Plants in Motion Tropism in plants

Background A stimulus is anything in the environment that causes a response in an organism. The response often involves movement either toward the stimulus or away from the stimulus. Plants respond to stimuli such as touch, light, and gravity. Some responses of a plant to an external stimuli are called tropisms A tropism is generally termed “positive” if growth is toward the signal and “negative” if it is away from the signal.

How Plants respond to stimuli or Tropisms in Plants

Geotropism Response in plants to respond to gravity. The stem/shoots show negative tropism. (Against gravity.) The roots show Positive (towards gravity.)

Importance of Geotropism provide firm anchorage for roots. ensure the plant can get adequate supply of water & mineral salts Picture from http://cbse.myindialist.com/biology-x-control-and-coordination-coordination-in-plants-movement-due-to-growth/

Phototropism Response to light. When a plant grows toward light it is called a positive response to light, or positive phototropism

Importance of Phototropism enables leaves to be in a position to receive as much sunlight as possible for photosynthesis Picture from http://herbarium.desu.edu/pfk/page11/page12/page13/page13.html

Hydrotropism Response to water. Example: plants moving to a higher humidity, roots moving to a greater concentration of water.

Importance of Hydrotropism ensures that a plant gets enough water as a raw material for photosynthesis & enough mineral salts to maintain normal growth Picture from http://www.tutorvista.com/content/biology/biology-iv/plant-growth-movements/paratonic-movements.php

Thigmotropism Response to touch. The stem bends and twists around any object it touches.

Importance of Thigmotropism Gives the plant additional support. Picture from http://wikipedia.com

Nastic Movement Rapid response of rapid movements of plant organs in response to a stimulus Used as a defense. Used to trap its prey in carnivorous plants. Picture from http://www.sunnysidescience.com/plant_responses.htm Picture from http://cdn-write.demandstudios.com/upload/1000/600/10/8/391618.jpg