Tropisms!!!!!!

WOOOO!!! Let's discuss TROPISMS! First, let's define what the word means.

Tropism- The growth of a biological organism, usually plants, in response to environmental stimulus. A definition never really hits it on the nail, so we'll discuss three types of tropisms.

1. Phototropism (no, there is no "h" in the word) is a plant's response to light. When the shoots grow towards the light, it's called positive phototropism. When the shoots grow away from the light, it's called negative phototropism. When the apical meristems on all sides of the plant absorb equal amounts of light the plant grows evenly; however, when light is only absorbed by apical meristems on one side of the plant, it will grow towards the light.

http://www.yksd.com/distanceedcourses/Courses09/Biology/lessons/FourthQuarter/Chapter13/13-1/images/II17phototropism1.gif

2. Geotropism is a plant's response to gravity, the roots always grow down through the soil from the seed no matter how you plant it.

http://www.omegagarden.com/images/photos/geotropism.jpg

In this image you will see 3 types of Geotropism.

• The first seed, which is planted sideways shows Transversal Geotropism, where the root extends sideways and pushes down through the soil due to gravity.
• The second seed, which is planted upside down shows Negative Geotropism, where the root pushes up and then pushes back down into the soil due to gravity.
• The third seed is planted normally, it shows Positive Geotropism, where the root grows straight down and pushes through the soil due to gravity once again.

3. Thigmotropism is the plant's response to touch or contact.

http://www.alphadictionary.com/images/flytrap.gif

I thought this image was a very good example of thigmotropism. As you can see, once the insect makes contact with the plant, the plant traps the insect for some good old NUTRITION!
That's really as simple as it gets. Some other plants use thigmotropism to protect themselves from predators who feed on their surfaces by closing their leaves.

Success!