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PLANT RESPONSES TO THE ENVIRONMENT

PLANT RESPONSES TO THE ENVIRONMENT. EXTERNAL STIMULI . What are the stimuli plants can respond to ? Water Sunlight Day length Gravity Touch Predators Chemicals Temperature . Two types of plant movements : Tropisms Nastic movements. TROPISMS.

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PLANT RESPONSES TO THE ENVIRONMENT

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  1. PLANT RESPONSES TO THE ENVIRONMENT

  2. EXTERNAL STIMULI • What are the stimuli plantscanrespondto? • Water • Sunlight • Daylength • Gravity • Touch • Predators • Chemicals • Temperature

  3. Twotypes of plant movements: Tropisms Nasticmovements

  4. TROPISMS • Growthmovementwheredirection of stimulusdeterminesdirection of growthmovement. • Tropisms: Phototropism Geotropism Thigmotropism Hydrotropisms Chemotropisms Thermotropism

  5. TROPISMS • A plant respondstoa stimulus by growingtowardsthe stimulus = positivetropism • OR • By growingawayfromthe stimulus = negativetropism.

  6. Tropisms

  7. RESPONSE TO LIGHT = PHOTOTROPISM

  8. Stems are positivelyphototropic; Roots are negativelyphototropic

  9. light Lightfromabovewill cause theshoot/ stem togrow upwardstowardsthelight. Auxins are produced in thegrowing tip and Stimulatecelldivision and elongation.

  10. Phototropism (Light)Auxins are light-shy and will move to the shady side when a shoot receives unilateral lighting. • There are more auxins on the shaded side of the shoot so the shaded side grows faster making the bright side bend towards the light… light light

  11. Phototropism Experiment • Setup the phototropism experiment as shown in the diagram using seedlings and a light source on one side of the box…

  12. Classicexperimentperformed by Charles Darwin

  13. What is therole of theauxins in phototropism?

  14. IMPORTANCE OF PHOTOTROPISM Enables leaves to be in the best position possible to receive adequate light for photosynthesis

  15. Geotropism (Gravity) • A plant’s response to gravity is called a geotropism – different parts of a plant have different responses to gravity… Shoots grow up Negative geotropism Roots grow down Gravity Positive geotropism

  16. Geotropism (Gravity) • Auxins speed up growth in shoots and slow growth in roots – if a plant is laid on its side, the auxinsproduced collect in the lower side of the root and stem • Auxins slow down growth on the lower side of the root, so the root curves down. Auxins speed up growth on the lower side of the stem, so the stem curves up.

  17. IMPORTANCE OF GEOTROPISM • Pulls roots down to anchor a plant • Roots can get needed water and • minerals if they stay in the soil NEXT

  18. Hydrotropism (Water) • A plant’s response to water is called hydrotropism– roots always grow towards water, a positive tropism • Roots will grow sideways or even upwards, towards water – roots always have a stronger response to water than gravity to ensure that a plant gets the water it needs Dry soil Wet soil

  19. Wet soil Wet soil Equal Hydration • When roots are well watered from all sides there is an equal amount of auxins in all parts of the roots, which grow at the same rate, so the roots grow out in all directions… Wet soil Wet soil

  20. Dry soil Wet soil Unequal Hydration • When roots are in soil with more water on one side, the auxins are not spread out evenly in the roots Dry soil Wet soil • There are more auxins on the wetter side of the roots, which grows slower than the dryer side, so the roots bend towards the water

  21. Thigmotropism Plants moving in response to touch. Positive is toward touch (vines wrap around structures) Negative is away from touch (some plants close up when touched) Why? To support leaves as they grow higher to reach the sun to make more food (photosynthesis).

  22. Rhododendronleavescurlup in thecold - thermotropism

  23. Importance of Thermotropism • In colder weather helps prevent water loss through stomata

  24. HELIOTROPISM • Flowerfollowssunthroughoutday e.g. sunflower

  25. Other plant responses - Dormancy • A period of inactivity in a mature seedbeforeit begins to grow • It’s like the seed is in a “sleep-state” • Remains dormant until conditions are right for growth and development of the new plant.

  26. Dormancy of seeds is broken by gibberellins

  27. VERNALISATION – Coldtreatment of seedstobreakdormancy. • Secretion of gibberellinsstimulated.

  28. PHOTOPERIODISM • Plantswillonlyfloweratcertaintimes of theyear. • Longdayplantsflower in summer – long day (more than 12 hrs of light), shortnight. • Shortdayplantsflower in winter – shortday (lessthan 12 hrs of light) and long night. • Dayneutralplantsflowerregardless of daylength.

  29. How do plantsprotectthemselvesfrombeingeaten?

  30. Thesethorns are modifiedleaves

  31. Plantsproducebitter-tastingtannins in youngleavestopreventanimalsfromeatingtheseleaves

  32. Theseleaveshavetheabilitytowarnothers in thevicinitytoproducetanninstopreventthemfrombeingeaten by thekudu.

  33. Secretions of poisonoussubstances e.g. Indigenous Euphorbia

  34. NASTIC MOVEMENTS • Plant movementswheredirection of movementwill NOT bedetermined by direction of stimulus.

  35. Circadian rhythms – sleep movements (nyctinasty)

  36. Nyctinasty

  37. Solar tracking (heliotropism)

  38. Response to mechanical stimuli (seismonasty)

  39. Seismonasty – a response totouch. This Venus Flytrapwillcloseit’s„jaws” whenaninsecttouchesthetriggerhairs onthe inner surface.

  40. Seismonasty – Mimosa pudica

  41. Seismonasty • Venus flytrap

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