The silkworm-the larva (immature form) of the domestic silk moth–produces silk: a fine, continuous protein fiber. A very large number of invertebrates can make some type of silken thread,including moths and butterflies, but also spiders and grasshoppers.These animals create a variety of silk fibers, which they use for a variety of purposes, such as making webs, creating nests, and spinning cocoons.Variations in silk production and use appear to be one of the most important factors in giving rise to the immense diversification of insect species, which often emerged because there were so many different ways to use so many different types of silk to establish unique niches (ecological roles).
1.Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
A.Variations in silk emerged because there were many ways for insects to use silk to establish unique niches.
B.Variations in silk production and use helped insects establish unique niches and contributed to species diversification.
C.The diversification of silk-producing insect species helps explain the emergence of unique niches.
D.Insects’ variations in silk production and use occurred partly due to the immense diversification of insects in various niches.
Evolutionary biologists estimate that the ability to make silk in the ancestors to present-day Lepidoptera (the order of insects that includes more than 180.000 species of butterflies and moths) first evolved some 250 million years ago. ▊For silkworms and the larvae of other moths and butterflies, silk became a tool for undergoing metamorphosis.▊Metamorphosis is the extraordinary process during which larvae, such as caterpillars or worms, change into adult forms, such as flying insects or spiders.▊The worms weave silk cocoons as a sort of second egg inside of which they essentially consume their previous body in order to grow a new winged one.▊The cocoon is both a receptacle for this complex biochemical process and a means of protecting the defenseless insect from the environment and predators while it is metamorphosing. The silk fibers render the cocoon less palatable while also making it more difficult for would-be predators to get at the tasty protein-rich prize inside.
2.According to paragraph 2, silk fibers have which of the following functions during the metamorphosis of silk moths?
A.They provide a source of energy during the process
B.They provide protein for the development of wings
C.They provide defense from threats.
D.They speed up biochemical processes.
Nonetheless, many animals are still happy to eat the vulnerable worms during metamorphosis, raising the question of why any organism would have evolved such a risky behavior in the first place. It seems counteradaptive if not downright suicidal.Evolutionary biologists are not entirely sure, though since some45-60 percent of all the animals on the planet undergo metamorphosis, it must confer some useful advantage. The strongest current theory suggests that metamorphosis permits insects to more fully utilize available food sources in their niche while avoiding intergenerational competition. In the case of silk moths, the larvae grow rapidly while eating the leaves of mulberry trees, but the adult moth form feeds solely on the nectar of flowers This permits any given environmental niche to support both more Norms and moths,conferring an evolutionary advantage.Metamorphosis also allows the wingless larval form to burrow into plants, fungi, and meat, which would likely harm the delicate wings of the subsequent adults. Since their larvae are such efficient feeding machines, some adult insects even have enough stored energy that they do not have to eat at all during their short lifespans, freeing them to concentrate all their energies on the more important tasks of mating and egg laying.
3.In paragraph 3, why does the author point out that silk moth larvae eat mulberry leaves but the adult moths feed on flower nectar?
A.To support the argument that moth larvae consume a greater amount of food than adult moths do
B.To illustrate how having different forms during an insect’s life cycle enables them to take advantage of multiple food sources
C.To indicate that environmental niches with widely varied food sources are capable of supporting many different species
D.To explain that adult silk moths cannot eat the same food as larval silk moths because the adults’ wings would be damaged
4.According to paragraph 3, which of the following increases the amount of time some insects are able to spend on reproduction?
A.Using energy from the food they ate as larvae
B.Burrowing into plants, fungi, or meat
C.Moving to a new environment to establish a unique niche
D.Spending more of their life span in their adult form than in their larval form
It is equally fortuitous that at least some silkworms are even capable of coevolving with humans in a way that led to the animal partnership that we call domestication. In the case of silkworms, it led to silk farming, a practice first developed by the Chinese, who established a lucrative transcontinental silk trade near the end of the first millennium B.C.E. Domestication is always a two-way street in which another species must have the inherent capacity to tolerate and cooperate with humans. Silkworms’ ability to tolerate domestication becomes evident if we compare them to spiders.Spiders actually produce a superior silken fiber, yet modern attempts at domesticating spiders have largely failed because they are very territorial creatures and will often eat one another if forced to live in close proximity. Indeed, spiders’ need to make silk as adults-rather than just during a larval stage as with silkworms-may explain why they do not coexist well with other members of their own species.As is the case with mammals like wolves and humans, in many insects social behaviors are linked to juvenile hormones that make them more cooperative than aggressive.However, in spiders these juvenile hormones just happen to interfere with the biochemical synthesis of silk. So for spiders to enjoy the many adaptive advantages that come from a lifetime of silk making, it appears they had to give up the many potentialbenefits of social cooperation.
5.The word “lucrative” in the passage is closest in meaning to
A.profitable
B.extensive
C.long-lasting
D.well-known
6.The word “inherent” in the passage is closest in meaning to
A.necessary
B.natural
C.available
D.unusual
7.According to paragraph 4, people use silkworms rather than spiders to obtain silk because
A.spiders produce small amounts of silk
B.spider silk is not high quality
C.spiders are aggressive toward humans
D.spiders cannot live together in groups
8.Paragraph 4 suggests which of the following about juvenile hormones?
A.They lead to aggressive behavior in humans, wolves, and other mammals.
B.They are formed during the synthesis of silk.
C.They help spiders synthesize silk.
D.They do not interfere with silk making by silkworms.
9.Look at the four squares [▊] that indicate where the following sentence could be added to the passage.Where would the sentence best fit?
This period of transformation begins with the preparation of a shelter for the individual animal.
10.Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
Silk is a fine protein fiber made by many animals.
A.Silkworms, moths, and butterflies make silk for their transformations from juvenile to adult body forms, but other invertebrates such as spiders use silk for different purposes.
B.Insect species that can produce many different types of silk are able to establish a wide variety of niches, but Lepidoptera are limited to a unique niche suited to the single type of silk that they produce.
C.Using silk to undergo metamorphosis can provide an evolutionary advantage because larvae and adults eat separate food sources.permitting greater overall species numbers.
D.The production of silk requires large amounts of energy, which means the larvae of insects and spiders need to eat large amounts of food.
E.The domestication of silkworms is possible due to the ability of silkworms to adapt to partnership with humans, unlike other species that make better silk.
F.The hormones that allow the production of silk also cause silkworms to remain in a juvenile state, which has made it possible to farm silk on a large scale since the first millennium B.C.E.
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