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Biology Form 5 Chapter 3 - Coordination & Response Part 6 - Plant Hormones

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Biology Form 5 Chapter 3 - Coordination & Response Part 6 - Plant Hormones

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Biology Form 5 Chapter 3 - Coordination & Response Part 6 - Plant Hormones

  1. 1. PLANT HORMONES
  2. 2. • Plants don’t have a brain.
  3. 3. • Some questions to think about. – How does a tree know when to drop its leaves? Copyright © 2010 Ryan P. Murphy
  4. 4. • When does a plant know when to grow, and when to remain dormant? Copyright © 2010 Ryan P. Murphy
  5. 5. • How does a tree know when spring has arrived and it’s time to create buds? Copyright © 2010 Ryan P. Murphy
  6. 6. • How can a plant move from one side to another? – It doesn’t even have muscles. Copyright © 2010 Ryan P. Murphy
  7. 7. • How does a plant know when to create flowers, and what color they should be?
  8. 8. • How does a plant know when the flower has been fertilized and it’s time to make seeds?
  9. 9. • How does a banana know when to ripen? Copyright © 2010 Ryan P. Murphy
  10. 10. • How does a banana know when to ripen? “Hey Phyllis” “I’m getting these strange marks on my peel.” Copyright © 2010 Ryan P. Murphy
  11. 11. • When does a seed know it’s time to germinate? Copyright © 2010 Ryan P. Murphy
  12. 12. • When does a seed know it’s time to germinate? – Too early, or too late could be fatal to the young plant. Copyright © 2010 Ryan P. Murphy
  13. 13. • When does a seed know it’s time to germinate? – Too early, or too late could be fatal to the young plant. Copyright © 2010 Ryan P. Murphy
  14. 14. • When does a seed know it’s time to germinate? – Too early, or too late could be fatal to the young plant. Copyright © 2010 Ryan P. Murphy
  15. 15. • When does a seed know it’s time to germinate? – Too early, or too late could be fatal to the young plant. Copyright © 2010 Ryan P. Murphy
  16. 16. • When does a seed know it’s time to germinate? – Too early, or too late could be fatal to the young plant. Copyright © 2010 Ryan P. Murphy
  17. 17. • Does anybody know the answer…?
  18. 18. • Answer: Plant Hormones. Copyright © 2010 Ryan P. Murphy
  19. 19.  New Area of Focus: Plant Hormones. Copyright © 2010 Ryan P. Murphy
  20. 20. • Plant hormones are chemicals that affect flowering; Copyright © 2010 Ryan P. Murphy
  21. 21. • Plant hormones are chemicals that affect flowering; aging; Copyright © 2010 Ryan P. Murphy
  22. 22. • Plant hormones are chemicals that affect flowering; aging; root growth; Copyright © 2010 Ryan P. Murphy
  23. 23. • Plant hormones are chemicals that affect flowering; aging; root growth; distortion, Copyright © 2010 Ryan P. Murphy
  24. 24. • Plant hormones are chemicals that affect flowering; aging; root growth; distortion, killing of leaves, Copyright © 2010 Ryan P. Murphy
  25. 25. • Plant hormones are chemicals that affect flowering; aging; root growth; distortion, killing of leaves, stems, Copyright © 2010 Ryan P. Murphy
  26. 26. • Plant hormones are chemicals that affect flowering; aging; root growth; distortion, killing of leaves, stems, and other parts; Copyright © 2010 Ryan P. Murphy
  27. 27. • Plant hormones are chemicals that affect flowering; aging; root growth; distortion, killing of leaves, stems, and other parts; prevention or promotion of stem elongation; Copyright © 2010 Ryan P. Murphy
  28. 28. • Plant hormones are chemicals that affect flowering; aging; root growth; distortion, killing of leaves, stems, and other parts; prevention or promotion of stem elongation; color enhancement of fruit; Copyright © 2010 Ryan P. Murphy
  29. 29. • Plant hormones are chemicals that affect flowering; aging; root growth; distortion, killing of leaves, stems, and other parts; prevention or promotion of stem elongation; color enhancement of fruit; prevention of leafing and/or leaf fall; Copyright © 2010 Ryan P. Murphy
  30. 30. • Plant hormones are chemicals that affect flowering; aging; root growth; distortion, killing of leaves, stems, and other parts; prevention or promotion of stem elongation; color enhancement of fruit; prevention of leafing and/or leaf fall; and many other conditions. Copyright © 2010 Ryan P. Murphy
  31. 31.  Plant hormones are chemicals that affect all aspects of the plants life. Copyright © 2010 Ryan P. Murphy
  32. 32. Some plant hormones :  auxin  gibberellin  cytokinin  ethylene  abscisic acid Copyright © 2010 Ryan P. Murphy
  33. 33. AUXIN
  34. 34. • Do plants move? Copyright © 2010 Ryan P. Murphy
  35. 35. • Plants do move, although this movement is very little. Copyright © 2010 Ryan P. Murphy
  36. 36. • Video! Phototropism in plants.
  37. 37.  Auxin: Promotes stem elongation and bud dormancy.  Phototropism: When plants grow toward a light source. Copyright © 2010 Ryan P. Murphy
  38. 38.  Auxin: Promotes stem elongation and bud dormancy.  Phototropism: When plants grow toward a light source. Copyright © 2010 Ryan P. Murphy
  39. 39. • A plant moves by elongating the cells on the opposite side of light, causing the plant to bend toward the light. Copyright © 2010 Ryan P. Murphy
  40. 40. • Activity! Feeling phototropism in plants. – Stand up tall, feet slightly apart, and bend toward the light. – What part of your body elongates / stretches, and which shrinks in? Copyright © 2010 Ryan P. Murphy
  41. 41. • Note: Plants do not have muscles, so the elongation and contraction occurs on a cellular level. Elongated Cells Shortened Cells Copyright © 2010 Ryan P. Murphy
  42. 42. • Auxin also… – Stimulates cell division. – Stimulates differentiation of phloem and xylem – Response of bending in response to gravity and light. – Delays growth of lateral buds. – Can induce fruit setting and growth in some plants. – Delays fruit ripening. – Stimulates growth of flower parts. Copyright © 2010 Ryan P. Murphy
  43. 43. • Auxin also… – Stimulates cell division. – Stimulates differentiation of phloem and xylem – Response of bending in response to gravity and light. – Delays growth of lateral buds. – Can induce fruit setting and growth in some plants. – Delays fruit ripening. – Stimulates growth of flower parts. Copyright © 2010 Ryan P. Murphy
  44. 44. • Auxin also… – Stimulates cell division. – Stimulates differentiation of phloem and xylem – Response of bending in response to gravity and light. – Delays growth of lateral buds. – Can induce fruit setting and growth in some plants. – Delays fruit ripening. – Stimulates growth of flower parts. Copyright © 2010 Ryan P. Murphy
  45. 45. • Auxin also… – Stimulates cell division. – Stimulates differentiation of phloem and xylem – Response of bending in response to gravity and light. – Delays growth of lateral buds. – Can induce fruit setting and growth in some plants. – Delays fruit ripening. – Stimulates growth of flower parts. Copyright © 2010 Ryan P. Murphy
  46. 46. • Auxin also… – Stimulates cell division. – Stimulates differentiation of phloem and xylem – Response of bending in response to gravity and light. – Delays growth of lateral buds. – Can induce fruit setting and growth in some plants. – Delays fruit ripening. – Stimulates growth of flower parts. Copyright © 2010 Ryan P. Murphy
  47. 47. • Auxin also… – Stimulates cell division. – Stimulates differentiation of phloem and xylem – Response of bending in response to gravity and light. – Delays growth of lateral buds. – Can induce fruit setting and growth in some plants. – Delays fruit ripening. – Stimulates growth of flower parts. Copyright © 2010 Ryan P. Murphy
  48. 48. • Auxin also… – Stimulates cell division. – Stimulates differentiation of phloem and xylem – Response of bending in response to gravity and light. – Delays growth of lateral buds. – Can induce fruit setting and growth in some plants. – Delays fruit ripening. – Stimulates growth of flower parts. Copyright © 2010 Ryan P. Murphy
  49. 49. • Auxin also… – Stimulates cell division. – Stimulates differentiation of phloem and xylem – Response of bending in response to gravity and light. – Delays growth of lateral buds. – Can induce fruit setting and growth in some plants. – Delays fruit ripening. – Stimulates growth of flower parts. Copyright © 2010 Ryan P. Murphy
  50. 50. • Auxin also… – Stimulates cell division. – Stimulates differentiation of phloem and xylem – Response of bending in response to gravity and light. – Delays growth of lateral buds. – Can induce fruit setting and growth in some plants. – Delays fruit ripening. – Stimulates growth of flower parts. Copyright © 2010 Ryan P. Murphy
  51. 51. • Auxin also… – Stimulates cell division. – Stimulates differentiation of phloem and xylem – Response of bending in response to gravity and light. – Delays growth of lateral buds. – Can induce fruit setting and growth in some plants. – Delays fruit ripening. – Stimulates growth of flower parts. Copyright © 2010 Ryan P. Murphy
  52. 52. • Auxin also… – Stimulates cell division. – Stimulates differentiation of phloem and xylem – Response of bending in response to gravity and light. – Delays growth of lateral buds. – Can induce fruit setting and growth in some plants. – Delays fruit ripening. – Stimulates growth of flower parts. Copyright © 2010 Ryan P. Murphy
  53. 53. • Auxin also… – Stimulates cell division. – Stimulates differentiation of phloem and xylem – Response of bending in response to gravity and light. – Delays growth of lateral buds. – Can induce fruit setting and growth in some plants. – Delays fruit ripening. – Stimulates growth of flower parts. Copyright © 2010 Ryan P. Murphy
  54. 54. GIBBERELLIN
  55. 55. • Which plant was given extra gibberellin hormones? Copyright © 2010 Ryan P. Murphy
  56. 56. • Which plant was given extra gibberellin hormones? Copyright © 2010 Ryan P. Murphy
  57. 57. • Plant B shows extra stem elongation over plant A. • Plant A is the normal plant / control while plant B is the variable. • What is the responding variable? Height Copyright © 2010 Ryan P. Murphy
  58. 58.  Gibberellins: Make stems longer. Copyright © 2010 Ryan P. Murphy
  59. 59. “My mom gave a lot of gibberellins as a young sprout and look what happened.”
  60. 60. • Gibberellins also… – Stimulates flowering in response to long days. – Breaks seed dormancy – Induces maleness in some flowers (sex expression). – Can cause fruit development. – Can delay dropping of leaves and citrus fruits. Copyright © 2010 Ryan P. Murphy
  61. 61. • Gibberellins also… – Stimulates flowering in response to long days. – Breaks seed dormancy – Induces maleness in some flowers (sex expression). – Can cause fruit development. – Can delay dropping of leaves and citrus fruits. Copyright © 2010 Ryan P. Murphy
  62. 62. • Gibberellins also… – Stimulates flowering in response to long days. – Breaks seed dormancy – Induces maleness in some flowers (sex expression). – Can cause fruit development. – Can delay dropping of leaves and citrus fruits. Copyright © 2010 Ryan P. Murphy
  63. 63. • Gibberellins also… – Stimulates flowering in response to long days. – Breaks seed dormancy – Induces maleness in some flowers (sex expression). – Can cause fruit development. – Can delay dropping of leaves and citrus fruits. Copyright © 2010 Ryan P. Murphy
  64. 64. • Gibberellins also… – Stimulates flowering in response to long days. – Breaks seed dormancy – Induces maleness in some flowers (sex expression). – Can cause fruit development. – Can delay dropping of leaves and citrus fruits. Copyright © 2010 Ryan P. Murphy
  65. 65. Fig. 28-19 Effect of Gibberellin
  66. 66. CYTOKININS
  67. 67.  Cytokinins: Promotes cell division. They are produced in growing areas like the tips. Root Tip Copyright © 2010 Ryan P. Murphy
  68. 68. ABSCISIC ACID
  69. 69.  Abscisic Acid: Opens and closes stomata, has role in seed dormancy.
  70. 70. • Note: Stomata are small pores (openings) for gas exchange. Copyright © 2010 Ryan P. Murphy
  71. 71. • Abscisic Acid… – Inhibits shoot growth (inhibits gibberellin). Copyright © 2010 Ryan P. Murphy
  72. 72. • Abscisic Acid… – Inhibits shoot growth. – Induces seeds to synthesize storage proteins. – Helps to recognize and fix wounding on an injured plant. Copyright © 2010 Ryan P. Murphy
  73. 73. • Abscisic Acid… – Inhibits shoot growth. – Induces seeds to synthesize storage proteins. – Helps to recognize and fix wounding on an injured plant. Copyright © 2010 Ryan P. Murphy
  74. 74. ETHYLENE
  75. 75. • What does the one bad apple do…? Copyright © 2010 Ryan P. Murphy
  76. 76. • What does the one bad apple do…? – Why? Copyright © 2010 Ryan P. Murphy
  77. 77. • What does the one bad apple do…? – Why? Copyright © 2010 Ryan P. Murphy
  78. 78. • One bad apple spoils the bunch because that bad apple is releasing ethylene gas which causes the others to ripen. Copyright © 2010 Ryan P. Murphy
  79. 79. • One bad apple spoils the bunch because that bad apple is releasing ethylene gas which causes the others to ripen. Copyright © 2010 Ryan P. Murphy
  80. 80. • One bad apple spoils the bunch because that bad apple is releasing ethylene gas which causes the others to ripen. – Remove ripe fruit from the bunch to keep fruit longer. Copyright © 2010 Ryan P. Murphy
  81. 81. • One bad apple spoils the bunch because that bad apple is releasing ethylene gas which causes the others to ripen. – Remove ripe fruit from the bunch to keep fruit longer. Copyright © 2010 Ryan P. Murphy
  82. 82.  Ethelyene: A gas that promotes fruit ripening. Copyright © 2010 Ryan P. Murphy
  83. 83. • Which of these methods will make your tomatoes ripen faster and why? • Putting them on a sunny windowsill. • Putting them in a paper bag. W O R K T O G E T H E R
  84. 84. • Ethylene also… – Stimulates the release of seed dormancy. – Stimulates shoot and root growth. – Stimulates leaf and fruit abscission. – Creates femaleness in flowers. – Stimulates flower opening. – Stimulates flower and leaf dying. Copyright © 2010 Ryan P. Murphy
  85. 85. • Ethylene also… – Stimulates the release of seed dormancy. – Stimulates shoot and root growth. – Stimulates leaf and fruit abscission. – Creates femaleness in flowers. – Stimulates flower opening. – Stimulates flower and leaf dying. Copyright © 2010 Ryan P. Murphy
  86. 86. • Ethylene also… – Stimulates the release of seed dormancy. – Stimulates shoot and root growth. – Stimulates leaf and fruit abscission. – Creates femaleness in flowers. – Stimulates flower opening. – Stimulates flower and leaf dying. Copyright © 2010 Ryan P. Murphy
  87. 87. • Ethylene also… – Stimulates the release of seed dormancy. – Stimulates shoot and root growth. – Stimulates leaf and fruit abscission. – Creates femaleness in flowers. – Stimulates flower opening. – Stimulates flower and leaf dying. Copyright © 2010 Ryan P. Murphy
  88. 88. • Ethylene also… – Stimulates the release of seed dormancy. – Stimulates shoot and root growth. – Stimulates leaf and fruit abscission. – Creates femaleness in flowers. – Stimulates flower opening. – Stimulates flower and leaf dying. Copyright © 2010 Ryan P. Murphy
  89. 89. • Ethylene also… – Stimulates the release of seed dormancy. – Stimulates shoot and root growth. – Stimulates leaf and fruit abscission. – Creates femaleness in flowers. – Stimulates flower opening. – Stimulates flower and leaf dying. Copyright © 2010 Ryan P. Murphy
  90. 90. • Class poll, Are plants more complicated, and perform exciting processes that you never thought of until studying plant hormones. Yes _______ No __________ Learn more about plant hormones (Advanced) at… http://www.plant-hormones.info/ Easier at… http://www.ext.colostate.edu/mg/gardennotes/145.html
  91. 91. •Involved in tropism
  92. 92. Plant responses to stimuli are given specific names: water gravitylight hydrotropism geotropismphototropism Are there different types of tropisms? Touch •Thigmotropism
  93. 93. Phototropism is a growth response to light Light Geotropism is a growth response to gravity
  94. 94. Which way up? How do plants always grow the right way up? Plants respond to gravity to grow in the right direction.
  95. 95. •Roots always grow towards water, which is positive hydrotropism. •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. How do roots respond to water?
  96. 96. How do roots and shoots respond to stimuli?  Shoots grow towards sunlight. They are positively phototropic. Plant stimuli affect certain parts of the plant in different ways.  Shoots grow away from gravity. They are negatively geotropic.  Roots grow away from sunlight. They are negatively phototropic.  Roots grow towards gravity. They are positively geotropic. What experiments can be used to test these ideas?
  97. 97. A shoot is: POSITIVELY PHOTOTROPIC NEGATIVELY GEOTROPIC
  98. 98. A root is:  POSITIVELY GEOTROPIC  NEGATIVELY PHOTOTROPIC
  99. 99. Advantages of a shoot growing:  Towards light:  To trap more light for photosynthesis  Away from gravity:  shoot of a germinating seed grows out of the soil  more chances for pollination & seed dispersal
  100. 100. I am growing towards gravity, but where is the water????
  101. 101. Advantages of a root growing towards gravity:  To anchor the plant  To search for water  To ensure that the root of a germinating seed always grows downwards, whatever, the position of the seed in the soil
  102. 102. Study the pictures below and then complete the table by putting a plus (+) if the shoot or root grows towards the stimulus and a minus (-) if it grows away from it. Stimulus Light Gravity Shoot Root
  103. 103. Study the pictures below and then complete the table by putting a plus (+) if the shoot or root grows towards the stimulus and a minus (-) if it grows away from it. Stimulus Light Gravity Shoot + - Root - +
  104. 104. Thigmotropism • Thigmotropism Plant’s growth response to touching a solid object • Tendrils and stems of vines (ex. Morning glory) coil when they touch an object • Allows vines to climb other plants / objects • Increases chance of finding light (for photosynthesis) • Auxin and Ethylene are thought involved.
  105. 105. Chemotropism • Chemotropism  plant’s growth in response to chemicals • Eg. After pollination, pollen tube grows down through stigma and style and enters ovule through micropyle
  106. 106. CHEMOTROPISM
  107. 107. • What type of tropism is shown in these pictures?
  108. 108. HISTORY TIME
  109. 109. The houseplant observation • For years, people noticed that houseplants tended to lean toward a source of light. • Charles Darwin and his son Francis in 1880, wondered why. How does a plant “know” where to lean?
  110. 110. Darwin’s Oats • The Darwins studied the leaning phenomenon in oats. • Oat coleoptiles are highly light sensitive, and growth is fairly rapid.
  111. 111. A Coleoptile is a :  hollow, cylindrical sheath that surrounds the primary leaf of a germinating monocot seed Coleoptile First leaf
  112. 112. Darwin Experiment 1 Oat shoots tend to bend toward the light. When the tip of the shoot is covered with a small cap, the shoot does not bend. Question: Why doesn’t the shoot with the cap bend toward the light?
  113. 113. One hypothesis... • The Darwins speculated: • the tip of the plant detects the light and communicates chemically with the part of the shoot that bends. • Question: How could they test these alternative explanations? • The cap itself prevents bending. • Light further down the shoot, rather than on the tip, causes bending.
  114. 114. Darwin Experiment 2 Some shoots were covered with small caps of glass. Others were covered with a sleeve that left the tip exposed but covered the lower shoot. • The cap itself prevents bending. • Light further down the shoot, rather than on the tip, causes bending. X X Conclusion : The tip is the place responsible for bending
  115. 115. Boysen-Jensen • Peter Boysen-Jensen continued Darwins’ experiments.
  116. 116. Boysen-Jensen 1 • Boysen-Jensen cut the tips off of oat coleoptiles • They did not bend toward the light. • Question: What does this tell us about the role of the tip in this phenomenon?
  117. 117. Boysen-Jensen 2 • Boysen-Jensen cut the tips off coleoptiles and put the tips back on. • These coleoptiles bent toward the light. Conclusion : The tip is responsible for growth
  118. 118. Boysen-Jensen 3 Boysen-Jensen then put a porous barrier (agar gel) and an impenetrable barrier (a flake of mica) between the shoot tip and the rest of the shoot. The shoot with an agar barrier bent toward the light. The shoot with the mica barrier did not. Conclusion : The head must have produced a diffusible chemical substance which stimulates growth
  119. 119. Boysen-Jensen 4 Boysen-Jensen took a tiny, sharp sliver of mica and pushed it into the coleoptile so that it cut off communication between the tip and the rest of the plant on one side only. If the sliver was on the side that was lit, it still leaned that toward the light, but if it was on the opposite side, the plant did not lean toward the light. Explanation of results : Higher concentration of that chemical that causes growth on the side opposite the light.
  120. 120. F.W. Went identified the factor that was causing plants to bend toward the light. Went first cut the tips off of oat coleoptiles and placed them on a block of agar and allowed juices from the tip to diffuse into the agar.
  121. 121. AUXINS
  122. 122. What is the effect of auxins on plant cells? Cells absorb water and elongate.
  123. 123. Three regions of a root tip Cell division region Cell differentiation region Cell elongation region Cells become specialised
  124. 124. Which region does auxin affect? Cell division region (root tip that makes auxin) Cell differentiation region (cells change their shape; no effect by auxin) Cell elongation region (auxin makes cells absorb water)
  125. 125. Explain why: markings have moved away from each other ONLY in the lower region. Cell elongation region
  126. 126. A shoot growing in even illumination grows straight up. Why? auxin Cells on both sides of the stem elongate equally.
  127. 127. A shoot growing in one-sided illumination.
  128. 128. A shoot growing in one-sided illumination grows towards light. How is it possible? Cells on the two sides of the stem GROW UNEQUALLY!!
  129. 129. Describe how a shoot bends towards one-sided illumination. Auxins are produced at the ___________ tip and diffuse down the stem. More auxin collects on the ____________ side of the stem. Auxins cause the cells to absorb water and so elongate in the cell elongation region. Thus the ___________ side grows more than the lighted one. This results in bending of the stem towards light. shoot shaded shaded
  130. 130. Effect of Auxin on Plant Parts positive growth negative growth root shoot auxin concentration Growth of plant low conc. high conc. auxin concentration plant growth shoot root No effect positive positive negative high conc. low conc.
  131. 131. -the concentration of auxins needed for maximum growth response in shoots inhibits root growth -the concentration that stimulates root growth is too low to stimulate shoot growth
  132. 132. GEOTROPISM
  133. 133. GEOTROPISM
  134. 134. GEOTROPISM
  135. 135. Gravitropism in shoots • In shoots, auxins are more concentrated on the lower side of the stem, causing the cells there to elongate. • Why is this gravitropism and not phototropism?
  136. 136. Gravitropism in roots • In roots, however, auxin concentration on the lower side of the root suppresses cell elongation. • The upper side of the root continues to grow, causing the roots to bend downward.
  137. 137. Geotropism in Root  The root tip produces auxins which diffuse to the elongation region  The auxins diffuse to the lower side due to gravity  High auxin concentration inhibits growth in root  The lower side grows slower than the upper side  The root bends downward
  138. 138. •AUXIN is produced in the • apical meristem at the tips of the shoots ( also known as COLEOPTILE) •From the tip of shoot, auxin move down to the region of cell elongation & stimulates growth of the cells. The cells become LONGER. •IMPORTANT TO KNOW
  139. 139. IMPORTANT INFORMATION TO KNOW ABOUT AUXIN • Auxin is sensitive to light. • It always moves away from light. • Auxin stimulates the elongation of cells in the shoots but, inhibits the elongation of cells in the roots
  140. 140. VIEW THE ACTUAL EXPERIMENT IN THE NEXT 3 SLIDES
  141. 141. NASTIC MOVEMENT
  142. 142. Nastic Movements  Nastic movements  plant movements  that occur in response to environmental stimuli  but are independent of the direction of stimuli  Quick, temporary movements in plants.  No plant growth, so they can be reversed.  Regulated by changes in water pressure of
  143. 143. Nastic movement in the sensitive plant (Mimosa pudica) SEISMONASTI Stimulus : touch
  144. 144. Thigmonastic Movements  Thigmonastic ‘thig-mah-NAS-tik’ movements  a type of nastic movement that occurs in response to touching or shaking a plant  Involve rapid plant movements  Ex. Venus flytrap
  145. 145. • see video
  146. 146. PLANT HORMONES AGRICULTURAL USES
  147. 147. 165 of © Boardworks Ltd 2007  growing cuttings  killing weeds.  ripening fruit Why are these purposes useful for gardeners and farmers? Plant hormones – • naturally-occurring chemicals • can also be produced synthetically • for use in gardening and agriculture such as: How can plant hormones be used?
  148. 148. Auxin promotes rooting
  149. 149. 167 of © Boardworks Ltd 2007 How are cuttings grown? To stimulate root growth, cuttings are dipped into rooting powder. This contains plant growth hormones. Cuttings are genetically identical to the parent plant. This allows growers to copy successful plants.
  150. 150. 168 of © Boardworks Ltd 2007 Fruit often has to travels thousands of miles from where it is picked to where it is sold in the shops. How are hormones used to ripen fruit? When the fruit reaches its destination, it can then be sprayed with artificial plant hormones to encourage ripening. Fruit is often picked before it is fully ripe. Why might this help keep the fruit edible? Unripe fruit is harder and less likely to bruise than ripe fruit when transported. Why might it be a good idea to wash fruit before eating it?
  151. 151. Ethylene and fruit ripening •With•Without
  152. 152. 170 of © Boardworks Ltd 2007 PARTHENOCARPY Parthenocarpy is the natural or artificially induced production of fruit without fertilization of ovules. (development of fruit without fertilization) This method produces seedless fruits Auxin is sprayed to the flower to stimulate it to turn into fruit. So no fertilization is required.
  153. 153.  Sometimes gardeners cut the tops off plants to make them more bushy
  154. 154. Auxins sometimes stop growth  auxin passes down the stem and prevents side branches growing out  so the plant grows tall and straight
  155. 155.  If the top is cut off from the plant:  flow of auxin stops  side branches will grow out
  156. 156. 174 of © Boardworks Ltd 2007
  157. 157. EXPERIMENTS USING OAT COLEOPTILES
  158. 158. no growth grows dark box few days later Conclusion : The tip is responsible for growth cut & replaced tip decapitated Experiments on Oat Coleoptiles
  159. 159. unilateral light few days later black covers Conclusion : the tip is the place responsible for bending Experiments on Oat Coleoptiles
  160. 160. Experiments on Oat Coleoptiles few days later dark box agar plate Conclusion : the head must have produced a diffusible chemical substance which stimulates growth
  161. 161. Experiments on Oat Coleoptiles bending directions 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 the tip is put aside mica plate Can the explanation still work ? bending directions
  162. 162. ANSWER THE FOLLOWING
  163. 163. Study the diagrams. What would you expect to happen and why. The shoot with the covered tip grows (straight up / towards light) because it (can sense light / cannot sense light).
  164. 164. Study the diagrams. What would you expect to happen and why. The shoot with the covered tip grows (straight up / towards light) because it (can sense light / cannot sense light).
  165. 165. The shoot with the exposed tip grows (straight up / towards light) because it (can sense light / cannot sense light).
  166. 166. The shoot with the exposed tip grows (straight up / towards light) because it (can sense light / cannot sense light).
  167. 167. Look at the diagrams below. What does this experiment tell you about the tip of the shoot and the part it plays in growth? Tip produces chemicals for growth.
  168. 168. Look at the diagrams below. How would you explain the results of this experiment? Bending resulted due to unequal amount of chemical . Light affects distribution of chemical.
  169. 169. QUESTION: MAY, 2009 Give a biological explanation for each of the following statements: cutting off the tip of a shoot will stop the shoot from getting taller but it will increase bushiness; (3)
  170. 170. EXPERIMENTS TO SHOW: 1. Geotropism in a shoot 2. Geotropism in pea radicles 3. Phototropism in oat coleoptiles 4. Phototropism in a shoot All make use of an apparatus called: clinostat
  171. 171. Clinostat: a motor rotates slowly  to make factors uniform (evenly distributed)  for control experiments  contains a cork disc which can be set to rotate in a vertical or horizontal plane by a motor
  172. 172. AIM: To show geotropism in a plant shoot. APPARATUS: CONTROL Give a precaution for this experiment. Even illumination. The apparatus was left for 3 days.
  173. 173. Why did the shoot attached to the clinostat grow horizontally ? As shoot rotated, gravity acted on all sides. No unilateral stimulus to respond to.
  174. 174. AIM: To show geotropism in pea radicles. APPARATUS:  The apparatus was left for 3 days.
  175. 175. QUESTION: MAY, 2005 A biology student wanted to test whether the position in which seeds are placed in the soil affects the direction of shoot and root growth. Design a simple experiment which the student can use to carry out this investigation.(5)
  176. 176.  Seeds of the same type are placed at different orientations in a single container.  A similar container is set up as a replicate.  Left in darkness for a few days.  Radicles are observed.
  177. 177. QUESTION: MAY, 2005 When growing plants from cuttings, farmers usually dip the cutting into Rooting Hormone powder before planting it in the soil. Briefly explain how this increases the chances of successful plant growth. (2) Roots are stimulated to form. Thus plant can absorb more water and ions for growth.
  178. 178. AIM: To show phototropism in oat coleoptiles. APPARATUS:
  179. 179. METHOD: 1. Thirty oat grains were soaked in water for 1 day. 2. Ten grains were placed in each of three small pots of compost and left to germinate. 3. When grown to a height of 1cm, they were treated as follows:  One set was covered with a large box, excluding light;  Another set was covered with a box with a slit at the side, allowing one-sided illumination;  The control was left in the light. 4. The pots were left at room temperature for a few days.
  180. 180. RESULT:  In the dark: coleoptiles were yellow, straight and very long.  In one-sided illumination: coleoptiles bent towards the light.  In the light: coleoptiles were green, straight and shorter than those in the dark. CONCLUSION:  The coleoptiles responded to the stimulus of one- sided illumination by growing towards it. Coleoptiles are positively phototropic.  Light is needed for chlorophyll to form.
  181. 181. AIM: To show phototropism in a shoot. APPARATUS: unilateral light unilateral light light-proof box clinostat A B
  182. 182. unilateral light unilateral light light-proof box clinostat 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... What has happened to the shoots of plants A and B ? A B
  183. 183. unilateral light unilateral light light-proof box clinostat A B What is the effect of the clinostat on the shoot of plant B ? The revolving clinostat cancel out the effect of unilateral light on the shoot of plant B.
  184. 184. Question: MAY, 2006 5. The experiment shows the effect of a stimulus on the growth of a root and a shoot. The seedlings were kept in the dark throughout the experiment.
  185. 185. a) Continue the diagram to show the direction of growth of the shoot and root in: i) the stationary ii) rotating clinostat. (4)
  186. 186. b) What type of stimulus response is exhibited by the seedlings? (1) Positive geotropism. c) Why were the seedlings kept in the dark? (2) Any changes observed would be due to gravity. d) Name the substance produced by the plant which brings about the growth changes. (1) Auxin
  187. 187. e) This experiment was investigated in an orbiting spacecraft where weightlessness is observed. Predict the results obtained in this situation. (1) Grow in all directions.
  188. 188. Under which condition (light/dark) was each seedling of bean grown? Grown in the light Grown in the dark
  189. 189. What is the advantage of a longer stem in seedlings grown in the dark? light dark
  190. 190. Four differences between a seedling growing in the light & another in the dark. In the light In the dark 1. Short, thick stem long, thin stem 2. Green shoot yellow shoot
  191. 191. Four differences between a seedling growing in the light & another in the dark. In the light In the dark 3. Broad leaves small leaves 4. Short internode long internode
  192. 192. QUESTION: MAY, 2009 Give a biological explanation for each of the following statements: the internodes of a shoot growing in the dark are longer than the internodes of a shoot growing in the light; (3)
  193. 193. Differences in the response shown by: A shoot in unilateral light A hand touching a hot object
  194. 194. Differences in the response shown by: A shoot in unilateral light A hand touching a hot object 1. Response in positive. 1. Response is negative 2. Slow response. 2. Rapid response 3. Response involves growth. 3. No growth involved 4. Response does not involve muscles and nerves. 4. Response involves muscles and nerves.

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