Plant Responses: Part 18SCIENCE: Wed. Feb. 16, Thurs. Feb.

17

What are plant responses?• All living organisms will respond to a stimulus,

including plants• A stimulus is anything in the environment that

changes an organism’s behavior– Example: If you are sitting in a dark room watching a movie and

you hear the telephone ring, you may jump. You have just responded to the stimulus by changing your behavior!

• Examples of plant stimuli: light, temperature, amount of water, gravity

Tropisms• Tropisms are responses of a

plant to an outside stimulus- Outside of an

organism- An example of an

inside stimulus would be the beating of your heart

We will learn about 3 types:• Thigmotropism• Phototropism• Gravitropism

Thigmotropism

• Thigma means touch in Greek

• If you touch certain plants, this changes the plant’s behavior

• E.g. in a pea plant, if something touches one of its stems/leaves, it will wrap itself around something

Phototropism• When a plant responds to light: a plant will

bend towards the light • If a plant is growing towards light, it is called

positive phototropism– If it is growing away from the light, it is called

negative phototropism

Gravitropism

• Response of a plant to gravity• Plants with roots growing downwards is called

positive gravitropism– If plants have a stem growing upwards, it is called

negative gravitropism

– Click to see animation