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Growth Response of Plants

Growth Response of Plants. Prepared by Ms W.S.Kwan. Plants have no nervous system. Can plants detect stimulus? Can plants response?. Tropism (Tropic Movement). A directional growth movement made by a part of a stationary plant in response to unilateral stimulus. stimulus. gravity.

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Growth Response of Plants

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  1. Growth Response of Plants Prepared by Ms W.S.Kwan

  2. Plants have no nervous system.Can plants detect stimulus?Can plants response?

  3. Tropism (Tropic Movement) A directional growth movement made by a part of a stationary plant in response to unilateral stimulus

  4. stimulus gravity unilateral light water tropism Types of Tropism geotropism phototropism hydrotropism

  5. Geotropism • Geotropism is the growth movement (growth response) shown by a plant part in response to gravity

  6. Investigation 17.1 To show Geotropism in Seedlings

  7. To show Geotropism in Seedlings Why is it necessary to leave the apparatus in darkness ? Ans: To avoid any stimulus from light.

  8. To show Geotropism in Seedlings What has happened to the radicles and plumules ? Ans: The radicles grow downwards, while the plumules grow upwards.

  9. To show Geotropism in Seedlings Do the radicles show positive geotropism (towards gravity) or negative geotropism (away from gravity)? Ans:Positive geotropism.

  10. What advantage do the seedlings have by showing such geotropism ? Ans: Roots grow downwards deep into the soil to provide a firm anchorage underground and absorb water and mineral salts in the soil.

  11. Importance of Geotropism(Roots grow towards gravity) • provide firm anchorage for roots • ensure the plant can get adequate supply of water & mineral salts

  12. Clinostat • for control experiments • contains a cork disc which can be set to rotate in a vertical or horizontal plane by a motor • Cancel out the effect of unilateral stimulus • to make factors uniform (evenly distributed)

  13. Investigation 17.2 To show the effect of Gravity by using a Clinostat

  14. plastic cover lined with moist blotting paper X in complete darkness Y What is the purpose of marking the radicles at equal intervals ? Ans:To find out which region of the radicle grows faster.

  15. plastic cover lined with moist blotting paper seedling in X X in complete darkness seedling in Y Y Does the direction of growth of the seedlings in clinostat X change ? Ans: The radicle of the seedlings in clinostat X bends downwards in response to the pull of gravity.

  16. plastic cover lined with moist blotting paper seedling in X X in complete darkness seedling in Y Y Does the direction of growth of the seedlings in clinostat Y change ? Why ? Ans: Since every side of the radicle of the seedling in clinostat Y is acted on by gravity, the radicle will grow straight horizontally.

  17. plastic cover lined with moist blotting paper seedling in X X in complete darkness seedling in Y Y What is the purpose of setting up clinostat Y ? Ans: Serve as a control for comparison.

  18. Shoots show negatively geotropic

  19. Phototropism • Phototropism is the growth movement (growth response) shown by a plant part in response to light.

  20. Investigation 17.3 To show Phototropism in Shoots

  21. A B C unilateral light unilateral light light-proof box clinostat in complete darkness What is the effect of the clinostat on the shoot of plant B ? Ans:The revolving clinostat cancel out the effect of unilateral stimulus (light) on the shoot of plant B.

  22. A B C unilateral light unilateral light light-proof box clinostat in complete darkness What has happened to the shoots of plants A and B ? Ans: The shoots in pot A respond by growing towards the light source. The shoot in pot B do not show any curvature but grow vertically upwards.

  23. A B C unilateral light unilateral light light-proof box clinostat in complete darkness What has happened to the shoot of plant C ? Ans:the shoots in pot C grow vertically upwards with slender and longer nodes(elongated), and carries smaller leaves which are yellow in colour (etiolated).

  24. A B C unilateral light unilateral light light-proof box clinostat in complete darkness What is the significance of phototropism to plants ? Ans:This tropism ensures that a plant gets enough light energy for photosynthesis.

  25. Importance of Phototropism(Shoots grow towards light source) • enables leaves to be in a position to receive maximum sunlight for photosynthesis

  26. Hydrotropism • Hydrotropism is the growth movement (growth response) shown by a plant part in response to water.

  27. Importance of Hydrotropism(Roots grow towards water supply) ensures that a plant gets • enough water as a raw material for photosynthesis & • enough mineral salts to maintain normal growth

  28. stimulus gravity unilateral light water tropism response Types of Tropism geotropism phototropism hydrotropism no response negative shoot positive root negative positive positive

  29. Mechanism

  30. Darwin Experiments

  31. cut & replaced tip few days later decapitated Experiments on Oat Coleoptiles dark box no growth grows Conclusions : The tip is responsible for the growth

  32. unilateral light few days later black covers Experiments on Oat Coleoptiles Conclusion : The tips are sensitive to light. (responsible for the detection of light)

  33. agar plate fewdayslater Experiments on Oat Coleoptiles dark box Conclusions : The tip must have produced a diffusible chemical substance which stimulates growth

  34. mica plate Experiments on Oat Coleoptiles bending directions bending directions Can the explanation still work ? the tip is put aside Explanation of results : The side with the tip has a higher concentration of that particular chemical, the growth rate is faster than the other side.

  35. Auxins • commonest plant hormones • produced by shoottip • regulate growth & other physiological processes in plants • promote growth by inducing cell elongation & cell division.

  36. shoot high conc. low conc. root auxin concentration plant growth high conc. low conc. shoot root Effect of auxin on Plant Parts positive growth Growth of plant auxin concentration negative growth Positive (promote) no effect Negative (inhibit) Positive (promote)

  37. Phototropism in Shoot • The shoot tip produces auxins which diffuse downward • The auxins diffuse to the shaded side due to the presence of unilateral light • High auxin concentration stimulates growth in shoot • The shaded side grows faster than the lighted side • The shoot bends towards the light

  38. Geotropism in Root • The auxins diffuse to the lower side due to gravity • High auxin concentration inhibits growth in root • The lower side of root grows slower than the upper side • The root bends downward

  39. ~END~

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