Question

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dead zones are areas near areas where heavy agricultural activity spills fertilizer runoff into the water systems. for example, an 8,500 square mile dead zone forms annually in the gulf of mexico near the site at which the mississippi river discharges. the mississippi river drains fertilizer runoff from farms throughout the midwest. when excessive nutrients, like nitrogen and phosphorus, from fertilizers enter the ocean, they rapidly increase productivity to promote a large algae bloom. however, when the algae die, the resulting bacterial decomposition of the plant matter depletes the oxygen in the water. as oxygen levels decline, animals may experience a variety of physiological effects. ultimately, mobile animals that can leave will flee the area while those that cannot flee will die. decreased oxygen levels—called hypoxia—in the early stages of dead zone formation present several threats to organisms. scientists examining the distribution of the atlantic croaker, a species of fish, determined that exposure to hypoxia is linked to a decline in the number and quality of eggs produced by females. other scientists have found that hypoxia decreases the activity of genes that control production of sex hormones and sexual differentiation in developing fish embryos. these scientists determined that 75% of the croaker fish develop in a hypoxic environment give rise to... dead zones are large areas in the ocean and other bodies of water that do not have enough oxygen to support marine life. approximately 400 dead zones have been found globally. these dead zones are typically linked to nitrogen and phosphorus contamination from agricultural runoff. the passage describes the formation and consequences of dead zones. what reasoning from the passage best explains how exposure to hypoxia can lead to species extinctions? a. the input of excessive nutrients from fertilizers promotes the growth of algae in watersheds. b. hypoxia decreases the abundance of females in a population and reduces reproductive output. c. species that are mobile are able to leave areas in which dead zones are forming. d. chronic hypoxia induces sex changes in fish, leading to an overabundance of females.

Explanation:

El pasaje explica que la hipoxia (baja concentración de oxígeno) en las zonas muertas se debe a la entrada de nutrientes excesivos (como nitrógeno y fósforo) en el océano. Estos nutrientes promueven el crecimiento de algas, las cuales, al morir y descomponerse, consumen oxígeno, lo que reduce los niveles de oxígeno en el agua. Los animales móviles (como peces) pueden dejar el área para sobrevivir, pero aquellos que no pueden (como algunas especies marinas) mueren. La hipoxia también puede tener otros efectos, como la disminución de la producción de hembras en ciertas especies de peces.

Answer:

B. Hypoxia decreases the abundance of females in a population and reduces reproductive output.