How does a plants ability to respond to a stimulus play a role in its evolution through Natural Selection?

Natural Selection

Like Animals, plants have developed a system that will help them regulate cellular responses to external stimuli.

​

​Plant Stimuli

Animals have a nervous and endocrine system that help them regulate the internal environment through elecrtic impulses and chemical signals called hormones.

​

Control and Regulation

While plants do not have a nervous or specific endocrine system, they do produce and secrete hormones that are used to ensure the growth of the plant organism.

​

Plant Hormones

Phototropism

• Stimulus: Light Energy

• Positive Tropism: Shoots grow towards light.

• Negative Tropism: Roots grow away from light.

Gravitropism or
(Geotropism)

• Stimulus: Gravity

• Positive Tropism: Roots grow towards gravity

• Negative Tropism: Shoots grow away from gravity.

Thigmotropism

• Stimulus: Touch

• Positive Tropism: Growth toward touch

• Negative Tropism: Growth away from touch.

Hydrotropism

• Stimulus: Water

• Positive Tropism: Root growth toward water

• Negative Tropism: Stem growth away from water.