单选题 Perhaps the most familiar plant movement belongs to one species of mimosa called the sensitive plant. Within seconds, it can lower its leaves and make its tiny leaflets close up like folding chairs. This movement is thought to be initiated by electrical impulses remarkably similar to nerve signals in animals. But without the animals' sophisticated motion machinery, the mimosa has had to be creative in devising a way to move.
For motion, the plant depends on tiny, bulb-shaped organs located at the base of each leaf stalk and leaflet. Called pulvini, these organs hold the plant parts in place. When the mimosa is stimulated—say, by a crawling insect or a sudden change in temperature—an electrical impulse sweeps through the plant. This causes potassium and then water to be shifted from certain cells in the pulvini to others, quickly turning one side of the organs flaccid. Because the pulvini can no longer support the leaves and leaflets, this shift results in a corresponding change in their position.

单选题 The passage is mainly concerned with the ______.

单选题 The author mentions folding chairs in the first paragraph in order to ______.

单选题 It can be inferred from the passage that the mimosa is called the sensitive plant because it ______.

单选题 According to the passage, the sensitive plant's leaves move quickly when parts of the pulvini ______.

单选题 According to the passage, what causes potassium and water in the mimosa to shift from some cells to others?