Information and Ideas

The scaly-foot gastropod (*Chrysomallon squamiferum*), a hydrothermal vent snail, possesses a unique shell structure composed of three distinct layers. The outermost layer is reinforced with iron sulfides, primarily greigite, which gives the shell a metallic appearance and magnetic properties. The middle layer consists of a spongy organic structure that acts as a shock absorber against mechanical attacks from predators. The innermost layer is made of aragonite, a common form of calcium carbonate. While researchers initially hypothesized that the iron-rich outer layer serves as a defense against chemical toxicity, recent studies demonstrate that its primary function is mechanical, dispersing the energy of crushing attacks from crabs and other predators by cracking along microscopic lines without compromising the underlying structural layers.

Based on the text, what is true of the outermost layer of the scaly-foot gastropod's shell?

Forest soil compaction from heavy machinery reduces soil macroporosity, which limits oxygen diffusion to tree roots. Some tree species, such as the black alder (*Alnus glutinosa*), adapt to oxygen-poor soils by developing hypertrophied lenticels—porous tissue structures on their trunks that facilitate gas exchange with the atmosphere. Ecologist Dr. Marcus Vance found that when *A. glutinosa* specimens grew in compacted soils, their root respiration rates remained stable despite low soil oxygen. However, when Vance artificially wrapped the trunks of these specimens with airtight barriers, their root respiration rates fell drastically.

Which choice most logically completes the text?

In 1938, museum curator Marjorie Courtenay-Latimer discovered an unusual fish among the catch of a local trawler in South Africa. The specimen was later identified by ichthyologist J.L.B. Smith as a coelacanth (*Latimeria chalumnae*), a lineage of lobe-finned fish previously believed to have gone extinct approximately 66 million years ago. While prehistoric coelacanth fossils are frequently found in shallow-water deposits, the modern species resides primarily in deep-sea habitats, such as volcanic slopes at depths of several hundred meters. This environmental shift explains why the coelacanth eluded scientific detection for decades, as deep-water ecosystems remained largely inaccessible to early marine biological surveys.

Based on the text, what is true of coelacanths?

The bar-headed goose (*Anser indicus*) is famous for its high-altitude migration over the Himalayas. Unlike most birds that fly at lower altitudes where oxygen is abundant, these geese routinely fly at altitudes exceeding 8,000 meters. To sustain flight in such hypoxic environments, the bar-headed goose possesses hemoglobin with an exceptionally high affinity for oxygen, allowing it to load oxygen at its lungs even under low pressure. Additionally, their capillaries are spaced closer together in their flight muscles compared to other geese, which decreases the diffusion distance for oxygen from the blood to the muscle cells. However, this adaptation does not significantly increase their overall aerobic capacity under sea-level conditions.

According to the text, which statement is true about the physiological adaptations of the bar-headed goose?

Planetary scientists studying Gale Crater on Mars have identified deposits of manganese oxides, minerals that on Earth form only under highly oxidizing conditions, often facilitated by atmospheric oxygen or microbial activity. Since Mars lacks a modern oxygen-rich atmosphere, some researchers inferred that the Martian atmosphere was once highly oxygenated. However, geologist Chloe Vance demonstrated in laboratory simulations that manganese can be oxidized by perchlorates—which are highly abundant in Martian soil—when exposed to ultraviolet radiation, even under anoxic conditions. Which choice most logically completes the text?

The hydrothermal vent worm *Alvinella pompejana* is known for its remarkable tolerance to extreme heat. Scientists hypothesized that the dense layer of filamentous bacteria coating the worm’s back acts as a protective thermal blanket, insulating it from the scalding vent water. To test this, researchers placed worms with intact bacterial layers and others with their bacterial layers removed into chambers that simulated fluctuating vent temperatures. If the bacteria functioned as an insulator, the worms without bacteria would show more rapid internal temperature fluctuations. However, the researchers found that internal temperature changes occurred at the same rate in both groups of worms. Which choice most logically completes the text?

Archaeologists analyzing organic residues on pottery vessels from the Neolithic site of Çatalhöyük discovered traces of milk fat along with barley husks. While some researchers have argued that milk was consumed exclusively as a liquid beverage, others point out that the pottery vessels were frequently heated to high temperatures. Liquid milk, when heated directly over open fires in unglazed pots, easily scorches and curdles, rendering it unpalatable. However, when barley is simmered in milk to create a thick porridge, the starches in the grain act as a stabilizing agent, preventing the milk from scorching during the cooking process. Which choice most logically completes the text?

Discovered in 1995 on the mouthparts of the Norway lobster (*Nephrops norvegicus*), the microscopic organism *Symbion pandora* belongs to the phylum Cycliophora. To anchor itself, the organism utilizes an adhesive disk located at its base, attaching to the lobster's sensory bristles, or setae. *Symbion pandora* does not prey on its host; instead, it consumes microscopic food debris generated when the lobster feeds. Intriguingly, its reproductive cycles are synchronized with the lobster's molting schedule. When the host sheds its exoskeleton, the organism initiates a sexual reproduction phase, producing free-swimming larvae that can quickly colonize the lobster's newly formed outer shell, thereby maintaining the association across generations.

Based on the text, what is true of *Symbion pandora*?

Great Zimbabwe, a medieval city in the southeastern hills of Zimbabwe, is renowned for its monumental stone walls. Constructed between the 11th and 15th centuries by the ancestral Shona people, these walls are unique because they were built entirely using dry-stone masonry, meaning no mortar was used to bind the granite blocks together. The largest structure, the Great Enclosure, has walls reaching heights of over 30 feet. While early European investigators incorrectly hypothesized that the city was built by foreign civilizations, modern archaeological evidence confirms that the local Shona population designed and constructed the complex. The walls likely served as a symbol of royal authority and prestige rather than primary defensive fortifications, given their layout and lack of defensive features.

According to the text, which statement is true about the construction of the walls at Great Zimbabwe?

Ancient Roman builders achieved extraordinary structural durability in maritime concrete structures, such as piers and breakwaters, by utilizing a specific mix of volcanic ash known as pozzolana. Unlike modern Portland concrete, which degrades when exposed to seawater, Roman concrete undergoes a beneficial chemical reaction upon contact with saline ocean water. Specifically, the seawater dissolves the volcanic crystals and tuffs within the concrete, which subsequently recrystallizes as a rare mineral called aluminous tobermorite. This mineral reinforces the cohesive structure of the concrete over centuries, rather than weakening it. Consequently, instead of eroding, Roman maritime concrete structures actually grow stronger over time when submerged in marine environments.

Based on the text, what is true of Roman maritime concrete when it is exposed to seawater?

In conservation chemistry, researchers analyzing seventeenth-century European oil paintings noticed that yellow paint layers containing lead-tin yellow (type I) show significantly less degradation in high-humidity environments than do those containing type II lead-tin yellow. The researchers determined that type I lead-tin yellow contains a high crystalline silicon dioxide fraction, which forms a protective matrix around the lead carboxylate complexes that are prone to moisture-induced degradation. Conversely, type II lead-tin yellow lacks this high crystalline silicon dioxide content, leaving its carboxylate complexes fully exposed to ambient water molecules.

Which choice most logically completes the text?

In subglacial lakes beneath the Antarctic Ice Sheet, primary production cannot rely on photosynthesis due to the absolute absence of sunlight. Instead, chemosynthetic microbes oxidize inorganic compounds, such as iron or sulfur, to generate energy. In Lake Mercer, researchers discovered high concentrations of dissolved organic carbon (DOC) alongside these chemosynthetic communities. Because the ice sheet has isolated the lake from the atmosphere for thousands of years, this DOC cannot have originated from recent photosynthetic activity. However, analysis revealed that the DOC molecules are structurally similar to those produced by marine phytoplankton, which require sunlight. Which choice most logically completes the text?

During boreal forest fires, the combustion of organic matter produces pyrogenic carbon (charcoal), which is highly resistant to microbial decomposition. Some ecologists hypothesized that this carbon represents a long-term sink that helps offset carbon dioxide emissions from the fire. However, researcher Maya Lin and her team demonstrated that pyrogenic carbon particles adsorb dissolved organic compounds from the soil, concentrating easily degradable nutrients. This process stimulates local soil microbe activity, which in turn increases the decomposition rate of nearby unburned soil organic matter. Therefore, while pyrogenic carbon itself remains stable, its presence in the soil may ______

Which choice most logically completes the text?

The Antarctic hair grass (*Deschampsia antarctica*) is one of only two flowering plant species native to Antarctica. To survive the region’s extreme cold and high ultraviolet (UV) radiation, the plant produces high concentrations of sucrose and specialized proteins, such as dehydrins. Sucrose acts as a natural cryoprotectant, preventing ice crystal formation within the plant's cells, while dehydrins stabilize cell membranes during sudden freezing events. Researchers have also observed that *D. antarctica* exhibits an unusually high rate of self-pollination, a reproductive strategy that minimizes its reliance on insect pollinators, which are extremely scarce in the harsh Antarctic environment.

Based on the text, what is true of the dehydrins produced by *Deschampsia antarctica*?

Scholars studying the evolution of Indo-European languages have traditionally relied on comparative reconstruction. Recently, researchers applied evolutionary biology models to vocabulary databases, treating words as traits that mutate over time. These models revealed that high-frequency basic vocabulary items, such as pronouns, mutate at a much slower rate than low-frequency terms, such as words for specific tools. Because high-frequency words are reinforced daily within a speech community, they remain highly resistant to replacement, whereas low-frequency words are more susceptible to borrowing during cultural contact. Thus, in an ancient language that experienced intense and prolonged contact with neighboring tongues, ______

Which choice most logically completes the text?

In a study of the history of technology and metallurgy, researchers analyzed copper artifacts from the Bronze Age in the Aegean region. It was previously assumed that smiths preferred copper sourced from nearby local mines due to transportation difficulties. However, chemical analysis of the isotopic signatures of trace lead impurities in these artifacts reveals that a substantial portion of the bronze objects found in coastal settlements matches copper deposits from distant western Mediterranean islands, whereas artifacts found in inland settlements match local mainland deposits. This pattern remained consistent even during periods of regional conflict that disrupted overland trade routes. Which choice most logically completes the text?

In paleoclimatology, the ratio of oxygen isotopes ($\delta^{18}\text{O}$) in stalagmites is used to reconstruct historical rainfall, as wetter periods typically result in lower $\delta^{18}\text{O}$ values in the precipitated calcium carbonate. However, researchers analyzing a stalagmite from Spain’s system of caves noticed that during a documented multi-decade drought in the thirteenth century, the stalagmite’s $\delta^{18}\text{O}$ values remained persistently low. They hypothesized that the cave's drip water during this dry spell was fed by a massive, deep aquifer that takes decades to filter water downward, rather than by immediate precipitation. If this hypothesis is correct, it suggests that the Spanish stalagmite ______

Which choice most logically completes the text?

In urban environments, some species of leafcutter bees (*Megachile*) have adapted to using synthetic materials for nest construction. Researchers J. MacIvor and A. Moore documented that *Megachile rotundata* collected pieces of polyurethane plastics, such as shopping bags, to build their brood cells. While traditional nests made of leaves allow moisture to escape, the non-porous plastic cells trapped moisture inside. This trapped moisture led to increased mold growth within the nests, which consequently reduced the survival rate of the offspring. However, the plastic-constructed nests also demonstrated a notable benefit: they experienced significantly fewer infestations by parasitic wasps compared to nests constructed from natural leaves.

Based on the text, what is true of the *Megachile rotundata* nests made from polyurethane plastics?

Cathedral termites (*Nasutitermes triodiae*) build massive mounds in northern Australia that can reach heights of up to eight meters. These structures are designed to maintain a stable internal environment despite external temperature fluctuations. To regulate internal carbon dioxide levels, the termites construct a complex network of flutes and ventilation shafts on the northern, sun-facing side of the mound. Research by biologist Dr. Fiona Vance demonstrates that these shafts rely on solar heating of the mound's outer walls to drive convective air currents, which continuously flush out stale air. Conversely, the subterranean nesting chambers remain sealed off from this ventilation loop to preserve the high humidity levels required for the survival of the termite larvae.

Based on the text, what is true of the ventilation shafts in the mounds of *Nasutitermes triodiae*?

In a 2018 study of the ancient city of Teotihuacan, archaeologist Linda Manzanilla analyzed the isotopic composition of human remains from different neighborhoods. She discovered that individuals buried in the multiethnic neighborhood center of Teopancazco consumed a diet rich in marine resources, such as fish and shellfish, which were imported from the Gulf Coast. In contrast, remains from the wealthier neighborhood of Tlajinga showed a diet dominated by terrestrial resources, specifically maize and small game. Manzanilla concluded that residents of poorer, multiethnic sectors had access to long-distance trade networks that supplied coastal foods, whereas wealthier enclave residents relied primarily on local agricultural production.

Based on the text, what is true of the diet of the individuals buried in Teopancazco?