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9.4 Plant Control Systems

9.4 Plant Control Systems. (pages 341 – 348). Organisms respond to stimuli:. In many cases, multicellular organisms move in response to events or conditions in the environment.

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9.4 Plant Control Systems

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  1. 9.4 Plant Control Systems (pages 341 – 348)

  2. Organisms respond to stimuli: In many cases, multicellular organisms move in response to events or conditions in the environment. These are all organisms responding to a stimulus: A moth flies towards a light, a zebra runs from a lion, a child dances to music

  3. Plants respond to stimuli too! What are the stimuli that cause reactions in plants? What caused the plants in the two pots to grow differently?

  4. What caused the plants in the pot to grow this way?

  5. Trophisms Phototrophism Gravitrophism • Phototrophism: the growth of a plant towards a light source. • Gravitrophism: the growth of a plant in response to the force of gravity.

  6. Phototrophism Phototrophism maximizes the amount of light absorbed by the plant’s leaves. How do plants bend towards a light source? Plants do not have muscles in their stems.

  7. Phototrophism (response to light) Cells on one side of the plant elongate and the stem curves.

  8. Phototrophism(Darwin and Darwin) Charles and Francis Darwin performed test on oat seedlings and concluded that the tip of the seedling somehow detects light. They speculated that a signal was sent downward from the plant tip.

  9. Phototrophism(Boysen and Jensen) Boysen and Jensen continued Darwins’ work. What was the nature of the signal that was coming from the tip? It was found that it must be a chemical signal. The chemical could diffuse through gelatin but not rock. Mica is impermeable to diffusion

  10. Summary of phototrophism results:

  11. Auxins: Plant Growth Chemicals Auxin: chemical produced in the plant tips that stimulates growth. If light shines on a plant from one side, the auxin moves from the plant tip to the shaded side of the stem. Active transport moves the auxin through the cells and downward.

  12. Auxin causes the shaded cells of the plant to grow longer than the cells on the lighted side. This causes the plant to curve towards the light.

  13. Gravitrophism (response to gravity) The stem of a plant placed on its side will respond by growing away from the pull of gravity. Stems show negative gravitrophism.

  14. When a root is turned on its side the root will grow downward. Roots show positive gravitrophism The mechanism of positive gravitrophism in roots is not fully understood.

  15. Naustic Response Mimosa Turgor pressure explains leaf movements in Mimosa, also known as the “sensitive plant”. This type of plant response is called nastic response. Nastic response also accounts for response in Venus Fly Trap.

  16. Cells and Complex Responses in Plants Venus Fly Trap Unwitting insects brush the leaf of the Venus fly trap. This triggers a sudden drop in turgor pressure. This causes the hinged leaf to close.

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