Comprehension III

Comprehension I

Read a transcript of part of a university lecture on Animal Behavior by a professor of Biology.

Professor:

We’re looking at animal behavior this week, and let’s turn now, class, to one of its most dramatic manifestations- animal mimicry. Organisms that are good to eat, or that are attacked for other reasons, often develop devices- through evolution, of course- techniques and devices to protect themselves from their attackers, in order to survive, and in order to reproduce and pass their genes on to the next generation. And one of these techniques, one of these strategies, is to look like something else, to look like something that is not good to eat, or something that is otherwise of no interest to the predator. An organism that does this, that resembles something else, is called a ‘mimic’, and the thing that it has evolved to resemble is called the ‘model’, while the predator that it is trying to mislead is called the ‘recipient’- the one that receives the misleading image.

Some mimics do this by adopting camouflage, which is a cryptic resemblance to something of no interest to its enemy, and by doing this, they become invisible, they are hidden. Many animals- insects, lizards, amphibians- mimic the abundant plant life in the habitat around them. I’m sure that you’ve seen green grasshoppers and brown moths that seem to be well-hidden on grass stems and tree trunks when they’re motionless. But the Leaf-tailed Gecko, a small lizard in Madagascar, is a master at this. It avoids its enemies by looking exactly like a cluster of old dead leaves. And there are various species of katydids, grasshopper-like insects, that have managed to duplicate the appearance of leaves with startling accuracy, in all stages of growth, some species looking like fresh green leaves and others looking like old decaying leaves- complete with leaf veins, weathered edges and mildew spots! These adaptations make these animals difficult or impossible for a predator to identify or even notice, and so these otherwise defenseless creatures are overlooked or passed by.

Other organisms defend themselves directly with stings or bites, or with poisons or other noxious chemicals, and such organisms often assume bold, characteristic colors and markings- called warning coloration- that warns a predator, reminds it, that this creature can inflict pain or discomfort, or that it tastes very bad. The bold orange-and-black pattern of the common Monarch Butterfly, or the black-and-yellow bands on a bumblebee, are such warning colorations.

And sometimes, this warning coloration is so effective that another species, a species that doesn’t have any of the protective devices of sting or poison or whatever, will adopt the same warning colors and pattern. This sort of mimicry is called ‘Batesian mimicry’. The name comes from the early zoologist, HW Bates, who, back in 1862, first suggested an explanation for the origins of mimicry based on Charles Darwin’s new Theory of Natural Selection. This was one of the earliest applications of Darwin’s ideas to an unknown biological phenomenon.

Now, Viceroy Butterflies taste good to many birds, but because they mimic the Monarch Butterfly model’s color pattern, because Viceroy Butterflies look like Monarch Butterflies, they are avoided, just like the Monarch is. In the same way, many harmless fly species resemble the bumblebee model, and also in this way they avoid being eaten by the recipients, birds. So these are Batesian mimics. There are several conditions that must be fulfilled, though, for a Batesian mimic to be successful- the mimic must of course share the same general region and habitat as its model, but the mimic must also be less numerous than its model, which must be relatively abundant. That way, the odds are that the recipient predator will sample an unpalatable model first, which is very important for keeping the trick effective.

A similar kind of mimicry is ‘Müllerian mimicry’- named after another early biologist- and in this sort of mimicry, both the model and the mimic are dangerous or taste bad. A very obvious example is the way that so many unrelated species of bees, wasps, and ants have assumed similar, bold, black-and-yellow or black-and-orange banded patterns. By doing this, Müllerian mimics present a united image that predators soon learn to be wary of.

There’s also another aspect of mimicry that I’d like to mention, too, and that’s the mimicry used by predators. This is called ‘aggressive mimicry’, and it is used to conceal or misrepresent a predator until its prey comes near enough to capture. Many mantids, for example, are green or brown, so that they blend in with their plant surroundings, but some tropical mantids are fantastically shaped and colored, like the beautiful Orchid Mantis, which resembles a petal of one of those tropical flowers, and it hides motionless next to one of these orchids until an insect comes within its reach. There’re also several green-colored vine and grass snakes of various families, which lie invisible among the tangled vines and branches of the jungle until they suddenly lash out to grab their prey.

Actually, there are an endless number of ingenious mimics in the natural world, and I recommend that you all try a Google Images search tonight for some more interesting examples of this fascinating behavior.

Now answer the following questions. You may use your notes to help you.

1). Why does the lecturer mention Charles Darwin?

(A) Darwin was the creator of evolutionary theory.

(B) Darwin’s theory was used to explain mimicry.

(D) Darwin separated Batesian and Müllerian mimicry.

2). What is the term used for an organism that is fooled by mimicry?

(A) The recipient

(B) The model

(D) The prey

3). Why does the lecturer mention katydids?

(A) Because they taste bad

(B) Because they resemble bumblebees

(D) Because they look like leaves

4). Some moths and butterflies have large, owl-like eyespots concealed on their underwings, which they can suddenly display to a predator. Which kind of mimicry is this an example of?

(A) Batesian mimicry

(B) Camoflage

(D) Aggressive mimicry

5). Which organism is presented as an example of Müllerian mimicry?

(A) The Viceroy Butterfly

(B) The Orchid Mantis

(D) The Leaf-tailed Gecko

6). Which would be the best title for this lecture?

(A) Animal Behavior

(B) Animal Creativity

(D) Animal Escapades

Answers:1:B 2:A 3:D 4:A 5:B 6:C

Comprehension II

Read a transcription of part of a lecture in biology class.

Prof:

You’ve been reading about animal behavior. Today we’ll discuss one of the most astonishing behaviors in the animal world: dancing bees. Did you know that bees can dance? Well, neither did scientists, until the 1960s. That’s when a German scientist, named, uh, Karl von Frisch, noticed something truly remarkable. As he was observing honeybees, he noticed that some of the bees, which he called scout bees, flew out of the hive to look for food. When a scout found a site where there was food, it flew back to the beehive and started dancing. This dance somehow told the other honeybees where the food was, because after the dance, some of the bees flew from the hive straight to the site of the food. Von Frisch called the bees that collect the food forager bees. He thought the scout bee’s dance told the forager bees three things — first, the smell of the food it had found; second, which direction to fly to reach the food; and third, the distance of the food site from the beehive. Von Frisch won the 1973 Nobel Prize for this discovery, but many scientists were skeptical of his theory. They didn’t believe it was the dance that led the forager bees to food. Instead, they thought it might be, oh, the smell of the food on the dancing bee, or maybe that they just followed the scout back to the food site. Well, very recently, some British scientists used a new type of radar to prove that von Frisch’s theory was indeed correct. It is the dance that communicates this information to other bees.

The British researchers found that scout bees perform two types of dances. If the food is near the hive, say, oh, about 50 or 60 meters away, the scout flies in a round pattern, like a circle. This tells the location, but not the direction, of the food site. If the site is farther away, the scout does what’s called a waggle dance. It flies in a pattern of ovals and vertical lines. The speed of the waggle dance tells other bees how far away the food site is. The slower the dance, the farther away the food. If the scout flies in a vertical line up the side of the beehive, it’s telling the foragers to fly directly toward the sun. If the scout flies vertically down the hive, it’s saying, “fly away from the sun.” Up is toward, down is away. If the scout flies at an angle to the hive, it’s telling the foragers to fly neither toward nor away from the sun, but in between. The bees have a special internal mechanism to know which angle they should fly, based on the sun, the hive and the food site. They can also measure the distance they fly by recording the motion of things they see as they fly past.

Now, um, one problem with von Frisch’s theory had been this: It seems to take the forager bees a long time to reach the food site. That’s why scientists thought that perhaps it wasn’t the waggle dance that led them there. For many years, scientists couldn’t follow the foragers after they left the hive,. because they didn’t have the technology. Just a few years ago, though, the British scientists solved this problem using a new type of radar. They were able to attach a, uh, small radio transmitter to forager bees — I don’t know how, but they did. This enabled them to follow the forager bees’ flight after they left the hive. The radar showed that foragers, do, in fact, fly straight to the area of the food site. They don’t follow the scout bee back to the site, because the scout goes into the hive after it finishes dancing. Well then, if the waggle dance does lead the foragers directly to the food site, why does it take so long for them to find the actual food? The answer is that the waggle dance leads the foragers only to the general area of the food. It doesn’t tell them the exact location of the flowers or plants that have the food. So the foragers have to spend a while flying around the area before they find the exact location of what they’re looking for.

Now answer the following questions. You may use your notes to help you.

1). Which aspect of bee behavior does the professor mainly discuss?

(A) Reproduction

(B) Hibernation

(D) Communication

2). Why does the professor mention radar?

(A) To explain how bees know which way to fly

(B) To show how a theory was proved correct

(D) To confirm the accuracy of the round dance

3). According to the professor, what does the waggle dance tell forager bees?

(A) The distance of the food site from the hive

(B) The exact location of the food at the site

(D) The weather conditions at the food site

4). Which way should forager bees fly if a scout bee flies up the side of the beehive in a vertical line?

(A) toward the west

(B) between sun and moon

(D) away from the sun

5). What can be inferred about how forager bees find food?

(A) They rely solely on the information from the waggle dance.

(B) They rely completely upon their senses of sight and smell.

(D) They use their senses to find the exact location of food.

Answers: 1:D 2:B 3:A 4:C 5:D

Comprehension III

Read a transcript of part of a lecture from a science class.

Prof:

Many people, including scientists, are confused about the distinction between nuts and seeds. Some dictionaries say a nut is also a seed, others say a nut is a fruit, and still others say a nut can be both a fruit and a seed. How can an average person tell the difference? Well, in a nutshell, nuts are seeds but seeds cannot be nuts. Clear as a bell, right?

Part of the confusion stems from the fact that seeds and nuts are classified differently for botanical purposes and culinary ones. Botanists — that is, scientists who study plants — define a seed as part of a flowering plant or tree that will grow into a new plant or tree if it’s buried in the ground and germinated. In this respect it’s similar to a human egg, which becomes an embryo when fertilized by sperm. Sometimes the plant embryo becomes enclosed in a covering, called an integument: I-N-T-E-G-U-M-E-N-T. The embryo plus its integument, therefore, constitute a seed. Um, sunflower seeds are good examples of this. You’ve got to crack open the black outer part, the integument, to eat the white embryo inside, right? That’s why we call them sunflower seeds, and not sunflower nuts.

However, it’s possible for an embryo to have no type of integument at all. As these embryos grow, the tissue surrounding them develops into a fruit. We see this form in many berries, as well as tomatoes, and in peanuts and beans. So an embryo, or seed, doesn’t need a covering to be called a fruit. Now, some plants produce a type of fruit called nuts. A nut is a plant fruit containing a single seed (with or without integument) that does not attach itself to the ovary, or, uh, inside wall of the nut. Nuts have a dry, tough outer shell that doesn’t crack open when the seed becomes mature. Acorns, chestnuts, and walnuts are good examples of nuts. In the botanical sense, a nut is a seed because it is a compound ovary; it contains both the seed and the fruit of a plant. Oft [false start] Usually, a plant’s seed can be separated from its fruit, like when you poke seeds from a watermelon. But with nuts, the part inside the outer shell contains both the seed and the fruit, and these can’t be pulled apart.

This inside part of the nut, the part inside the outer shell, is called a kernel. The kernel is definitely not a nut. It’s a fruit. People often eat the kernel, and when they do this, they say that they are eating a nut — for example, “I’m eating a pecan,” or “I’m eating a chestnut.” What they should be saying, technically, is “I’m eating pecan meat,” or “I’m eating a chestnut kernel.” In the same sense, a peanut typically refers to the entire package of seed-slash-fruit encased in its outer shell, as well as to the edible inner seed-slash-fruit. So, while a nut is botanically classified as a seed, it is primarily in this culinary sense that people confuse nuts and seeds.

Because a nut in cuisine is more, uh, loosely defined than a nut in botany, the term “nut” gets slapped on many seeds that are not true nuts. Almonds, for example, are mistakenly called nuts, even though they are actually the edible seeds of plants called drupes, as are coconuts and pistachio nuts. Cashews are another example of nuts that are really seeds, along with Brazil nuts, which are seeds that come from capsules. In culinary language, any kernel used in cooking that is found within a shell may be labeled as a nut. One attribute nuts and seeds have in common is that both are highly nutritious. Nuts are a great source of energy because they have lots of oil, and are also an excellent source of protein, fiber, magnesium and zinc. Additionally, recent [false start] recent studies have also shown they are beneficial for the blood and heart. Many seeds are packed with vitamin E, which is touted for its anti-aging properties. Nuts and seeds are good not only for humans, but also for wildlife, a fact confirmed each fall when animals such as squirrels, chipmunks and jays can be seen busily storing nuts to avoid starvation in the coming winter cold.

Now answer the following questions. You may use your notes to help you.

1). What is the lecture mainly about?

(A) The history of integuments

(B) The distinction between seeds and nuts

(D) The nutritional value of nuts and seeds

2). According to the professor, how do botanists define a seed?

(A) It is the part of a plant that will reproduce itself when germinated.

(B) It is any kernel used in cooking that is found within a shell.

(D) It is a plant embryo completely encased in an integument.

3). Why does the professor mention kernels?

(A) To compare chestnut seeds with watermelon seeds

(B) To highlight the confusion between nuts and seeds

(D) To illustrate a point about compound ovaries

4). What is true of both nuts and seeds?

(A) They have an embryo plus an integument.

(B) They have a plant fruit unattached to an ovary.

(D) They will grow into new plants when buried.

Answers: 1:B 2:A 3:B 4:C

Comprehension IV

Read a transcript of a part of a university science lecture on Island Biogeography.

Professor:

Today I’d like to look at the topic of island biogeography- the study of plant and animal distributions on islands. Studies in this field ballooned soon after the publication of MacArthur and Wilson’s seminal Theory of Island Biogeography in 1967.

Their theory is a simple, elegant bit of reasoning that was a major breakthrough in modern ecological thought. The Theory of Equilibrium in Island Biogeography says that the number of kinds of plants and animals on an undisturbed island- that is, a natural island unaffected by man or other calamity- is determined by two processes, immigration and extinction. In other words, the number of species on an island is the sum of the species that arrive, breed and live there successfully, minus the number of species that arrive but fail to breed or that eventually become extinct.

If a new island starting with zero kinds of birds lies near a mainland that has 100 kinds of birds, then a certain percent of those mainland species are eventually going to find their way to the island. When the first species arrives and establishes itself, the potential number of immigrants decreases by one, since there are now only 99 potential immigrant species available from the mainland. At the same time, the potential for extinctions increases by one, because with the arrival of the first species, there is now also one species that could become extinct, where at first there was none.

You may have heard of Krakatoa, which was famously all but destroyed by a volcanic explosion, exterminating every living thing on it, back in 1883. Well, between 1883 and 1933, 34 species of birds became established there, but 5 of them also became extinct. Then, from 1933 to 1985, 14 more species established themselves, while 8 went extinct. As the theory predicts, the rate of immigration declines as the island avifauna matures. As equilibrium approaches, turnover continues, but the total number of different species levels off. When the overall bird population finally reaches a mature equilibrium- when the arrival rate of new species balances the extinction rate of unsuccessful species- the island may host anywhere from only a few to almost all of those 100 mainland species, depending on the island’s overall receptivity.

Papua New Guinea has a very rich avifauna- almost 800 species of birds- while nearby Bali only has about 300 species. Why? There are several factors that determine these numbers, and we now need to consider them.

The most obvious factor is island size. Papua New Guinea is over fifty times the area of Bali. There’s just more space available on a bigger island, so there’s more food, more places to hide, bigger territories- simply speaking, room for more birds. And the more individuals of a species there are, the bigger the gene pool, the greater the breeding opportunities, and the less danger of extinction.

But size alone is not the whole story. Just as important is the variety of habitats. A larger island is likely to have more different habitats- forest, grassland, scrub, lakes, marshes- while a small island may offer only a single habitat of sand and palm trees. Islands with multiple habitats, multiple niches, can maintain more species. With just one or two habitats available, the species list is going to be very short.

This can be seen by comparing islands that are otherwise the same size- as between coral atolls and volcanic islands, for instance. The Tuamotos Islands and the islands of Tonga both lie in the middle of the south Pacific. Both comprise many small islands with a total land area of about 800 square kilometers, but while the Tuamotos are all coral atolls with a maximum altitude of seven meters, Tonga also includes a couple of volcanic islands, one rising to 1033 meters, offering montane habitat in addition to lowlands. As we’d expect, the bird variety on Tonga- 75 species- is somewhat higher than the 57 species on the Tuamotos.

Another important factor is the island’s distance from the mainland or other species sources. Its colonists will have to come from whatever lands are nearby- and oceanic islands, islands farther away from these sources, will receive fewer species- though hardier ones- than will coastal islands closer to species sources, simply because it’s harder, even for a bird, to get to a more distant location. This is why the Hawaiian Islands, ten times the area of the Louisiade Archipelago, has fewer native birds. The Louisiades lie only 200 km from species-rich New Guinea, while the Hawaiian Islands are 3,000 km from anywhere.

So these are the main determinants of island species capacity- size, habitat diversity, and degree of isolation. And it turns out that MacArthur and Wilson’s theory can be applied to other sorts of “islands”, to other geographical areas that are isolated in some way by their surroundings. Just as an island is separated from other land by the ocean, lakes are isolated from other lakes by dry land, so that fish have as great a challenge in colonizing lakes as, say, rodents do in colonizing islands. Mountain tops are islands, separated from other mountain tops by ecologically quite different plains and valleys. And national parks are islands of original habitat isolated by the human developments around them.

Today, such areas as national parks, forest preserves and other protected natural areas are increasingly becoming isolated fragments in a clipped and cultivated world. And it with these that lessons learned from the studies of island biogeography are being applied. In our western parks, for instance, the successful re-introduction and management of large mammals like the wolf and birds like the California condor depend on research into territorial demands and ecological requirements, crucial population sizes, and individual emigration to surrounding areas, where the impact on humans can be significant.

Now answer the following questions. You may use your notes to help you.

1). What is this lecture mainly about?

(A) How islands develop and mature

(B) How species migrate to islands

(D) How many species islands can accommodate

2). Which of these is most likely NOT an island in the broader sense?

(A) A pond

(B) A city park

(D) A valley

3). Why does the Louisiade Archipelago host more bird species than the Hawaiian Islands?

(A) It is closer to New Guinea

(B) It is composed of coral atolls

(D) It is more natural and undisturbed

4). Why does the lecturer introduce Krakatoa?

(A) As an example of a new island

(B) As a proof of MacArthur and Wilson’s theory

(D) As an exception to MacArthur and Wilson’s theory

5). Which is NOT a significant determinant of island species density?

(A) Surface area

(B) Recent geology

(D) Proximity to other islands

6). Why does the lecturer mention other concepts of “island”?

(A) To show practical uses for MacArthur and Wilson’s theory

(B) To demonstrate MacArthur and Wilson’s insight

(D) To augment the basic theory

Answers: 1:C 2:D 3:A 4:B 5:B 6:A

Comprehension V

Read a transcript of a part of a university lecture by a professor on the possibility of life on Mars.

Professor:

The planet Mars has been in the news recently, because it is going to pass very close to us soon. So this might be a good time to talk about the Red Planet.

The possibility of there being life on Mars has been a topic of speculation for more than a hundred and fifty years- ever since its “canals” were mapped by an Italian astronomer, Giovanni Schiparelli, back in 1877. He drew the first reasonably realistic map of Mars, and it included a system of “canali’ across its surface. In Italian, “canali” just means “channels”- it doesn’t imply artificial structures at all- but the idea caught on, and it was gradually developed, with a lot of help from fertile imaginations, into the concept of a complex, planet-wide irrigation system. Although most serious astronomers did not buy into this, the idea of an Earth-like planet- perhaps colder and dryer, and probably without any Martians- endured right up to the beginning of the Space Age, when Mars was still thought to have polar ice caps and a reasonable atmosphere. It also showed seasonal color changes that some thought could be some kind of primitive plant life blooming.

But in the 1960s, NASA’s Mariner missions sent back images of something very different, of a cratered, moon-like Mars. Both the polar caps and the atmosphere turned out to be almost pure CO2, and the density of its atmosphere was only one-hundredth of Earth’s. And the “blooming plant life” turned out to be only a lot of dust, blown around by strong seasonal winds.

In some ways, though, Mars became more interesting. It had giant volcanoes. It had a vast maze of canyons. And it showed evidence of having had flowing water on its surface sometime in its distant past.

And the possibility of living organisms on Mars could still not be ruled out. Now, you should realize that it is a lot easier to prove that something exists than it is to prove that something doesn’t exist. Once you’ve discovered something, you’ve got it in the bag- but it’s harder to prove that something’s not there, because no matter how much you look without finding it, it could still be hiding under the next rock. So scientists continue to look under the Martian rocks.

The Viking mission in 1976 included three biological experiments- the Labelled Release experiment, the Pyrolytic Release experiment, and the Gas Exchange experiment.

The Labelled Release experiment mixed a Martian soil sample with water and Carbon-14 marked organic materials, and if any micro-organisms ate the materials, Carbon-14 would appear in any released gases. The Pyrolytic Release experiment simply incubated an unadulterated soil sample in a simulated Martian atmosphere containing Carbon-14 marked CO2. Then the sample was heated to break down- or pyrolytize- any organic material that’d been produced, and again the gases were tested for Carbon-14. And finally, the Gas Exchange experiment put a Martian soil sample into an organic “chicken soup” of marked chemicals, and if any of these were consumed by micro-organisms, the Carbon-14 would again be detected in the released gases.

None of these experiments were successful. That is, none of them produced clear results detecting life forms. Most scientists now agree that the experiments were flawed- all of the results can be explained as purely chemical processes that do not require the presence of life. However, there is now evidence, as I said, that Mars once had significantly more water, and now scientists are considering the possibility that the planet once has life- but that it went extinct when conditions on Mars got worse.

A meteorite called ALH84001- catchy name, eh?- was discovered in Antarctica in 1984, and it is one of a dozen meteorites that scientists believe, because of their age and composition, came from Mars. But ALH84001 is special- it carries with it three pieces of evidence for life on Mars. First, it carries polyclitic aromatic hydrocarbons, which is something that dead organisms often decompose into. And second, it has tiny carbonate globules that resemble mineral alterations that primitive Earth bacteria cause. And then third, it carries very tiny- 10- to 100-nanometer- ovoids that may actually be fossil bacteria. And all three of these pieces of evidence lie within a few micrometers of each other in a crack in the meteorite’s surface. Together they are strong evidence for the existence of life in Mars’s past.

But the real research on this is just beginning. Maybe we’ll learn more when we’ve heard back from NASA’s Phoenix mission.

Now answer the following questions. You may use your notes to help you.

1). What are “canali”?

(A) canyons

(B) canals

(D) channels

2). What is this lecture mainly about?

(A) Exploring life on Mars

(B) Proving there’s life on Mars

(D) Disproving there’s any life on Mars

3). Judging from the lecture, how would you describe the results of the Viking biological experiments?

(A) Inconclusive

(B) Exciting

(D) Too complex

4). Which is NOT true of meteorite ALH84001?

(A) It was discovered by Schiaperelli.

(B) It fell in Antarctica.

(D) It contains evidence for micro-organisms.

5). What are scientists now focussing their research on?

(A) Meteorites

(B) Better experiments

(D) Polycyclic aromatic hydrocarbons

6). According to the lecture, why is it difficult to disprove the existence of life on Mars?

(A) Test results are always ambiguous.

(B) Scientists can never completely agree.

(D) Definitive research is always incomplete.

Answers: 1:D 2:C 3:A 4:A 5:C 6:D

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