Directions: Now answer the questions.
1. What is the main purpose of the lecture?
A. To discuss environmental phenomena that have changed the phosphorus cycle
B. To illustrate how interrupting the phosphorus cycle can affect the environment
C. To describe how phosphorus ends up in the atmosphere
D. To explain how phosphorus gets recycled in the environment
2. Which human activities that influence the phosphorus cycle does the professor mention? Choose 2 answers.
B. Building dams on rivers
C. Polluting the oceans
D. Making and using fertilizer
3. Why does the professor discuss underwater volcanoes?
A. To describe the location of most of the phosphorus on Earth
B. To point out the difficulty of studying the phosphorus cycle
C. To describe a step in the phosphorus cycle
D. To illustrate the differences between two phases in the phosphorus cycle
4. What can be inferred about the professor’s view on phosphorus getting washed into rivers?
A. She is unconcerned because phosphorus is a beneficial nutrient.
B. She is concerned about the quantity of phosphorus entering the waterways.
C. She thinks that the amount of research conducted on the topic is excessive.
D. She is frustrated that most of her students are unaware of the phenomenon.
5. What comparison does the professor make involving phosphorus and nitrogen?
A. Sediment on the ocean floor contains more nitrogen than phosphorus.
B. The atmosphere contains more nitrogen than phosphorus.
C. Nitrogen requires more time to get recycled than phosphorus does.
D. Phosphorus is more important than nitrogen to the development of fish.
6. Listen to Track
A. She realizes that the students are struggling with the concept.
B. She is surprised that the student knew the answer to her question.
C. She thinks that the answer to the question is obvious.
D. She thinks that this phase of the cycle has an unusual name.
Listen to part of a lecture in an ecology class.
So we’ve been talking about nutrients, the elements in the environment that are essen-tial for living organisms to develop, live a healthy life, and reproduce. Some nutrients are quite scarce; there just isn’t much of them in the environment, but fortunately, they get recycled. When nutrients are used over and over in the environment, we call that a nutrient cycle. Because of the importance of nutrients and their scarcity, nutrient recy-cling is one of the most significant ecosystem processes that we’ll cover in this course.
The three most important nutrient cycles are the nitrogen cycle, the carbon cycle, and the one we’re gonna talk about today, the phosphorus cycle.
So, the phosphorus cycle has been studied a lot by ecologists because, like I said, phos-phorus is an important nutrient, and it’s not so abundant. The largest quantities are found in rocks and at the bottom of the ocean. How does phosphorus get there? Well, let’s start with the phosphorus in rocks. The rocks get broken down into smaller and smaller par-ticles as they’re weathered—they’re weathered slowly by rain and wind over long periods of time. Phosphorus is slowly released as the rocks are broken down, and it gets spread around into the soil. Once it’s in the soil, plants absorb it through their roots.
So that’s the reason people mine rocks that contain a lot of phosphorus? To help with agriculture?
Uh-huh. They mine the rock, artificially break it down, and put the phosphorus into agricultural fertilizers. So humans can play a role in the first part of the phosphorus cycle—the breaking down of rocks and the spreading of phosphorus into the soil—by speeding up the rate at which this natural process occurs, you see?
Now. … after the phosphorus is in the soil, plants grow, they use phosphorus from the soil to grow. And when they die, they decompose, and the phosphorus is recycled back into the soil. Same thing with the animals that eat those plants … or eat other animals that have eaten those plants. We call all of this the land phase of the phosphorus cycle. But, a lot of the phosphorus in the soil gets washed away into rivers by rain and melting snow. And so begins another phase of the cycle. Can anyone guess what it’s called? Nancy?
Uh, well, if the one is called the land phase, then this has to be called the water phase, right?
Yes. That’s such a difficult point, isn’t it? In a normal water phase, rivers eventually empty into oceans, and once in the oceans, the phosphorus gets absorbed by water plants like algae. Then fish eat the algae … or eat other fish that have eaten those plants.
But the water phase is sometimes affected by excessive fertilizers. If not all of the phos-phorus gets used by the crops, and large amounts of phosphorus gets into the rivers, this could cause rapid growth of water plants in the river, which can lead to the waterways getting clogged with organisms, which can change the flow of the water … Several cur-rent studies are looking at these effects, and I really do hope we can find a way to deal
with this issue before these ecosystems are adversely affected.
OK? Of course another way that humans can interrupt the normal process is fishing. The fishing industry helps bring phosphorus back to land. In the normal water phase, the remaining phosphorus makes its way—settles—to the bottom of the ocean and gets mixed into ocean sediments.
But remember, this is a cycle: the phosphorus at the bottom of the ocean has to some-how make its way back to the surface . . to complete the cycle, to begin the cycle all over again. After millions of years, powerful geological forces, like underwater volcanoes, lift up the ocean sediments to form new land. When an underwater volcano pushes sub-merged rock to the surface, a new island is created. Then, over many more years, the phosphorus-rich rocks of the new land begin to erode … and the cycle continues.
What about … well, you said that the nitrogen cycle is also an important nutrient cycle.
And there’s a lot of nitrogen in the atmosphere, so I was wondering: Is there a lot of phosphorus in the atmosphere too?
Good question, George. You’re right to guess that phosphorus can end up in Earth’s atmosphere … it can move from the land or from the oceans to the atmosphere, and vice versa. However, there’s just not a substantial amount of it there, like there is with nitrogen. It’s a very minimal quantity.
Listen again to part of the lecture. Then answer the question.
Can anyone guess what it’s called? Nancy?
Uh, well, lithe one is called the land phase, then this has to be called the water phase, right?
Yes. That’s such a difficult point, isn’t it?
What does the professor mean when she says this:
That’s such a difficult point, isn’t it?