BIOL 111 Lecture Notes - Gametophyte, Epicotyl, Gamete
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4 Apr 2012
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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: