Tropisms vs. Nastic Movements

  • Have you ever seen the Windex commercial where one window is cleaned with Windex, the other window with a no-name brand cleaner, and the plant pulls itself over to the window cleaned with Windex? What was the plant trying to get to?  windex commercial

    Plants do respond to their environments although generally not that quickly.

    A tropism is a plant's response to an external stimulus that comes from a particular direction. Tropism comes from a Greek root word that means "turning." Plant Tropisms are named after its stimulus.

    Tropisms can be: positive- plant grows or bends toward the stimulus

    OR negative- plant grows or bends away from the stimulus

    touching solid object

    A nastic movement is a plant's response that does not depend on the direction of the stimulus. An example of a nastic movement would be when you touch a mimosa plant. The movement of the plant has nothing to do with the direction of the stimulus. Look at the images below and see what happens when you touch this "sensitive plant".

    Before touch  after touch

    If I give you some examples of plants in different situations do you think you could apply the terms from above? Could you tell me the mimosa plant responds with a nastic movement? If I said grass follows the sun through the course of the day could you tell me that is a positive phototropism? Click on the link to the left to take the quiz and see if you can tell what type of tropism or nastic movement is being described. Remember tropisms can be positive or negative so use those terms in combination with the different tropisms. When you're finished return to the Going Green home page.