Roots

Plant organ systems

What are the primary functions of roots?

Fibrous and taproot systems

Dicots Monocots

Root structure

Root cap

• Parenchyma• Perception of

gravity

Notice how the growing zone has no root hairs or lateral roots!

Growth among soil particles would result in shear forces.

Zone of Maturation - cell differentiation

ProtodermGround MeristemProvascular

Zone of Cell Elongation - cell expansion

Zone of Cell Division - new cells by mitosis

Root Cap - penetration, padding

Mucilage Slough Cells

Root Tip Senses GravityAuxin Hormone ProducedAuxin Accumulates on LowerGrowth Inhibited on Lower…Relative to UpperRoot Curves Downward

Gravitropism

Root Hairs Increase Surface Area

Root Hairs Secrete Acid (H+)

H+ Cation Exchange w/Minerals

Mineral Uptake into Roots

Water and Mineral Uptake

Region of maturation

Mature root structure

Monocot root, c.s.

Dicot root, c.s.

Phloem

Xylem

Endodermis

Endodermis regulates mineral absorption

Lateral (branch) roots

Endodermis Pericycle

Endodermis Pericycle

Specialized roots• Storage roots

Propagative roots

Pneumatophores

Aerial roots

Aerial roots – velamen (orchids)

Contractile roots

Prop roots

Root nodules

Root nodules

Parasitic roots• Witchweed

•Support

•Conduction

•Growth

Stem functions

Vascular bundle arrangementof roots and stems

Roots

Stems

Monocot Dicot

Dicot stem anatomy

Coleus stem vascular bundles

Dicot stem anatomy

Secondary growth of dicot stems

heartwood sapwood

secondary xylem

secondary phloem

Annual rings of phloem

phloem

fibers

LenticelsLenticels

Lenticels

Specialized stems

Cladophyll

Thorns

Tendrils

That’s a big stem!• Baobab (Adonsonia digitata) grow up to

45 ft. in diameter

That’s a big stem!

Redwoods grow up to 350 ft tall; 30 ft. dia.

Bristlecone pines

• Oldest organism – 4767 yrs. old