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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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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
Plants use hormones to coordinate their growth in response to internal and external factors • Internal Factors: repair , reproduction • External Factors: light, gravity, nutrients, competition
Auxins • Allow plants to move in response to light
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
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
Gibberellins • Work with auxins to promote cell elongation • Work alone to promote leaf growth and flowering • Also control fruit development Without Gibberellins With Gibberellins
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
Abscisic acid (ABA) • Inhibits plant growth • Slows down growth and induces dormancy
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
Plant responses to an external stimulus • Positive Tropism: growth toward a stimulus • Negative Tropism: growth away from a stimulus
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
Gravitropism/Geotropism • Growth in response to gravity • Stems show negative gravatropism • Roots show positive gravatropism
Thigmotropism • Bending and growth in response to touch • Eg. Vines grow around other objects for support
Chemotropism • Growth in response to certain chemicals in the environment
Hydrotropism • Special type of chemotropism • Growth in response to water
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
Venus fly trap uses turgor responses to catch insects • Sunflowers use it to trach the sun like a moving satellite dish
Plant Adaptations • Read pg 563-567 and summarize very briefly each of the adaptations plants can make to various conditions.