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Session 10 powerpoint 2013

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Session 10 powerpoint 2013

  1. 1. RHS Level 2 Certificate Week 10 – Plant growth, development and control
  2. 2. Learning Outcomes           State what is understood by growth and development. State that simple cell division produces growth and results in an increase in size. Describe how competition for water, nutrients, light and space can influence growth. Describe two examples of how auxin influences plant growth. Describe what is meant by the term phototropism. Define the term: ‘photoperiodism’. 1.7 State the basic changes that occur when woody dicotyledons undergo secondary growth/thickening. 1.8 State how strengthening tissue can be established in monocotyledons allowing perennial growth to occur. 1.9 Review the internal differences between monocotyledons and dicotyledons.
  3. 3. Review of growth  Takes place by mitosis  At the meristems  Meristems – vascular cambium, cork cambium, apical meristem, pericycle
  4. 4. Growth and Development  Growth and development – what is the difference?  Plant growth = increase in size.  Plant development = maturation of plant, formation of plant organs such as flowers etc. The progress of a plant from juvenility, through maturity to senescence and ultimately death.
  5. 5. Competition and growth  Key factors required for growth are sufficient light, water, nutrients, oxygen and carbon dioxide and suitable temperature.  Competition means these may not be available to plants  Use of plant spacing in horticulture to provide optimum conditions for growth  Competition may mean death or reduced size or yield
  6. 6. Plant Growth Regulators 1  Control the way in which plants grow. For example that roots grow downwards and shoots upwards.  Chemicals produced by the plant which control the speed and location of the division of cells and the differentiation of those cells once produced
  7. 7. Plant Growth Regulators 2      Auxin stimulates plant cells to increase in length especially near to stem and root tips. It also promotes fruit formation Cytokinins promote cell division (mitosis) and delay the senescence of leaves. Gibberellins promote cell division and elongation of the stem. They also promote flowering and bolting in ‘long day’ plants and seed germination. Ethylene promotes ripening of fruit and senescence of leaves and flowers. Induces abscission of leaves in deciduous plants (the process of leaf fall). It also is responsible for causing the closing of stomata Abscisic acid maintains dormancy in seeds and possibly in buds. Stomatal closing.
  8. 8. Auxin and tropisms Tropisms are growth responses to external stimuli  Phototropism – plants grow toward the light (positive) or away from it (negative – esp. in roots)  Geotropism – may be positive (growth towards gravitational pull) or negative (growth away)  Thigmatropism – growth towards touch.  Auxin migrates in the stem to cause cell elongation that causes the above growth responses 
  9. 9. Day length and growth      The growth responses of plants to the length of day light hours is called photoperiodism. Triggers flowering, leafy growth, formation of bulbs and tubers etc in some species Day Neutral plants are not affected by day length Short Day plants – flower when the day length is short (night is long). Long Day plants – flower when the day length is long (night is short)
  10. 10. Secondary Growth in Dicots •New xylem cells are formed on the inside of the procambium (vascular cambium) •New phloem cells on the outside •As new xylem cells are formed they build up layers of xylem – linked by the pits in the walls of the tube cells •Old phloem cells are crushed and disrupted by the expansion in the girth of the stem
  11. 11. Annual Rings  Concentric rings of secondary xylem  Alternating bands of early and late wood  Early wood – Xylem cells with large diameter, thin walls. Produced in Spring  Late wood – Xylem cells with smaller diameter, thicker walls. Produced in Summer and early Autumn
  12. 12. Learning outcomes           State what is understood by growth and development. State that simple cell division produces growth and results in an increase in size. Describe how competition for water, nutrients, light and space can influence growth. Describe two examples of how auxin influences plant growth. Describe what is meant by the term phototropism. Define the term: ‘photoperiodism’. State the basic changes that occur when woody dicotyledons undergo secondary growth/thickening. State how strengthening tissue can be established in monocotyledons allowing perennial growth to occur. Review the internal differences between monocotyledons and dicotyledons.

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