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Plant Hormones

Plant Hormones. A hormone is a complex chemical produced in very small amounts Usually they are produced in one part of an organism and travel to another part to effect a target cell Insulin is an example of a hormone we studied in the human digestive system.

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Plant Hormones

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  1. Plant Hormones

  2. A hormone is a complex chemical produced in very small amounts • Usually they are produced in one part of an organism and travel to another part to effect a target cell • Insulin is an example of a hormone we studied in the human digestive system

  3. Plants use hormones to coordinate their growth in response to internal and external factors • Internal Factors: repair , reproduction • External Factors: light, gravity, nutrients, competition

  4. Auxins • Allow plants to move in response to light

  5. In the stem • Auxin molecules move away from the light source and cause cell elongation in the cells farthest from the light. • This causes the plant to bend toward the light

  6. In the root • Auxins have the opposite effect • High concentrations of auxin inhibits elongation so these cells are shorter and the cell bends away from light

  7. Gibberellins • Work with auxins to promote cell elongation • Work alone to promote leaf growth and flowering • Also control fruit development Without Gibberellins With Gibberellins

  8. Cytokinins • Promote cell division and cell differentiation • Involoved in seed germination and flowering • Also prevent cells from aging and can be sprayed on cut flowers to keep them fresh

  9. Abscisic acid (ABA) • Inhibits plant growth • Slows down growth and induces dormancy

  10. Ethylene • Causes ripening of fruit • Also produced in large amounts by over-ripe fruit • Used in conjunction with CO2 to control fruit ripening for commercial use • Unripe fruit is stored in CO2 to prevent ripening during transport then the fruit is stored in ethylene to ripen before being sold

  11. Tropisms and Turgor Responses

  12. Plant responses to an external stimulus • Positive Tropism: growth toward a stimulus • Negative Tropism: growth away from a stimulus

  13. Phototropism • Bending and growth of a plant in response to a light source • Leaves and Stems usually show positive phototropism • Roots usually show negative phototropism

  14. Gravitropism/Geotropism • Growth in response to gravity • Stems show negative gravatropism • Roots show positive gravatropism

  15. Thigmotropism • Bending and growth in response to touch • Eg. Vines grow around other objects for support

  16. Chemotropism • Growth in response to certain chemicals in the environment

  17. Hydrotropism • Special type of chemotropism • Growth in response to water

  18. Turgor Response • Rapid movement in response to a stimulus • Due to changes in turgor pressure • The rigidness in a plant cell due to high water content

  19. Venus fly trap uses turgor responses to catch insects • Sunflowers use it to trach the sun like a moving satellite dish

  20. Plant Adaptations • Read pg 563-567 and summarize very briefly each of the adaptations plants can make to various conditions.

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