题目内容
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Successful stem cell research will hopefully lead to _____.
A．the cloning of any human beings.
B．the cure of many otherwise incurable diseases.
C．the abandonment of antibiotics and vaccines.
D．the realization of human's dream of immortality.
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While it's true that just about every cell in the body has the instructions to make a complete human, most of those instructions are inactivated, and with good reason: the last thing you want for your brain cells is to start churning out stomach acid or your nose to mm into a kidney. The only time cells truly have the potential to turn into any and all body parts is very early in a pregnancy, when so called stem cells haven't begun to specialize.
Yet this untapped potential could be a terrific boon to medicine. Most diseases involve the death of healthy cells—brain cells in Alzheimer's, cardiac cells in heart disease, pancreatic cells in diabetes, to name a few; if doctors could isolate stem cells, then direct their growth, they might be able to furnish patients with healthy replacement tissue.
It was incredibly difficult, but last fall scientists at the University of Wisconsin managed to isolate stem cells and get them to grow into neural, gut, muscle and bone cells. The process still can't be controlled, and may have unforeseen limitations; but if efforts to understand and master stem cell development prove successful, doctors will have a therapeutic tool of incredible power.
The same applies to cloning, which is really just the other side of the coin; true cloning, as first shown with the sheep Dolly two years ago, involves taking a developed cell and reactivating the genome within, resetting its developmental instructions to a pristine state. Once that happens, the rejuvenated cell can develop into a full fledged animal, genetically identical to its parent.
For agriculture, in which purely physical characteristics like milk production in a cow or low fat in a hog have real market value, biological carbon copies could become routine within a few years. This past year scientists have done for mice and cows what Ian Wilmut did for Dolly, and other creatures are bound to join the cloned menagerie in the coming year.
Human cloning, on the other hand, may be technically feasible but legally and emotionally more difficult. Still, one day it will happen. The ability to reset body cells to a pristine, undeveloped state could give doctors exactly the same advantages they would get from stem cells: the potential to make healthy body tissues of all sorts, and thus to cure disease. That could prove to be a true "miracle cure".
The writer holds that the potential to make healthy body tissues will ______.
A．aggravate moral issues of human cloning
B．bring great benefits to human beings
C．help scientists decode body instructions
D．involve employing surgical instruments
All of the following are steps involved in true cloning EXCEPT ______.
A．selecting a stem cell
B．taking a developed cell
C．reactivating the genome within the developed cell
D．resetting the developmental instructions in the cell to its original state
Scientists can go on the stem cell research because ______.
A．scientists spurn the government and Mr. Bush's veto.
B．other countriesare enthusiastically experimenting on embryonic stem cells.
C．Mr. Bush's veto does not stop stem cell research completely.
D．all the scientists in America are furious with Mr. Bush.
A.a single type of multipotent stem cell found in the bone marrow
B.differentiated cells that first developed in the fetal liver, but now reside in the bone marrow
C.division of differentiated cell types while circulating in the blood
D.stem cells that became committed to each specific blood celll type during embryonic development
Which of the following statements is NOT true according to the passage？
A．Nearly every cell in the human brain has the instructions to make a complete human.
B．It is impossible for a cell in your nose to turn into a kidney.
C．It is possible to turn out healthy replacement tissues with isolated stem cells.
D．There will certainly appear some new kind of cloned animal in the near future.
The new work, performed in South Korea, represents "a major advance in stem cell research. It could help spur a medical revolution as important as antibiotics and vaccines", says Robert Lanza of Advanced Cell Technology (ACT), a company in Worcester, Mass., that's also investigating the promising stem cell strategy called therapeutic cloning.
"However, now that the methodology is publicly available", Lanza adds, "I think it is absolutely imperative that we pass laws worldwide to prevent the technology from being abused for reproductive-cloning purposes".
While some fertility doctors and a religious cult have claimed success at creating a pregnancy via cloning, they've offered no convincing proof. In contrast, the South Korean research is being reported at the meeting of the American Association for the Advancement of Science in Seattle and will appear in an upcoming Science. "This is reality", says stem cell researcher John Gearhart of Johns Hopkins University. "Here is a bona fide, refereed journal saying that a human embryo has been cloned and a cell line derived from it".
Although ACT has not yet published a report of a cloned human blastocyst, Lanza says that the South Korean success is "consistent with our own results". Therapeutic cloning appeals to Lanza and physicians because cells made this way could have the same DNA as a patient's cells do and thus avoid rejection after they're transplanted.
Seeking a compromise that would permit this strategy to be pursued, many scientists have called for legislation that would ban cloning to produce a baby but allow the creation of cloned embryos to generate stem cells for research or therapies. "The debate has been very polarized", notes bio-ethicist Laurie Zoloth of Northwestern University in Evanston.
According to the text, stem cells are hard to obtain because _____.
A．human embryos are very short-lived outside a human body.
B．human embryos are extremely hard to be cloned.
C．human genetic identity is difficult to be defined.
D．human cloning is strongly opposed by some researchers.
The power of ADAS cells to transform. into bone, cartilage and even neurons has been studied for years in test tubes. But Jeffrey Gimble, who studies human ADAS cells at Louisiana State University in Baton Rouge says Longaker's report is an important step forward. "Actually repairing a defect in an animal model had never been done. This is an excellent study." If the same technique works in humans, these cells could be coaxed to mend broken bones and correct other defects in tens of thousands of surgical procedures each year in which bone grafts and prosthetics are now necessary.
Longaker's group tested the ability of ADAS cells to heal four-millimetre-long fractures surgically-induced in the skulls of mice. In 12 weeks, the cells filled 70 to 90 per cent of the defects, while untreated animals had only unorganized bone formation in less than 10 per cent of the fractures. No extreme genetic manipulation or treatment of the cells was necessary. ADAS cells began manufacturing bone when they were simply laid onto a biodegradable polymer that contained apatite, a compound that naturally occurs in bone. Furthermore, the ADAS cells performed as well as bone marrow stromal cells, which would seem to be more natural architects of bone. It remains to be seen whether human ADAS cells will build bone as effectively. But researchers are excited about the prospects. Human bone marrow stromal cells are already being used in clinical trials as sources of skeleton-building material, but the ADAS cells may have some significant advantages.
Longaker reports that ADAS cells grow seven times faster than the bone marrow cells in the laboratory. And it is relatively easy to harvest more than a litre of fat tissue, even from patients who are not obese. Bone marrow is much less plentiful and must be removed in a painful surgical procedure. Of course, liposuction itself is not a pleasant operation. But according to the American Society of Plastic Surgeons, more than 300,000 people volunteered to have the procedure in 2003 simply for cosmetic reasons. "If the procedure was the first step to healing broken bones or replacing other tissue its popularity could only grow," says Gimble. "Just think of that."
Gimble speaks highly of Longaker in that ______.
A．his work made an unprecedented achievement in the field
B．he proved that ADAS cells contributed a lot to cell therapy
C．his work paved way for ADAS cell application in clinical trials
D．he cured an animal defect that had never been repaired before
It can be inferred from the last paragraph that ______.
A．the House and Senate are furious with Mr. Bush on behalf of the scientists.
B．research based on adult stem cells must be more promising than embryonic ones.
C．many countries, except America, are keen on experimenting embryonic stem cells.
D．the UK is enthusiastic about experimenting on adult stem cells.
A．innovations.
B．the natural sciences.
C．technical applications.
D．apparently useless information.
