TOEFL Listening Practice: Lecture03
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MP3 – SoundCloud
Answer
- D
- A
- C
- Produces four: NO
Ejects spores: YES
Protrudes into air: NO
Contains pores: YES - C
- A
Transcript
| Professor: | Now, we’ve been talking about the different methods of reproductions in animals. Today I wanna begin talking about the spore dispersal of mushrooms. Now before we start talking about this topic, let’s take a closer look at a mushroom. So by definition, a mushroom is a structure produced by a fungus during its life cycle with the primary purpose to hold and release spores, which contain the necessary genetic information for reproduction. You can think of spores as fungi seeds. Mushrooms produce and drop millions of spores with the intention that some of them will germinate, fuse together, and grow into new mycelium. Yes! Anthony? |
| Anthony: | Humm..Hi Professor Can you tell me what mycelium is? |
| Professor: | I am glad you ask that. Mycelium is the organism from which mushrooms are created. To make a comparison, the mycelium is the tree, the mushrooms it produces are the apples, and the spores created by the mushrooms are the apple seeds. |
| Now I want all of you to take a look at the structure of a mushroom. You see a mushroom consists of a stalk topped by a flat or cup-shaped cap. On the underside of the cap, there are tissues that produce cells which produce spores. These spore-producing cells are found in several different structures. In the next class, I will examine these structures by individually starting with the gills, moving on to the pores, and ending with the teeth. Now in the remainder of this lecture when I mention the word gills, you know that it refers to one type of a structure found on on the underside of the mushroom’s cap. | |
| Here is the important part to remember. There are actually two different types of cells that produce spores: one is called basidia and the other is called asci. | |
| The basidia are held out from the gill surface and protrude into the air space between two gills. Thus, throughout their development, the spores are exposed to the atmosphere between the gills. Basidia produce four spores. When the spores are ready, they are discharged a short distance into the space between the gills. The spores then fall out of the cap and are carried away in the wind. Most spores land within three feet of the mushroom that produced them, but they can be carried much further. If the spore lands in a good spot, it germinates, producing the mycelium of a new individual fungus. | |
| With asci, the spores are fully contained within an outer covering. When the spores mature, the tip of the ascus breaks open and the spores are forcibly ejected through the top of the asci and are then carried away by the wind. | |
| Whether the spores are dispersed from basidia or asci, many people once thought that mushrooms reproduced by passively dropping their spores, after which the reproductive spores would hopefully get picked up by the wind or carried away by animals. But new research shows that mushrooms take a more active role in spreading their spores. They actually “make wind” to carry their spores about. Yes! Anthony? | |
| Anthony: | Hold on! How can mushrooms make wind if they can’t move? |
| Professor: | Well, they make wind by creating airflow, and they create airflow by allowing their moisture to evaporate. You see, a mushroom is essentially doing nothing to protect its water from completely evaporating. Evaporation allows them to cool off, as this phase changing from liquid water to water vapor uses up heat energy. You know that cold air is more dense than warm air, and has a tendency to flow and spread out so the evaporation also creates water vapor, which is less dense than air. The two forces help carry the spores out of the mushroom, and they give them a little lift. The lift can carry spores up to 4 inches both horizontally and vertically. Keep in mind, mushrooms often live on the forest floor, where wind wouldn’t be expected to reach them. The ability to create wind helps give the spores a better chance at finding a new, moist location to land on and to begin growing. |