WHAT IS TROPISM?

Tropism is the growth in response to an external or environmental stimulus. 

TROPO = TURN

STIMULUS = SOMETHING THAT CAUSES A REACTION

Tropism can be either NEGATIVE or POSITIVE.

When there is a negative tropism, the plant moves "AWAY" from the stimulus and when there is positive tropism, the plant moves "TOWARDS" the stimulus.

TYPES OF TROPISM

PHOTOTROPISM

This is the movement of plant towards LIGHT.

Positive Phototropism - The Stem Tip moves toward the stimulus to get maximum light for photosynthesis.

Negative Phototropism - The Root Tip moves away from the stimulus which lessens the effects of drying out.

This type of tropism is important as it helps the plant and its leaves be in the best condition for it to be able to receive enough light for photosynthesis.

GEOTROPISM

Geo = Earth

This is the growth of plants in response to GRAVITY.

Positive Geotropism - The Root Tip moves toward gravity or toward the center of the earth which gives it more chance of finding moisture.

Negative Geotropism - The Stem Tip moves away from gravity or away from the center of the earth which gives it more chance of finding light.

This type of tropism is important as when roots are pulled down to support the plant, it makes it possible for the roots to the get the needed water and minerals.

THIGMOTROPISM

The growth of plants in response to TOUCH or CONTACT.

*In the animation shown above, the tendrils of the plant feels the solid object near to it, which results to the coiling response.

Positive Thigmotropism - The movement of plant toward touch or contact.

Negative Thigmotropism - The movement of plant away from touch or contact. There are some cases when plants close up when they are touched.

This type of tropism is important as it serves as support to the leaves as they grow higher to reach the sun to make more food.