Unit 11: PlantsResponse to the Environment

Response to the EnvironmentThey know what's happening...

Tropism:The growth or movement of a plant in RESPONSE to a STIMULUS.

Plant responding to touch stimulus

Person responding to heat stimulus

Lack of response to a stimulus

a.k.a Tropic Responses

1. Phototropism2. Gravitropism3. Thigmotropism

1. Phototropism

Photo = LIGHT

Tape the correct picture in the box.

Phototropism is a plant’s response to light. It will grow TOWARDS any light source that it senses. Because you know, photosynthesis. (They need lots of light)

2. GravitropismTape the correct picture in the box.

Gravitropism is a plant’s response to gravity. No matter what way you turn a plant, it will grow stem up and roots down. They can tell up from down.

Gravi = GRAVITY

Root growing down

Root growing down

Root growing down

Plant growing up

Plant growing up

Plant growing up Plant growing up

Seed = right side up

Seed = upside down Seed = sideways

3. ThigmotropismTape the correct picture in the box.

Thigmotropism is a plant’s response to touch. Some plants (like vines) feel to wrap themselves around something. Other plants like venus fly traps, sense touch and close up.

Thigmo = touch

Hormones: Not Just For PeopleHormones are like chemical text messages. They signal cells to start or stop doing certain things. In plants, hormones control things like rate of cell growth, shape of cells, and fruit ripening.

How hormones work - just read this partWhen certain situations arise, hormones increase or decrease based on the need. Then they cause the plant to respond in a certain way.

It would be like if you really like a person, so you increase the amount of texts you send them. If they like you back, they will probably respond to you. Then you will be happy.

If they don’t like you back, they will probably not respond to you. Then you will be sad.

Situation ----> Hormone Level ----> ResponseNot enough water

is reaching the roots because they

are too short

Plant makes more AUXIN

(AUXIN levels increase)

AUXIN tells roots cells to divide more, causing them to grow longer

Situation ----> Hormone Level ----> Response

Plant is too short to get sunlight

Plant makes more GIBBERELLIN(GIBBERELLIN

levels increase)

GIBBERELLIN causes the stem cells to divide more,

making the plant grow taller

gibberellin gibberellingibberellin

gibberellin gibberellingibberellingibberellin

gibberellingibberellingibberellingibberellingibberellin

Situation ----> Hormone Level ----> Response

Bananas picked before they were ripe. Too green to

make banana bread

Put them in a paper bag to collect the

ETHYLENE (ETHYLENE levels

increase)

ETHYLENE gets absorbed into the banana peel cells, causing them to

ripen faster. Now you can make banana bread!

ETHYLENE

ETHYLENEETHYLENE

ETHYLENEETHYLENE

ETHYLENE

ETHYLENE

Situation ----> Hormone Level ----> ResponsePlant is growing too

fast. There aren’t enough nutrients

available to support growth, plant is thin

and skinny

Plant makes less CYTOKININ

(CYTOKININ levels decrease)

Less CYTOKININ causes cells to divide more

slowly, causing plant growth to slow down

cytokinin

cytokinin

Hormone Overview - Just FYI

Hormones Other StuffHormones are what control a plant's response to the environment. Plants respond to their needs (similar to you) like water, sunlight, and support.

At the bottom of your notesIf you had to guess what HYDROTROPISM was a response to what would you guess based on the word?

Write your answer at the bottom of your notes.

Picture is unrelated to

the question.