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Chapter 8 Section 5

Chapter 8 Section 5. Plant responses and Growth. Tropism. A plants growth response toward or away from a stimulus Plant grows toward a stimulus: positive tropism Plant grows away from a stimulus: negative tropism Three important stimuli Touch Light Gravity. Examples of Tropisms.

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Chapter 8 Section 5

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  1. Chapter 8 Section 5 Plant responses and Growth

  2. Tropism • A plants growth response toward or away from a stimulus • Plant grows toward a stimulus: positive tropism • Plant grows away from a stimulus: negative tropism • Three important stimuli • Touch • Light • Gravity

  3. Examples of Tropisms • Plant showing response to touch • Thigmotropism • Positive tropism • Grows toward object they are touching • Example: bladderworts, grapes, morning glories

  4. Examples of Tropisms • Plant showing response to light • Phototropism • Positive tropism • Grows toward light

  5. Examples of Tropisms • Plants showing response to gravity • Gravitropism • Negative tropism on stem • Gravity it pulling down, yet plant grows up • Positive tropism on roots • Roots grow down, direction gravity pulls

  6. Hormones and Tropisms • Hormones • Produced by a chemical that affects how the plant grows and develop • Auxin • Speeds up the rate at which a plant’s cell grows • Plants hormones also control… • Tropism • Germination • Formation of leaves, stems, roots • Shedding of leaves • Development/ripening of fruit

  7. How does auxin control a plants response to light • Auxin builds up in shaded side of a stem • Cells on shaded side of the stem begin to grow faster • Cells on stem’s shaded side are longer than those on sunny side • Stem bends toward light

  8. Seasonal Changes: Photoperiodism • What triggers a plant to flower? • The amount of DARKNESS a plant receives • Photoperiodism • A plant’s response to seasonal changes in length of night and day • Critical night length • The number of hours of darkness that determines whether or not a plant will flower

  9. Long-Day/Short-Day Plant • Short-day plants • Flower when nights are longer than a critical length (fall/winter) • Long-day plants • Flower when nights are shorter than a critical length (spring/summer) • Day-neutral plants • Flowering cycle is not sensitive to period of light and dark

  10. Dormancy • A period when an organism’s growth or activity stops

  11. Life SpanS of Angiosperms • Annuals • Angiosperms that complete a life cycle within one growing season • Most have herbaceous stems • Biennials • Angiosperms that complete a life cycle in two years • Once flowers produce seeds, the flower dies • Perennials • Angiosperms that live for more than two years • Ex. peony

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