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Growth and Development

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McGill University
Biology (Sci)
BIOL 111
Irene Gregory- Eaves

22/09/11 All organisms show growth and development: Growth: Quantitative irreversible increase in any cell parameters (eg. height, volume, weight, number in populations, etc…) Development: Qualitative changes in body structure or function at certain stages of life cycle (eg. Development of organs [organogensis], achieving final shape [morphogenesis] and size juvenile/adult phase, etc…) - Growth and development (size and shape) regulated by hormones 1) absicic acid: stress hormone 2) auxins: promotes stem elogation 3) brassinosteroids: related to steroid hormones in mammals 4) cytokinins: cell devision 5) ethylene: fruit ripening 6) gibberellins: seed germination Growth graph: (number of cell per mL) vs Time  S shape graph - Small population, logarithmic growth, stationary phase (stable population) Effect of auxins on plant growth: Tropic Growth Movements: shoot tips show positive phototropic growth - coleoptile (conical structure which emerges from the soil) contains first leaf: o Auxin hormone stimulates shaded cells to grow more than cells in the light, causing plant to bend towards the light o Light perceived by apical tip of the coleoptile, bend occurs below - Cell on its side: gravity pulls auxins to the bottom side = more growth, growth of cells at bottom force plant to bend upwards - Toxic to roots – inhibits root growth, root will grow opposite way than stem will grow, cells exposed to auxin will grow less so root will bend towards cells with auxin - Promotes apical dominance: diverts resources to upward growth of plants, if apical part is cut lateral braches will grow. Seed Germination: Development of seed will depend on: - Size of the seed: Small seeds germinate in response to light, if they are too deep they cannot reach the surface before exhausting resources found in cotyledon - Seeds dormancy: Absicisc acid (ABA) allows for seed dormancy. When ABA leeches out - Gibberellins present: = germination - Strength of seed coat: strong coat = difficult for roots to penetrate the seed coat Light requirement for seed germination: 22/09/11 - White/Red light (663 nm) is needed for germin
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