Explicit Details

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?

Iron is an essential micronutrient for human health, but excess levels can lead to tissue damage. In 2001, researchers discovered that the liver secretes a peptide hormone called hepcidin, which serves as the primary regulator of systemic iron balance. Hepcidin acts by binding to ferroportin, the only known cellular iron exporter found on the surface of macrophages and enterocytes. Upon binding, hepcidin induces the internalization and degradation of ferroportin. This action directly halts the release of iron into the blood plasma, effectively lowering circulating iron levels. Consequently, when hepcidin levels are abnormally low, ferroportin remains active, leading to excessive iron absorption and accumulation in vital organs.

According to the text, how does hepcidin affect circulating iron levels?