Transcript Plant Responses - Madison County Schools

Plant Responses
Tropism
• A plant’s growth response toward or away
from a stimulus.
• Positive if it grows TOWARDS the stimulus.
• Negative if it grows AWAY from the stimulus.
• These can be in response to LIGHT, TOUCH OR
GRAVITY.
Light
• Light =PHOTO
• Phototropism is when a plant grows toward
the light.
• This is positive.
Gravity
• Plants’ roots grow down while the stems and
leaves grow up.
• Gravity comes from the center of Earth.
• GRAVITROPISM
• So ROOTS-show positive gravitropism
• So STEMS (shoots) and leaves show negative
gravitropism
• A plant laying on its side will have the stems grow
up toward the sun and the roots grow downward
Touch
• Thigmotropism– growth in response to touch
• Vines, green beans have tendrils that will coil
around a wire, fence or another tree.
touch
gravity
light
Hormones
• Plants have hormones that cause them to
respond to these stimuli.
• They also control other activities such as
germination, formation of flowers, shedding
of leaves, etc.
Seasons
• Photoperiodism-a response to a seasonal change
based on the amount of light and darkness each day.
• Short day—means they like long nights so
they bloom in the fall and winter. Ex-poinsettia
• Long day mean they like short nights so they
bloom in the spring and summer. Ex.-clover
• Some must have a certain number of hours of darkness—
critical night length
• Others are not sensitive to periods of light and dark and are
called day –neutral plants.
Dormancy
• Inactive period
• Deciduous—lose leaves all at one time to
survive freezing temperatures and lack of
liquid water.
– The chlorophyll actually breaks down to reveal the
hidden colors of red and yellow.
• Evergreen- can keep leaves all year b/c leaves
are needle shaped and help snow fall off of
them and conserve water loss.
Life span
• Annual-plants live one year
• Biennials-plants complete a 2 year life cycle
• Perennials-plants that live for many years