How plants respond to stimuli

What’s a stimulus? Things in the environment that can cause change or a reaction Ex. Change in temperature, a loud noise, the presence of a predator Extra: The Plural form of stimulus is Stimuli The reaction to a stimulus is called a response

Can Plants respond to stimuli? YES! Plants respond to: Sunlight Water Gravity Touch We call these responses Tropisms

What’s a tropism? A tropism is a plant’s movement in response to its environment.

Tropisms can be positive or negative movement TOWARD the stimulus Movement AWAY from the stimulus

Phototropism Movement of plants toward light Plant response: Stems and leaves turn toward light Why? Maximize amount of sun for photosynthesis to make their food. Phototropism http://www.youtube.com/watch?NR=1&v=KQOC_bPrqFs&safety_mode=true&persist_safety_mode=1

Geotropism Movement of plants in response to gravity plant response: 1. roots grow down toward gravity 2. shoot, stems, and leaves grow up away from gravity Why? Allows plants to grow properly and get nutrients and sunlight http://www.youtube.com/watch?v=mYZXax8V_L0&feature=related&safety_mode=true&persist_safety_mode=1

Hydrotropism Movement of plant toward water. Plant response: roots will move toward water Why? Water is needed for photosynthesis, to transport nutrients, and turgor pressure http://virtualastronaut.tietronix.com/textonly/act25/text-plants.html

Thigmotropism Plants moving in response to touch. Plant response: 1. Positive is toward touch (vines wrap around structures) 2. Negative is away from touch (some plants close up when touched) Why? to reach sunlight (positive) or to protect itself (it’s movement may scare away a predator) http://www.youtube.com/watch?v=8HeedWWe6VA&feature=related&safety_mode=true&persist_safety_mode=1

Review

Geotropism Gravity causes a response in plant growth In the picture above, which part of the plant exhibits positive tropism, and which exhibits negative tropism?

Hydrotropism The way a plant grows or bends in response to water Why would it be important for some parts of a plant to be pulled toward water?

Thigmotropism Plants bend and grow because of touch. What are some other ways a plant can be “touched”?

Phototropism The way a plant grows or bends in response to light. Why do you think sunflowers were given their nickname?

Draw the pictures

Hydroptropism

Geotropism

Phototropism

Geotropism

Phototropism

Thigmotropism

TROPISM QUIZ Identify the type of tropism in the following pictures

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7 http://www.youtube.com/watch?v=Ze8NV7cvW8k&feature=results_main&playnext=1&list=PL5464C68C7644DD4D&safety_mode=true&persist_safety_mode=1

8

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10 http://www.youtube.com/watch?v=8SkKuwbmR5Y&feature=related&safety_mode=true&persist_safety_mode=1

11 http://www.youtube.com/watch?v=9sggQQuBU40&feature=related&safety_mode=true&persist_safety_mode=1

12

13 http://www.youtube.com/watch?v=mYZXax8V_L0&safety_mode=true&persist_safety_mode=1

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15 http://www.youtube.com/watch?v=8HeedWWe6VA&feature=fvsr&safety_mode=true&persist_safety_mode=1

16 http://www.youtube.com/watch?v=FC5eBkDJbMs&feature=BFa&list=PL5464C68C7644DD4D&lf=results_main&safety_mode=true&persist_safety_mode=1

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18 http://www.youtube.com/watch?v=Zq3UuHlPLQU&feature=related&safety_mode=true&persist_safety_mode=1

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20 http://www.youtube.com/watch?v=frmyzIhD29Q&safety_mode=true&persist_safety_mode=1