问题 选择题

植物通过叶片与外界进行气体交换,叶片结构中与气体交换密切相关的细胞是(  )

A.表皮细胞

B.保卫细胞

C.叶肉细胞

D.叶脉细胞

答案

气孔主要分布在叶片的下表皮,当气孔张开时,叶片内的水分吸收热量变成水蒸气,经气孔扩散到外界空气中.因此,气孔是植物体蒸腾失水的“门户”,也是植物体与外界进行气体交换的“窗口”.如图

保卫细胞壁因外侧较薄而内侧较厚,保卫细胞吸水时,细胞膨胀,细胞厚度增加,两细胞分离,气孔张开;保卫细胞失水时,细胞收缩,细胞厚度减小,两细胞并合,气孔闭合.所以保卫细胞的作用是控制气孔的开闭.

故选:B

阅读理解

In today’s throw away society, dealing with the city’s growing mountain of waste is an inereasing challenge for the city countil(市议会)。

Recently. Edinburgh is faced with the problem of dssposing of(处理)about250,000

Million tons of waster a year . Despite different ways to dispose of much of it in a green manner---largely through encouraging tecycling---its aging facilities such as the Powderhall landfill do not have the ability to deal with it.

The European Union(EU) has issued a new policy, regulating how such mountains of waster are to hr disposed of. The five councils (Edinburgh. East Lothian. West Lothian. Midlethian and Borders) face fine around $18million a year from 2013 it they don’t inerease recycling levels and rely less on landfill. With this in mind, the coumlls got together with the idea of building a lage incinerator plant (垃圾焚烧厂)to burn half of the waste produced in their districts. But the plan fell apart after the change of target levels by a new UK government waste policy which required that no more than 25% of the city’s waste should be disposed of in this way by 2025.

After the plan was abandoned, a private company which already transported millions of tons of the city’s wast by train to a landfill site near Dunbar, offered an alternative soution when it suggested opening a huge waste site near Portobello.

Since Powderhall is supposed to close in 2015, it seemed necessary for the members of the Edinburgh Council to accept the suggestion. But soon they turned it down—after 700 local objections reached them—because it would have meant hundreds of lorries a day making loud noise through heavily populated areas.

That still leaves eth council with a problem. By 2013,only50%of 1995 levels of waste will benllewed to be sent to landfill. Even if recveling large are met, there will still be a large amount of rubbish to be burnt up. Due build an Edinburgh and Midlothian councils have now decided to work together to build an ineinerator plant as time to find a solution is fast running out.

小题1:The main way of handling waste in a green manmer in Edinburgh is       .

A.recyeling

B.restoring

C.burying

D.burning小题2:The five councils worked out a plan to build an incinerator plant to       .

A.reduce the roast of burying waste

B.meets the EU requirements

C.speed up waste recycling

D.tempter landfill sites小题3:The city council of Edinburgh rejected the suggestion to open a huge landfill site near Portobello because     .

A.a name from a private company

B.the comelier was not interested in it

C.it was not supports by EU

D.the local poodle was waist it小题4:What is the final dream an Edinburgh and Midlothian Country?

A.To open a new landfill nearby

B.To close the powder hall landfill in 2015

C.To set up a plan for burning waste

D.To persuade people to deduce their waste.

单项选择题