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B7: Coordination and Response

B7: Coordination and Response. 7.2 Tropic responses. What is a tropism?. Plants grow towards or away from stimuli The growth response is called a tropism. Shoots will grow towards light – a positive tropism. light. Shoots will grow against gravity – a negative tropism. gravity.

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B7: Coordination and Response

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  1. B7: Coordination and Response 7.2 Tropic responses

  2. What is a tropism? • Plants grow towards or away from stimuli • The growth response is called a tropism Shoots will grow towards light – a positive tropism light Shoots will grow against gravity – a negative tropism gravity

  3. The stimuli • Phototropism is the growth response towards or away from light • Geotropism is the growth response with or against gravity phototropism geotropism

  4. Putting it all together: • Complete this table:

  5. How do plants grow to the light? light • A hormone called auxin is made in the tip of the shoot • Auxin causes shoot cells to enlarge • When light is directly overhead, auxin diffuses equally down the shoot • The shoot grows straight up

  6. How do plants grow to the light? Auxin at work • When light is directional, the auxin moves to the shaded side of the shoot • The cells on the shaded side elongate more than the cells on the lighted side • The shoot grows towards the light light

  7. Phototropism experiment

  8. How do plants respond to gravity? shoots grow up negativegeotropism roots grow down gravity positivegeotropism

  9. How do plants respond to gravity? • Auxin is made in the shoot and root tips • Auxin causes slowed growth in root cells • When a plant is laid on its side, auxin collects in the lower cells • The lower cells in the shoot elongate and the shoot grows upwards • The lower cells in the root slow in growth and the roots grow down Phototropism and geotropism

  10. Textbook Questions • Complete the following summary questions: • P153 exercise 1 • P155 exercises 1, 2 and 3 • Complete the following exam-style questions: • P156 question 4

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