You will be given a definition of a task first, then some input of the task.
Given a scientific passage and an answer, generate a question for the given answer.

Passage: Like all organisms, plants detect and respond to stimuli in their environment. Unlike animals, plants can't run, fly, or swim toward food or away from danger. They are usually rooted to the soil. Instead, a plant's primary means of response is to change how it is growing. Plants also don't have a nervous system to control their responses. Instead, their responses are generally controlled by hormones , which are chemical messenger molecules. Answer: hormones
Output:
Instead of a nervous system, plant responses are generally controlled by what type of molecules, which serves as chemical messengers?