KEY CONCEPT Plant hormones guide plant growth and development.

1. KEY CONCEPTPlant hormones guide plant growth and development.

2. Hormones are chemical messengers. produced in one part of an organism stimulates or suppresses activity in another part Often have adaptive advantages Plant hormones regulate plant functions.

3. Gibberellins Ethylene Cytokinins Auxins Abscisic acid Five major groups of plant hormones

4. Gibberellins are plant hormones that produce dramatic increases in size. • ending seed dormancy • rapid growth of young seedlings • rapid growth of some flower stalks

5. some fruits picked before they are ripe sprayed with ethylene to ripen when reach destination Promotes abscission The detachment of leaves, flowers, or fruits • Ethylene causes the ripening of fruits.

6. final stage in cell division produced in growing roots, seeds, and fruits involved in growth of side branches • Cytokinins stimulate cytokinesis.

7. Auxins lengthen plant cells in the growing tip. • stimulates growth of primary stem • controls some forms of tropism • A tropism is the movement of plant in response to an environmental stimulus.

8. Abscisic acid Promotes dormancy in plant buds, maintains dormancy in seeds, and causes stomata to close

9. A tropism is a response in which a plant grows either toward or away from an environmental stimulus Tropisms

10. Plants can respond to light, touch, gravity, and seasonal changes. • Phototropism is the tendency of a plant to grow toward light. • auxins build up on shaded side of stem • cells on shaded side lengthen • causes stem to bend toward light

11. Solar tracking, also called heliotropism, is the motion of leaves or flowers as they follow the sun’s movement across the sky.

12. climbing plants and vines plants that grow in direction of constant wind • Thigmotropism is a plant’s response to touch-like stimuli.

13. positive gravitropism is downward growth (roots) negative gravitropism is upward growth (shoots) • Gravitropism is a plant’s response to Earth’s gravitational pull.

14. Chemotropism Plant growth that occurs in response t oa chemical is called chemotropism An example of chemotropism is the growth of a pollen tube after a flower is pollinated.

15. Thigmonastic movements Occur in response to touch, such as the closing of the leaf trap of a Venus’ flytrap around an insect. Nyctinastic movements Occur in response to the daily cycle of light and dark,such as the cyclical vertical and horizontal positioning of leaves in prayer plants. Nastic Movements

16. triggers some plants to flower triggers fall colors/winter dormancy of deciduous trees • Photoperiodism is a response to the changing lengths of day and night. • Vernalization is the promotion of flowering by cold temperatures • Farmers often plant wheat seeds in the fall so that the seedlings can be exposed to winter temperatures and will flower before summer droughts begin