Primary & Secondary Growth
Apical & Lateral MeristemPlant Biology Part 3 -
Growth
Type of Growth
Primary growth: grow in lengthSecondary or lateral growth: grow
in girth (diameter, width)
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
Meristematic Cells (Meristem)Undifferentiat
ed plant cells2 types:
Apical Lateral
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)
Root Apical Meristem
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
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
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
Apical Dominance
Terminal bud inhibits the growth of axillary bud
What advantage does this provide for the plant?
Apical Dominance What would happen to plant growth if the
terminal bud was cut off? Explain why pruning shrubs makes them
busier.
Apical Dominance
http://www.mun.ca/biology/desmid/brian/BIOL3530/DB_12/fig12_13.jpg
Secondary / Lateral GrowthThickening of roots and shootsAdds strength to plant structureGrowth due to lateral meristemNever occurs in leavesOccurs in mature part of woody
plants
Secondary Growth
Accounts for the rings formed in tree trunks
http://www.uic.edu/classes/bios/bios100/labs/vasccamb.jpg
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
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