The sauropod dinosaurs were gigantic, long-necked herbivores (plant eaters) that flourished during the Jurassic period (201-145 million years ago). At the same time that the sauropods were evolving, so too were the conifers, a group of plants best known to us today as trees like pines and firs. Most modern conifer foliage (leaves) can provide enough energy value to be a significant food source. The foliage also responds well to being eaten by regrowing quickly. If early conifers were like modern ones, both the relative density and amount of conifer foliage available would make the exploitation of this resource by an herbivore worthwhile. But conifers also present challenges to the animals that eat them, a situation that also likely prevailed in the past.
One problem is that the foliage of many conifer species contains toxic chemicals. Once ingested, these chemicals do not always attack the animal’s digestive system, but they can interfere with or resist attempts to break down the plant matter. As a result, few modern vertebrates (animals having a backbone) exploit this food source, although in the past some did, such as the extinct American mastodon, as do some living species such as the snowshoe hare and a bird known as the white- tailed ptarmigan. Like all plants, conifers also contain a compound known as cellulose, the main ingredient in the cell walls of plants that helps give them shape and support, and which forms most of the fiber in plant food. Cellulose contains valuable carbohydrates, and in some modern vertebrates, such as cattle, up to 80 percent of the digestible energy from plant matter is derived from cellulose that has been broken down by bacteria in the animals’ digestive tract. Cellulose, however, is extremely tough and relatively resistant to digestion, and vertebrate leaf eaters must deal with the problem by having long, specialized digestive tracts with fermentation chambers for bacteria that aid digestion. There are two basic kinds of fermentation systems: foregut fermentation, where the food is broken down in a specialized group of stomachs, and hindgut fermentation, in which the plant material stays in a special branch of the intestine known as a caecum. Hindgut fermentation is used by horses, elephants, gorillas, and some birds as well. Therefore, other archosaurs (the animal group that includes both modern birds and ancient dinosaurs) could have done this too, and this is the system most likely used by sauropods.
As if this weren’t enough, a conifer-eating dinosaur would have had to deal with another problem. Most of the known Jurassic conifer leaflets actually were small to medium-sized, blade-shaped structures that were sometimes closely adjoined to the woody twigs to which they were attached, more like the foliage of the living monkey puzzle tree than the long, slender needles of pine trees. Small, dainty feeders like the white-tailed ptarmigan can use their small beaks or mouths to pluck needles precisely and selectively, but a large herbivore inevitably takes in some quantity of wood with each bite. They are necessarily bulk feeders, too big to be precise and too hungry to be picky. Wood contains lignin, even more difficult to digest than cellulose; no known living vertebrate can digest this at all. Termites (an insect that feeds on wood) are one of the few known multicellular organisms that can digest lignin, owing to single-celled animals in their intestines that secrete enzymes that break it down. As an overall food source, however, tree-like conifers still had possibilities: they were reasonably abundant, and if a way could be found to deal with the toxins and lignin present in their foliage, they could offer a sustainable food source to any animal capable of reaching it and somehow extracting enough nutrition once it was ingested. Reaching that food required a long neck, and digesting it required an effective digestive system.
Paleontologist James Farlow believes that sauropods were likely hindgut specialists. The fermenting chambers in their stomachs yielded nutrients at a slow but steady rate, allowing the animals to extract usable energy from tough plant products. To make this process pay off in terms of energy yield, the animals had to take in and retain very large quantities of vegetation that was continually in the process of being broken down. This would have required having a big body to carry it around.
1
The sauropod dinosaurs were gigantic, long-necked herbivores (plant eaters) that flourished during the Jurassic period (201-145 million years ago). At the same time that the sauropods were evolving, so too were the conifers, a group of plants best known to us today as trees like pines and firs. Most modern conifer foliage (leaves) can provide enough energy value to be a significant food source. The foliage also responds well to being eaten by regrowing quickly. If early conifers were like modern ones, both the relative density and amount of conifer foliage available would make the exploitation of this resource by an herbivore worthwhile. But conifers also present challenges to the animals that eat them, a situation that also likely prevailed in the past.
The word “prevailed”in the passage is closest in meaning to
Awas a problem
Bbegan
Cwas widespread
Dgrew worse
2
The sauropod dinosaurs were gigantic, long-necked herbivores (plant eaters) that flourished during the Jurassic period (201-145 million years ago). At the same time that the sauropods were evolving, so too were the conifers, a group of plants best known to us today as trees like pines and firs. Most modern conifer foliage (leaves) can provide enough energy value to be a significant food source. The foliage also responds well to being eaten by regrowing quickly. If early conifers were like modern ones, both the relative density and amount of conifer foliage available would make the exploitation of this resource by an herbivore worthwhile. But conifers also present challenges to the animals that eat them, a situation that also likely prevailed in the past.
According to paragraph 1， which TWO of the following help explain why conifer foliage is an important food source for herbivores? To receive credit, you must select TWO answer choices.
AIts shape makes it easier to eat than other kinds of plants.
BIt grows back quickly after being eaten.
CIt presents fewer challenges to herbivores that eat it than do other plants.
DIt is available in relatively large amounts.
3
One problem is that the foliage of many conifer species contains toxic chemicals. Once ingested, these chemicals do not always attack the animal’s digestive system, but they can interfere with or resist attempts to break down the plant matter. As a result, few modern vertebrates (animals having a backbone) exploit this food source, although in the past some did, such as the extinct American mastodon, as do some living species such as the snowshoe hare and a bird known as the white- tailed ptarmigan. Like all plants, conifers also contain a compound known as cellulose, the main ingredient in the cell walls of plants that helps give them shape and support, and which forms most of the fiber in plant food. Cellulose contains valuable carbohydrates, and in some modern vertebrates, such as cattle, up to 80 percent of the digestible energy from plant matter is derived from cellulose that has been broken down by bacteria in the animals’ digestive tract. Cellulose, however, is extremely tough and relatively resistant to digestion, and vertebrate leaf eaters must deal with the problem by having long, specialized digestive tracts with fermentation chambers for bacteria that aid digestion. There are two basic kinds of fermentation systems: foregut fermentation, where the food is broken down in a specialized group of stomachs, and hindgut fermentation, in which the plant material stays in a special branch of the intestine known as a caecum. Hindgut fermentation is used by horses, elephants, gorillas, and some birds as well. Therefore, other archosaurs (the animal group that includes both modern birds and ancient dinosaurs) could have done this too, and this is the system most likely used by sauropods.
Paragraph 2 suggests which of the following reasons for believing that sauropods likely used hindgut fermentation systems?
AA foregut fermentation system would have been insufficient to deal with the many toxic chemicals found in conifer foliage.
BFossils show that sauropods did not have the specialized group of stomachs that characterizes foregut specialists.
CSauropods were similar in size to large modern animals that use hindgut fermentation, such as elephants.
DSauropods are related to modern birds and probably had similar digestive systems.
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One problem is that the foliage of many conifer species contains toxic chemicals. Once ingested, these chemicals do not always attack the animal’s digestive system, but they can interfere with or resist attempts to break down the plant matter. As a result, few modern vertebrates (animals having a backbone) exploit this food source, although in the past some did, such as the extinct American mastodon, as do some living species such as the snowshoe hare and a bird known as the white- tailed ptarmigan. Like all plants, conifers also contain a compound known as cellulose, the main ingredient in the cell walls of plants that helps give them shape and support, and which forms most of the fiber in plant food. Cellulose contains valuable carbohydrates, and in some modern vertebrates, such as cattle, up to 80 percent of the digestible energy from plant matter is derived from cellulose that has been broken down by bacteria in the animals’ digestive tract. Cellulose, however, is extremely tough and relatively resistant to digestion, and vertebrate leaf eaters must deal with the problem by having long, specialized digestive tracts with fermentation chambers for bacteria that aid digestion. There are two basic kinds of fermentation systems: foregut fermentation, where the food is broken down in a specialized group of stomachs, and hindgut fermentation, in which the plant material stays in a special branch of the intestine known as a caecum. Hindgut fermentation is used by horses, elephants, gorillas, and some birds as well. Therefore, other archosaurs (the animal group that includes both modern birds and ancient dinosaurs) could have done this too, and this is the system most likely used by sauropods.
According to paragraph 2， which of the following is true of the two different fermentation systems used by vertebrate leaf eaters?
AThey both break down food in a specialized group of stomachs.
BThey both contain bacteria that helps vertebrate leaf eaters digest cellulose.
CThey both keep plant material in the caecum, a branch of the intestine.
DThey both are used by horses, elephants, gorillas, and some birds.
5
As if this weren’t enough, a conifer-eating dinosaur would have had to deal with another problem. Most of the known Jurassic conifer leaflets actually were small to medium-sized, blade-shaped structures that were sometimes closely adjoined to the woody twigs to which they were attached, more like the foliage of the living monkey puzzle tree than the long, slender needles of pine trees. Small, dainty feeders like the white-tailed ptarmigan can use their small beaks or mouths to pluck needles precisely and selectively, but a large herbivore inevitably takes in some quantity of wood with each bite. They are necessarily bulk feeders, too big to be precise and too hungry to be picky. Wood contains lignin, even more difficult to digest than cellulose; no known living vertebrate can digest this at all. Termites (an insect that feeds on wood) are one of the few known multicellular organisms that can digest lignin, owing to single-celled animals in their intestines that secrete enzymes that break it down. As an overall food source, however, tree-like conifers still had possibilities: they were reasonably abundant, and if a way could be found to deal with the toxins and lignin present in their foliage, they could offer a sustainable food source to any animal capable of reaching it and somehow extracting enough nutrition once it was ingested. Reaching that food required a long neck, and digesting it required an effective digestive system.
The word “inevitably” in the passage is closest in meaning to
Arepeatedly
Bunfortunately
Cunavoidably
Daccidentally
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As if this weren’t enough, a conifer-eating dinosaur would have had to deal with another problem. Most of the known Jurassic conifer leaflets actually were small to medium-sized, blade-shaped structures that were sometimes closely adjoined to the woody twigs to which they were attached, more like the foliage of the living monkey puzzle tree than the long, slender needles of pine trees. Small, dainty feeders like the white-tailed ptarmigan can use their small beaks or mouths to pluck needles precisely and selectively, but a large herbivore inevitably takes in some quantity of wood with each bite. They are necessarily bulk feeders, too big to be precise and too hungry to be picky. Wood contains lignin, even more difficult to digest than cellulose; no known living vertebrate can digest this at all. Termites (an insect that feeds on wood) are one of the few known multicellular organisms that can digest lignin, owing to single-celled animals in their intestines that secrete enzymes that break it down. As an overall food source, however, tree-like conifers still had possibilities: they were reasonably abundant, and if a way could be found to deal with the toxins and lignin present in their foliage, they could offer a sustainable food source to any animal capable of reaching it and somehow extracting enough nutrition once it was ingested. Reaching that food required a long neck, and digesting it required an effective digestive system.
Why does the author discuss the fact that termites are one of the few known multicellular organisms that can digest lignin?
ATo argue that sauropods must have produced enzymes in their intestines similar to those produced by termites
BTo challenge the idea that sauropods were capable of eating wood
CTo provide an example of a nonvertebrate bulk feeder that eats wood
DTo emphasize how difficult it is for most animals to digest wood and its contents
7
As if this weren’t enough, a conifer-eating dinosaur would have had to deal with another problem. Most of the known Jurassic conifer leaflets actually were small to medium-sized, blade-shaped structures that were sometimes closely adjoined to the woody twigs to which they were attached, more like the foliage of the living monkey puzzle tree than the long, slender needles of pine trees. Small, dainty feeders like the white-tailed ptarmigan can use their small beaks or mouths to pluck needles precisely and selectively, but a large herbivore inevitably takes in some quantity of wood with each bite. They are necessarily bulk feeders, too big to be precise and too hungry to be picky. Wood contains lignin, even more difficult to digest than cellulose; no known living vertebrate can digest this at all. Termites (an insect that feeds on wood) are one of the few known multicellular organisms that can digest lignin, owing to single-celled animals in their intestines that secrete enzymes that break it down. As an overall food source, however, tree-like conifers still had possibilities: they were reasonably abundant, and if a way could be found to deal with the toxins and lignin present in their foliage, they could offer a sustainable food source to any animal capable of reaching it and somehow extracting enough nutrition once it was ingested. Reaching that food required a long neck, and digesting it required an effective digestive system.
According to paragraph 3， eating habits of large herbivores differ from those of the white-tailed ptarmigan in which of the following ways?
ALarge herbivores eat a different kind of foliage.
BLarge herbivores are more selective when chopsing what foliage to eat.
CLarge herbivores digest pine needles more easily.
DLarge herbivores are more likely to ingest wood when eating certain foliage.
8
As if this weren’t enough, a conifer-eating dinosaur would have had to deal with another problem. Most of the known Jurassic conifer leaflets actually were small to medium-sized, blade-shaped structures that were sometimes closely adjoined to the woody twigs to which they were attached, more like the foliage of the living monkey puzzle tree than the long, slender needles of pine trees. Small, dainty feeders like the white-tailed ptarmigan can use their small beaks or mouths to pluck needles precisely and selectively, but a large herbivore inevitably takes in some quantity of wood with each bite. They are necessarily bulk feeders, too big to be precise and too hungry to be picky. Wood contains lignin, even more difficult to digest than cellulose; no known living vertebrate can digest this at all. Termites (an insect that feeds on wood) are one of the few known multicellular organisms that can digest lignin, owing to single-celled animals in their intestines that secrete enzymes that break it down. As an overall food source, however, tree-like conifers still had possibilities: they were reasonably abundant, and if a way could be found to deal with the toxins and lignin present in their foliage, they could offer a sustainable food source to any animal capable of reaching it and somehow extracting enough nutrition once it was ingested. Reaching that food required a long neck, and digesting it required an effective digestive system.
Which of the following can be inferred from paragraph 3 about the Jurassic conifer foliage that sauropods would have eaten?
AIt was not available in large quantities.
BIt was located high above the ground.
CIt was more easily digested by birds than by sauropods.
DIt was a primary source of energy for termites.
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One problem is that the foliage of many conifer species contains toxic chemicals. [■] Once ingested, these chemicals do not always attack the animal’s digestive system, but they can interfere with or resist attempts to break down the plant matter. As a result, few modern vertebrates (animals having a backbone) exploit this food source, although in the past some did, such as the extinct American mastodon, as do some living species such as the snowshoe hare and a bird known as the white- tailed ptarmigan. [■] Like all plants, conifers also contain a compound known as cellulose, the main ingredient in the cell walls of plants that helps give them shape and support, and which forms most of the fiber in plant food. [■] Cellulose contains valuable carbohydrates, and in some modern vertebrates, such as cattle, up to 80 percent of the digestible energy from plant matter is derived from cellulose that has been broken down by bacteria in the animals’ digestive tract. [■] Cellulose, however, is extremely tough and relatively resistant to digestion, and vertebrate leaf eaters must deal with the problem by having long, specialized digestive tracts with fermentation chambers for bacteria that aid digestion. There are two basic kinds of fermentation systems: foregut fermentation, where the food is broken down in a specialized group of stomachs, and hindgut fermentation, in which the plant material stays in a special branch of the intestine known as a caecum. Hindgut fermentation is used by horses, elephants, gorillas, and some birds as well. Therefore, other archosaurs (the animal group that includes both modern birds and ancient dinosaurs) could have done this too, and this is the system most likely used by sauropods.
Look at the four squaresthat indicate where the following sentence could be added to the passage
A second problem has required vertebrates to develop special ways of digesting some of a plant’s most important nutritional content.
Where would the sentence best fit？Click on a square sentence to the passage.
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The sauropods were large, long-necked dinosaurs that likely fed on conifer leaves.
AEarly conifers had lower levels of toxic chemicals in their leaves than do modern conifers, which explains why sauropods were able to eat them and why so few species can today.
BSauropods, like modern vertebrates such as cows and horses, had stomachs and intestines that were able to resist the bacteria found in the cells of plants and were therefore able to avoid getting sick.
CSauropods needed big enough bodies to hold the large amounts of vegetation they ingested, which was broken down by their digestive systems and turned into energy.
DAssuming conifers from the Jurassic period were like modern ones, their foliage would have been an available and potentially nutritious food source for sauropods but also would have presented difficulties.
EConifer foliage is hard to digest, and so sauropods had to evolve the kind of digestive systems that could extract needed nutrition from these plants.
FStudying the digestive systems of termites has helped scientists better understand how sauropods’ digestive systems were able to deal with the toxins found in conifer foliage.
