首页
登录
职称英语
Atmospheric pressure can support a column of water up to 10 meters high. But
Atmospheric pressure can support a column of water up to 10 meters high. But
游客
2024-02-23
34
管理
问题
Atmospheric pressure can support a column of water up to 10 meters high. But plants can move water much higher. the sequoia tree can pump water to its very top, more than 100 meters above the ground. Until the end of the nineteenth century, the movement of water in trees and other tall plants was a mystery. Some botanists hypothesized that the living cells of plants acted as pumps. But many experiments demonstrated that the stem of plants in which all the cells are killed can still move water to appreciable heights. Other explanations for the movement of water in plants have been based on root pressure, a push on the water from the roots at the bottom of the plant. But root pressure is not nearly great enough to push water to the tops of tall trees. Furthermore, the conifers, which are among the tallest tress, have unusually low root pressures.
If water is not pumped to the top of a tall tree, and if it is not pushed to the top of a tall tree, then we may ask.. How does it get there? According to the currently accepted cohesion-tension theory, water is pulled there. The pull on a rising column of water in a plant results form the evaporation of water at the top of the plant. As water is lost form the surface of the leaves, a negative pressure, or tension, is created. The evaporated water is replaced by water moving from inside the plant in unbroken columns that extend from the top of a plant to its roots. The same forces that create surface tension in any sample of water are responsible for the maintenance of these unbroken columns of water. When water is confined in tubes of very small bore, the forces of cohesion(the attraction between water molecules)are so great that the strength of a column of water compares with the strength of a steel wire of the same diameter. This cohesive strength permits columns of water to be pulled to great heights without being broken. [br] According to the passage, why does water travel through plants in unbroken columns?
选项
A、Root pressure moves the water very rapidly.
B、The attraction between water molecules is strong.
C、The living cell of plants push the water molecules together
D、Atmospheric pressure supports the columns.
答案
B
解析
主旨题。根据原文,为什么水以不断水柱的形式在植物中运输?A项根压使水移动得很快。B项水分子之间的力很强。C项植物的活细胞将分子推到一起。D项大气压支撑水柱。
转载请注明原文地址:https://tihaiku.com/zcyy/3476026.html
相关试题推荐
WhydoestheFoundationconcentrateitssupportonbasicratherthanapplied
Zoosareunderalotofpressurethesedaystojustifytheirexistence.Int
Zoosareunderalotofpressurethesedaystojustifytheirexistence.Int
Zoosareunderalotofpressurethesedaystojustifytheirexistence.Int
Atmosphericpressurecansupportacolumnofwaterupto10metershigh.But
Atmosphericpressurecansupportacolumnofwaterupto10metershigh.But
Atmosphericpressurecansupportacolumnofwaterupto10metershigh.But
[originaltext]Religiousandprivateschoolsreceivelittleornosupportfr
[originaltext]Religiousandprivateschoolsreceivelittleornosupportfr
Forthispart,youareallowed30minutestowriteacampaignspeechinsupport
随机试题
[originaltext]M:I’mafraidIdidn’tearthwhatDr.Brownwassayingjustnow.
[audioFiles]audio_eufm_j01_295(200910)[/audioFiles]A、Heusuallytalksquietly.
Itishardtogetanyagreementontheaccuratemeaningoftheterm"social
TheStudentUnionhasrecentlyagreedtosetupanEnglishClub.Itaimsto
从文体上说,公文不属于( )。A.记叙文 B.说明文 C.议论文 D.实
某建筑施工单位聘请张某担任钢筋工,双方签订劳动合同,约定劳动试用期4个月,4个月
信托的设立至少应当包括的构成要素有()。A.信托目的 B.信托行为 C.信
肝阳上亢证与肝火炽盛证的鉴别依据是A.头重足飘B.急躁易怒C.眩晕耳鸣D.头目胀
纳税人的下列行为中,应当按纳税人同类应税消费品的最高销售价格作为计税依据计征消费
施工合同履行中,由于设计变更需要确定变更价款,而报价单中没有适用于变更工作的单价
最新回复
(
0
)