Precursors of these cells differentiate in response to dimers of SPEECHLESS, MUTE, and FAMA proteins with SCREAM or SCRM2 (“scream two”). They’re not o·o·cytes, but these cells’ function may be regulated by aluminum-activated malate transporters like QUAC1 (“quack one”). A “master switch” of metabolism, the potassium channel GORK, is primarily studied in these cells. The kinase BLUS1 mediates (*) phototropin signaling in these cells. These cells activate an H-plus-ATPase in response to blue light, which increases their turgor pressure, (10[1])as do antitranspirants (10[1])like abscisic acid. In organisms (10[1])that use crassulacean (10[1]-5[1])acid metabolism, these cells activate (-5[1])at night, (10[1])allowing (-5[1])carbon dioxide to enter. For 10 points, name these cells that flank stomata (10[1])in pairs on the undersides of plant leaves. ■END■ (10[3])