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LESSON PLANSPAGES 1–4

BACK FROM THE DEAD

OBjECTivEUnderstand how scientists are using biotechnology to try to bring extinct animals back to life.

LEssOn1. Project the PDF of the article, “Back From the Dead,” on a whiteboard and/or print the article for students (see next four pages). Ask students: What does the word extinct mean? (No individuals of a species remain alive.)

2. Ask students how scientists might bring an extinct species back to life. Then enlarge the diagram “How to Make a Mammoth” on page 2. Have a volunteer read the steps.

3. Read the text beneath the article’s headline. “Should scien-tists bring extinct species back to life?” Poll the class and record the results. Ask students for reasons supporting their opinions; record them on the note.

4. Have the class read the article silently. Afterward, repeat the poll about whether scientists should revive extinct species. Are the results different now? Ask the students to explain why they changed their minds or kept the same opinion.

5. Have students write an essay that states and supports their opinion after reading the article.

NATIONAL SCIENCE EDUCATION STANDArDS:Grades 5-8: Reproduction and heredityGrades 9-12: Molecular basis of heredityNEXT GENErATION SCIENCE STANDArDS:LS3A: Inheritance of traits COmmON COrE STATE STANDArD:rEADING INFOrmATIONAL TEXT: 1. Write arguments to support claims using sufficient evidence.

STANDARDS

• VIDEO EXTRA: Watch a video about bringing species back from extinction at: www.scholastic.com/scienceworld.

• Check out the teacher resources at this interactive website about cloning and other aspects of genetics: http://learn.genetics.utah.edu/content/tech/cloning/.

RESOuRCES

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DisCussiOnAsk students: How do you think scientists decide which species to try to revive? (For instance, DNA may be available only from certain species.) Would you be more in favor of bringing some species back than others? What would influence your decision?

ASSESSmENT pACkAGEAssessments are tailored to different science disciplines and the Common Core State Standards. All four files can be found at the end of this document.

BIOLOGY/COMMON CORE: PERSUASIVE WRITINGWHAT DO yOu THINk?Use this work sheet to help students write a well-supported opinion essay about whether or not scientists should resurrect extinct species.

CHEMISTRY: READING COMPREHENSIONFIGHTING FuNGuS Students read a passage and answer questions about how a chemical imbalance caused the extinction of the gastric-brooding frog and many other amphibians.

EARTH SCIENCE: READING COMPREHENSIONA MAMMOTH EXTINCTION Have students read a passage and answer questions about how a warming climate may have contributed to the disappearance of woolly mammoths.

PHYSICS: READING COMPREHENSIONZAPPING CELLS An electric current helps cloned eggs to grow. Use this reading passage to help students learn about electricity in the human body.

LESSON PLANS

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Biology: Genetics // Chemistry: Biochemistry // earth sCienCe: Environment // PhysiCs: Technology

1 Science World • www.scholastic.com/scienceworld

Back from the dead

should scientists bring extinct species back to life?

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How to Make a wooLLY MaMMotHscientists may be able to use a frozen cell from a mammoth that’s been dead for thousands of years to bring the

species back from extinction. an elephant—the mammoth’s closest living relative—would carry the baby clone.

1 isolate the nucleus of a

viable mammoth cell from a frozen carcass.

2 Remove the nucleus from the

egg of an elephant and replace it with the mammoth nucleus.

3 Chemically or electri-

cally stimulate the cell to make it begin dividing.

4 Place the egg in the uterus

of an elephant. it will take almost two years to develop.

5 if the pregnancy

is successful, the elephant gives birth to a baby mammoth.

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Until the 1980s, Australia was home to a very odd amphibian: the gastric-brooding frog. The strange thing about this frog was that the female laid her eggs in water, and

once the male fertilized them, she swallowed the eggs whole. Her tadpoles grew inside her stomach. When the baby frogs were fully developed, the mother burped them out of her mouth!

This strange species fascinated scientists. But soon after researchers discovered gastric-brooding frogs in the early 1980s, a fungal infection wiped all of them out. The species became extinct.

Now, three decades later, the gastric-brooding frog may come back to life. Scientists are trying to use biotechnology—the artificial manipulation of living things—to resurrect the baby-burping frog, as well as species that have been extinct much longer.

“Just imagine looking at a saber-toothed cat, or a woolly mammoth, or a giant ground sloth—things our ancestors saw,” says Hank Greely, a bioethicist at Stanford University in California. “That’s plausible now.”

reviving a speciesWhy bring back extinct species? One

reason is to increase biodiversity, which has declined in many areas as species die off. When an ecosystem has a wide variety of animals and plants, there’s a better chance that at least some of them will survive

natural disasters, disease outbreaks, or climate change.

“All of these ‘de-extinction’ projects are focused on trying to increase the complexity and diversity of the natural world,” says Mike Archer, a paleontologist at the University of New South Wales in Australia. Archer is leading the team that’s trying to bring back the gastric-brooding frog.

When Archer set out to revive the frog 5 years ago, the first thing he needed was an intact nucleus from one of its cells. Nuclei contain an organism’s DNA. This chemical carries the hereditary information that determines an animal’s traits.

Scientists have been using nuclei from living animals to create clones, or genetically identical copies, of those animals for many years (see Cloning Timeline, p. 3). But when an animal dies, its cells decompose and the DNA inside its nuclei begins to break down.

watCh a video online

www.scholastic.com /scienceworld

4 Bonus skills sheets

www.scholastic.com /scienceworld

Dna transFer: Under a microscope, a researcher injects an egg with genetic material to create a clone.

mammoth nUcleUs

eGG

a pipette holding the egg in place

a pipette injecting genetic material

elephant eGG

SUBSCRIBERS ONLY

This makes cloning an extinct species much harder than cloning a living one.

Luckily, back in the 1970s, another scientist had frozen some gastric-brooding frog tissue and saved it. Archer examined cells from the frozen sample and was excited to find that their nuclei appeared intact.

The next step was to find an egg. In traditional cloning, scientists take an egg cell from a female of the same species and remove its nucleus. Then they replace it with the nucleus of a regular cell from the body of the individual they want to clone. When the egg starts to divide, the new cells contain copies of the donor animal’s DNA.

But no one had saved any gastric-brooding frog eggs. That meant Archer had to try

something else: inserting the cell nucleus of the extinct frog into the egg of another species. He started collecting eggs laid by great barred frogs, a common species in Australia.

Over the next few years, Archer’s team injected thou-sands of great barred frog eggs with gastric-brooding frog nuclei. None of them grew. But the researchers kept trying and adjusting their technique.

Finally, about two years ago, one of the eggs started dividing. When Archer tested the growing ball of cells, or embryo, he found gastric-brooding frog DNA inside.

“That told us that the extinct animal’s DNA was driving the devel-opment of a new frog,” he says.

de-extinction plansSo far, none of the eggs have grown past

the embryo stage into baby frogs. Archer and his colleagues aren’t sure why. But if they can solve that problem, says Archer, “I’m hopeful that within a few years we should have this frog back.”

Archer’s attempt is the farthest along, but other teams of scientists want to use similar techniques to bring back other extinct species, like the woolly mammoth. These hairy relatives of elephants roamed the frozen tundra of Siberia until they died out about 5,000 years ago. Scientists have found many

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cLoning tiMeLinescientists first cloned animals more than 60 years ago. since then, breakthroughs in cloning technology have brought them closer to being able to revive extinct species.

3 Science World • www.scholastic.com/scienceworld

mammoth mUmmY: this baby mammoth’s body, discovered under permafrost in siberia in 2007, still had some Dna inside.

scientists create the first cloned animal—a tadpole—by extracting a cell nucleus from a developing embryo and inserting it into an egg that has had its nucleus removed.

1952Dolly the sheep, the first mammal cloned using the body cell of an adult animal, is born in scotland. dolly becomes famous and brings lots of attention to cloning.

1996

buried mammoth fossils and, in a few cases, the frigid conditions have helped preserve some DNA. A group of South Korean and Russian researchers hopes to use this material to bring mammoths back to life one day (see How to Make a Woolly Mammoth, p. 2).

Ben Novak, a biolo-gist at the University of California, Santa Cruz, wants to use genetic techniques to bring back the extinct passenger pigeon. These sleek, gray-blue birds used to flock over the Northeastern U.S. in groups of a billion or more. But by the late 1800s, they had been hunted to extinction by trappers who sold them for people to eat. Bringing them back would help restore biodiversity to the forest ecosystems in which they lived, says Novak.

ethical concernsTechnology may have made it possible

to bring back extinct species. But does that mean it’s a good idea?

Hank Greely, the Stanford bioethicist, studies the ethical implications of technolo-gies like cloning. He thinks de-extinction has many potential benefits, including helping ecosystems recover. But Greely says

scientists working on these projects should be very careful. Many of the environments that extinct species once inhabited have changed since they lived there, he says. If a long-gone species is reintroduced, it could become an invasive species that upsets the current ecosystem.

Some conservation-ists also worry that if scientists can bring extinct animals back, no one will care about keeping endangered species from becoming extinct in the first place.

“If this were to undercut efforts to conserve currently existing species, that

would be a tragedy,” says Greely.Archer doesn’t think that will happen. In

fact, he says, the cloning techniques scientists develop to bring back extinct species could be used to breed endangered animals too.

Many of the species scientists want to bring back became extinct because people hunted them or ruined their habitats, argues Archer. Humans even helped spread the fungus that killed off gastric-brooding frogs.

“They shouldn’t be gone, and we did it,” says Archer. “I think we have a moral responsibility to try to fix what we broke.”

—Mara Grunbaum

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Cells from a dead banteng, a type of wild asian cattle, produce a healthy cloned calf—raising hope that cloning can help save endangered species.

scientists report that they used frozen cells to clone the bucardo, an extinct spanish goat. But the clone, born with lung defects, lived only seven minutes.

Researchers clone the first domestic cat. The kitten is named cc, for “Copy Cat.” some companies begin offering to clone pets—but it’s very expensive.

cominG Back? the gastric-brooding frog, now extinct, birthed babies through its mouth.

Core Questionshould scientists try to bring back extinct species? Cite evidence from the article to support your opinion.

2001 2003 2009

Gone For noW: passenger pigeons were hunted to extinction in the 1800s.

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BIOLOGY/common core: persuasive writing

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whaT dO YOu ThInk?In “Back From the Dead,” you learned that scientists are trying to bring extinct species back to life. Not all scientists believe it is a good idea to resurrect organisms that have died out. Use this work sheet to write an opinion essay explaining your view about whether scientists should bring extinct species back to life. Use facts from the article to support your opinion.

Step 1. State your opinion. (Clearly state your opinion about whether scientists should try to bring species back from extinction.)

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Step 2. Gather supporting evidence. (Provide at least two arguments that support your opinion. Consider the benefits or dangers of reviving extinct species.)

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Step 3. Summarize the topic. (Write a brief summary for people who aren’t familiar with the science of bringing back extinct species.)

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Step 4. Write your essay on a separate piece of paper:

• Introduce the reader to the topic with your summary.

• Write a paragraph that states your opinion and includes your supporting arguments. Be sure to include relevant details.

• Conclude by briefly restating your opinion.

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chemistry: REadInG COMPREhEnSIOn

FIGhTInG FunGuSIn “Back From the Dead,” you read about scientists who are trying to bring extinct species back to life. One species they are trying to revive is the gastric-brooding frog. This frog was driven to extinction in part by a fungal infection that causes a deadly chemical imbalance. Read the following passage to learn about this chemical killer and how scientists hope to stop it from wiping out other species of amphibians. Then answer the questions that follow.

FATAL FUNGUSA microorganism is killing off many of the world’s amphibians. The chytrid fungus

(Batrachochytrium dendrobatidis) has infected at least 200 species. Many of those species have already become extinct. Can scientists stop this killer?

The chytrid fungus kills by causing a chemical imbalance. Healthy amphibians absorb water and chemicals called electrolytes through their skin. Electrolytes are charged particles that carry electrical signals to the body’s cells. These electric pulses are critical to the functioning of nerves, muscles, and the heart.

The chytrid fungus prevents amphibians from properly taking in electrolytes through their skin. Scientists have found that infected frogs have low levels of potassium and sodium ions. Without these electrolytes to help carry electrical signals to the heart, the frogs die.

There is some promising news: A bacterium called Janthinobacterium lividum appears to protect amphibians against the deadly fungus. The bacterium produces a chemical that prevents the growth of the chytrid fungus. J. lividum already exists on the skin of many amphibians. Scientists are considering ways to introduce the protective microbe to other amphibian populations.

QuESTIOnS1. Roughly how many amphibian species have been infected with the chytrid fungus?A 2B 200 C 2,000D all of them

2. Which of the following is NOT true?A Amphibians absorb water through their skin.B The chytrid fungus is critical to the functioning of

nerves and muscles.C Electrolytes carry electrical signals in the body.D A lack of electrolytes can be deadly to frogs.

3. Use context clues to choose the best definition for absorb.A releaseB reduceC feelD take in

4. How does Janthinobacterium lividum protect amphibians?A It produces electrolytes for amphibians to use.B It kills all other bacteria in the area.C It prevents the growth of the chytrid fungus.D It removes electrolytes from amphibians’ skin.

5. Which of the following sentences is best supported by information in the passage?A There is no hope for saving the world’s amphibians.B Janthinobacterium lividum will protect all amphibians

from the chytrid fungus.C The chytrid fungus is a big problem for amphibians, but

scientists may find a way to fight it.D Scientists are not concerned about the effects of the

chytrid fungus on amphibians.

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earth: REadInG COMPREhEnSIOn

Name:

a MaMMOTh EXTInCTIOnIn “Back From the Dead,” you read about scientists who are trying to bring extinct species back to life. Many factors can cause a species to disappear. Read the following passage to learn about evidence for what may have killed off woolly mammoths. Then answer the questions that follow.

MAMMOTH MYSTERYWhat caused woolly mammoths to vanish from the planet? Many scientists blame the

extinction of the species on overhunting by humans. But new findings indicate that another factor also played a role in their demise.

Mammoths once roamed most of northern North America and Siberia. Fossil evidence suggests that these hairy, elephantlike animals completely disappeared roughly 10,000 years ago. That’s around the same time that humans first moved into North America and began hunting them.

But researchers now believe hunting wasn’t the only thing killing off mammoths. By looking at the ages of fossilized mammoth bones, scientists can tell that mammoth populations were in decline before people arrived. The likely culprit: a warming climate.

The extinction of woolly mammoths coincided with the end of a glacial period, a time when Earth’s climate was cool and large sheets of ice covered much of Earth’s surface. As the climate warmed, new types of plants replaced the cold-weather grasses that the giant herbivores ate. Many mammoths may have starved because their digestive systems weren’t adapted to break down the new plants.

QuESTIOnS1. When did woolly mammoths disappear?A about 10,000 years agoB at the end of a glacial periodC at roughly the same time humans moved into North

AmericaD all of the above

2. Which of the following is an opinion?A Mammoths disappeared roughly 10,000 years ago.B A glacial period is a time when large ice sheets cover

much of Earth’s surface.C Mammoths ate cold-weather grasses.D Humans should not have hunted mammoths.

3. Use context clues to choose the best definition for coincided with.A causedB had nothing to do withC happened at the same time asD prevented

4. Which of the following is NOT thought to have contributed to the extinction of woolly mammoths? A Earth’s climate changed.B Earth’s temperature cooled.C The plants in North America changed.D Humans hunted mammoths.

5. Which of the following best describes the author’s main purpose in writing this article?A to provide readers with interesting information about

mammothsB to explain how humans can drive animals to extinctionC to describe how Earth’s climate changed 10,000 years

agoD to explain what scientists think drove woolly mammoths

to extinction

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physics: REadInG COMPREhEnSIOn

ZaPPInG CELLSIn “Back From the Dead,” you read that one way scientists coax cells into dividing is by using electric current. Read the passage below to learn about electricity in the body and how electrical therapy could play an important role in medicine. Then answer the questions that follow.

IT’S ELECTRICElectricity powers many devices, but did you know that the human body is an electric machine too?

Electricity plays an important role in our muscular and nervous systems.

Scientists first began learning about electricity in the body in the late 1700s. That’s when an Italian researcher named Luigi Galvani found that he could make the legs of a dead frog twitch by bringing them into contact with an electric current.

Today, biologists know that an animal’s nerves form a network that transmits electrical signals throughout the body. A nerve cell does this by allowing positively charged ions to enter the cell. The charge from the ions flows along the nerve cell until it reaches the end, and then the signal moves to the next nerve cell. When the signal reaches a muscle cell, positively charged ions enter it. The ions cause proteins inside the cell to change shape. That makes the muscle cell contract, and a body part moves—just like Galvani’s frog legs.

Some researchers have recently found that electricity may help certain cells regenerate after an injury. Rat nerve cells that have been cut regrow more quickly when they are exposed to a mild electric current. After more testing, electrical therapy could someday help people recover from nerve injuries.

QuESTIOnS1. Which role does electricity play in biological systems?A transmitting nerve signalsB causing muscle contractionsC speeding nerve repair after injuryD all of the above

2. Which of the following statements is NOT supported by the passage?A The human body uses electricity.B Nerve cells transmit electrical signals.C If you touch a dead frog, you’ll feel an electric shock.D A mild electric current can aid healing.

3. Use context clues to choose the best definition for regenerate:A contractB regrowC sparkD bend

4. According to the passage, which statement best describes what happens when a nerve cell transmits an electrical signal?A Positively charged ions enter the cell.B The nerve cell contracts.C You feel a tingling sensation.D all of the above

5. Which statement best describes the purpose of the last paragraph?A to persuade doctors to use electrical therapy on their

patientsB to explain how the study of electricity in the body could

help peopleC to reassure people that nerve injuries can be repairedD to entertain readers with an amusing story