Plant biology - Growth
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Primary & Secondary Growth
Apical & Lateral MeristemPlant Biology Part 3 -
Growth
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Type of Growth
Primary growth: grow in lengthSecondary or lateral growth: grow
in girth (diameter, width)
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Primary Growth
Increase height for better clearance to sunlight
Roots burrow deep into soil to access nutrients and for structural stability
Occurs in: Herbaceous plants Young plants Tips of roots and shoots of woody plants
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Meristematic Cells (Meristem)Undifferentiat
ed plant cells2 types:
Apical Lateral
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Apical Meristem
Undifferentiated cells at the tips of plant roots and shoots (buds)
Cells that divide enable the plant to grow longer (deeper into the ground, and taller)
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Root Apical Meristem
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Root ZonesZone of maturation:
cells differentiate into different types of cells
Zone of elongation: allows the root to get deeper within the soil
Meristematic region: rapid mitosis of undifferentiated meristematic cells
Root cap: protects the meristematic region
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Shoot Apical Meristem
Located in budsTerminal / Apical
bud: at the tip of a growing stem
Axillary / Lateral bud: at points along the stem where lateral branches form
Terminal / Apical bud
Axillary / Lateral bud
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Shoot Apical Meristem
http://www.uwgb.edu/biodiversity/herbarium/trees/axillary_lateral_bud02.jpghttp://www.fs.fed.us/pnw/olympia/silv/local-resources/glossary/images/apical.jpg
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Apical Dominance
Terminal bud inhibits the growth of axillary bud
What advantage does this provide for the plant?
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Apical Dominance What would happen to plant growth if the
terminal bud was cut off? Explain why pruning shrubs makes them
busier.
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Apical Dominance
http://www.mun.ca/biology/desmid/brian/BIOL3530/DB_12/fig12_13.jpg
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Secondary / Lateral GrowthThickening of roots and shootsAdds strength to plant structureGrowth due to lateral meristemNever occurs in leavesOccurs in mature part of woody
plants
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Secondary Growth
Accounts for the rings formed in tree trunks
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http://www.uic.edu/classes/bios/bios100/labs/vasccamb.jpg
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Lateral Meristem
Cork Cambium Outer lateral meristem Makes dermal tissue called cork / periderm
barkVascular Cambium
Inner lateral meristem Outer surface makes phloem bark Inner surface makes xylem reason for
growth, creates the tree rings seen in trunks of woody plants
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Comparing Plant Growth
Growth Effect MeristemPrimary Height
deep rootsRoot Apical meristemShoot Apical meristem apical/terminal budaxillary/lateral bud
Secondary / Lateral
Width / girth
Lateral meristemCork cambiumVascular cambium