Roots take up water and hold the plant in the soil．题目和参考答案——青夏教育精英家教网—

题目内容

Roots take up water and hold the plant in the soil．

答案：
解析：

根吸收水分，并将植物固定在土壤中。

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相关题目

All plant cells are able to take up water. Even dead ones do to a certain degree. Absorption of water by dead cell walls makes wood swell(肿胀). In common land plants, the living cells of roots take up most of the water. Land plants without roots do exist, however. Those greenish-yellow lichens(苔藓)you see on tree trunks and on rocks in the high mountains have no roots. Half a billion years ago, when water plant started to invade the land, the first primitive land plants did not have roots; they were marsh (沼泽) plants.

Even among the flowering plants, one finds rootless forms. These flowering plants are the so-called higher plants because they evolved more recently and are thus considered higher on the evolutionary scale. In the Peruvian desert, there grows one of these rootless higher plants, a bromeliad. It is a relative of the pineapple. Even if this plant had roots, they would be of no use, because where the plant grows, it never rains. The plant gets its water exclusively from the dew it collects at night, when its leaves cool off. Such rootless plants, of course, can be moved with ease, but they will only grow when they are placed out in the open. If they are placed too near a house, the radiation from the heat of the house prevents the leaves from cooling and so prevents dew from forming, and the plant dies. In the southern United States and in Puerto Rico, one sees bromeliads growing high above the streets on the insulation of electric wires. These plants get their water from rain, and the only soil they ever come in contact with is the dust that may blow on their leaves.

Wood swells because of _______.

A. the dead cell walls B. tiny drops of water entering the dead cell

C. the growth of the cell D. the death of the cell

From the passage we know that the evolutionary scale is arranged according to ______.

A. evolutionary cycles B. heights and depths

C. time D. kinds

The bromeliad is a plant that _______.

A. has useless roots B. is a pineapple

C. can grow anywhere D. takes up water through its leaves

Which of the following is NOT true?

Water plants existed before land plants.

Only living plant cells take up water.

The greenish-yellow lichens are uncommon land plants.

The living cells of roots absorb more water than the rest of the plant.

The most suitable title for this passage is ______.

A. water intake by cells B. rootless plantsC. plant in the desert D. higher plants

All plant cells are capable of taking up water. Even dead ones do to a certain degree. Absorption（吸收）of water by dead cell walls makes wood become larger. In common land plants, the living cells of roots take up most of the water. Land plants without roots do exist, however. Those greenish-yellow lichens（苔藓）you see on rocks in the high mountains have no roots. Half a billion years ago, when water plants started to enter the land, the first land plants did not have roots.
Even among the flowering plants, one finds rootless forms. These flowering plants are “the higher plants” because they evolved（进化）recently and are thus considered higher on the evolutionary scale（进化度）. In the Peruvian desert, there grows one of these rootless higher plants, a bromeliad. It is a relative of the pineapple. Even if this plant had roots, they would be of no use, because where the plant grows, it never rains. The plant gets its water only from the dew（露水）it collects at night, when its leaves cool off. Such rootless plants, of course, can be moved with ease, but they will only grow when they are placed out in the open. If they are placed too near a house, the radiation from the heat of the house prevents the leaves from cooling and so prevents dew from forming, and the plant dies. In the southern United States and in Puerto Rico, one sees bromeliads growing high above the streets on the insulation（绝缘物）of electric wires. These plants get their water from rain, and the only soil they ever come in contact with is the dust that may blow on their leaves.
64．From the passage we know that the evolutionary scale is graded according to _______ .
A. evolutionary cycles B. heights and depths
C. time        D. kinds
65．The “bromeliad” is a plant that _______ .
A．has useless roots             B. is a pineapple
C．can grow anywhere D. takes up water through its leaves
66．The most suitable title for this passage is “_______ ”.
A. Absorption of water by plants   B. Rootless plants
C. Plants in the desert       D. Higher plants

All plant cells are capable of taking up（吸收）water. Even dead ones do to a certain degree. Absorption（吸收）of water by dead cell walls makes wood become larger.
In common land plants, the living cells of roots take upmost of the water. Land plants without roots do exist, however. Those greenish-yellow lichens（苔藓）you see on rocks in the high mountains have no roots. Half a billion years ago, when water plants started to enter the land, the first land plants did not have roots.
Even among the flowering plants, one finds rootless forms. These flowering plants are “the higher plants” because they evolved（进化）recently and are thus considered higher on the evolutionary scale（进化度）.
In the Peruvian desert, there grows one of these rootless higher plants, a bromeliad. It is a relative of the pineapple. Even if this plant had roots, they would be of no use, because where the plant grows, it never rains. The plant gets its water only from the dew（露水）it collects at night, when its leaves cool off. Such rootless plants, of course, can be moved with ease, but they will only grow when they are placed out in the open. If they are placed too near a house, the radiation from the heat of the house prevents the leaves from cooling and so prevents dew from forming, and the plant dies.
In the southern United States and in Puerto Rico, one sees bromeliads growing high above the streets on the insulation（绝缘物）of electric wires. These plants get their water from rain, and the only soil they ever come in contact with is the dust that may blow on their leaves.
【小题1】Wood becomes larger because of .

A．dead cell walls	B．water entering dead cells
C．the growth of cells	D．the death of cells

【小题2】From the passage we know that the evolutionary scale is graded according to .

A．evolutionary cycles	B．heights and depths
C．time	D．kinds

【小题3】The “bromeliad” is a plant that .

A．has no roots	B．is a pineapple
C．can grow anywhere	D．takes up water through its leaves

【小题4】The most suitable title for this passage is “ ”.

A．Absorption of water by plants	B．Rootless plants in America
C．Plants in the desert	D．Higher plants

Have you ever wondered why the roots of the plants always know which way to grow—into the soil but not above it? Some British scientists have recently solved this mystery.
It turns out that roots have special hairs that tie them into the soil and help them grow their way past obstacles, a team at the John Inners Center in Norwich reports in the February 29 issue of Journal Science.
“The key is in the fuzzy(有绒毛的)coat of hairs on the roots of plants,” says professor Liam Dolan. “We have found a growth control system that enables these hairs to find their way and to become longer when their path is clear.”
Root hairs explore the soil in much the same way a person would feel their way in the dark. If they come across an obstacle, they make their way around until they can continue growing in an opening. In the meantime, the plant is held in place as the hairs grip(紧紧抓住)the soil.
The hairs are guided by a clever chemical trick. A protein(蛋白质) at the tip of the root hairs called RHD2 helps them to take calcium(钙) from the soil. Calcium makes the hairs grow, and produce more RHD2, and take more calcium.
But when an obstacle blocks the hair’s path, or the hair reaches the surface of the soil, the cycle is broken and growth starts in another direction.
This system gives plants the flexibility to explore a complex environment and to live in even the most unpromising soils, says Dolan.
In poor soils such as in parts of Australia and Africa, native plants have adapted by producing enormous numbers of root hairs. A better understanding of this adaptation will allow scientists to develop hairy rooted crops that can grow in unfriendly environments.
According to Dolan, “Research in the John Inners Center is taking a breeding approach to increase hair length in wheat but it will be some time before new cultivars(栽培变种) are developed.”
【小题1】The passage is mainly about _______.

A．why the roots of plants grow into the soil but not above it

B．how the roots of plants grow into the soil but not above it

C．the process of plants growth

D．a growth control system of plants

【小题2】How does the circle work?

A．RHD2 takes calcium from the soil, which makes hairs grow, and produce RHD2 and take more calcium

B．Roots take RHD2 and calcium from the soil and produce RHD2

C．Roots make hairs grow, and produce RHD2, and take more calcium

D．RHD2 takes protein, which makes hairs grow, and produce RHD2, and take more calcium

【小题3】We can infer from the last paragraph that ________.

A．hairy rooted crops can grow better in unfriendly environments

B．a new cultivar of wheat with long hair has been developed by scientists

C．a new cultivar of wheat with long hair is still on test

D．the roots of plants always know which way to grow

Have you ever wondered why the roots of the plants always know which way to grow—into the soil but not above it? Some British scientists have recently solved this mystery.

It turns out that roots have special hairs that tie them into the soil and help them grow their way past obstacles, a team at the John Inners Center in Norwich reports in the February 29 issue of Journal Science.

“The key is in the fuzzy(有绒毛的)coat of hairs on the roots of plants,” says professor Liam Dolan. “We have found a growth control system that enables these hairs to find their way and to become longer when their path is clear.”

Root hairs explore the soil in much the same way a person would feel their way in the dark. If they come across an obstacle, they make their way around until they can continue growing in an opening. In the meantime, the plant is held in place as the hairs grip(紧紧抓住)the soil.

The hairs are guided by a clever chemical trick. A protein(蛋白质) at the tip of the root hairs called RHD2 helps them to take calcium(钙) from the soil. Calcium makes the hairs grow, and produce more RHD2, and take more calcium.

But when an obstacle blocks the hair’s path, or the hair reaches the surface of the soil, the cycle is broken and growth starts in another direction.

This system gives plants the flexibility to explore a complex environment and to live in even the most unpromising soils, says Dolan.

In poor soils such as in parts of Australia and Africa, native plants have adapted by producing enormous numbers of root hairs. A better understanding of this adaptation will allow scientists to develop hairy rooted crops that can grow in unfriendly environments.

According to Dolan, “Research in the John Inners Center is taking a breeding approach to increase hair length in wheat but it will be some time before new cultivars(栽培变种) are developed.”

1.The passage is mainly about _______.