戴爾美語---托福聽力考滿分秘訣- TPO 19 解題示範

Marine Biology (Plant Life in Salt Marshes)

Professor

Ok, today we are going to continue our discussion of plant life in coastal salt marshes of North America.

Salt marshes are among the least inviting environments for plants. The water is salty, there is little shade and the ocean tide comes in and out, constantly flooding the marsh, so the variety of plants found in salt marshes is limited, but there is a plant genus that thrives there, the Spartina.

In fact, the Spartina genus is the dominant plant found in salt marshes. You can find one type of the Spartina, Saltmarsh Cordgrass, growing in low marsh areas. In higher marsh areas, you are likely to find a Spartina commonly called salt-meadow hay. (1) So how is the Spartina able to survive in an environment that would kill most plants? Well, it is because salt marsh grasses have found ways to adapt to the conditions there.

First of all, they are able to withstand highly saline conditions. One really interesting adaptation is the ability to reverse the process of osmosis. Typically, the process of osmosis works... Well, when water moves through the wall of a plant cell, it will move from the side containing water with the lowest amount of salt into the side containing the highest amount of salt. So imagine what would happen if a typical plant suddenly found itself in salt water. The water contained in the plant cells, that’s water with very little salt, would be drawn out toward the seawater, water with a lot of salt. So you can see the fresh water contained in the plant will be removed and the plant will quickly lose all its water and dehydrate. But what about the Spartinas? Well, they allow a certain amount of salt to enter their cells, bringing the salt content of the water within the plant, to a slightly higher concentration than that of the surrounding seawater. (2) So instead of fresh water moving out of the plant cells, salt from the seawater enters, reverse osmosis, and this actually strengthens the cells.

Another adaptation to the salty environment is the ability to excrete excess salt back to the environment. That’s why you might see a Spartina shimmering in the sunlight. (6) What’s reflecting the light is not salt from seawater that has evaporated, although that’s a good guess. But it is actually the salt that came from within the plant. Pretty cool, eh? You can really impress your friends and family with that little tidbit the next time you are in a salt marsh. 

But coping with salt is not the only challenge for plants in the salt marsh. Soil there is dense and very low in oxygen, so Spartinas have air tubes, air enters through tiny openings on the leaves, the tubes provide direct pipe line for oxygen, carrying it down the leaves, through the stems and into the roots, where it is needed. (3) If you pull up a Spartina, you might even notice some reddish mud on some of the roots. This is caused by oxygen reacting with iron sulfide in the soil, and it produces iron oxide or rust.

Now, although the Spartinas have adapted several chemical and physical mechanisms that allow them to thrive in salt water and to feed oxygen to their roots. (4) There is yet another aspect of the harsh environment that they have to adapt to, the force of the tides and occasional violent storms. Wind and water are constantly crashing into these plants. So as you might have guessed, they have developed a means of solidly anchoring themselves into the soil. How? Well, they have tough sort of underground stems called rhizomes. Rhizomes from one plant grow through the muddy soil and interlock with those of other nearby plants. The plants form a kind of colony, a community that will survive and perish together. Because alone as single plants, they cannot survive. Of course the plants in these colonies also need tough resilient stems above the soil, stems that can bend a lot but not break as water constantly crashes into them.

(5) So in addition to the interlocking underground rhizomes, they have yet another adaptation, and it’s ... well, we are back to reverse osmosis again, by adjusting the osmotic pressure so that the cells are always fully inflated. The plant is able to withstand great pressure before snapping, so Spartinas may look like simple marsh grass, but they are really a wonder of chemistry, physics and structural engineering that allows them to survive and even thrive in an environment in which most other plants will wilt and die within hours.

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題目(共6題)：

1. What is the lecture mainly about? 

A. The effect of the tidal flow on the salt marsh 

B. Ways that some plants have adapted to living in salt marshes

C. The process of osmoses in plants 

D. Differences between plants that grow in salt marshes and plants that grow

   elsewhere

答案：B

解析：Professor: ...... So how is the Spartina able to survive in an

environment that would kill most plants? Well, it is because salt marsh grasses have found ways to adapt to the conditions there.  

在教授的自問自答中，說明講座的主題是Spartina能在鹽沼中生活的原因，就是因為找到適應環境的方式。

關鍵訊號詞：how is the Spartina able to ...... / it is because......

2. What is one result of reverse osmosis in the spartina?

A. Salt from sea water strengthens the plant's cells.

B. All parts of the plant are able to receive oxygen.

C. Salt evaporates oil the stems and leaves of the plant.

D. Water is unable to move across the plant cell wails.

答案：A

解析：Professor: ...... So instead of fresh water moving out of the plant cells, salt from the seawater enters, reverse osmosis, and this actually strengthens the cells.

從教授講解中可知，reverse osmosis會強化細胞。

關鍵訊號詞：instead of ...... / this actually ......

3. Why does the professor mention reddish mud on the roots of a spartina?

A. To illustrate the high density of salt-marsh soil 

B. To explain how spartina rhizomes move through the soil 

C. To point out the problems spartinas face in getting fresh water

D. To provide evidence that oxygen is present in the spartina s roots

答案：D

解析：Professor: ...... If you pull up a Spartina, you might even notice some reddish mud on some of the roots. This is caused by oxygen reacting with iron sulfide in the soil, and it produces iron oxide or rust.  

教授說明Spartina的根部會出現reddish mud是因為iron sulfide與oxygen的反應會產生iron oxide or rust，藉此佐證spartina的根部存在oxygen。

 

關鍵訊號詞：This is caused by ......

4. In what way are rhizomes important for spartinas?

A. They allow plants to remain cool in direct sunlight 

B. They reduce the possibility of plants being uprooted during storms

C. They help plants in dense soil process oxygen. 

D. They reduce the concentration of salt in the surrounding seawater.

答案：B

解析：Professor: ...... There is yet another aspect of the harsh environment that they have to adapt to, the force of the tides and occasional violent storms. Wind and water are constantly crashing into these plants. So as you might have guessed, they have developed a means of solidly anchoring themselves into the soil. How? Well, they have tough sort of um ... underground stems called rhizomes. 

教授說明spartinas通過rhizomes能牢牢地將自己固定在土壤中。

關鍵訊號詞：another aspect of ...... / How? ......

5. What can be inferred about the process that prevents spartinas from breaking in violent storms? 

A. It is the same process that helps them survive being immersed in saltwater.

B. The process is also responsible for causing their air tubes to form.

C. The process sometimes damages their rhizomes.

D. Many other pants have developed a similar process.

答案：A

解析：Professor: ...... So in addition to the interlocking underground rhizomes, they have yet another adaptation, and it’s ... well, we are back to reverse osmosis again教授重提之前的reverse osmosis，而reverse osmosis就是幫助Spartinas在鹽水中生存的機制。  

關鍵訊號詞：they have yet another ......

6. Why does the professor say this?

(Professor: ... What’s reflecting the light is not salt from seawater that has evaporated, although that’s a good guess. But it is actually the salt that came from within the plant.)

A. To point out an incorrect conclusion

B. To clarify the meaning of a term 

C. To admit that there is little evidence of the phenomenon she just described

D. To emphasize the difference between a fact and an opinion

答案：A

解析：

Professor: ... What’s reflecting the light is not salt from seawater that has evaporated, although that’s a good guess. But it is actually the salt that came from within the plant.

教授表示雖然前面是個不錯的猜想，但是結論缺不正確。在but之後開始闡述正確的結論。

關鍵訊號詞：although ...... / But it is actually ......

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