Narrator: Listen to part of a lecture in an ecology class.
Professor: Mutualism is a relationship between two organisms in which both organisms benefit in some way. They may share resources—one may provide water while the other provides food. For example, our bodies have bacteria in our guts that break down food and provide us with essential vitamins and nutrients, while the bacteria is nourished by that very food. Let’s take what you read for this week and see if we can apply mutualism to it. Who can give me a couple of examples of mutualism? Tom?
Male Student: Well, uh, how about fungus… plants and fungus?
Professor: Good example. Please, go on.
Male Student: Well, like, the mycorrhiza… the symbiotic relationship between a fungus and a plant. There is a mutualistic relationship between the fungus and the plant, right?
Professor: Nice. Mycorrhiza is a mutualistic relationship that exists between fungi and a vast majority of plant species on Earth. Good. Can you name another kind of mutualistic relationship that a plant can have with a fungus?
Female Student: OK, well, I’m not sure if algae are plants or not… but don’t fungi interact with algae? I think it’s called a lichen.
Professor: And that relationship does what? Tell me more.
Female Student: The fungus needs food. So it benefits from the sugar that the algae create through photosynthesis. And then the algae benefit from the stable structure that the fungus provides through its, um… filaments.
Professor: Good. That’s great. So now, let’s return to the first kind of mutualism that Tom mentioned—the mycorrhizal relationship that exists between fungus and most of the Earth’s plants. In this relationship, the fungus provides access to water, or moisture, because the fungus is highly absorbent. And also, it provides access to nutrients that aren’t available to the plant unless the fungus is there. In exchange, the fungus receives carbohydrates from the plant. So what do you think happens if you own a plant, and you give your plant soil and water? If there is fungus in the soil, will it still have a mutualistic relationship with the plant?
Female Student: Well, not necessarily. It won’t if the plant no longer needs to have a mutualistic relationship with the fungus, because it’s already being provided water and nutrients.
Professor: OK, good. So this is a great example of how humans can alter relationships and ecosystems—by changing the relationships between organisms, including microorganisms. Hypothetically, what might happen if we created a product that killed all fungi?
Male Student: Maybe a lot of plants would die?
Professor: Maybe. Or at least, they’d have to find another way to obtain the water and nutrients that the fungi were making available to them. Let’s move on… what other kinds of relationships can exist between organisms? We’ve talked about mutualism… there were two more kinds of relationships mentioned in your reading this week.
Male Student: Commensalism and parasitism.
Professor: Can you define those terms for me? And maybe give an example of each, please?
Male Student: Commensalism is when one organism benefits without harming or helping the other one. So an example would be, um, those fish that ride on sharks. The sharks provide the fish with transportation, but the fish don’t hurt or help the sharks. And parasitism is when an organism benefits at the expense of the other. So one organism is getting something out of the relationship, which harms the other. An example of that… hmm… well, like a bad bacteria? In humans? Anything that would make you sick, I guess. Say, malaria.
Professor: Nice work. So to sum up what we covered today, when we’re looking at how organisms relate, it’s important not to see microorganisms like bacteria or fungi as all good or all bad. It depends on the nature of their interactions, and many of those relationships are necessary for the survival of entire species. In this way they’re actually—they can be—critical to maintaining ecological balance.
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What does the class mainly discuss? |
Gist-content. The class discusses three different kinds of relationships that organisms can have with one another—mutualism, commensalism, and parasitism. |
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| ✗ | A How fungi choose certain plants with which to form mutualistic relationships |
The professor does not cover differences among specific plants, or fungi choosing among these plants. |
| ✗ | B The impact that human beings have on plant life |
This issue is discussed in an example given in the lecture, but it is not the main focus of discussion. |
| ✗ | C The role of a particular plant species in an ecosystem |
The discussion is not about a particular plant species. |
| ✓ | D How organisms in an ecosystem are affected by one another |
Correct. The discussion is about the ways in which organisms in an ecosystem can affect each other. |
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According to the professor, which of the following is true of the mycorrhizal relationship between fungi and plants? |
Detail. The professor states that the mycorrhizal relationship exists between fungi and “a vast majority” of the world’s plants. |
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| ✗ | A It is uncommon in plant life. |
The opposite is true. The professor states that this relationship exists between fungi and “a vast majority” of the world’s plants. |
| ✓ | B The mycorrhizal relationship is widespread among the Earth’s plants. |
Correct. The phrase “a vast majority” means that the phenomenon is widespread. |
| ✗ | C The mycorrhizal relationship between fungi and plants is not well understood. |
The professor does not suggest this in the lecture. |
| ✗ | D The fungi not involved in a mycorrhizal relationship die more readily. |
The professor does not suggest this in the lecture. |
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Which of the following is an example of mutualism? |
Detail. According to the professor, mutualism is a relationship between two organisms in which both organisms benefit from the relationship. |
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| ✗ | A Fungi and plants occupying separate environments in an ecosystem. |
This is not an example of mutualism. |
| ✗ | B Plants benefit from the presence of fungi, but fungi do not benefit from the presence of plants. |
This is an example of commensalism, not mutualism. |
| ✗ | C Plants provide oxygen to fungi, while the fungi provide benefits to a different organism. |
This three-part relationship is not an example of mutualism. |
| ✓ | D Plants provide carbohydrates to fungi, while the fungi provide plants with access to water and nutrients. |
Correct. This is an example of mutualism that is discussed in the lecture. |
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According to the professor, what is a possible impact of human behavior on ecosystems? |
Detail. The professor states that human behavior can affect the balance of ecosystems by influencing the relationships between other organisms. |
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| ✓ | A It can influence relationships between other organisms. |
Correct. The example the professor gives is of a human providing a plant with soil and water. She notes that this can influence the relationship between the plant and fungi in the soil. |
| ✗ | B It often leads to the destruction of entire ecosystems. |
The professor does not indicate anything this extreme in the lecture. |
| ✗ | C It is the cause of an overall decrease in biodiversity. |
This idea is not mentioned in the lecture. |
| ✗ | D It can encourage new species to develop. |
This idea is not mentioned in the lecture. |
Narrator: Listen again to part of the lecture. Then answer the question.
Professor: So this is a great example of how humans can alter relationships and ecosystems—by changing the relationships between organisms, including microorganisms. Hypothetically, what might happen if we created a product that killed all fungi?
Narrator: Why does the professor say this:
Professor: Hypothetically, what might happen if we created a product that killed all fungi?
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Why does the professor say this? |
Function of What Is Said. In this quote, the professor discusses human intervention in a relationship between organisms. She mentions this in order to invite the students to consider one possible outcome of this intervention. |
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| ✗ | A To suggest that human beings are rarely destructive toward plants |
The professor does not suggest this in the highlighted quote. |
| ✗ | B To defend human behavior with regard to caring for plants |
The professor does not suggest this in the highlighted quote. |
| ✓ | C To introduce a theoretical situation for the purpose of discussion |
Correct. The word “hypothetical” means it has not happened, although it could. |
| ✗ | D To illustrate a way human behavior might benefit plants |
Nothing in the lecture suggests that this hypothetical situation might benefit plants. |
Narrator: Listen again to part of the lecture. Then answer the question.
Professor: Hypothetically, what might happen if we created a product that killed all fungi?
Male Student: Maybe a lot of plants would die?
Professor: Maybe. Or at least, they’d have to find another way to obtain the water and nutrients that the fungi were making available to them.
Narrator: What does the professor imply when she says this:
Professor: Or at least, they’d have to find another way to obtain the water and nutrients that the fungi were making available to them.
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What does the professor imply when she says this? |
Inference. In this quote, the professor suggests that killing fungi could have a negative impact on plants. This could especially be true in the absence of an alternative source of water and nutrients. |
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| ✗ | A Plants would benefit from humans in lieu of fungi. |
The professor’s statement does not imply that plants would benefit from humans in any way. |
| ✗ | B The death of plants would cause land to become uninhabitable for humans. |
Nothing in the lecture suggests this possibility. |
| ✓ | C The elimination of fungi could damage plants, unless plants find another source of nutrition. |
Correct. The professor implies that killing fungi could indirectly cause damage to plants that depend upon fungi for water and nutrients. |
| ✗ | D The most efficient way to destroy plants is to remove fungi from their habitats. |
The professor does not suggest anything about the efficiency of different methods of destroying plants. |