Practice these TOEFL iBT listening tests to help you score high in the TOEFL Listening Section. Check the correct answers and audio transcripts below. This video is in the series of NEW TOEFL iBT Tests 2015.
Listen to part of a talk in a botany class.
Professor
OK. So we’ve talked about some different types of root systems of plants, and I’ve
shown you some pretty cool slides, but now I want to talk about the extent of the root
system—the overall size of the root system . . . the depth. I want to tell you about one
particular experiment. I think you’re going to find this pretty amazing. OK. So there
was this scientist . . . this very meticulous scientist decided that the best place to see a
whole root system—to actually see how big the entire system got—the best place
would be to grow it . . . where?
Female Student
Um, water?
Professor
In water. So he took rye plants—it was rye plants—and he started growing them in
water. Now, you’ve all heard of growing stuff in water before, right?
Male Student
It’s done commercially, right? Uh, like to grow vegetables and flowers?
Professor
Right. They grow all kinds of commercial crops in water. So, if you’re growing things
in water, you can add the fertilizer. What do you need to do to that water besides put
fertilizer in it? Anyone ever actually tried to grow plants in water? You must bubble
water through it. Bubble gas through it. I’m sorry, you must bubble gas through it. So,
gas, you have to bubble through. Think about the soil we talked about last week,
about growing plants in soil. Think about some of you who have killed your favorite
houseplants, ‘cause you loved them too much. If you overwater, why do your favorite
houseplants die?
Female Student
Oh, no oxygen.
Professor
Not enough oxygen for the roots . . . which do what twenty-four hours a day in all seasons?
Female Student
Respiration?
Professor
Respire . . . respiration . . . they breathe. So, if you just stick rye plants in water, it
doesn’t make a difference how much fertilizer you add, you also need to bubble gas
through the water, so they have access to that oxygen. If they don’t have that, they’re
in big trouble. OK. So this guy—this scientist—grew a rye plant in water so he could
see the root system how big it got—its surface area. I read about this and the book
said one thousand kilometers of roots. I kept thinking: this has to be a mistake. It just
doesn’t make any sense to me that . . . that . . . that could be right. But that’s what all
the books have, and no one’s ever corrected it. So, let me explain to you about this rye
plant. If you take a little seed of many grasses—and remember rye is a grass; if you
take a tiny little seed and you germinate it—actually, take one of my least favorite
grasses that starts growing about May. What’s my least favorite grass that starts
growing about May?
Male Student
Crabgrass.
Professor
Crabgrass.
Remember how I showed you in the lab, one little seed starts out producing one
little shoot. Then at a week or so later you’ve got about six shoots, and then, three
weeks later you’ve got about fifteen shoots coming out all directions like this—all
those little shoots up there? Well, that’s what they did with the rye. And the little
seedling started and pretty soon there were several shoots, and then more shoots. In
the end, that one single seed produced eighty shoots, with an average of fifty centimeters
of height . . . from one seed. Eighty shoots coming out, average fifty centimeters
high. When they looked at the shoot versus the root surface, they found that the
shoot surface, with all of its leaves, had a total surface area of about five square
meters. Now, here’s the biggie, when they looked at the root surface area, you would
expect that the root and the shoot would be in balance, right? So, they should be
pretty close in terms of surface area, right?
Male Student
Uh-un.
Professor
What’s that? Did somebody say “no”? Well, you’re absolutely correct. Instead of five
square meters, the root system was found to have more than two hundred square
meters of surface area. Where did all of that extra surface area come from? Who did
it? Who was responsible for all those extra square meters of surface area? What did
roots do to increase their surface area?
Female Student
Root hairs.
Professor
Root hairs, that’s exactly it. So those root hairs were responsible for an incredible
chunk of surface area. They constantly have to be spread out in the water so they can
absorb minerals from the fertilizer, and of course they need oxygen access as well.
Correct Answers:
1. A
2. C
3. A
4. B
5. C
6. D