AP Environmental Science 8.XII: Global Change

Practice AP Environmental Science questions on global change, climate impacts, and environmental responses.

[Maximum number: 1]

Questions 19-20 refer to the information below. In the 1960s and 1970s the Texas horned toads and lizards were found all over Central and North Texas. However, in 1977 the Texas horned lizard was put on the threatened species list because of many reasons, one being the invasion of the invasive species, the fire ant. The fire ant pushed out the harvester ants (big red ant), which was the majority of the horny toad's/lizard's diet. In addition, farmers began to use pesticide to get rid of the fire ants, an action that also killed the red ants.

In toxicology, many pesticides, like those used to control the fire ant, are tested according to the $\mathrm{LD}_{50}$ levels. $\mathrm{LD}_{50}$ levels are best described by which of the following?

A

The level that kills 50 pests in 50 minutes

B

The level that kills 50 pests out of 500

C

The level that kills the pests but leaves 50 percent of the predators alive

D

The level that kills 50 percent of the pest population of a particular species

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EIN-3.A—Define lethal dose 50% (LD₅₀) question 1