Plant Responses to the Environment

Plant Tropisms

•When you hear the word

“tropism”, what do you think of?

Maybe it reminds you of the words “tropical island”

Or “Tropical rainforest?”

Or maybe you’re just a tired student who is sick of hearing about plants

and just wants a stinking answer?!?!

I swear, if she makes me take notes on plants

again, I will throw this book at the wall and run

for the hills!

So here are the facts…

• Plant tropisms–Plants respond to an environmental stimulus by growing in a particular direction

–Growth in response to a stimulus is called a tropism

• Like a 7th-grader’s attitude, a tropism can be positive or negative

Forget that book report, I’m going to IM my friends

all night!

I better hurry up and get this

report finished..then I’ll have more time

for math problems!

POSITIVE NEGATIVE

• Light Tropism–When you place a houseplant so that it gets light from only one direction, such as a window, what happens?

–You may have noticed that the plant will start bending towards the light

• This is known as phototropism

• Gravity Tropism– Plant growth also changes in

response to the direction of gravity– This change is called gravitropism– If a plant is placed on its side or

turned upside down, the shoot tips have a negative gravitropism (away from the center of the Earth) and the roots have a positive gravitropism (towards center of Earth).

This plant is on its side, and the shoots still grow upward!

Seasonal Changes

• Plants living in regions with cold winters can detect changes in seasons because the days get shorter and nights get longer

• The opposite happens when spring and summer approach

• Plants respond to the change in the length of day

Length of Day– short-day plants flower when night length is

long– long-day plants flower when night length is

short

Seasons and Leaf Loss

– Evergreen trees shed some of their leave year-round so that some leaves are always on the tree

• leaves are often covered with a thick cuticle to protect leaves from cold and dry weather

– Deciduous trees lose all of their leaves around the same time each year (either cold or dry season)• loss of leaves

helps plants survive low temperatures or long periods without rain

Seasons and Leaf Color – leaves of deciduous

trees may change color before they are lost

– as fall approaches, green chlorophyll breaks down and orange and yellow pigments are revealed

– they’re usually hidden by the green chlorophyll, but they are always present