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更多“All cells produce proteins and nucleic acids which are”相关的问题
A、your white blood cells secret auto antibodies that destroy your own beta cells.
B、your white blood cells mistake your pancreatic beta cells for foreign invaders.
C、your pancreatic beta cells lose their ability to produce insulin
D、All of the above
A、Although all cell types can divide, only stem cells differentiate after division.
B、Stem cells are able to divide to produce populations of cells that differentiate into a related set of cells.
C、Stem cells divide asymmetrically to give rise to one daughter cell that remains a stem cell, and a second daughter cell that differentiates into one or more cell types.
D、Stem cells have a special type of cell division in which they form small stems that then pinch off to give rise to the daughter cell.
Which of the following statements is NOT true of the passage？
A．It discusses fertility clinics.
B．It defines stem cells.
C．It mentions artificial fertilization.
D．It identifies the origins of stem cells.
A．Although all cell types can divide,only stem cells differentiate after division．
B．Stem cells are able to divide to produce populations of cells that differentiate into a related set of cells．
C．Stem cells divide asymmetrically to give rise to one daughter cell that remains a stem cell, and a second daughter cell that differentiates into one or more cell types．
D．Stem cells have a special type of cell division in which they form small stems that then pinch off to give rise to the daughter cell．
A hematopoietic stem cell is defined as
A．a cell with extensive self-renewal and proliferative potential
B．a cell only to produce daughter cells with identical characteristics
C．a cell with the capacity to differentiate into the progenitors of all the blood cell lineages
D．a cell With the capacity to produce some hematopoietic growth factors such as SCF，GM-CSFs，et．a1．
E．a cell with the capacity to express some specific surface antigens such as CD34
请根据短文的内容，回答题。
Sugar Power for Cell Phones
Using enzymes commonly found in living cells, a new type of fuel cell produces small amounts of electricity from sugar. If the technology is able to succeed in mass production, you may some day share your sweet drinks with your cell phone.＜br＞
In fuel cells, chemical reactions generate electrical currents. The process usually relies on precious metals, such as platinum. In living cells, enzymes perform. a similar job, breaking down sugars to obtain electrons and produce energy.＜br＞
When researchers previously used enzymes in fuel cells, they had trouble keeping them active,says Shelley D. Minteer of St LouisUniversity. Whereas biological cells continually produce fresh enzymes, there&39;s no mechanism in fuel cells to replace enzymes as they quickly degrade.＜br＞
Minteer and Tamara Klotzbach, also of St LouisUniversity, have now developed polymers that wrap around an enzyme and preserve it in a microscopic pocket. "We tailor these pockets to provide the ideal microenvironment for the enzyme," Minteer says. The polymers keep the enzyme active for months instead of days.＜br＞
In the new fuel cell, tiny polymer bags of enzyme are embedded in a membrane that coats one of the electrodes. When glucose from a sugary liquid gets into a pocket, the enzyme oxidizes it, releasing electrons and protons. The electrons cross the membrane and enter a wire through which they travel to the other electrode, where they react with oxygen in the atmosphere to produce water. The flow of electrons through the wire constitutes an electrical current that can generate power.＜br＞
So far, the new fuel cells don&39;t produce much power, but the fact that they work at all is exciting, says Paul Kenis, a chemical engineer at the University of Illinois at Urhana-Champaign.＜br＞
"Just getting it to work," Kenis says, "is a major accomplishment."＜br＞
Sugar-eating fuel cells could be an efficient way to make electricity. Sugar is easy to find. And the new fuel cells that run on it are biodegradable, so the technology wouldn&39;t hurt the environment.＜br＞
The scientists are now trying to use different enzymes that will get more power from sugar. They predict that popular products may be using the new technology in as little as 3 years.＜
According to the first paragraph， when can we share our sweet drinks with our cell phones？ 查看材料
A.When enzymes can be commonly found in living cells
B.When the technology of producing a new type of fuel cell appears
C.When the technology of a new type of fuel cell is suitable for mass production
D.When the technology of mass producing cell phones appears
Sugar Power for Cell Phones
Using enzymes commonly found in living cells, a new type of fuel cell produces small amounts of electricity from sugar. If the technology is able to succeed in mass production, you may some day share your sweet drinks with your cell phone.
In fuel cells, chemical reactions generate electrical currents. The process usually relies on precious metals, such as platinum. In living cells, enzymes perform. a similar job, breaking down sugars to obtain electrons and produce energy.
When researchers previously used enzymes in fuel cells, they had trouble keeping them active, says Shelley D. Minteer of St Louis University. Whereas biological cells continually produce fresh enzymes, there's no mechanism in fuel ceils to replace enzymes as they quickly degrade.
Minteer and Tamara Klotzbach, also of St Louis University, have now developed polymers that wrap around an enzyme and preserve it in a microscopic pocket. "We tailor these pockets to provide the ideal microenvironment" for the enzyme, Minteer says. The polymers keep the enzyme active for months instead of days.
In the new fuel cell, tiny polymer bags of enzyme are embedded in a membrane that coats one of the electrodes. When glucose from a sugary liquid gets into a pocket, the enzyme oxidizes it, releasing electrons and protons. The electrons cross the membrane and enter u wire through Which they travel to the other electrode, where they react with oxygen in the atmosphere to produce water. The flow of electrons through the wire constitutes an electrical current that can generate power.
So far, the new fuel cells don't produce much power, but the fact that they work at all is exciting, says Paul Kenis, a chemical engineer at the University of Illinois at Urbana-Champaign. "Just getting it to work," Kenis says, "is a major accomplishment."
Sugar-eating fuel cells could be an efficient way to make electricity. Sugar is easy to find. And the new fuel cells that mn on it are biodegradable,, so the technology wouldn't hart the environment. The scientists are now trying to use different enzymes that will get more power from sugar. They predict that popular products may be using the new technology in as little as 3 years.
According to the first paragraph, when can we share our sweet drinks with our cell phones？
A．When enzymes can be commonly found in living cells.
B．When the technology of producing a new type of fuel cell appears.
C．When the technology of a new type of fuel cell is suitable for mass production.
D．When the technology of mass producing cell phones appears.
PART C
Directions: You will hear three dialogues or monologues. Before listening to each one, you will have 5 seconds to read each of the questions which accompany it. While listening, answer each question by choosing A, B, C or D. After listening, you will have 10 seconds to check your answer to each question. You will hear each piece ONLY ONCE.
听力原文： Green plants can produce their own food. They use substances in the environment. This process is known as photosynthesis. In contrast, all animals including humans, get their food either directly from plants or indirectly by eating animals which have eaten plants. So animals take in a wider range of foods than plants.
Plants are generally stationary. They do not have the power of locomotion. Animals, on the other hand, can usually move around. Therefore, plants appear to be less sensitive than animals although they respond in some ways to light, heat, physical contact and other stimuli.
In external appearance plants are usually green. They grow in a branching fashion at their extremities. Their growth continues throughout their lives. Animals, however, are very diverse in their external appearance. Their growth pattern is not limited to their extremities but is evenly distributed. Growth occurs in a definite period of time.
The most basic difference between plants and animals is in the unit of structures and functions: i.e. , the cell. Plant cells have a wall which is nonliving in chemical nature whereas animal cells do not have this characteristic.
What is the most fundamental difference between plants and animals？
A．Plants produce their own food but animals don't.
B．Plant cells have a wall which is non-living in chemical nature but animal cells haven't.
C．Plants are green but animals aren't.
D．Plants can't move but animals can.
听力原文：W: ok, last night you were supposed to read an article about human bones. Are there any comments about it？
M: well, to begin with, I was surprised to find out there were so much going on in bones. I always assumed they were pretty lifeless.
W: Well, that's an assumption many people make. But the fact is bones are made of dynamic living tissue that requires continuous maintenance and repair.
M: Right. That's one of the things I found so fascinating about the article the way the bones repair themselves.
W: Ok. So can you tell us how the bones repair themselves.
M: Sure. See, there are two groups of different types of specialized cells in the bone that work together to do it. The first group goes to an area of the bone that needs repair. This group of cells produce the chemical that actually breaks down the bone tissue, and leaves a hole in it. After that the second group of specialized cells comes and produce the new tissue that fills in the hole that was made by the first group.
W: Very good. This is a very complex process. In fact, the scientists who study human bones don't completely understand it yet. They are still trying to find out how it all actually works. Specifically, because sometimes after the first group of cells leaves a hole in the bone tissue, for some reason, the second group doesn't completely fill in the hole. And this can cause real problems. It can actually lead to a disease in which the bone becomes weak and is easily broken.
M: ok, I get it. So if the scientists can figure out what makes the specialized cells work, maybe they can find a way to make sure the second group of cells completely fills the hole in the bone tissue every time. That'll prevent the disease from every occurring.
(31)
A．Two different types of bones in the human body.
B．How bones help the body move.
C．How bones continuously repair themselves.
D．The chemical composition of human bones.
The idea of a fish being able to generate electricity strong enough to light lamp bulbs--or even to run a small electric motor--is almost unbelievable, but several kinds of fish are able to do this. Even more strangely, this curious power has been acquired in different ways by fish belonging to very different families.
Perhaps the best known are the electric rays, or torpedoes(电鳐), of which several kinds live in warm seas. They possess on each side of the head, behind the eyes, a large organ consisting of a number of hexagonal shaped cells rather like a honeycomb. The cells are filled with a jelly-like substance, and contain a series of flat electric plates. One side, the negative side, of each plate, is supplied with very fine nerves, connected with a main nerve coming from a special part of the brain. Current passes from the upper, positive side of the organ downwards, to the negative, lower side. Generally it is necessary to touch the fish in two places, completing the circuit, in order to receive a shock.
The strength of this shock depends on the size of the fish, but newly born ones only about 5 centime-tres across can be made to light the bulb of a pocket flashlight for a few moments, while a fully grown torpedo gives a shock capable of knocking a man down, and, if suitable wires are connected, will operate a small electric motor for several minutes.
Another famous example is the electric eel. This fish gives an even more powerful shock. The system is different from that of the torpedo in that the electric plates run longitudinally(纵向) and are supplied with nerves from the spinal(脊骨) cord. Consequently, the current passes along the fish from head to tail. The electric organs of these fish are really altered muscles and like all muscles are apt (likely) to tire, so they are not able to produce electricity for very long.
The power of producing electricity may serve these fish both for defence and attack.
It can be seen from the passage that（）.
A.the capacity to generate electricity is the distinctive characteristic of the fish
B.the current travels in an upward direction from the positive side to negative side in torpedo's electric cells
C.some fish can produce enough electricity to drive a number of electric motors
D.the torpedo' s electric cells have a shape with six sides
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