小站备考
托福
托福听力
Delta 听力

红DeltaTest4听力The Role of Ethylene原文文本答案解析+音频录音mp3

展开
Tip:单击查看句义;划选/双击查生词

[00:00.00]W: Several of the processes related to growth and aging in plants involve the effects of hormones.[00:06.37]Today I’ll talk about two aging processes—the ripening of fruit and the falling of leaves in autumn.[00:13.43]These processes involve a hormone called ethylene.[00:18.07]What is ethylene? [00:20.50]It’s a chemical, a gas produced by plants as a hormone.[00:25.07]Ethylene is unique among plant hormones because it’s the only hormone that’s a gas.[00:31.41]The gaseous state is important because it enables ethylene to move through the plant.[00:37.69]Like all other hormones, ethylene triggers certain responses in the plant.[00:42.86]Ethylene is associated with a variety of aging processes.[00:47.44]One example of the aging process is the ripening of fruit.[00:52.26]The ripening of fruit involves several changes in structure and metabolism. [00:57.82]Some of these changes are aging processes.[01:00.91]One change is the weakening of cell walls, which softens the fruit.[01:06.29]Another is the decrease in chlorophyll content, which causes the fruit to lose its greenness.[01:12.38]Ethylene initiates or hastens both of these changes and also causes some ripened fruit to drop from the plant.[01:20.84]A chain reaction occurs during ripening, as ethylene triggers aging.[01:26.43]The aging cells then release more ethylene. [01:29.84]Because ethylene is a gas, the signal to ripen spreads from fruit to fruit.[01:35.24]You’ve heard the expression “One bad apple spoils the whole lot.”[01:39.24]Well, it really is true! Yes, Randy?
[01:42.97]M: So, when we buy fruit, like peaches that are still kind of green, and we store them in a plastic bag, and the peaches ripen faster—is this because of ethylene? [01:54.56] I mean, I think I get it. The bag traps the ethylene gas, and this speeds up the ripening.
[02:00.49]W: Right. That’s exactly what happens.[02:02.97]Ethylene accumulates inside the plastic bag, and this starts a chain reaction. [02:08.24]The signal to ripen spreads from one peach to another, and this causes all of the peaches to ripen faster.
[02:14.80]By the way, the role of ethylene was discovered in sort of an interesting way. [02:20.13]A century ago, citrus growers used to ripen fruit by “curing” it in sheds that were heated by kerosene stoves.[02:27.95] The growers thought it was the heat from the stoves that ripened the fruit. [02:31.93] However, they later discovered that the fruit didn’t ripen after they started using newer, cleaner-burning stoves.[02:39.13]Botanists figured out that the reason the fruit ripened in the sheds with kerosene stoves was because of ethylene—not heat—because, as it turns out, ethylene is a by-product of kerosene combustion.[02:52.85]Nowadays, a lot of fruit is ripened in huge storage containers that have ethylene gas piped in.[03:00.58]It’s a new variation on the old curing shed. [03:04.19]But in other cases, storage facilities have to slow down the ripening caused by natural ethylene. [03:10.54] For example, apples are stored in bins that are flushed with carbon dioxide. [03:15.94] Circulating the air with carbon dioxide prevents ethylene from accumulating, and carbon dioxide slows down the action of whatever ethylene isn’t flushed away.[03:26.85]This is how apples can be stored for several months before they’re shipped to supermarkets.
[03:32.23]Another aging process in plants where ethylene plays a role is the falling of leaves in autumn.[03:38.89]When a leaf falls from a tree, the breaking point is a layer near the base of the leaf’s stalk.[03:46.54]A change in the balance of two hormones—ethylene and auxin—controls the falling of leaves.[03:54.11] An aging leaf produces less and less auxin, a hormone that stimulates cell growth.[04:00.90] The drop in auxin makes the cells of the breaking layer more sensitive to ethylene.[04:06.54] As the influence of ethylene becomes stronger, the cells start producing enzymes that weaken the cell walls of the breaking layer.[04:15.54]Finally, with the help of wind or rain, the leaf breaks away at that layer and falls from the tree.

1.What is the lecture mainly about?

你的答案:
正确答案:A
题目解析:
 后才能查看题目解析,还没有账号? 马上注册
该教授主要讨论乙烯在植物老化过程中的作用。 教授说Several of the processes related to growth and aging in plants involve the effects of hormones. Today I’ll talk about two aging processes—the ripening of fruit and the falling of leaves in autumn. These processes involve a hormone called ethylene.

学习页面

Medi

terr

anean

加强 + 政府 + 名词后缀

加强的政府——管理

原文例句

加入生词

本文生词 0

色块区域是你收藏过的生词;

查询次数越多,颜色越深哦~

显示文中生词

登录后才能收藏生词哦,现在登录注册>

本文重点词 45

文中加粗单词为本文重点词;

根据词频与核心词范围精心挑选,托福考试必掌握词汇。

显示文中重点词
学习本文词汇

文中划选/双击的生词、加粗重点词已收纳至词盒

可随时点击词盒查看哦~

只有在词句精学模式下才能开启词盒功能哦~

我知道了

词盒
收藏
笔记
我的笔记
5000
保存
反馈