Plant Movements and Growth Responses

Chapter 11.8

What is Plant Movement?• Plant movement is a response to stimuli such

as touch which allows the plant to move in a way that protects itself.

Example of Plant Movement:

• The Mimosa Plant responds to touch. Its leaves droop when touched in order to look less appealing to grazing animals and to protect it from rain and hail.

How Does This Happen?

Plant movement happens when the plasma membranes allow potassium and other ions to leak out of the cells, causing outward osmosis to occur. This means turgor pressure decreases in the plant cells causing the plant to wilt.

What are Growth Responses?

Growth responses are changes in how the plant grows due to its environmental factors. This is also known as tropism, which is growth toward or away from a stimulus. Examples of these factors include light and gravity. There are two types of growth responses: phototropism, and gravitropism.

What is Phototropism?

• Phototropism is growth towards light. • Cells on the lighted side of a sprout stop

growing, while the cells on the shaded side of a sprout continue to elongate. This results in the sprout growing towards the light.

How to Auxins Effect Phototropism?

• In phototropism, the tip or the shoot produces an auxin that causes bending.

• At first The auxin is spread evenly down all sides if the shoot, but it is transported horizontally as well. When light is only on one side of the spout the auxin moves from the lighted side to the shaded side. The auxin stimulates the synthesis of enzymes which allow the cells on the shaded side to elongate.

What is Gravitropism?

• Gravitropism is growth towards or away from Earth’s gravitational pull.

• Different parts of a plant react differently to gravity.– Negatively gravitropic- grows away from the earth

(Ex: stems.)– Positively gravitropic- grows towards the earth (Ex:

roots.)

Video!

Moving plant video