单选题Why does life on earth depend much on the oceans?A Sea plants produce most of the oxygen in the atmosphere.B Carbon dioxide is converted into oxygen in oceans.C The oceans provide an invaluable food resource.D Productivity of fisheries can feed 80 mill

Passage 2
If the population of the earth goes on increasing at its present rate, there will eventually not be enough resources left to sustain life on the planet. By the middle of the 21st century, if present trends continue, we will have used up all the oil that drives our cars, for example. Even if scientists develop new ways of feeding the human race, the crowded conditions on earth will make it necessary for us to look for open space somewhere else. But none of the other planets in our solar system are capable of supporting life at present. One possible solution to the problem, however, has recently been suggested by an American scientist, Professor Carl Sagan.
Sagan believes that before the earth's resources are completely exhausted it will be possible to change the atmosphere of Venus and so create a new world almost as large as earth itself. The difficulty is that Venus is much hotter than the earth and there is only a tiny amount of water there.
Sagan proposes that algae organisms, which can live in extremely hot or cold atmospheres and at the same time produce oxygen, should be bred in conditions similar to those on Venus. As soon as this has been done, the algae will be placed in small rockets. Spaceships will then fly to Venus and fire the rockets into the atmosphere. In a fairly short time, the algae will break down the carbon dioxide into oxygen and carbon.
When the algae have done their work, the atmosphere will become cooler, but before man can set foot on Venus it will be necessary for the oxygen to produce rain. The surface of the planet will still be too hot for men to land on it but the rain will eventually fall and in a few years something like earth will be reproduced on Venus.
On Venus there is a lot of__________.

A. water
B. carbon dioxide
C. carbon monoxide
D. oxygen

Passage 2
If the population of the earth goes on increasing at its present rate, there will eventually not be enough resources left to sustain life on the planet. By the middle of the 21st century, if present trends continue, we will have used up all the oil that drives our cars, for example. Even if scientists develop new ways of feeding the human race, the crowded conditions on earth will make it necessary for us to look for open space somewhere else. But none of the other planets in our solar system are capable of supporting life at present. One possible solution to the problem, however, has recently been suggested by an American scientist, Professor Carl Sagan.
Sagan believes that before the earth's resources are completely exhausted it will be possible to change the atmosphere of Venus and so create a new world almost as large as earth itself. The difficulty is that Venus is much hotter than the earth and there is only a tiny amount of water there.
Sagan proposes that algae organisms, which can live in extremely hot or cold atmospheres and at the same time produce oxygen, should be bred in conditions similar to those on Venus. As soon as this has been done, the algae will be placed in small rockets. Spaceships will then fly to Venus and fire the rockets into the atmosphere. In a fairly short time, the algae will break down the carbon dioxide into oxygen and carbon.
When the algae have done their work, the atmosphere will become cooler, but before man can set foot on Venus it will be necessary for the oxygen to produce rain. The surface of the planet will still be too hot for men to land on it but the rain will eventually fall and in a few years something like earth will be reproduced on Venus.
CarlSagan believes that Venus might be colonized from earth because__________.

A. it might be possible to change its atmosphere
B. its atmosphere is the same as the earth's
C. there is a good supply of water on Venus
D. the days on Venus are long enough

Passage 2
If the population of the earth goes on increasing at its present rate, there will eventually not be enough resources left to sustain life on the planet. By the middle of the 21st century, if present trends continue, we will have used up all the oil that drives our cars, for example. Even if scientists develop new ways of feeding the human race, the crowded conditions on earth will make it necessary for us to look for open space somewhere else. But none of the other planets in our solar system are capable of supporting life at present. One possible solution to the problem, however, has recently been suggested by an American scientist, Professor Carl Sagan.
Sagan believes that before the earth's resources are completely exhausted it will be possible to change the atmosphere of Venus and so create a new world almost as large as earth itself. The difficulty is that Venus is much hotter than the earth and there is only a tiny amount of water there.
Sagan proposes that algae organisms, which can live in extremely hot or cold atmospheres and at the same time produce oxygen, should be bred in conditions similar to those on Venus. As soon as this has been done, the algae will be placed in small rockets. Spaceships will then fly to Venus and fire the rockets into the atmosphere. In a fairly short time, the algae will break down the carbon dioxide into oxygen and carbon.
When the algae have done their work, the atmosphere will become cooler, but before man can set foot on Venus it will be necessary for the oxygen to produce rain. The surface of the planet will still be too hot for men to land on it but the rain will eventually fall and in a few years something like earth will be reproduced on Venus.

Algae are plants that can__________.
查看材料

A．live in very hot temperatures
B．live in very cold temperatures
C．manufacture oxygen
D．all of the above

共用题干
第一篇

Putting Plants to Work

Using the power of the sun is nothing new.People have had solar-powered calculators and buildings with
solar panels（太阳能电池板）for decades. But plants are the real experts. They' ve been using sunlight as an
energy source for billions of years.
Cells in the green leaves of plants work like tiny factories to convert sunlight, carbon dioxide（二氧化
碳）,and water into sugars
and starche（淀粉）,stored energy that the piants can use. This conversion
process is called photosynthesis (光合作用）Unfortunately, unless you' re a plant, it's difficult and
expensive to convert sunlight into storable energy. That's why scientists are taking a closer look at exactly
how plants do it.
Some scientists are trying to get plants,or biological cells that act like plants, to work as very small
photosynthesic power stations. For example, Maria Ghirardi of the National Renewable Energy Laboratory in
Golden. Cobo.,is working with green algae（水藻）.She's trying to trick them into producing hydrogen
instead of sugars when they perform photosynthesis. Once the researchers can get the algae working efficient-
ly ,the hydrogen that they produce could be used to power fuel cells in cars or to generate electricity.
The algae are grown in narrow-necked glass bottles to produce hydrogen in the lab. During photosynthe-
sis , plants normally make sugars or strchds. "But under certain conditions,a lot of algae are able to use the
sunlight energy not to store starch , but to make hydrogen."Ghirardi says. For example ,algae will produce hy-
drogen in an airfree environment. It' s the oxygen in the air that prevents algae from making hydrogen most of
the time.
Working in an airfree environment, however, is difficult. It's not a practical way to produce cheap
energy. But Ghirardi and her colleagues have discovered that by removing a chemical called sulfate（硫酸盐）
from the environment that the algae grow in, they will make hydrogen instead of sugars,even when air
is present.
Unfortunately, removing the sulfate also makes the algae's cells work very slowly,and not much
hydrogen is produced. Still ,the researchers see this as a first step in their goal to produce hydrogen efficiently
from algae. With more work,they may be able to speed the cells' activity and produce larger quantities
of hydrogen.
The researchers hope that algae will one day be an easy-to-use fuel source. The organisms are cheap to
get and to feed, Ghirardi says,and they can grow almost anywhere:"You can grow them in a reactor, in a
pond. You can grow them in the ocean. There's a lot of flexibility in how you can use these organisms."

Algae are able to use solar energy to produce hydrogen when_______________.
A:they are grown in narrow-necked bottles
B:there is no oxygen in the air
C:there is enough oxygen in the air
D:enough starch is stored

If the population of the earth goes on increasing at its present rate, there will eventually not be enough resources left to sustain life on the planet.By the middle of the 21st century,if present trends continue, we will have used up all the oil that drives our cars,for example.Even if scientists develop new ways of feeding the human race,the crowded conditions on earth will make it necessary for lus to look for open space somewhere else. But none of the other planets in our solar system are capable of supporting life at present. One possible solution to the problem, however,has recently been suggested by American scientist, Professor Carl Sagan.
Sagan believes that before the earth's resources are compleetely exhausted it will be possible to change the atmophere of Venus and so create a new world almost as large as earth itself. The difficult is that Venus is much hotter than the earth and there is only a tiny amount of water there.
Sagan proposes that algae organisms that can live in extremely hot or cold atmospheres and at the same time produce oxygen,should be bred in condition similar to those on Venus.As soon as this has been done, the algae will be placed in small rockets. Spaceship will then fly to Venus and fire the rockets into the atmosphere .In a fairly short time, the alge will break down the carbon dioxide into oxygen and carbon.
When the algae have done theri work, the atmosphere will become cooler,but befor man can set foot on Venus it will be neccessary for the oxygen to produce rain. The surface of the planet will still be too hot for man to land on it but the rain will eventually fall and in a few years something like earth will be reproduced on Venus.
Inte long run, the most insoluble problem caused by population growth on earth will probably be the lack of ______.

a.food
b.oil
c.space
d.resources

共用题干
第一篇

Plant Gas

Scientists have been studying natural sources of methane（甲烷，沼气）for decades but hadn't regarded plants as a producer, notes Frank Keppler, a geochemist（地球化学家）at the Max Planck Institute for Nuclear Physics in Heldelberg,Germany. Now Keppler and his colleagues find that plants,from grasses to trees,may also be sources of the greenhouse gas.This is really surprising, because most scientists assumed that methane production requires an oxygen-free environment.
Previously,researchers had thought that it was impossible for plants to make significant amounts of the gas. They had assumed that microbes（微生物）need to be in environments without oxygen to produce methane.Methane is a greenhouse gas, like carbon dioxide.Gases such as methane and carbon dioxide trap heat in Earth's atmosphere and contribute to global warming.
In its experiments, Keppler's team used sealed chambers（室，房间；腔）that contained the same concentration of oxygen that Earth's atmosphere has.They measured the amounts of methane that were released by both living plants and dried plant material,such as fallen leaves.
With the dried plants,the researchers took measurement at temperatures ranging from 30 degrees Celsius to 70 degrees C.At 30 degrees C.,they found,a gram of dried plant material released up to 3 nanograms（微克）of methane per hour(One nanogram is a millionth of a gram). With every 10-degree rise in temperature,the amount of methane released each hour roughly doubled.
Living plants growing at their normal temperatures released as much as 370 nanograms of methane per gram of plant tissue per hour. Methane emissions tripled when living and dead plant was exposed to sunlight.
Because there was plenty of oxygen available,it's unlikely that the types of bacteria(bacterium的复数，细菌）that normally make methane were involved. Experiments on plants that were grown in water rather than soil also resulted in methane emissions.That's another strong sign that the gas came from the plants and not soil microbes.
The new finding is an"interesting observation,"says Jennifer Y. King,a biogeochemist（生物地球化学家）at the University of Minnesota in St. Paul. Because some types of soil microbes consume methane,they may prevent plant-produced methane from reaching the atmosphere.Field tests will be needed to assess the plant's influence,she notes.

What was scientists' understanding of methane?
A:It was produced from plants.
B:It was not a greenhouse gas.
C:It was produced in oxygen-free environments.
D:It traps more heat than any other greenhouse gas.

An Essential Scientific Process

All life on the earth depends upon green plants. Using sunlight, theplants produce their own food. Then animals feed upon the plants. They take inthe nutrients the plants have made sted. But that’s not all.Sunlight also helps a plant produce oxygen. Some of the oxygen is used by theplant, but a plant usually produces me oxygen than it uses. The excess oxygenis necessary f animals other ganisms to live.

The process of changing light into food oxygen is calledphotosynthesis. Besides light energy from the sun, plants also use water carbon dioxide. The water gets to the plant through its roots. The carbondioxide enters the leaves through tiny openings called stomata. The carbondioxide travels to chloplasts, special cells in the bodies of green plants.This is photosynthesis takes place. Chloplasts contain the chlophyllsthat give plants their green col. The chlophylls are the molecules thattrap light energy. The trapped light energy changes water carbon dioxide toproduce oxygen a simple sugar called glucose.

Carbon dioxide oxygen move into out of the stomata. Watervap also moves out of the stomata. Me than 90 percent of water a planttakes in through its roots escapes through the stomata. During the daytime, thestomata of most plants are open. This allows carbon dioxide to enter the leavesf photosynthesis. As night falls, carbon dioxide is not needed. The stomataof most plants close. Water loss stops.

If photosynthesis ceased, there would be little food other ganicmatter on the earth. Most ganisms would disappear. The earth’s atmospherewould no longer contain oxygen. Photosynthesis is essential f life on ourplanet.

　　词汇：

nutrient n.营养物

ganism n.生物体，有机体

carbon dioxide n.二氧化碳

chloplast n.叶绿体

molecule n.分子

vap n.水蒸气

oxygen n.氧气

photosynthesis n.光合作用

chlophyll n.叶绿素

glucose n.葡萄糖

cease v.停止

　　注释：

1.Then animals feed upon the plants.动物以植物为食。

　　练习：

5.Another good title f this passage would be

A.Oxygen Carbon Dioxide.

B.Plants Their Roots.

C.How Photosynthesis Wks.

D.Why Our Earth Needs Water.

An Essential Scientific Process

All life on the earth depends upon green plants. Using sunlight, theplants produce their own food. Then animals feed upon the plants. They take inthe nutrients the plants have made sted. But that’s not all.Sunlight also helps a plant produce oxygen. Some of the oxygen is used by theplant, but a plant usually produces me oxygen than it uses. The excess oxygenis necessary f animals other ganisms to live.

The process of changing light into food oxygen is calledphotosynthesis. Besides light energy from the sun, plants also use water carbon dioxide. The water gets to the plant through its roots. The carbondioxide enters the leaves through tiny openings called stomata. The carbondioxide travels to chloplasts, special cells in the bodies of green plants.This is photosynthesis takes place. Chloplasts contain the chlophyllsthat give plants their green col. The chlophylls are the molecules thattrap light energy. The trapped light energy changes water carbon dioxide toproduce oxygen a simple sugar called glucose.

Carbon dioxide oxygen move into out of the stomata. Watervap also moves out of the stomata. Me than 90 percent of water a planttakes in through its roots escapes through the stomata. During the daytime, thestomata of most plants are open. This allows carbon dioxide to enter the leavesf photosynthesis. As night falls, carbon dioxide is not needed. The stomataof most plants close. Water loss stops.

If photosynthesis ceased, there would be little food other ganicmatter on the earth. Most ganisms would disappear. The earth’s atmospherewould no longer contain oxygen. Photosynthesis is essential f life on ourplanet.

　　词汇：

nutrient n.营养物

ganism n.生物体，有机体

carbon dioxide n.二氧化碳

chloplast n.叶绿体

molecule n.分子

vap n.水蒸气

oxygen n.氧气

photosynthesis n.光合作用

chlophyll n.叶绿素

glucose n.葡萄糖

cease v.停止

　　注释：

1.Then animals feed upon the plants.动物以植物为食。

　　练习：

1.In the first paragraph，the wd “excess” means

A.heavy.

B.extra.

C.green.

D.liquid.

Passage 2
If the population of the earth goes on increasing at its present rate, there will eventually not be enough resources left to sustain life on the planet. By the middle of the 21st century, if present trends continue, we will have used up all the oil that drives our cars, for example. Even if scientists develop new ways of feeding the human race, the crowded conditions on earth will make it necessary for us to look for open space somewhere else. But none of the other planets in our solar system are capable of supporting life at present. One possible solution to the problem, however, has recently been suggested by an American scientist, Professor Carl Sagan.
Sagan believes that before the earth's resources are completely exhausted it will be possible to change the atmosphere of Venus and so create a new world almost as large as earth itself. The difficulty is that Venus is much hotter than the earth and there is only a tiny amount of water there.
Sagan proposes that algae organisms, which can live in extremely hot or cold atmospheres and at the same time produce oxygen, should be bred in conditions similar to those on Venus. As soon as this has been done, the algae will be placed in small rockets. Spaceships will then fly to Venus and fire the rockets into the atmosphere. In a fairly short time, the algae will break down the carbon dioxide into oxygen and carbon.
When the algae have done their work, the atmosphere will become cooler, but before man can set foot on Venus it will be necessary for the oxygen to produce rain. The surface of the planet will still be too hot for men to land on it but the rain will eventually fall and in a few years something like earth will be reproduced on Venus.
Man can eventually land on Venus only when__________.

A. the algae have done their work
B. the atmosphere becomes cooler
C. there is oxygen
D. it rains there

Passage 2
If the population of the earth goes on increasing at its present rate, there will eventually not be enough resources left to sustain life on the planet. By the middle of the 21st century, if present trends continue, we will have used up all the oil that drives our cars, for example. Even if scientists develop new ways of feeding the human race, the crowded conditions on earth will make it necessary for us to look for open space somewhere else. But none of the other planets in our solar system are capable of supporting life at present. One possible solution to the problem, however, has recently been suggested by an American scientist, Professor Carl Sagan.
Sagan believes that before the earth's resources are completely exhausted it will be possible to change the atmosphere of Venus and so create a new world almost as large as earth itself. The difficulty is that Venus is much hotter than the earth and there is only a tiny amount of water there.
Sagan proposes that algae organisms, which can live in extremely hot or cold atmospheres and at the same time produce oxygen, should be bred in conditions similar to those on Venus. As soon as this has been done, the algae will be placed in small rockets. Spaceships will then fly to Venus and fire the rockets into the atmosphere. In a fairly short time, the algae will break down the carbon dioxide into oxygen and carbon.
When the algae have done their work, the atmosphere will become cooler, but before man can set foot on Venus it will be necessary for the oxygen to produce rain. The surface of the planet will still be too hot for men to land on it but the rain will eventually fall and in a few years something like earth will be reproduced on Venus.

In the long run, the most difficult problem caused by population growth on earth will probably be the lack of__________.
查看材料

A．food
B．oil
C．space
D．resources

Passage 2
If the population of the earth goes on increasing at its present rate, there will eventually not be enough resources left to sustain life on the planet. By the middle of the 21st century, if present trends continue, we will have used up all the oil that drives our cars, for example. Even if scientists develop new ways of feeding the human race, the crowded conditions on earth will make it necessary for us to look for open space somewhere else. But none of the other planets in our solar system are capable of supporting life at present. One possible solution to the problem, however, has recently been suggested by an American scientist, Professor Carl Sagan.
Sagan believes that before the earth's resources are completely exhausted it will be possible to change the atmosphere of Venus and so create a new world almost as large as earth itself. The difficulty is that Venus is much hotter than the earth and there is only a tiny amount of water there.
Sagan proposes that algae organisms, which can live in extremely hot or cold atmospheres and at the same time produce oxygen, should be bred in conditions similar to those on Venus. As soon as this has been done, the algae will be placed in small rockets. Spaceships will then fly to Venus and fire the rockets into the atmosphere. In a fairly short time, the algae will break down the carbon dioxide into oxygen and carbon.
When the algae have done their work, the atmosphere will become cooler, but before man can set foot on Venus it will be necessary for the oxygen to produce rain. The surface of the planet will still be too hot for men to land on it but the rain will eventually fall and in a few years something like earth will be reproduced on Venus.

CarlSagan believes that Venus might be colonized from earth because__________.
查看材料

A．it might be possible to change its atmosphere
B．its atmosphere is the same as the earth's
C．there is a good supply of water on Venus
D．the days on Venus are long enough

根据下列内容，回答196-200题。
If the population of the earth goes on increasing at its present rate, there will eventually notbe enough resources left to sustain life on the planet. By the middle of the 21st century, if presenttrends continue, we will have used up all the oil that drives our cars, for example. Even if scien-tists develop new ways of feeding the human race, the crowded conditions on earth will make itnecessary for us to look for open space somewhere else. But none of the other planets in our solarsystem are capable of supporting life at present. One possible solution to the problem, however,
has recently been suggested by an American scientist, Professor Carl Sagan.
Sagan believes that before the earth's resources are completely exhausted it will be possible tochange the atmosphere of Venus and so create a new world almost as large as earth itself. The dif-ficulty is that Venus is much hotter than the earth and there is only a tiny amount of water there.
Sagan proposes that algae organisms, which can live in extremely hot or cold atmospheres andat the same time produce oxygen, should be bred in conditions similar to those on Venus. As soonas this has been done, the algae will be placed in small rockets. Spaceships will then fly to Venusand fire the rockets into the atmosphere. In a fairly short time, the algae will break down the car-bon dioxide into oxygen and carbon.
When the algae have done their work, the atmosphere will become cooler, but before mancan set foot on Venus it will be necessary for the oxygen to produce rain. The surface of the planetwill still be too hot for men to land on it but the rain will eventually fall and in a few years some-thing like earth will be reproduced on Venus.
In the long run, the most difficult problem caused by population growth on earth willprobably be the lack of __________.

A.food
B.oil
C.space
D.resources

共用题干
第一篇

Plant Gas

Scientists have been studying natural sources of methane（甲烷，沼气）for decades but hadn't regarded plants as a producer, notes Frank Keppler, a geochemist（地球化学家）at the Max Planck Institute for Nuclear Physics in Heldelberg,Germany. Now Keppler and his colleagues find that plants,from grasses to trees,may also be sources of the greenhouse gas.This is really surprising, because most scientists assumed that methane production requires an oxygen-free environment.
Previously,researchers had thought that it was impossible for plants to make significant amounts of the gas. They had assumed that microbes（微生物）need to be in environments without oxygen to produce methane.Methane is a greenhouse gas, like carbon dioxide.Gases such as methane and carbon dioxide trap heat in Earth's atmosphere and contribute to global warming.
In its experiments, Keppler's team used sealed chambers（室，房间；腔）that contained the same concentration of oxygen that Earth's atmosphere has.They measured the amounts of methane that were released by both living plants and dried plant material,such as fallen leaves.
With the dried plants,the researchers took measurement at temperatures ranging from 30 degrees Celsius to 70 degrees C.At 30 degrees C.,they found,a gram of dried plant material released up to 3 nanograms（微克）of methane per hour(One nanogram is a millionth of a gram). With every 10-degree rise in temperature,the amount of methane released each hour roughly doubled.
Living plants growing at their normal temperatures released as much as 370 nanograms of methane per gram of plant tissue per hour. Methane emissions tripled when living and dead plant was exposed to sunlight.
Because there was plenty of oxygen available,it's unlikely that the types of bacteria(bacterium的复数，细菌）that normally make methane were involved. Experiments on plants that were grown in water rather than soil also resulted in methane emissions.That's another strong sign that the gas came from the plants and not soil microbes.
The new finding is an"interesting observation,"says Jennifer Y. King,a biogeochemist（生物地球化学家）at the University of Minnesota in St. Paul. Because some types of soil microbes consume methane,they may prevent plant-produced methane from reaching the atmosphere.Field tests will be needed to assess the plant's influence,she notes.

Which of the following about methane is not mentioned in the passage?
A:Plants growing in soil release methane.
B:Plants growing in water release methane.
C:Soil microbes consume methane.
D:Microbes in plants produce methane.

共用题干
第一篇

Plant Gas

Scientists have been studying natural sources of methane（甲烷，沼气）for decades but hadn't regarded plants as a producer, notes Frank Keppler, a geochemist（地球化学家）at the Max Planck Institute for Nuclear Physics in Heldelberg,Germany. Now Keppler and his colleagues find that plants,from grasses to trees,may also be sources of the greenhouse gas.This is really surprising, because most scientists assumed that methane production requires an oxygen-free environment.
Previously,researchers had thought that it was impossible for plants to make significant amounts of the gas. They had assumed that microbes（微生物）need to be in environments without oxygen to produce methane.Methane is a greenhouse gas, like carbon dioxide.Gases such as methane and carbon dioxide trap heat in Earth's atmosphere and contribute to global warming.
In its experiments, Keppler's team used sealed chambers（室，房间；腔）that contained the same concentration of oxygen that Earth's atmosphere has.They measured the amounts of methane that were released by both living plants and dried plant material,such as fallen leaves.
With the dried plants,the researchers took measurement at temperatures ranging from 30 degrees Celsius to 70 degrees C.At 30 degrees C.,they found,a gram of dried plant material released up to 3 nanograms（微克）of methane per hour(One nanogram is a millionth of a gram). With every 10-degree rise in temperature,the amount of methane released each hour roughly doubled.
Living plants growing at their normal temperatures released as much as 370 nanograms of methane per gram of plant tissue per hour. Methane emissions tripled when living and dead plant was exposed to sunlight.
Because there was plenty of oxygen available,it's unlikely that the types of bacteria(bacterium的复数，细菌）that normally make methane were involved. Experiments on plants that were grown in water rather than soil also resulted in methane emissions.That's another strong sign that the gas came from the plants and not soil microbes.
The new finding is an"interesting observation,"says Jennifer Y. King,a biogeochemist（生物地球化学家）at the University of Minnesota in St. Paul. Because some types of soil microbes consume methane,they may prevent plant-produced methane from reaching the atmosphere.Field tests will be needed to assess the plant's influence,she notes.

To test whether plants are a source of methane,the scientists created_______.
A:an oxygen-free environment
B:an environment with the same concentration of oxygen as the Earth has
C:a carbon dioxide-free environment
D:an environment filled with the greenhouse gas

An Essential Scientific Process

All life on the earth depends upon green plants. Using sunlight, theplants produce their own food. Then animals feed upon the plants. They take inthe nutrients the plants have made sted. But that’s not all.Sunlight also helps a plant produce oxygen. Some of the oxygen is used by theplant, but a plant usually produces me oxygen than it uses. The excess oxygenis necessary f animals other ganisms to live.

The process of changing light into food oxygen is calledphotosynthesis. Besides light energy from the sun, plants also use water carbon dioxide. The water gets to the plant through its roots. The carbondioxide enters the leaves through tiny openings called stomata. The carbondioxide travels to chloplasts, special cells in the bodies of green plants.This is photosynthesis takes place. Chloplasts contain the chlophyllsthat give plants their green col. The chlophylls are the molecules thattrap light energy. The trapped light energy changes water carbon dioxide toproduce oxygen a simple sugar called glucose.

Carbon dioxide oxygen move into out of the stomata. Watervap also moves out of the stomata. Me than 90 percent of water a planttakes in through its roots escapes through the stomata. During the daytime, thestomata of most plants are open. This allows carbon dioxide to enter the leavesf photosynthesis. As night falls, carbon dioxide is not needed. The stomataof most plants close. Water loss stops.

If photosynthesis ceased, there would be little food other ganicmatter on the earth. Most ganisms would disappear. The earth’s atmospherewould no longer contain oxygen. Photosynthesis is essential f life on ourplanet.

　　词汇：

nutrient n.营养物

ganism n.生物体，有机体

carbon dioxide n.二氧化碳

chloplast n.叶绿体

molecule n.分子

vap n.水蒸气

oxygen n.氧气

photosynthesis n.光合作用

chlophyll n.叶绿素

glucose n.葡萄糖

cease v.停止

　　注释：

1.Then animals feed upon the plants.动物以植物为食。

　　练习：

4.This passage is primarily developed by

A.explaining a process.

B.telling a sty.

C.comparing contrasting.

D.convincing the reader of plants’ imptance.

An Essential Scientific Process

All life on the earth depends upon green plants. Using sunlight, theplants produce their own food. Then animals feed upon the plants. They take inthe nutrients the plants have made sted. But that’s not all.Sunlight also helps a plant produce oxygen. Some of the oxygen is used by theplant, but a plant usually produces me oxygen than it uses. The excess oxygenis necessary f animals other ganisms to live.

The process of changing light into food oxygen is calledphotosynthesis. Besides light energy from the sun, plants also use water carbon dioxide. The water gets to the plant through its roots. The carbondioxide enters the leaves through tiny openings called stomata. The carbondioxide travels to chloplasts, special cells in the bodies of green plants.This is photosynthesis takes place. Chloplasts contain the chlophyllsthat give plants their green col. The chlophylls are the molecules thattrap light energy. The trapped light energy changes water carbon dioxide toproduce oxygen a simple sugar called glucose.

Carbon dioxide oxygen move into out of the stomata. Watervap also moves out of the stomata. Me than 90 percent of water a planttakes in through its roots escapes through the stomata. During the daytime, thestomata of most plants are open. This allows carbon dioxide to enter the leavesf photosynthesis. As night falls, carbon dioxide is not needed. The stomataof most plants close. Water loss stops.

If photosynthesis ceased, there would be little food other ganicmatter on the earth. Most ganisms would disappear. The earth’s atmospherewould no longer contain oxygen. Photosynthesis is essential f life on ourplanet.

　　词汇：

nutrient n.营养物

ganism n.生物体，有机体

carbon dioxide n.二氧化碳

chloplast n.叶绿体

molecule n.分子

vap n.水蒸气

oxygen n.氧气

photosynthesis n.光合作用

chlophyll n.叶绿素

glucose n.葡萄糖

cease v.停止

　　注释：

1.Then animals feed upon the plants.动物以植物为食。

　　练习：

2.Which of the following does not move through a plant’s stomata?

A.Carbon dioxide.

B.Water vap.

C.Oxygen.

D.Food.