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