Narrator: Listen to part of a lecture in a biology class. The class has been learning about animal adaptations.
Professor: Alright, let’s continue the discussion from last class… we were talking about defense mechanisms, or means of self-protection, that animals have developed to defend themselves. These anti-predator adaptations come in a wide variety of forms… and serve many purposes.
For example, some mechanisms might allow an animal to avoid detection… others might startle or distract a predator… or even help the animal escape quickly. And, well… some animals have developed ways of fighting back or physically defending themselves when attacked. Some even have their own “weapons”… now what might those look like?
The most obvious are probably the physical structures you see… say, horns… or claws. Of course, most of these are used by predators to attack prey, but these features can also be used for defense, um—used as defense mechanisms! Take spines—sharp, needle-like structures—a good example here is the African crested porcupine. These rodents are only about 75 centimeters in length, but they are almost entirely covered with spines. The spines covering the animal’s sides—and back—are each over 30 centimeters long, and they are extremely sturdy.
Now, porcupines are herbivores… which means, well… they only eat plants. So the spines are clearly not for attacking prey. But they definitely know how to use them to defend themselves! When disturbed, the porcupine initially tries to “puff up”… to appear larger, to scare off the predator. But if that doesn’t work, well… they attack. The porcupine will actually run backwards toward the attacker, trying to stab them with the sturdier spines found on their backside. Now, remember, these animals aren’t even 1 meter long, and weigh no more than 25 or 30 kilograms… but they are able to kill leopards, lions, and even humans if they need to defend themselves.
OK… but not all defense mechanisms are visible, like spines or horns. Some animals use chemical warfare… venom or other poisonous chemicals. These toxins might be housed inside structures already made for defense… fangs and spines are great examples. But sometimes the venom might simply cover the skin of the animal… an attacker would taste the chemical before actually eating the animal.
Here is something really fascinating though. There are a couple of animals that use other animals as weapons. One such animal is the blanket octopus.
So, a fully mature female can grow to be almost 2 meters long. However, the males only grow to be a few centimeters long… it actually took scientists decades to figure out that there even were males, because no one could ever find them! Now, the full grown females can spread out their blanket-like body to scare off potential predators, but the smaller males and the immature females need a little more help. As it turns out, the blanket octopus is immune to the venom found in the highly poisonous Portuguese man-of-war. The octopus actually hunts the man-of-war for its poisonous tentacles—a Portuguese man-of-war has several of them. The octopus tears off a tentacle, and then carries it around to whip anything that tries to attack.
And if you thought that was an innovative weapon, then you’ll appreciate the boxer crab, also called the pom-pom crab. They get their name because they carry a certain stinging sea anemone—a Triactis producta—around in each claw. The anemones look like little pom-poms, or puffy boxing gloves, but are actually thought to be among the most poisonous of the sea anemone family. The crab uses these living pom-poms to sting its attackers. The sea anemone gets a pretty good deal too – by getting carried around, it has better access to floating food particles.
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What is the lecture mainly about? |
Gist-content. The professor discusses the use of weapons by animals as a defense mechanism. |
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| ✓ | A The use of a defense mechanism by various animals |
Correct. The lecture primarily discusses the use of weapons by animals in self-defense. |
| ✗ | B Predators that threaten the African crested porcupine |
Some potential predators of the African crested porcupine are mentioned, but this is not the focus of the lecture. |
| ✗ | C One way that animals avoid detection by predators |
Avoiding detection is mentioned, but this is not the main topic discussed in the lecture. |
| ✗ | D The application of animal toxins in medicine |
This topic is not mentioned in the lecture. |
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According to the lecture, what are three weapons used by animals to protect themselves from attack? Choose 3 answers. |
Detail. Various animal weapons are discussed throughout the lecture. |
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| ✗ | a Quick evasion |
This is mentioned as a defense mechanism, but not as a weapon. |
| ✓ | b Toxins |
Correct. The presence of toxins in spines, in fangs, or even on the skin was discussed. |
| ✓ | c A poisonous sea anemone |
Correct. The example of the boxer crab using a poisonous sea anemone as a weapon was given. |
| ✗ | d Avoidance of detection |
This is mentioned as a defense mechanism, but not as a weapon. |
| ✓ | e Spines |
Correct. The example of the African crested porcupine using its spines to stab predators was given. |
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According to the lecture, when do African crested porcupines attack? |
Detail. The professor notes that generally, African crested porcupines first attempt to “puff up,” to appear larger than they are, in an attempt to scare off predators. If that doesn’t work, the porcupine will attack the predator. |
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| ✗ | A Only when faced with predators larger than themselves |
The size of the African crested porcupine is discussed, but not the size of its predators. |
| ✗ | B Only once they are fully grown |
The age at which the African crested porcupine attacks was not mentioned in the lecture. |
| ✓ | C When their attempts to scare a predator away fail |
Correct. The first defense is to puff up, in order to scare the predator away. If this does not work, they will attack. |
| ✗ | D Whenever they are startled by a potential predator |
The professor indicates that they generally attempt to scare the predator away first, by puffing up. |
Narrator: Why does the professor say this:
Professor: And, well… some animals have developed ways of fighting back or physically defending themselves when attacked. Some even have their own “weapons”… now what might those look like?
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Function of What Is Said. In this quote, the professor explains the use of weapons by animals in self-defense. She then rhetorically asks what these weapons might look like, in order to pivot to introducing examples of such weapons. |
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| ✗ | A To admit a flaw in her own logic |
She is not pointing out any flaws in her own logic in this quote. |
| ✗ | B To express momentary confusion |
The professor does not indicate any confusion in this quote. |
| ✗ | C To ask students to describe how animal weapons look |
By asking “now what might those look like?”, the professor is not actually inviting students to give a physical description of animal weapons. She is rhetorically introducing her next topic. |
| ✓ | D To introduce the next topic |
Correct. The professor is asking the question rhetorically, as a way to introduce her next topic of discussion—some examples of animal weapons. |
Narrator: Why does the professor say this:
Professor: Here is something really fascinating though. There are a couple of animals that use other animals as weapons.
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Function of What Is Said. In this quote, the professor is introducing an unusual concept—the use, by animals, of other animals as weapons. |
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| ✗ | A To question whether a fascinating theory should be trusted |
The professor is not discussing the issue of whether to trust this fascinating theory. |
| ✗ | B To emphasize the importance of further study in this area |
She is not emphasizing any need for further study. |
| ✗ | C To explain how certain animals use fangs effectively |
The professor has previously discussed fangs, and is now transitioning to a new topic. |
| ✓ | D To present an unexpected type of defense mechanism |
Correct. The professor indicates that it is “fascinating,” and thus unexpected, that some animals use other animals as a weapon. |
Narrator: Listen again to part of the lecture. Then answer the question.
Professor: Now, porcupines are herbivores… which means, well… they only eat plants. So the spines are clearly not for attacking prey. But they definitely know how to use them to defend themselves! When disturbed, the porcupine initially tries to “puff up”… to appear larger, to scare off the predator.
Narrator: What does the professor imply when she says this:
Professor: When disturbed, the porcupine initially tries to “puff up”… to appear larger, to scare off the predator.
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Inference. In this quote, the professor begins by talking about a porcupine’s spines, but then says that “the porcupine initially tries to ‘puff up’… to appear larger, to scare off the predator.” The implication is that these porcupines will generally try to scare a predator away initially, and will only attack with their spines if that tactic fails. |
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| ✗ | A The porcupine is typically successful at scaring off predators. |
The degree of success of this initial tactic is not mentioned. |
| ✗ | B The porcupine prefers to escape detection or run away from predators. |
Escaping detection and running away are not mentioned as defense mechanisms used by the porcupine. |
| ✓ | C The porcupine is likely to attempt to scare a potential predator away before attacking. |
Correct. In this quote, the professor indicates that the first line of defense is to “puff up” to scare the predator. The professor implies that the porcupine will only tend to attack if this scare tactic does not work. |
| ✗ | D The porcupine has few natural predators. |
No information is given regarding the number of natural predators the porcupine has. |