Session 74: 6.L.2.2 Explain how plants respond to external stimuli (including dormancy and forms of tropism) to enhance survival in an environment. Changes in environmental conditions can affect the survival of individual organisms and entire species. Dormancy is a period of inactivity in a mature seed prior to germination; seed remains dormant until conditions are favorable for growth and development of the new plant. Plants have mechanisms that enable them to respond to their environment. Plants grow, reproduce, and shift the position of their roots, stems and leaves in response to environmental conditions such as gravity, sunlight, temperature and day length. Tropism is a plant’s turning or bending movement toward or away from an external stimulus such as light, heat or gravity. If the tropism is positive, the plant grows toward the stimulus. If the tropism is negative, the plant grows away from the stimulus. This enhances the survival rate for that plant in a given environment. NEXT

Warm Up 1. What is this bat doing? 2. Notice the location of the stamens in this flower. How does their location ensure the reproduction of this plant?

Changes in environmental conditions can affect the survival of individual organisms and entire species.

Dormancy is a period of inactivity in a mature seed prior to germination; seed remains dormant until conditions are favorable for growth and development of the new plant.

Dormancy can happen to mature plants as well; when growth and activity are temporarily stopped, usually due to environmental conditions. When do plants go dormant?

Plants have mechanisms that enable them to respond to their environment. Plants grow, reproduce, and shift the position of their roots, stems and leaves in response to environmental conditions such as gravity, sunlight, temperature and day length.

TROPISM- There are many types of tropisms : Phototropism Geotropism Tropism is a plant’s turning or bending movement of an organism toward or away from an external stimulus such as light, heat or gravity. (“tropo” – ”turn”) There are many types of tropisms : Phototropism Geotropism Thigmotropism Hydrotropism Chemotropism Thermotropism . 3 main types If the tropism is positive, the plant grows toward the stimulus. If the tropism is negative, the plant grows away from the stimulus. Is the plant above responding positively toward sunlight? What about gravity? NEXT

Ex. Stems growing toward the window to get to the light PHOTOTROPISM (“Photo” – light) The growth response of a plant in response to light direction is called phototropism. Ex. Stems growing toward the window to get to the light NEXT

IMPORTANCE OF PHOTOTROPISM Enables leaves to be in the best position possible to receive adequate light for photosynthesis NEXT http://www.darienps.org/teachers/otterspoor/botany/tropisms/Gravitropismwlight.jpg

Geotropism is the growth of a plant in response to gravity. (“Geo” – Earth) Geotropism is the growth of a plant in response to gravity. Negative Geotropism Positive Geotropism It is the growth of a plant towards the center of the earth-down with gravity. Ex. roots growing down Negative Geotropism It is the growth of a plant away from the center of the earth-opposite from the pull of gravity Ex. stems grow up Positive Geotropism NEXT

IMPORTANCE OF GEOTROPISM Pulls roots down to anchor a plant Roots can get needed water and minerals if they stay in the soil NEXT

CORN TROPISM LAB http://www.youtube.com/watch?v=iFCdAgeMGOA&feature=related

Thigmotropism is the growth of a plant in response to touch/contact. (“Thigmo” – “touch”) Thigmotropism is the growth of a plant in response to touch/contact. Photo by Christopher Meloche Tendrils on a sweet pea Discovery Ed Clip on Plants Responsive to Touch Vines growing on a wall or fence NEXT

All of this enhances the survival rate for that plant in a given environment.

Time for a StudyJam on Plant Adaptations: http://studyjams.scholastic.com/studyjams/jams/science/plants/plant-adaptations.htm

Written Response#1: A plant is placed on a windowsill facing the sun. After a week, the plant is rotated away from the sun. How will the plant most likely respond?

SOME OTHER TYPES OF TROPISM NEXT

Chemotropism THERMOTROPISM HYDROTROPISM (“Therm” – “heat”) Thermotropism is the tendency of plants or other organisms to bend toward or away from heat. Ex. curling of Rhododendron leaves in response to cold temperatures. HYDROTROPISM (“hydro” – “water”) Hydrotropism is the growth in response to water. Ex. roots growing toward moisture Chemotropism (“Chemo” – chemical”) Chemotropism is movement caused by chemical stimuli. Ex. Growth of a pollen tube is always towards the ovules so that reproduction can occur NEXT