Woody plants produce a great variety of chemical compounds to provide protection against other plants, diseases, and herbivores (plant-eating animals) big and small. These chemicals can be found in just about any part of the plant (for example, the waxy surface of apple leaves contains toxins to repel certain insects). They can also be emitted into the air in considerable quantities, which explains why pinewoods have a strong fragrance and the eucalyptus-dominated bushlands of Australia have a blue haze. These chemicals seep out through the bark or the holes in a leaf (the stomata) or ooze out of special glands, often on teeth around the leaf edge (as found, for example, in pines, alder, and willows) usually when the leaf is young but sometimes (as in certain willows) even late in life.
Some chemical defenses are highly toxic and will kill attackers in small doses. Known as “qualitative” defenses, they work in low concentrations. These include alkaloids present in plants such as the tansy ragwort, which is notorious for killing cattle and horses when ingested. Other chemicals work by building up in the herbivore. Referred to as “quantitative” defenses, they become more effective the more they accumulate in the animal’s body.Classic examples are phenolic resins in creosote bushes and tannins found in a number of plants. Tannin is a “protein precipitant which gradually makes food less digestible, so herbivores end up starving and having stunted growth. These often have the effect of causing the herbivore to move elsewhere. It is possible, for example, that the endangered British red squirrel is declining not through competition with the introduced North American gray squirrel, as commonly thought, but because of acorns. Acorns (nuts from oak trees) contain digestion inhibitors that gray squirrels can disarm but red squirrels cannot. Red squirrels do well in conifer tree plantations, feeding on the more nutritious pine seeds, and where there are no oaks to give the gray squirrels a competitive edge.
Plants are not immune to the effects of chemical defenses.Spanish moss, which hangs from trees in the southern United States and in South America, never grows on pines, presumably because of the resins pine trees secrete. Perhaps the best-known example of antiplant chemical defenses was first reported in the first century AD. by Pliny the Elder, who wrote that “the shadow of walnut trees is poison to all plants within its compass.” Walnuts and related trees contain the chemical juglone, which, seeping from the roots.reduces the germination of competitors, stunts their growth, and even kills nearby plants, resulting in open-canopied walnut groves having very little growing under them. Tomatoes, apples, rhododendrons, and roses are very susceptible, but many grasses, vegetables, and Virginia creeper will happily live under walnuts.
Defensive chemicals are costly for the plant to produce and store; many are toxic to the plant producing them. Oaks may put up to 15 percent of their energy production into chemical defenses (which explains why stressed trees are most prone to attack: they have less energy available to produce defenses). Thus, although there may be large pools of defenses available where attacks are common and ferocious, it makes evolutionary sense in lesser situations to produce the chemicals in earnest only when they are needed. Oaks (and a number of other trees) manage with low concentrations of tannins in their leaves, but once part of the canopy is attacked, the tree will produce tannins in large quantity More than that, the tannins released into the air are detected by surrounding oaks and they in turn will produce more tannins in preparation for the onslaught. In a similar way, willow trees in Alaska that had their leaves eaten by snowshoe hares produce shoots with lower nutritional concentration and higher levels of lignin and deterrent phenols, thus rendering them less palatable. These “induced” defenses may have an effect for some time: birch trees can remain unpalatable for up to three years after being eaten.Expensive defenses are saved not only when they are not needed but also where. The North American aspen has been shown to produce fewer tannins in trees growing on fertile soils: it is cheaper to replace lost material than to defend it. Similarly, more is invested in defenses where herbivores and diseases are more common.
1
Woody plants produce a great variety of chemical compounds to provide protection against other plants, diseases, and herbivores (plant-eating animals) big and small. These chemicals can be found in just about any part of the plant (for example, the waxy surface of apple leaves contains toxins to repel certain insects). They can also be emitted into the air in considerable quantities, which explains why pinewoods have a strong fragrance and the eucalyptus-dominated bushlands of Australia have a blue haze. These chemicals seep out through the bark or the holes in a leaf (the stomata) or ooze out of special glands, often on teeth around the leaf edge (as found, for example, in pines, alder, and willows) usually when the leaf is young but sometimes (as in certain willows) even late in life.
According to paragraph 1, what do pines, alders, and willows all have in common?
AWhen their tree leaves grow old, the leaves continue to emit chemicals.
BWhen they dominate an area, the chemicals they produce create a colored haze.
CTheir chemical compounds remain in protective areas inside the tree bark
DThey have glands near the edges of their leaves from which chemicals seep.
2
Some chemical defenses are highly toxic and will kill attackers in small doses. Known as “qualitative” defenses, they work in low concentrations. These include alkaloids present in plants such as the tansy ragwort, which is notorious for killing cattle and horses when ingested. Other chemicals work by building up in the herbivore. Referred to as “quantitative” defenses, they become more effective the more they accumulate in the animal’s body.Classic examples are phenolic resins in creosote bushes and tannins found in a number of plants. Tannin is a “protein precipitant which gradually makes food less digestible, so herbivores end up starving and having stunted growth. These often have the effect of causing the herbivore to move elsewhere. It is possible, for example, that the endangered British red squirrel is declining not through competition with the introduced North American gray squirrel, as commonly thought, but because of acorns. Acorns (nuts from oak trees) contain digestion inhibitors that gray squirrels can disarm but red squirrels cannot. Red squirrels do well in conifer tree plantations, feeding on the more nutritious pine seeds, and where there are no oaks to give the gray squirrels a competitive edge.
According to paragraph 2, chemicals that function as qualitative.defenses protect plants by
Apoisoning herbivores that consume even small amounts of the plants
Bmaking the plants difficult for some herbivores to digest
Cinterfering with the growth of herbivores that consume the plants frequently
Dcausing herbivores to move elsewhere in order to avoid the plants
3
Some chemical defenses are highly toxic and will kill attackers in small doses. Known as “qualitative” defenses, they work in low concentrations. These include alkaloids present in plants such as the tansy ragwort, which is notorious for killing cattle and horses when ingested. Other chemicals work by building up in the herbivore. Referred to as “quantitative” defenses, they become more effective the more they accumulate in the animal’s body.Classic examples are phenolic resins in creosote bushes and tannins found in a number of plants. Tannin is a “protein precipitant which gradually makes food less digestible, so herbivores end up starving and having stunted growth. These often have the effect of causing the herbivore to move elsewhere. It is possible, for example, that the endangered British red squirrel is declining not through competition with the introduced North American gray squirrel, as commonly thought, but because of acorns. Acorns (nuts from oak trees) contain digestion inhibitors that gray squirrels can disarm but red squirrels cannot. Red squirrels do well in conifer tree plantations, feeding on the more nutritious pine seeds, and where there are no oaks to give the gray squirrels a competitive edge.
In paragraph 2, why does the author provide the information that red squirrels do well in conifer plantations where there are no oaks?
ATo argue that red squirrels compete successfully against gray squirrels because the gray squirrel’s diet lacks nutrition
BTo emphasize the care with which red squirrels choose a new habitat
CTo suggest that the further decline of the endangered British red squirrel can be prevented
DTo support the idea that competition with the gray squirrel may not be the main cause of the red squirrel’s decline
4
Plants are not immune to the effects of chemical defenses.Spanish moss, which hangs from trees in the southern United States and in South America, never grows on pines, presumably because of the resins pine trees secrete. Perhaps the best-known example of antiplant chemical defenses was first reported in the first century AD. by Pliny the Elder, who wrote that “the shadow of walnut trees is poison to all plants within its compass.” Walnuts and related trees contain the chemical juglone, which, seeping from the roots.reduces the germination of competitors, stunts their growth, and even kills nearby plants, resulting in open-canopied walnut groves having very little growing under them. Tomatoes, apples, rhododendrons, and roses are very susceptible, but many grasses, vegetables, and Virginia creeper will happily live under walnuts.
In paragraph 3, which of the following can be inferred from the discussion of walnut trees and the chemical juglone?
AWalnut tree defenses are more effective than the chemical defenses of pine trees.
BPlants that also contain juglone in their roots, such as tomatoes and apples, can live under walnut trees
CSome species, such as Virginia creeper, actually grow better in the presence of juglone than in other locations.
DPlant chemical defenses may not affect all species in the same way.
5
Defensive chemicals are costly for the plant to produce and store; many are toxic to the plant producing them. Oaks may put up to 15 percent of their energy production into chemical defenses (which explains why stressed trees are most prone to attack: they have less energy available to produce defenses). Thus, although there may be large pools of defenses available where attacks are common and ferocious, it makes evolutionary sense in lesser situations to produce the chemicals in earnest only when they are needed. Oaks (and a number of other trees) manage with low concentrations of tannins in their leaves, but once part of the canopy is attacked, the tree will produce tannins in large quantity More than that, the tannins released into the air are detected by surrounding oaks and they in turn will produce more tannins in preparation for the onslaught. In a similar way, willow trees in Alaska that had their leaves eaten by snowshoe hares produce shoots with lower nutritional concentration and higher levels of lignin and deterrent phenols, thus rendering them less palatable. These “induced” defenses may have an effect for some time: birch trees can remain unpalatable for up to three years after being eaten.Expensive defenses are saved not only when they are not needed but also where. The North American aspen has been shown to produce fewer tannins in trees growing on fertile soils: it is cheaper to replace lost material than to defend it. Similarly, more is invested in defenses where herbivores and diseases are more common.
The phrase “prone to” in the passage is closest in meaning to
Aunnecessary to
Bsubject to
Cdifficult to
Dbeneficial to
6
Defensive chemicals are costly for the plant to produce and store; many are toxic to the plant producing them. Oaks may put up to 15 percent of their energy production into chemical defenses (which explains why stressed trees are most prone to attack: they have less energy available to produce defenses). Thus, although there may be large pools of defenses available where attacks are common and ferocious, it makes evolutionary sense in lesser situations to produce the chemicals in earnest only when they are needed. Oaks (and a number of other trees) manage with low concentrations of tannins in their leaves, but once part of the canopy is attacked, the tree will produce tannins in large quantity More than that, the tannins released into the air are detected by surrounding oaks and they in turn will produce more tannins in preparation for the onslaught. In a similar way, willow trees in Alaska that had their leaves eaten by snowshoe hares produce shoots with lower nutritional concentration and higher levels of lignin and deterrent phenols, thus rendering them less palatable. These “induced” defenses may have an effect for some time: birch trees can remain unpalatable for up to three years after being eaten.Expensive defenses are saved not only when they are not needed but also where. The North American aspen has been shown to produce fewer tannins in trees growing on fertile soils: it is cheaper to replace lost material than to defend it. Similarly, more is invested in defenses where herbivores and diseases are more common.
According to paragraph 4, which of the following is true about oaks and their chemical defenses?
AStressed oaks must spend even more than 15 percent of their energy to produce defensive chemicals.
BThe leaves of oaks have lower quantities of tannins than the other parts of oaks have.
COaks produce larger amounts of defensive chemicals when a neighboring oak releases such chemicals.
DOaks produce large quantities of defensive chemicals throughout the year, even before attacks occur.
7
Defensive chemicals are costly for the plant to produce and store; many are toxic to the plant producing them. Oaks may put up to 15 percent of their energy production into chemical defenses (which explains why stressed trees are most prone to attack: they have less energy available to produce defenses). Thus, although there may be large pools of defenses available where attacks are common and ferocious, it makes evolutionary sense in lesser situations to produce the chemicals in earnest only when they are needed. Oaks (and a number of other trees) manage with low concentrations of tannins in their leaves, but once part of the canopy is attacked, the tree will produce tannins in large quantity More than that, the tannins released into the air are detected by surrounding oaks and they in turn will produce more tannins in preparation for the onslaught. In a similar way, willow trees in Alaska that had their leaves eaten by snowshoe hares produce shoots with lower nutritional concentration and higher levels of lignin and deterrent phenols, thus rendering them less palatable. These “induced” defenses may have an effect for some time: birch trees can remain unpalatable for up to three years after being eaten.Expensive defenses are saved not only when they are not needed but also where. The North American aspen has been shown to produce fewer tannins in trees growing on fertile soils: it is cheaper to replace lost material than to defend it. Similarly, more is invested in defenses where herbivores and diseases are more common.
According to paragraph 4, what is one way that willow trees in Alaska react to having their leaves eaten by snowshoe hares?
AThey increase their production of shoots and leaves to make up for the leaves they lost.
BThey increase their investment in the production and storage of tannins.
CThey make new growth less edible by increasing the amount of protective chemicals.
DThey become highly stressed, which puts them at greater risk for further attacks.
8
Defensive chemicals are costly for the plant to produce and store; many are toxic to the plant producing them. Oaks may put up to 15 percent of their energy production into chemical defenses (which explains why stressed trees are most prone to attack: they have less energy available to produce defenses). Thus, although there may be large pools of defenses available where attacks are common and ferocious, it makes evolutionary sense in lesser situations to produce the chemicals in earnest only when they are needed. Oaks (and a number of other trees) manage with low concentrations of tannins in their leaves, but once part of the canopy is attacked, the tree will produce tannins in large quantity More than that, the tannins released into the air are detected by surrounding oaks and they in turn will produce more tannins in preparation for the onslaught. In a similar way, willow trees in Alaska that had their leaves eaten by snowshoe hares produce shoots with lower nutritional concentration and higher levels of lignin and deterrent phenols, thus rendering them less palatable. These “induced” defenses may have an effect for some time: birch trees can remain unpalatable for up to three years after being eaten.Expensive defenses are saved not only when they are not needed but also where. The North American aspen has been shown to produce fewer tannins in trees growing on fertile soils: it is cheaper to replace lost material than to defend it. Similarly, more is invested in defenses where herbivores and diseases are more common.
According to paragraph 4. what do North American aspens have in common with oaks?
AThey both require fertile soil to produce defensive chemicals.
BThey both tend to be attacked in the canopy before other tree parts.
CThey both increase the energy spent on defensive chemicals when under attack.
DThey both remain unpalatable for several years after an attack.
9
Some chemical defenses are highly toxic and will kill attackers in small doses. Known as “qualitative” defenses, they work in low concentrations. These include alkaloids present in plants such as the tansy ragwort, which is notorious for killing cattle and horses when ingested. Other chemicals work by building up in the herbivore. Referred to as “quantitative” defenses, they become more effective the more they accumulate in the animal’s body.Classic examples are phenolic resins in creosote bushes and tannins found in a number of plants. [■]Tannin is a “protein precipitant which gradually makes food less digestible, so herbivores end up starving and having stunted growth. These often have the effect of causing the herbivore to move elsewhere. [■]It is possible, for example, that the endangered British red squirrel is declining not through competition with the introduced North American gray squirrel, as commonly thought, but because of acorns. [■]Acorns (nuts from oak trees) contain digestion inhibitors that gray squirrels can disarm but red squirrels cannot. Red squirrels do well in conifer tree plantations, feeding on the more nutritious pine seeds, and where there are no oaks to give the gray squirrels a competitive edge. [■]
Look at the four squaresthat indicate where the following sentence could be added to the passage
This explains why certain species are disappearing from, some habitats.
Where would the sentence best fit？Click on a square sentence to the passage.
10
Woody plants produce a number of chemicals that provide protection against herbivores, diseases, and other plants.
ASome chemical defenses are highly toxic and can kill in low concentrations; others work either by building up in the herbivore to make food less digestible or by making the plant itself unpalatable.
BThe ability of walnut and other trees to release from their roots defensive chemicals that can kill competing plants or reduce their rate of germination was discovered as early as the first century AD.
CWhen the canopies of trees such as oaks, willows, and birches are attacked, the trees respond by producing chemicals that stop the growth of their shoots and leaves.
DTrees emit defensive chemicals into the air that can protect against attackers or limit competition from other plants.
EDefensive chemicals are costly for the plant to produce and store, and thus any plants produce them in large quantities only when predator attacks are likely.
FTrees growing on fertile soils are better able to resist diseases and herbivores and are therefore able to produce a larger number of defensive chemicals that result in a long-lasting induced defense.
