth hybrid?
2. Explain why fragments of DNA cannot be used in the cloning of long-extinct animals.
3. Aside from understanding how the woolly mammoth became extinct, what else might theremains of a 23,000-year-old woolly mammoth tell scientists?
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New Hope After a Long Search
If defective genes can cause disease, can replacingthose genes with healthy genes prevent disease?Because genes hold the blueprints for the humanbody, they also hold the codes for many types ofdisease. For that reason, researchers all over theworld are experimenting with DNA and genetherapy to find cures for diseases such as cancer,arthritis, and immune-system-related illnesses.
Replacing DNADNA is the chemical in the nuclei of cells thatcodes and stores genetic information. In 1990,scientists experimenting with gene therapyinserted healthy DNA into children sufferingfrom a rare condition called Severe CombinedImmunodeficiency (SCID). Children with SCIDhave little or no immunity to disease and mustlive in sterile environments. Scientists hypothe-sized that the healthy DNA would reproduceand replace the DNA that caused the disease.
By April 2000, after receiving gene therapy,two infants in France with a form of SCID were showing signs of recovery. After one year,their bodies began reproducing the healthyDNA. Many of their symptoms disappeared.Researchers working with the infants must nowwait to see how long the positive effects last.
Researchers use several methods to insertDNA into patients. Healthy genes can be trans-ferred into cells by chemicals, by a very tiny
needle, or by attaching genes to certain viruses.Diseases caused by a single gene are the bestchoices for gene therapy. Single genes can beisolated and reproduced more easily.
Concerns About Gene TherapyIn June 2000, two international teams of scientistscompleted a basic map of human DNA. Called theHuman Genome Project, this accomplishmentwas viewed as “a revolution in medical science.”Scientists were able to identify and to put in orderthe 3.1 billion units of biological information thatmake up the human genetic code.
Gene research is raising many questions,however. Some people worry that the informa-tion it reveals could be misused. They fear thatif insurance companies or employers find outthat a person’s genes might cause a particulardisease, then that person might not be able toget health insurance or a job. The U.S. govern-ment already has started addressing some ofthese issues with new laws that prevent compa-nies from denying insurance or employmentbased on genetic information.
Another concern is that some people mightwant to change genes that do not cause disease.They might want to produce a baby with highintelligence or a baby with a certain eye or haircolor. Many people feel it is wrong to use genetherapy this way.
4Activity
CriticalThinking
Applying Critical Thinking Skills1. While researching the effects of gene therapy on children with SCID, what would scientists have
used for their control group?
2. What are some possible advantages of gene therapy over other types of treatment?
3. Do you think the risks of misusing gene research outweigh the benefits? Explain.
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5ActivitySaving Tropical Rain ForestsProblem
Solving
In 1800, there were 2.9 billion hectares of tropi-cal rain forests in the world. There are fewerthan 1.4 billion hectares today. In the last 40years alone, more than 0.4 billion hectares oftropical rain forest have been destroyed. Rainforests contain more than half of the world’sanimals and plants. Thousands of these plantsand animals are found nowhere else on Earth.Once destroyed, they are lost forever.
Nature’s Medicine CabinetThe rain forest also is a valuable source of medi-cine. In fact, 25 percent to 40 percent of all drugscome from tropical rain forest plants. Scientistshave identified more than 2,000 plants thatmight have a use in the treatment of cancer.
Rain forests play a role in Earth’s climate.Sometimes called the “lungs of the Earth,”they help filter out excess carbon dioxide in the air which, in turn, helps regulate Earth’stemperature.
The Root of the ProblemThe world’s growing population is responsiblefor the disappearing rain forests. Businesses cutdown trees to sell the wood for constructionand for fuel. Farmers burn forests to makeroom for grazing cattle and for growing crops.
In 1998, 20 percent of Roraima, a state innortheastern Brazil, was destroyed by fires thatburned out of control. They were set by localfarmers using the “slash-and-burn” method togrow crops during a time of drought in theregion. For generations, they have used thesame method.
History Offers a SolutionTo save the rain forests, some researchers arelooking to the past for help. They have learnedthat ancient civilizations in the Amazon regionmanaged to grow crops without destroying theforest. They did this by clearing only small, circu-lar patches of land. Within a few years, the peoplestopped planting the area. Then the forest plants,including fruit trees, would begin to grow againand animals would move back into the area.
Some environmentalists would like to seefarmers who live in rain forest areas use similartechniques. To slow down the logging of theforests, they are encouraging businesses to cre-ate tree farms that can be grown for commercialuse and then replanted to be harvested again.
Applying Problem Solving Skills1. People who rely on rain forest land to earn a living probably have a different view of the value of
rain forests than people who live in other parts of the world. How do you think these two view-points might differ? Which group’s viewpoints might be focused on short-term goals? Whichgroup would be more interested in long-term goals? Explain.
2. Since 1800, approximately what percentage of the rain forest has been destroyed? If 0.4 billionhectares of rain forest continue to be destroyed every 40 years, how many years will it take beforeall of the rain forests are gone?
3. What do you think would be the best way to prevent the destruction of tropical rain forests?
Name Date Class
Rain forests filter out excess carbon dioxide in the air andrelease oxygen.
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Waste-Eating Bacteria
Although some bacteria are harmful, some areuseful. In fact, some bacteria can be used toclean up toxic spills and waste sites. When toxicchemicals are spilled or toxic garbage ends upin a landfill, they can contaminate the soil, air,and water nearby. If the toxins are not con-tained, they can get into the groundwater andcontaminate the water you drink. The U.S.Geological Survey, the Environmental Protec-tion Agency, and private companies have founda way to clean up some of these toxins withbacteria. This process is called bioremediation.
In 1987, a company in Pella, Iowa, discoveredthat three of its underground storage tanks wereleaking. The tanks contained penta, a toxicwood preservative. The city’s groundwater wasin danger of becoming contaminated. The com-pany was eager to clean up the spill and usedbioremediation to do it.
Putting Bacteria to WorkFlavobacteria are a kind of bacteria that love toeat penta. The bacteria eat the penta and leavebehind carbon dioxide, water, and other harmlesscompounds. When the penta are gone, the bacte-ria die. Within a year, the level of penta in the soilat Pella had dropped by two thirds and still wasdeclining. The cleanup was cheap and quick.
Bioremediation has been used for many yearsby sewage-treatment plants to clean wastewater.However, scientists still are learning how it canbe used most effectively for toxic waste cleanup.The first step in the process is to release the cor-rect type of bacteria at the spill site. Then nutri-ents important for bacterial growth are added.
Some bacteria used for cleanups already exist inthe soil, and scientists need only to add nutrientsto the soil to speed the cleanup. If the bacteriadon’t exist in the soil at the spill site, companiesthat grow bacteria for bioremediation can supplythem. A spill might require a special mix of fouror five kinds of bacteria to work.
Not Always EffectiveNot all spills can be cleaned up this way. If thetemperature is too cold, some bacteria cannot sur-vive. To warm the contaminated soil, it is some-times mixed with bacteria in a bioreactor. Thebioreactor acts like an incubator, keeping the soilwarm enough to allow the bacteria to do their job.Even with bioreactors, bioremediation can’t workin some clay soils. Furthermore, scientists haven’tfound bacteria to break down every toxic chemi-cal. Some chemicals are too dense for air to pene-trate, and some bacteria need air to survive.
6Activity
CriticalThinking
Applying Critical Thinking Skills1. Name some possible positive effects of bioremediation. Name some possible negative effects.
2. How could bioremediation affect the way companies dispose of toxic wastes?
Name Date Class
Contaminanttoxic wood preservative
Microorganism
End Productscarbon dioxidewaterother harmless compounds
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7ActivityDying Frogs Give
Ecological CluesProblemSolving
In the late 1970s and early 1980s, frogs began to disappear in Australia. It was an epidemicthat spread from southeast Queensland up the coast. In 1989, Australia found out it wasnot alone. At the First World Congress ofHerpetology (biologists who study amphibiansand reptiles are known as herpetologists), sci-entists shared stories and realized that frogswere dying in alarming numbers. To date, twoamphibian orders, 14 families, and 93 specieshave been affected.
The nearly 5,000 species of amphibians,including frogs, are said to be nature’s warningflags. Their deaths, say scientists, are cause forconcern. Because amphibians are more sensitiveto changes in the environment, changes in theirnumbers might be a sign of a more seriousenvironmental problem.
Frog FungusResearchers have identified a possible cause, achytrid fungus. The fungus, which lives in thesuperficial layer of the frog’s skin, coats the bellyand underside of the legs. Scientists can’t alwayssee the fungus on frogs. Sometimes it turns brightred, but usually it just sits there, waiting to kill.
The fungus is fatal only to adult frogs. Tad-poles are not affected. They can, however, carrythe disease. Scientists believe the fungus attacksthe keratin protein in frogs. Because tadpoleshave keratin only in their mouths, it doesn’taffect their breathing ability. After metamor-phosis, keratin becomes part of the frog’s
whole body. Frogs breathe and take in waterthrough their skin, particularly their under-sides. As the fungus spreads, it kills them eitherby suffocating them or by releasing a toxin.
Is there more than one cause?The fungus probably is not the only thing caus-ing frogs to die throughout the world. Climatechanges, pollution, and increased ultraviolet radi-ation due to the thinning of the ozone layer eachmight have an effect. However, frogs in protectedareas, like rain forests and zoos, are dying, too.
In the United States alone, the fungus hasinfected amphibians at the Bronx Zoo, thePhiladelphia Zoo, and the Shedd Aquarium inChicago. In Yosemite National Park, three of sevennative frog and toad species have disappeared.Deaths in parks, zoos, and wetlands are more likelythe result of a global problem like fungus, ratherthan a local problem like water pollution.
Of all the places in the world facing thisproblem, Australia remains the hardest hit with46 species infected so far. Worldwide, scientistscontinue their research. Much more needs to bedone, including confirming that the fungus is,indeed, the cause of the declining frog popula-tion. Scientists also want to gain a better under-standing of the life cycle of the fungus and itsability to spread. They also want to work withDNA to identify how many strains of the fun-gus exist. Until then, conservation methods arebeing put in place in an effort to maintainwhat’s left of the frog population.
Applying Problem Solving Skills1. How might the frog fungus be spreading to remote and protected areas like rain forests, wetlands,
and zoos?
2. What kinds of conservation efforts might be used to help maintain the frog population?
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Using Photosynthesis to Reduce World Hunger
Billions of research dollars are spent each year onthe problem of world hunger. One solution mightlie with photosynthesis. Photosynthesis is theprocess by which plants use energy, carbon diox-ide, and water to produce food. Photosynthesis,however, is not efficient. Even plants considered tobe extremely good at the process store only aboutone percent of the solar energy they receive. Scien-tists believe that by improving the process of pho-tosynthesis, they can increase crop yields.
A Key EnzymeThe RuBisCO enzyme is the target of much of theresearch. RuBisCO captures carbon dioxide andhelps convert it into starches, sugars, and othercompounds. Even though RuBisCO is the world’smost abundant protein, it is slow and inefficient.
Recently, scientists found a more efficient formof RuBisCO in red algae. If they can replace theRuBisCO in some plants with the more efficientform, or if they can change it to resemble the redalgae type, then photosynthesis might becomemore efficient. With improved efficiency, grain andother crops could be produced at a faster rate.
Some researchers say that there is no provenconnection between increased photosynthesisand improved crop yields. Other researchersclaim to have increased wheat yields by as muchas 10 percent to 12 percent in a two-yearperiod—just by temporarily boosting theprocess of photosynthesis.
Looking at AlternativesAlthough improving the process of photosyn-thesis seems to hold promise for solving worldhunger, scientists are a long way from making itwork. In the meantime, other researchers areworking on different ways to improve the effi-ciency of photosynthesis. One process is called“supercharging.” This process forces largeamounts of carbon dioxide into a plant’s cellsto make photosynthesis more efficient.
8Activity
ProblemSolving
Applying Problem Solving Skills1. Photosynthesis requires light, carbon dioxide, and water. Do you think that improving the effi-
ciency of photosynthesis could make up for a lack of one or more of these elements? Explain.
2. Besides increasing crop yields, what other advantages could improving photosynthesis provide?
3. Assume that more efficient photosynthesis means increased crop yields. What would happen ifphotosynthesis became too efficient?
Name Date Class
CO2 O2
Speeding up the process of photosynthesis could increase the rateat which crops are produced.
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9ActivityRescuing Endangered PlantsCritical
Thinking
Did you know that many plants in the UnitedStates are endangered? More than one in tennative plants are at risk. Currently, 735 speciesof plants in the United States are on the endan-gered list, and well over 100 species are candi-dates for being placed on the list.
Borrowing from Native PlantsOne reason scientists want to save native plantsis for their potential use as crops. Most NorthAmerican food crops were brought here byEuropean settlers. These foods aren’t native toNorth America and often are not resistant todiseases and pests common here. This is wherewild species come in.
If a food crop, such as potatoes, is threatenedby a disease, scientists can turn to the wildspecies for traits that make it naturally diseaseresistant. They can crossbreed the potato with anative plant to get a type of potato that is moreresistant. Crossbreeding commercial crops withnative crops also can produce a hardier plantthat is not as susceptible to insects. This allowsfarmers to rely more on organic farming, orfarming without pesticides.
One plant that grows in the United Statesthat is becoming extinct is the wild rice plant.The wild rice plant lives on the bank of a singlestream in Texas. Botanists are interested in thisparticular plant because it can survive drier
and hotter conditions than most other types of rice plants. Such traits might be needed ifEarth’s average temperature continues toincrease. Even in the short term, these traits are necessary in central Texas where drought is not uncommon.
Another threat to native plants is the spread ofgenetically engineered crops. The crops, calledbiotech crops, are genetically altered to be resis-tant to insects, diseases, and fungi. If the seedsfrom the biotech crops pollinate with otherplants, such as weeds that surround the cropfields, the weeds could become even moreaggressive and threaten fragile native species. Inone study, wind-carried pollen caused biotechseeds to create hybrid plants 91 m away from theoriginal crop.
Weighing the BenefitsAlthough most experts see value in savingnative plants, there is argument over the cost ofsaving them. Some experts say the diversity ofplant species must be preserved for the healthof the planet. Others say the cost for savingeach plant is so high that people must deter-mine its possible value before society pays thehigh cost of saving a species. In addition, someseed companies and farmers do not want togive up what they see as the money-savingpotential of biotech crops.
Applying Critical Thinking Skills1. Saving wild plant species is expensive. Do you think the government should spend its limited
resources to save native plants? Explain your answer.
2. What do you think about saving only those plants that might have a possible use to humans?Give reasons for your answer.
3. Why could weeds that crossbreed with biotech crops become more aggressive?
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Coral Reefs at Risk
Coral reefs are one of the ocean’s most beautifuland practical wonders. Reef colonies are hometo large numbers of plants and animals. Eventhough reefs cover only two percent of theocean floor, they contain nearly 25 percent ofthe ocean’s species. The reefs also protect shore-lines from erosion.
Years in the MakingCoral reefs are built over thousands of years bycoral polyps and tiny, single-celled algae. Thecoral take in the algae and the algae carry onphotosynthesis inside the coral. The algae helpthe coral change calcium salts in seawater into ahard calcium carbonate structure that makesup a reef. After the polyps die, they leavedeposits of this hard substance. Living polypsbuild on these deposits.
Even though coral reefs appear to be hard,they are fragile. Corals must have warm seawa-ter to live in, but not too warm. They are foundin tropical areas of the world. The water theylive in also must be clean. If it isn’t, their feed-ing tentacles can be clogged by sediment.Corals also need sunlight for the process ofphotosynthesis, so they cannot survive in watermore than 150 m deep.
Threats to a Fragile EcosystemMore than one quarter of the world’s coralreefs have been destroyed by pollution,tourism, overfishing, and the forces of nature.Tourists who take pieces of coral or buy it forsouvenirs contribute to reef destruction. Boatspollute the water with petroleum products,sewage, and litter. Overfishing also upsets thebalance of the reefs. Boaters crash into thereefs, and swimmers often bump or stand onthe coral, causing it to weaken. Waves causedby hurricanes can cut through them. Higherwater temperatures over time, possibly due toglobal warming, also have been blamed forcoral damage.
Many national and international groups areworking to save the coral reefs. However, insome nations, such as Indonesia, at least half ofthe reefs are already gone. In parts of the IndianOcean, rising water temperatures already havedestroyed 90 percent of the coral reefs.
10Activity
CriticalThinking
Applying Critical Thinking Skills1. Coral animals depend on algae to help them build reefs and obtain food for growth. How might
the algae benefit from living inside the coral polyps?
2. Tourism and activities, such as fishing and diving, can help support a nation’s economy. Should resi-dents take more steps to protect the coral reefs even if it will hurt their economy? Why or why not?
3. Some scientists compare the loss of coral reefs to the loss of rain forests. How are the conse-quences similar?
Name Date Class
Coral PolypTentacle
Mouth
Internal wall
Body wall
Limestone cup
Connectingtissue
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11ActivityAfraid of Snakes?Critical
Thinking
Although many people are afraid of snakes,only about 8,000 people in the United Statesare bitten by venomous snakes each year. Ofthose bitten, about 12 to 15 people die.
Most Snakes Not PoisonousOf the many species of snakes in the UnitedStates, only about 20 are poisonous. Theseinclude rattlesnakes, copperheads, cotton-mouths, and coral snakes. Rattlesnake bites areserious, though rarely fatal. Snakebites usuallyoccur the most between April and October inthe southern and southwestern states.
Most venomous snakes in the United States,are called pit vipers. Their name stems from thedeep pits located in their cheeks between theireyes and nostrils. The pits are heat receptorsthat help the snakes detect their prey and gaugehow much venom to use to kill it.
Exercise CautionThe safest way to avoid a snakebite is to practicecaution. Step on a log, rather than over it. If asnake is on the other side, it will hear you andhave time to move. Lift stones, wood, or otherobjects on the ground with a stick instead ofyour bare hands.
When camping, set up your tent in a clearingand do not gather firewood in the dark. If youmust walk around at night, use a flashlight andwear boots. When hiking, do not put your handsor your feet in places that you cannot see, suchas the crevices of rocks or brush-covered holes.
Nature’s MasqueradeMany harmless snakes have defenses that mighttrick you or their predators into being afraid ofthem. The North American hognose snake is
one harmless snake that is able to make itselflook fierce. When threatened, it flattens its headand neck until it looks much larger than itreally is. Then it opens its mouth to discourageits enemies. If this trick fails, it rolls over ontoits back and plays dead.
Some harmless snakes frighten their enemieswith behaviors that resemble those of poiso-nous snakes. The king snake and rat snakevibrate their tails against dry leaves to mimicthe sound of a rattlesnake. The markings on aharmless scarlett king snake are similar to thoseof the poisonous coral snake.
Snakes are an important part of Earth’secosystem. They help control the number ofrodents, and therefore control the spread of dis-eases carried by rodents. In most cases, snakeswill bite humans only when attacked, surprised,or injured. Most slither away when approachedor stay hidden to avoid human contact.
Applying Critical Thinking Skills1. What role does venom play in the survival of venomous snakes?
2. To avoid being bitten by a snake, what clothing would you suggest that someone wear while hik-ing in the woods or on rocky terrain?
3. If so few deaths are caused by poisonous snakes, why do you think so many people fear them?
Name Date Class
Fang Venom duct
Groovefor venom
Venom is forced out of openings in fangs
MLCT 11 01C MSS02Poisonous snakes have hollow fangs connected by a narrowtube to a venom duct.
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Global Warming andMigration Patterns
A spectacular scene unfolds in many parts ofthe world each spring and fall. Birds, by thethousands, begin their long flights to their sea-sonal nesting grounds. Birds migrate mainlybecause the availability of their food changeswith the seasons.
As they make their semiannual journeys (someover thousands of miles), migrating birds mustfind places to eat and rest along the way. Theymight stay in a habitat for several days beforecontinuing their trek. Birds look for habitats thatprovide a plentiful source of food, as well as saferesting places in forests, fields, or on water.
Detour AheadBird scientists, known as ornithologists, fearthat global warming might threaten the tempo-rary habitats that birds have come to depend onduring their migration. Higher global tempera-tures could cause coastal flooding and destroyfeeding areas and habitats.
Global warming also might cause a majorchange in migration routes. If global warmingdestroys traditional feeding centers, birds willneed to go outside their regular migrationroutes to find food to replenish their reservesand complete their journeys.
Experts also are concerned that a delay infinding food might mean birds will have lesstime to mate. This could result in a decrease inthe population of some species.
Adapting to SurviveSome birds already are beginning to adapt to climate changes. On the East Coast of the
United States, some birds are making longerlayovers on their routes to find food. In centralEurope, some migratory birds are delaying thestart of their migration. Britain’s and Finland’sfinch populations are moving farther north,and some of Europe’s thrush population havestopped migrating altogether.
Some scientists fear that global warming isoccurring at such a fast pace that some speciesmight not be able to adapt quickly enough. Thiscould reduce the size of bird populations andpossibly lead to the extinction of some species.
12Activity
ProblemSolving
Applying Problem Solving Skills1. Why do you suppose bird migration patterns usually follow coastal areas, mountain ranges, and
river valleys?
2. How might a change in migratory routes affect the ecosystems that existed on the old migratoryroutes? The new migratory routes?
Name Date Class
Atlantic flyway
Major Migration Flyways
Mississippi flywayCentral flywayPacific flyway
The four main North American migration routes, or flyways, runnorth and south along coasts, mountain ranges, and river valleys.
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13ActivityThe Everglades—Protecting a
Delicate BalanceCriticalThinking
In the early part of the twentieth century, whenrainwater and springwater filled the creeks andlakes around Orlando, Florida, the water emptiedinto the Kissimmee River. It flowed south intoLake Okeechobee before spreading across the flat,wide-open land. The sheet of slow-moving waterwas 80 km wide but only a few centimeters deep.It eventually created the Everglades, a shallowriver system that flows into the Gulf of Mexico.The Everglades was a thriving ecosystem richwith crab, fish, alligators, and wading birds.
Everglades National Park was established in1947. One of its main purposes was to provide asafe haven for the many kinds of South Floridawading birds. Aside from the American alligator,the wading birds of the Everglades were themost-watched creatures in the park. At one time,the Everglades was home to 2.5 million wadingbirds. Yet, even though they were protected in anational park, the number of South Florida wad-ing birds decreased dramatically—by an esti-mated 90 percent.
Draining the Life Out of the EvergladesIn the 1950s and 1960s, a series of canals andlevees were constructed in this area. They werebuilt to prevent flooding and to drain large areasfor farming and development. Billions of liters ofwater were pumped into the Atlantic Ocean andthe Gulf of Mexico. This severely disrupted theecosystem of the Everglades. Less water meantfewer nutrients to support the animals andplants that lived there.
The changes in the water flow also affectedthe levels of salt in the water. Some species wereable to tolerate the salty water and salty food;others were not. Aquatic plant life died. Fish,such as the sheep’s head minnow, sailfin molly,
and marsh killifish, were able to survive in thesalty water. However, they couldn’t survive with-out the food and shelter previously provided byaquatic plant life that had disappeared.
Wading Birds Move OnWithout these fish to feed on, the wading birdsmoved to other areas. Many moved to Louisianawhere water levels stayed constant and theycould find enough fish to eat. As a result, alliga-tors and other animals in the Everglades lostsome of their food supply.
Then, in the mid-1990s, record rains restoredthe flow of freshwater in the Everglades. TheEverglades almost reached the level it had beenat before construction of the canals and levees.Biologists studied the new conditions. Theyfound that vegetation, fish, and invertebrateslike crabs, spiders, and dragonflies returned.Unfortunately, the new supply of freshwaterhad no effect on the wading birds. Scientistsstill are doing research to find out why thesebirds are not returning to the Everglades.
Applying Critical Thinking Skills1. Why did the inflow of freshwater from above-average precipitation cause vegetation, invertebrates,
and fish to return to the Everglades?
2. How did the plants and animals of the Everglades reveal to scientists the state of the ecosystem?
3. Make a hypothesis about why the wading birds are not flocking back to the Everglades. Thenexplain how you might test your hypothesis.
Name Date Class
Lower water tables reduced the population of snails, which arethe primary food source for Everglades snail kites.
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The Human Body in Space
Since the beginning of the space program, NASAhas been monitoring the bodies of animals andhumans to see how they react to extended periodsin space. Space does have some negative physicaleffects on astronauts, as NASA already knows.
Weightlessness Takes a TollThe circulatory system of astronauts is affectedin space. On Earth, the heart pumps bloodmore forcefully to the upper body than to thelower body, where gravity helps the blood flowalong. In space, the heart continues to pumpthe blood more forcefully to the upper bodywithout the balancing force of gravity pullingthe blood to the lower body. This uneven bloodflow causes astronauts’ faces to become puffyand their lower bodies to become thin.
The shape of the spine also changes in space.Without the force of gravity pushing the verte-brae closer together, the spine stretches out andcauses pain in some cases.
Another system affected in space is thebody’s balancing system. To balance itself, thebrain takes in information from the eyes, mus-cles and tendons, and a set of sensors (calledthe vestibular apparatus) in the inner ear. Inspace, the only balancing information that canbe relied on comes in through the eyes, soastronauts have difficulty moving around.
The most serious problem for astronauts,however, is bone loss. In space, the bones loseminerals such as calcium, potassium, andsodium. The bone loss in the legs can be ashigh as ten percent, and even exercise doesn’tcompletely solve the problem.
Laboratory in SpaceWith the completion of the InternationalSpace Station (ISS), NASA will be able tostudy some of the effects of long-term expo-sure to weightlessness. NASA also plans toexpand its studies to better understand howthe immune system is affected and how radiation, which is much higher in space,affects humans. Radiation can pose serioushealth threats, including cancer and neurolog-ical damage.
Because people working together on the ISSwill be in small spaces for long periods of time,NASA plans to study how working in confinedspaces affects astronauts’ personalities.
14Activity
CriticalThinking
Applying Critical Thinking Skills1. What does NASA expect to gain by studying the effects of long-term space travel?
2. Do you think an international orbiting space station was a good idea? Why or why not?
3. Describe what you think NASA’s space program might be like in 50 years. What types of projectsdo you think NASA will be working on? What might NASA already have accomplished by thenthat it has not accomplished now?
Name Date Class
U.S. astronaut Ellen Ochoa plays her flute while floating weightless in space.
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15ActivityAre sports drinks beneficial?Critical
Thinking
Sports drinks, or glucose-electrolyte beverages,were first developed for athletes to replace bodyfluids lost through sweat during exercise. Onlyrecently have they become popular amongcasual exercisers and nonathletes.
Today, consumers are being bombarded with avariety of claims about which sports drink tobuy. How do you choose? Are these beverages allthe same, or do some provide benefits not foundin others? What ingredients, if any, are beneficial?
High-Performance BenefitsWhen used to replace fluids, sports drinks canprovide real benefits for athletes and nonath-letes alike. Drinking enough fluid to preventdehydration has been proven to improve exer-cise performance. If a person exercises and doesnot replace the fluid and salt lost by sweating,performance decreases. A loss of body fluid canaffect the heart’s performance and lower bloodpressure. If exercise continues for longer thanone hour, replacing carbohydrates, as well aslost fluids, becomes important.
The ideal sports drink contains water, carbo-hydrates, salt, and other electrolytes. Carbohy-drates, in the form of sugars, not only make thedrink pleasant-tasting, they also provide energy.To be most beneficial, sports drinks shouldcontain between four percent and eight percentcarbohydrates. This helps the body absorb thefluid quickly.
Fluid ReplacementWhen the body loses water, it also loses elec-trolytes. The major electrolytes added to sportsdrinks are sodium, potassium, and phosphate.Sodium is a recommended additive because itincreases the absorption of sugar and water and
helps restore the body’s volume of plasma.Sodium also helps maintain the natural desire ofthirst. And sodium helps the body retain thefluid once it’s consumed.
Water, rather than sports drinks, might be abetter choice for those who exercise less than 30 min. Fluid replacement is more importantthan energy replacement in this instance. How-ever, sports drinks are an excellent choice forendurance athletes who need water for hydrationplus carbohydrates for energy. Endurance athletesuse water to cool themselves during events inhigh-temperature weather. However, they pourthe water over their bodies rather than drink it.
The fluid that athletes and exercisers chooseshould depend on what tastes good, and thesport in which they are participating. Peoplewho exercise always should consume adequateamounts of fluid to maintain peak performance.
Applying Critical Thinking Skills1. From a health perspective, why is it important that a sports drink taste good to the person drinking it?
2. During which activities would water be a better choice than a sports drink?
Name Date Class
Signs of Dehydration
1. Thirst 2. Loss of appetite 3. Lethargy 4. Anxiety 5. Nausea and dizziness 6. Irritability 7. Cramps 8. Fatigue 9. Headache10. Dark urine
Thirst is a poor indicator of dehydration. Dehydration can happenquickly and have serious consequences. Watch for these signs andprotect yourself.
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More Is Not Always Better
Most people need to eat foods containing ironto stay healthy. Iron is an important part ofhemoglobin, the pigment that gives blood itscolor. Hemoglobin carries oxygen. In fact, oxy-gen binds to the iron in hemoglobin.
If you have too little iron, your blood will notbe able to carry enough oxygen to your bodytissues. As a result, you will have headaches, feeltired, and your heart will beat rapidly in aneffort to carry more oxygen to your cells.
Iron OverloadHowever, for a small percentage of the popula-tion, iron is a poison. About 1 million Americanshave a condition called hereditary hemochro-matosis (HH). Their bodies absorb too much ironfrom their food and they become overloaded withiron. Most adults absorb ten percent to 15 percentof the iron they consume. People with HH absorbabout 30 percent of the iron in the food they eatand about 50 percent of the iron in vitamins.
HH is caused by a genetic defect and is rela-tively easy to treat. At this time, no cure existsfor HH, but early detection and treatment can
prevent serious illness. Unfortunately, manypeople do not know that they have HH until ithas caused serious problems. Nearly 95 percentof HH cases go undiagnosed.
In its early stages, the condition has many different symptoms—fatigue, weakness, sorejoints—which could be caused by any numberof diseases. Severe symptoms can take decadesto show up. In 70 percent of cases, the conditionis found in people 40 to 60 years old. That’sbecause many of these patients suffer from liver cancer, heart disease, diabetes, and arthri-tis. Only during treatment of these diseases dodoctors discover the cause—decades of ironbuildup from HH.
Early DetectionThere is now hope for earlier detection. Someexperts suggest adding a test for iron levels toall standard blood tests. One medical testinglaboratory recently started testing all blood foriron levels. The Centers for Disease Control andPrevention in Atlanta is working to make earlytesting for HH a standard practice.
16Activity
CriticalThinking
Applying Critical Thinking Skills1. Hemochromatosis is relatively common, so why do you think doctors sometimes overlook this
condition?
2. A diet rich in iron is good for most people. After reading this article, do you think it’s a good ideato eat spinach and other foods rich in iron or to avoid them? Explain.
3. One of the most common conditions in the world is caused by too little iron in the diet. Too littleiron can lead to anemia, a condition with symptoms similar to some symptoms of hemochro-matosis—dizziness, weakness, and headache. To prevent anemia, iron often is added to breadsand cereals. But the extra iron is a problem for those with hemochromatosis. Do you think it’s agood idea to add iron to foods? Why or why not?
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17ActivityThe High Risks of SmokingCritical
Thinking
Most people are aware that cigarette smokinghas been linked to lung cancer in humans. Butdid you know that the U.S. Department ofHealth considers cigarette smoking to be theprincipal cause of unnecessary, preventable ill-ness and early death?
Links to Other DiseasesIn addition to lung cancer, the long list of ill-nesses linked to cigarette smoking includes heartdisease; gum disease; mouth, esophageal, larynx,bladder, kidney, stomach, pancreas, and coloncancers; and cancer of the reproductive tissuesand organs. Studies show that the risk of coloncancer remains high for people who smoke evendecades after they quit. Smokers are ten timesmore likely than nonsmokers to develop emphy-sema or bronchitis, and smokers suffer morefrom asthma and respiratory infections.
Recently, the National Cancer Institute founda link between cigarette smoking and nutrition.They discovered that smokers tend to eat fewerfruits and vegetables and less fish and poultrythan nonsmokers. These foods are healthy, con-tain generous amounts of vitamins A and C,and are thought to be helpful in the preventionof cancer.
Another study showed that smoking increasesthe risk of death in people with diabetes. Therisk of death was especially high for women withdiabetes who smoke. Diabetes normally causespeople to have a higher risk of heart disease.Because smoking accelerates heart disease,people with diabetes should avoid smoking.
Slower HealingDoctors who perform plastic surgery havefound that patients who smoke suffer moreskin loss after surgery than nonsmokers. Thenicotine in cigarettes causes the blood vessels ofsmokers to constrict. The lack of blood circu-lating in the affected skin doesn’t allow it toheal properly.
Many health risks are linked to cigarettesmoking, and scientists are continuing to findmore. In fact, smoking even poses health risksto those who don’t smoke. Environmentaltobacco smoke can increase a nonsmoker’s riskof heart disease by up to 30 percent.
Applying Critical Thinking Skills1. Imagine that your friend has been experimenting with cigarette smoking. What facts would you
use to persuade your friend to stop smoking?
2. What type of results from skin graft surgery to repair burned skin would you expect in a patientwho is a nonsmoker compared to a patient who smokes?
3. With all the health hazards connected with cigarette smoking, why do you suppose people con-tinue to smoke?
Name Date Class
Tobacco smoke contains more than4,000 chemicals including:
ammoniaarsenic
benzenecadmium
carbon monoxideformaldehyde
hydrogen cyanidelead
nickelurethane
vinyl chloride
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New Hope for Treating Spinal Cord Injuries
The human body has an amazing ability torepair itself. For nearly a century, doctors, sci-entists, and researchers believed the centralnervous system, however, was unable to repairitself. Now, experts are saying that repairingnerves and nerve impulses—once unthink-able—might be possible in the near future.
Each year, some 10,000 Americans receivespinal cord injuries. Scientists are hopeful thatthey might be able to treat this once untreatablecondition. New treatments, ranging from drugtherapy to tissue transplantation, have putresearchers closer than ever to understandingnerve growth and repair.
Blueprints for Stem CellsOne of the more promising but controversialtreatments involves the use of embryonic stem(ES) cells. Researchers have found that humanstem cells from fetal tissue can, under the rightconditions, develop into almost any kind of cellneeded by the human body. ES cells can bedescribed as “unprogrammed” cells. They cantake on the characteristics of just about any typeof cell. This means that ES cells have the potentialto repair nerves and grow tissues and possiblyeven entire organs.
If ES cells were turned into nerve or braincells, they could be used to treat spinal cordinjuries as well as other disorders of the centralnervous system, such as Alzheimer’s and Parkin-son’s diseases. However, because ES cells aretaken from aborted fetuses or from embryosmade in test tubes, ethical and moral issues needto be considered. As a result, scientists also have
tried using ES cells from mouse, sheep, pig, rab-bit, and hamster embryos.
When researchers transplanted ES cells intoadult rats with damaged spinal cords, they dis-covered that the ES cells caused the productionof myelin. Myelin is the protective coating thatinsulates nerves. A nerve whose myelin hasbeen rebuilt might be restored to its full func-tion. For people confined to a wheelchair, thatcould mean regaining movement of a limb orcontrol over bowel and bladder functions.
Making a ConnectionIn addition to ES cell research, scientists arelooking at ways to encourage injured nerves toreestablish connections with one another. Onesuch experiment involved rats who receivedinosine, a compound found naturally inhumans. The introduction of inosine into therats caused the regrowth of nerve fibers in fourout of five rats. This demonstrated to scientiststhat the nerves are capable of reestablishingconnections. In another experiment, tissuefrom a pig’s snout was transplanted into a ratwith an injured spinal cord. The myelin in therat’s nerve cells regrew, and nerve impulseswere restored.
Many years of research and experimentationlie ahead for each of these treatments. Althoughmoral and ethical discussions must take placein the medical and scientific communities, sci-entists are encouraged by their rapid progress.For the first time, doctors might be able to offernew hope to patients who were once told theywould never walk again.
18Activity
ProblemSolving
Applying Problem Solving Skills1. ES cells have the capacity to become almost any kind of human cell. What other medical prob-
lems, in addition to nerve regrowth, might be solved by their use?
2. An estimated 200,000 Americans are paralyzed by old injuries. Might scientists’ new understand-ing of nerve growth and repair help them? If so, how?
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19ActivityMore than Skin DeepCritical
Thinking
Jim Lewis and Jim Springer are identical twins.They both married women named Linda. Bothlater divorced and then married women namedBetty. They gave their first sons the same nameand had dogs named Toy. While in school, bothliked math and hated spelling. They drive thesame kind of car, like to vacation at the samebeach in Florida, and both enjoy woodworkng.They both bite their fingernails.
What is unusual about these twins is that theywere adopted by different families when they wereonly four weeks old. They didn’t grow up togetherand didn’t find each other again until they were39 years old. Their environments were different,so what caused them to be so much alike?
Heredity vs. EnvironmentFor many years, scientists believed that the envi-ronments people grow up in form their personal-ities. Because most identical twins are raised inthe same house by the same parents, their person-alities are expected to be similar. However, thistheory did not explain how identical twins raisedapart could be so similar. It also did not explainhow brothers and sisters who were not twins butwere raised together could be so different.
Scientists now think heredity might be just as important as environment in forming per-sonality. Scientists at the University of Min-nesota have studied about 60 pairs of identical
twins who were adopted by different families asbabies and raised in different environments. Totheir surprise, they found that identical twinsraised apart had many similar personality traits.
Because many of these twins had similar per-sonalities, scientists thought it could be a resultof their shared genes and not how they wereraised. In fact, according to statistics from thestudy, 80 percent of the traits shared by thetwins were the same—from their physical characteristics to their opinions.
Scientists DisagreeThe debate over twin studies is intense, however.Factors that influence behavior are complex anddifficult to isolate for the sake of studies.
In general, most scientists now agree thatthere is a genetic basis for intelligence and per-sonality. The debate now centers on whatimpact environment and personal choicesmight have on inherited genetic tendencies.
Applying Critical Thinking Skills1. Which do you think is more important in forming personality—environment or heredity?
Explain your answer.
2. Give an example of a personality trait you have in common with a family member. Is it a result ofyour environment or heredity? Explain.
3. Do all the traits that Jim Lewis and Jim Springer have in common seem to be linked to a geneticfactor? Do all the traits mentioned in the passage mean that scientists should study inheritedcharacteristics? Explain.
Name Date Class
Naturally occurringmultiple births Probability
twins
triplets
quadruplets
quintuplets
1 in 80 births
1 in 6,400 births
1 in 512,000 births
1 in 40,960,000 births
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Fighting Disease ThroughImmunization
Thanks to vaccines, serious diseases that wereonce common threats are now under control.Before a polio vaccine was developed, as manyas 20,000 cases were reported in the UnitedStates. As a result of vaccinations against thedisease, only 5,000 cases of polio were docu-mented worldwide in 1999.
Building Up ImmunityVaccines cause the body’s natural immune systemto work against the diseases. A solution madefrom weakened bacteria or viruses that cause dis-ease is injected into the body. The immune systemthan develops antibodies against the disease. Afterthe required number of booster shots, the vacci-nated person is protected from the illness.
The United States requires that all childrenreceive certain vaccines before they start school.Some exceptions are made for families who areopposed to vaccines.
Why Use VaccinesAs with all medications, risks and side effects areassociated with vaccines. Common side effectsinclude fever, soreness at the site of injection, andcrankiness. Severe side effects are rare and affectless than one percent of people who are vaccinated.The risks associated with disease are much greaterthan those associated with getting a vaccination.
For example, diphtheria is an infectious dis-ease of the upper respiratory system. Symptomsinclude fever, sore throat, and tiredness. Thedisease sometimes can cause heart failure andlead to death.
Polio, mumps, and measles are viral diseases.Polio produces a range of symptoms, the most common of which is paralysis of certainvoluntary muscles. Fever, congestion, and arash are symptoms of measles. Complicatedcases of measles can, however, lead to pneumo-nia and even death. Mumps causes swelling of the salivary glands and, in rare cases,can lead to a dangerous inflammation ofthe brain.
Haemophilus influenzae type b is a diseasethat can cause death, permanent brain damage,meningitis, pneumonia, sepsis, arthritis, andskin and throat infections.
Chicken pox (varicella) is a highly contagiousviral disease. In addition to blisterlike sores onthe skin, it can cause skin infections, brainswelling, and pneumonia.
Hepatitis A and B are viral diseases of theliver. Symptoms include yellow skin or eyes,fatigue, nausea, and sore joints (in the case ofhepatitis B). The diseases eventually causesevere liver damage or liver cancer.
20Activity
CriticalThinking
Applying Critical Thinking Skills1. Some children are not receiving recommended immunizations. List at least four reasons why
parents might not immunize their children.
2. Do you think risks posed by immunizations outweigh risks of the diseases themselves? Explain.
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21ActivityInvasive SpeciesProblem
Solving
In a healthy ecosystem, predators and parasitescontrol the populations of the organisms theyeat. When many species are abundant in a com-munity, it is considered stable. But, when a newspecies is accidentally or deliberately intro-duced into an ecosystem, it can disrupt theecosystem’s stability. These species, called inva-sive species, don’t have natural predators tokeep them in check.
Most invasive species are introduced byhumans when they import goods, experimentwith non-native species, or empty ballast tanksof ships filled with foreign waters. Invasivespecies pose one of the greatest environmentalthreats worldwide and cost the United Statesnearly $137 billion a year.
Animal InvadersThe introduction of the sea lamprey to theGreat Lakes is an example of what can happenwhen a new species is accidentally introduced.When the Welland Ship Canal was completedin 1833, it opened a path from the AtlanticOcean to Lake Erie through the St. LawrenceRiver. The sea lamprey slowly spread through-out Lake Erie and the other Great Lakes.
By 1960, the large lamprey population killedoff many other fish and caused a decline in thenumbers of whitefish, sturgeon, and trout.Eventually, scientists began using chemicals tobring the lamprey population under control—ata cost of $13 million a year.
Another example is the introduction of gypsymoths. In 1866, a scientist who was hoping tobreed a better silkworm brought gypsy moths toMassachusetts. Today, these moths destroy 4
million hectares of trees each year in southernCanada, the midwestern United States, andTexas. Scientists now are using parasitic waspsand insecticides to try to control the moths.
Plant InvadersPlants also can disrupt ecosystems. Purpleloosestrife spreads across 480,000 hectares ofland in a year. Originally imported as an herb, italso was carried here in sheep wool and in theballast of ships. Kudzu vines, which were broughtto the United States from Japan and China,were introduced to help prevent soil erosion.Today, the vines blanket many forests in thesoutheastern states.
Efforts to combat invasive species include theuse of pesticides, the introduction of natural preda-tors, and the restrictions of non-native species.
Applying Problem Solving Skills1. In some cases, foreign species have been introduced into ecosystems without disrupting them. Name
four things a scientist would want to know before introducing a new species into an ecosystem.
2. What explains the overpopulation of animals such as the lamprey and the gypsy moth?
3. How could the methods that are now being used to control sea lampreys further affect the stabil-ity of the Great Lakes ecosystem?
4. What would happen if a tourist visiting the Amazon in South America brought back a piranhaand released it into one of the Great Lakes? Would it pose a threat to that ecosystem? Explain.
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Sea lampreys attach themselves to fish feeding on their blood andtissues.
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Nitrogen Fertilizers—Too Much of a Good Thing?
It takes a lot of food to feed the 6 billion peopleon this planet. Thanks to the invention of nitro-gen fertilizers, however, more of the world’spopulation now has enough to eat. Nitrogenfertilizers help plants grow and increase theamount of crops that are harvested. The use ofall this nitrogen fertilizer, however, can causesome environmental and health problems.
Decades of RunoffIn the 1960s, researchers first noticed lakes andrivers that were suffering from the effects oflarge amounts of nitrogen. Too much nitrogenresults in excessive plant growth in water. Plantssuch as algae choke out other life-forms thatcannot get enough oxygen. Decades later,researchers say nitrogen fertilizers are having anegative effect on forests and coastal waters, aswell. Nitrogen washes off farmland and intorivers, lakes, and oceans. Much of the nation’sland no longer can absorb or break it down.
In the 1980s, scientists found that well waterin a northeastern Iowa community had beencontaminated. The water contained dangerouslevels of nitrates, a kind of by-product of nitro-gen fertilizer. Scientists traced the problem backto the increased use of nitrogen fertilizer by localcorn growers.
Corn needs a lot of fertilizer, so farmers werespreading manure on their land, applying nitro-gen fertilizer to the crops, and growing legumesevery other season. (Legumes, such as soybeans,leave nitrogen in the soil even after harvest.)This triple dose of nitrogen became part of theagricultural runoff that seeped into the ground-water and made the area’s well water unsafe.
In addition to making drinking water unsafe,nitrogen can kill water plants and algae. Withplants and algae gone, fish and other livingorganisms that rely on them for food also disappear.
Even though nitrogen is good for plants andhelps them grow, too much of it affects thetrees and soils of the world’s forests. Nitrates inacid rain take important minerals out of thesoil. Nitrates also can get into the leaves of thetrees. This makes the trees grow, but becausethe soil lacks necessary minerals, the trees areweak. They become targets for mildew, insects,and disease.
Possible SolutionsRecognizing the dangers of excess nitrogen isthe first step in fixing the problem. To help,farmers can rotate their crops. First, they canplant legumes to leave nitrogen in the soil.Then they can plant corn to take nitrogen out of the soil. If farmers plant soybeans oneyear and corn the next, the nitrogen left by thesoybeans lets them use less nitrogen fertilizerduring a corn crop year.
Another way for farmers to cut back on the use of nitrogen fertilizer is to monitor thesoil carefully. The need for fertilizer changeswith weather and crop conditions. If farmersare able to predict nitrogen levels in their crops,they can adjust the amount of fertilizer neededby that crop at different times during the growing season. Because wetlands naturallyabsorb nutrients like nitrogen, another way to reduce excess nitrogen is to restore thenation’s wetlands.
22Activity
ProblemSolving
Applying Problem Solving Skills1. Detail the journey of nitrogen, from application on a farm to runoff in the ocean. Where would it
go and how might it affect the environment?
2. Do the benefits outweigh the problems caused by nitrogen-based fertilizer? Justify your answer.
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23ActivityThe High Cost of Wetlands
DestructionProblemSolving
Muddy waste. That’s what wetlands look like tosome people. So, filling them in and pavingthem over seems like a good idea, right? Notnecessarily. Wetlands are important to the envi-ronment. They provide a natural habitat inwhich wildlife can thrive. They help preventflooding of farmland and housing communi-ties. They even act as a natural water filter formany environmental and chemical pollutants.
Unfortunately, within a 200-year period end-ing in the 1980s, 53 percent of the wetlands inthe United States were destroyed. Even now,28,000 hectares to 36,000 hectares of wetlandscontinue to be destroyed each year.
Loss and DestructionMajor wetland losses occurred during the landdevelopment boom from the mid-1950s to themid-1970s. A federal farm policy now discour-ages the draining of wetlands for use as crop-lands, but land development continues. TheArmy Corps of Engineers, which has theauthority to issue permits for the draining anddestruction of wetlands, grants 90 percent of allrequests it receives.
Large areas of aquatic plant life have beenkilled off in the Chesapeake, Florida, and Tampabays as well as in branches of the PotomacRiver. The loss of coastal marshes is particularlygreat in Florida, Texas, California, Louisiana,and in the Northeast.
Aquatic plant life is at the heart of the foodchain in these areas. Wetland plants, such asarrow arum, pickerelweed, and spatterdock,absorb nutrients and are a source of much-needed food and shelter for the animals, fish,and insects that live there.
In addition to destroying wildlife habitats,the loss of wetlands can increase flooding.Because wetlands store extra water like asponge, they are better at preventing floodsthan dams and reservoirs.
A wetlands ecosystem acts as an air and waterpurifier. Approximately 80 percent of wetlandswater comes from agricultural runoff. Thatwater can contain fertilizers, sediment, andother pollutants. Wetlands control these pollu-tants by acting as a kind of natural filter, trap-ping sediment and absorbing excess nutrients.
Restoring Nature’s FilterVoluntary programs might help restore theseecosystems and their benefits. For example, theWetlands Reserve Program pays money tolandowners who restore wetlands. As a way to con-trol flooding, the Conservation Reserve Programgives farmers money for not farming or developingparts of their land. Finally, individuals and envi-ronmental groups are helping by lobbying Con-gress and transplanting aquatic plants in wetlands.
Applying Problem Solving Skills1. Compare and contrast manufactured flood control systems such as dams and levees with nature’s
flood prevention system, the wetlands.
2. What are the benefits of transplanting wetland’s plant life?
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Wetlands help to purify air and water.
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Activity 1 ______________________ page 1New Status for an Old Life-Form
1. Recognizing Logical Thought: Studentsshould write at least two questions. Questionsmight include: How is the organism differentfrom other organisms in the same domain?Can the organism be traced back to any otherorganism in that domain?
2. Extrapolating Data/Information: Answerswill vary, but students should take intoaccount that archaeabacteria can withstandhigh and low temperatures, high salinity, andlow oxygen levels.
Activity 2 ______________________ page 2The Mechanics of Memory
1. Clarifying Issues: Answers will vary. Studentsshould explain in simple language that neuronsare made of a cell body, the dendritic field, andaxons connected by pathways called synapses.The cell body contains the nucleus. Inputoccurs in the dendritic field, and messagestravel along axons and through synapses toother neurons. With repeated actions, axonscome closer together and become morefocused. As people grow from childhood, theylose unnecessary synapses so that necessaryconnections become stronger. Throughoutpeople’s lives, they continue to form newsynapses as they learn.
2. Evaluating Information: Answers will vary.Students should relate to an incident in theirlives in which practice or study improved theirmastery of a situation.
Activity 3 ______________________ page 3Cloning the Woolly Mammoth
1. Drawing Conclusions: Although the woollymammoth and the elephant are closely related,one major obstacle to producing a mammothhybrid might be the elephant’s inability to acceptthe embryo and carry it to full-term birth.
2. Recognizing Cause and Effect: Fragments ofDNA cannot be used in the cloning of long-extinct animals because the fragments do notcontain cell nuclei, which are necessary to
direct the cell’s activities.3. Observing and Inferring: By studying the
remains of a 23,000-year-old woolly mam-moth, scientists might be able to understandthe Siberian environment in which the animallived. Scientists might be able to tell what thewoolly mammoth ate and drank and what itwas doing when it died.
Activity 4 ______________________ page 4New Hope After a Long Search
1. Recognizing Cause and Effect: The controlgroup would consist of children who had thedisease but were not treated with gene therapy.
2. Drawing Conclusions: It could prevent diseaserather than just treat it. It addresses the causeof the disease rather than the effects. A one-time procedure could result in a lifetime cure.
3. Making Judgments: Answers will vary, but stu-dents should recognize that there are risks aswell as benefits to consider. Their answersshould examine the overall merits of each.
Activity 5 ______________________ page 5Saving Tropical Rain Forests
1. Comparing and Contrasting; Developing aPerspective: Students should recognize that peo-ple who rely on the rain forest to earn a livingare more interested in the short-term goals ofearning money and feeding their families. Theirneeds are more immediate, which would make itmore difficult to identify with the long-rangeeffects of their actions. People who do not live inthe area probably would be able to focus moreeasily on the long-term implications becausetheir livelihoods are not directly affected.
2. Extrapolating Data/Information: approxi-mately 50 percent; approximately 140 years
3. Generating and Assessing Solutions: Answerswill vary. Some students will agree that theancient farming techniques are a possible solu-tion. Others might suggest that more research isneeded. Students might suggest that nationalagencies train farmers to use techniques that donot cause long-term harm. They also might rec-ommend that logging companies research the
Answer KeyCritical ThinkingProblem Solving
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long-term advantages to raising and logging plan-tations where trees are grown for commercial use.
Activity 6 ______________________ page 6Waste-Eating Bacteria
1. Drawing Conclusions: Answers will vary. Posi-tive effects: Bioremediation could help cleanup toxic chemical spills efficiently withoutcausing any environmental damage. Negativeeffects: Bioremediation might release disease-causing bacteria accidentally.
2. Making Predictions or Interpretations:Answers will vary but could include ways thatcompanies might maintain bioreactors orlandfill sites for toxic waste and use bacteria toclean the soil continually.
Activity 7 ________________ page 7Dying Frogs Give Ecological Clues
1. Making a Hypothesis: Because the fungus isappearing in remote and protected areas as wellas in the wild, it’s possible that the fungus isspreading because the frogs are changing theirhabitat or are being introduced into new envi-ronments by humans. Also, if the developmentof the fungus is related to other environmentalfactors, such as water pollution or the thinningof the ozone layer, the fungus could be spread-ing as a result of that factor or factors.
2. Generating and Assessing Solutions: Answerswill vary. Conservation methods could includekeeping frogs in their natural habitat ratherthan moving them from an infected area toone that might not be infected; cleaning thekeratin protein buildup off the frogs; raisingtadpoles and introducing them into the wildafter their metamorphosis into frogs; contin-ued herpetology research; and developing afungicide to kill the chytrid fungus.
Activity 8 ________________ page 8Using Photosynthesis to Reduce World Hunger
1. Recognizing Cause and Effect: Even if photo-synthesis is improved, plants that lack any ofthese essential elements still would not pro-duce a maximum yield.
2. Observing and Inferring: Answers will vary,but students might infer that the quality of
individual crops could be improved, that morecrops could be grown in a shorter period oftime, or that less fertilizer might be required.
3. Making Predictions or Interpretations: Ifphotosynthesis became too efficient, it couldmean that ecosystems could be thrown off bal-ance or that some people would have morefood than they could use.
Activity 9 ________________ page 9Rescuing Endangered Plants
1. Developing a Perspective: Answers will vary.Some students probably will say that it isworth it to save species for future generationsand for the role they play in the ecosystem.Others might say that it is more important tospend the money on other worthy causes.
2. Recognizing Logical Thought: Answers willvary. Many plants that have no known use nowmight have important uses in the future. Sav-ing plants that aren’t useful to humans is stillnecessary because other organisms mightdepend upon these plants for survival. On theother hand, with budget restrictions, someplants might be targeted for saving while oth-ers are allowed to become extinct. In this situa-tion, it would be best to determine whichplants are likely to be useful in the near future.
3. Recognizing Cause and Effect: If the weedscrossbreed with biotech crops that are resistantto pests, for example, the weeds will have fewernatural predators. Without as many naturalpredators to control their growth, the weedsbecome even more widespread and could pos-sibly choke out more fragile plants.
Activity 10______________________ page 10Coral Reefs at Risk
1. Making Inferences: Students might say thatthe algae gain protection and nutrition by liv-ing inside the coral polyps.
2. Developing a Perspective: Answers will vary.Some students might answer that the economyis more important than protecting the reefs.Others might say that if no efforts are made topreserve the undersea world, there might notbe any corals or other plant and animal life leftin the future to support the economy.
Answer Key (continued)
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3. Comparing and Contrasting: Students shouldrecognize that rain forests, like coral reefs, sup-port thousands of different life-forms. Theirdestruction can disrupt food chains and resultin the extinction of life-forms.
Activity 11______________________ page 11Afraid of Snakes?
1. Drawing Conclusions: protection from preda-tors; allows them to capture food
2. Extrapolating Data/Information: hikingboots, long pants, gloves
3. Making a Hypothesis: Answers will vary. Stu-dents might refer to their appearance, theirexploitation in the media, or the fear of beingbitten by any type of wild animal.
Activity 12______________________ page 12Global Warming and Migration Patterns
1. Recognizing Cause and Effect: Migrationroutes are based on the availability of food forrefueling. Coastal areas, mountain ranges, andriver valleys provide a seasonal bounty ofmuch-needed food.
2. Recognizing Logical Thought: Answers willvary, but students should realize the impact onfood chains that would result from the pres-ence or absence of the birds.
Activity 13______________________ page 13The Everglades—Protecting a Delicate Balance
1. Recognizing Cause and Effect: High levels ofprecipitation resulted in significant amounts offreshwater being introduced into the Ever-glades. When the construction of canals andlevees made the water saltier, plants and ani-mals died off or moved. When water becamemore plentiful and less salty, plants and ani-mals were able to thrive once again.
2. Observing and Inferring: In the case of thebirds and plants, the decrease of their popula-tions revealed that the ecosystem was affected.The inability of some species to adapt to condi-tions, such as extra salty water and shallowerwater, revealed that the characteristics andamounts of water were critical to their survival.
3. Making a Hypothesis: Hypotheses will vary.Students might deduce that the birds have
reestablished themselves in other areas and willnever return. Students should explain how theywould test their hypotheses. In this case, theymight propose studying the populations of thebirds in other states to see if they remain relativelyconstant. Accept any reasonable hypothesis and test.
Activity 14 ________________ page 14The Human Body in Space
1. Observing and Inferring: Students shouldrecognize that by studying the effects of long-term space travel, NASA will be able to deter-mine what is safe and what is not safe forfuture astronauts and come up with methodsto remedy some situations.
2. Making Judgments: Answers will vary. Somestudents might say that the space station was agood idea because it supports more spaceresearch and encourages international cooper-ation. Some students might say it was a badidea because of the expense or because themoney could have been spent on other spaceprojects that might seem more useful.
3. Making Predictions or Interpretations:Answers will vary, but students should be creative in their predictions. Answers mightinclude reference to travel to other galaxies,orbiting space cities or colonies, or space travelthat is available to everyone.
Activity 15______________________ page 15Are sports drinks beneficial?
1. Drawing Conclusions: A person will be morelikely to drink adequate amounts of fluid andbecome hydrated if he or she likes the taste ofthe drink.
2. Extrapolating Data/Information: Activitieslasting less than 30 min might only requirewater to replace fluids, while sports drinksmight be more beneficial if the activityrequires greater endurance.
Activity 16 ________________ page 16More Is Not Always Better
1. Recognizing Cause and Effect: Becausehemochromatosis masquerades as so many dif-ferent diseases, it is possible that doctors oftendo not recognize it.
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2. Recognizing Contradictions: Althoughhemochromatosis is a relatively commongenetic condition, only about one in 200 peo-ple have it. Thus, the odds are that you do nothave it and it is better to eat foods rich in iron.
3. Drawing Conclusions: Although adding ironto foods can harm some people, it probablydoes much more good than harm. If peoplesuffering from hemochromatosis are identifiedand told how to take care of their condition,they can avoid the foods with added iron.
Activity 17 ________________ page 17The High Risks of Smoking
1. Developing a Perspective; Summarizing/Syn-thesizing: Students might list all the health haz-ards connected with smoking. They might telltheir friend they are concerned for his or herhealth as well as their own, because exposure tosmoke places them at risk, as well.
2. Drawing Conclusions: Patients who are non-smokers probably would experience greatersuccess from the skin graft. Their blood wouldhave a better chance of reaching the newlygrafted skin.
3. Drawing Conclusions: Answers will vary butmight include addiction, social pressure, or habit.
Activity 18 ________________ page 18New Hope for Treating Spinal Cord Injuries
1. Making Predictions or Interpretations:Answers will vary but could include replacementof damaged heart tissue in heart attack victims;improved insulin production in diabetics; cre-ation of human tissue banks; regeneration ofskin for burn victims; and reatments for arthri-tis, multiple sclerosis, muscular dystrophy, blind-ness, and more.
2. Drawing Conclusions: Yes. Because scientistshave learned recently that the central nervoussystem is capable of repairing itself, it won’tmatter to the body if the injury is old or new.The treatment for old and new injuries usingES cell transplantation will be the same.
Activity 19 ________________ page 19More than Skin Deep
1. Drawing Conclusions: Answers will vary but might include that personality is formed by a combination of environmental factors and heredity.
2. Making Inferences: Answers will vary. Traitsstudents have in common with family mem-bers who do not live with them might be attributed to heredity. Adopted students might attribute their personality traits to their environment.
3. Evaluating Information: Students should notethat some traits mentioned in the article, suchas having wives with the same name, are merecoincidences and are not indicators of inher-ited traits.
Activity 20 ________________ page 20Fighting Disease Through Immunization
1. Drawing Conclusions: Prohibitive cost, religiousbeliefs, possible adverse reactions to the vaccines,ignorance of the immunization schedule itself andthe successive boosters needed for some of the dis-eases, and the misconceptions that the diseaseshave been eradicated or are difficult to contractare some reasons parents choose not to immunize.
2. Evaluating Information: In most healthy chil-dren, the risks posed by the diseases themselvesare much more dangerous than the side effectsthat might occur from the vaccines.
Activity 21 ________________ page 21Invasive Species
1. Recognizing Cause and Effect: Answers willvary but might include any four of the follow-ing: existence of predators; characteristics ofexisting plants and animals in that ecosystem;characteristics of new species—diet, mating pat-terns, resistance to disease, adaptability to cli-mate; or a method to remove the species ifnecessary.
2. Drawing Conclusions: The species that wereintroduced had no natural predators in thecommunities into which they were introduced.
3. Making Predictions or Interpretations: Stu-dents should recognize that the chemicals beingused to control the lampreys could affect the
Answer Key (continued)
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plants and animals that are native to the area.4. Recognizing Cause and Effect: Students
should deduce that the piranha might pose ashort-term threat but that the colder climatewould limit its ability to survive.
Activity 22 ________________ page 22Nitrogen Fertilizers—Too Much of a Good Thing?
1. Extrapolating Data/Information: Answerswill vary but might include the following:Some of the nitrogen applied to farm soilwould likely be absorbed by the crops in thefield. Some would stay in the soil, and the restwould become part of the agricultural runoffand flow into nearby water. In water, the nitro-gen would provide nutrition for aquatic plants,but it could cause algae to bloom excessively,depleting some of the water’s oxygen andkilling some organisms.
2. Developing a Perspective: The benefits of anitrogen-based fertilizer are that it can increasecrop yields and can help produce enough foodfor Earth’s population. Problems associatedwith it can include environmental contamina-tion, water pollution, and the destruction ofplants and wildlife. Students should discusswhether benefits outweigh the problems andjustify their conclusions.
Activity 23 ______________________ page 23The High Cost of Wetlands Destruction
1. Comparing and Contrasting: Manufacturedflood control is less efficient and more costlythan nature’s flood prevention system.
2. Recognizing Logical Thought: Transplantingwetlands plants will help restore the ecosystem.Adding plants where there are none (or replac-ing plants that don’t belong with ones that do)will likely restore the food chain and bring ani-mals, fish, and insects back to the wetland area.Also, the quality of water will improve becausethe newly transplanted plants can trap sedimentand absorb pollutants and excess nutrients.
