Roots Chapter 5 Botany

How Roots Develop  Seed germinates into radicle  From radicle ( immature plantlet)  Forms first root  Becomes thick taproot with adventitious roots or a fibrous root system

Root Structure Composed of four zones: Composed of four zones: 1.Root cap 2.Region of cell division 3.Region of elongation 4.Region of maturation

Root Cap Thimble shaped mass of parenchyma cells that cover the tip of each root Thimble shaped mass of parenchyma cells that cover the tip of each root

Root Cap Functions 1.Protect delicate young root 2.Make slime for lubrication of root 3.Promote bacteria growth-increases Nitrogen reserve 4.Cells live less than 1 week 5.Regenerates cells 6.Contains amyloplasts (starch grains) 7.Act as gravity sensors

Gravitropism  Plant roots grow “down”  If you move a plant the roots turn toward the center of the earth within 30 minutes

Region of Cell Division 1.Apical meristem-region of active mitosis 2.Makes root cap 3.Cell division occurs along cap edges 4.Cells divide every 12 to 36 hours 5.Cells are cube shaped with large nuclei and small vacuoles

Apical Meristem Divided into three areas: 1.Protoderm becomes epidermis 2.Ground meristem produces parenchyma cells of cortex 3.Procambium produces primary xylem and primary phloem

Region of Elongation  Merges with apical meristems and extends from root tip  Cells grow several times in original length and width  Remainder of root remains stationary as secondary tissues and increase root girth

Region of Maturation  Cells differentiation into cell types  Also know as region of differentiation  Root-hair zone

Root Hairs  Adhere to soil particles  Increase absorptive root surface  Tubular extensions of epidermal cells-not all separate cells  Very numerous look like fine down  Transplanted plants lose root hairs reduce ability to absorb water and transplanted plants must have shade water and pruning.

Interior of Root  Cuticle-thick cuticle on root hairs and allows water to be absorbed and doesn’t against bacteria  Cortex- Parenchyma cells  Store food  Tissue-many cells thick  Endodermis -Cortex of root has suberin cell walls, suberin bands called Casparian strips on the radical and transverse walls, prevents water leaking out  Vascular Cylinder-lies to inside of endodermis, conducts food and water

Vascular Cylinder  Pericycle –cells continue to divide and make lateral branch roots  Xylem conducts water and dissolved minerals  Phloem conducts dissolved glucose from the leaves to the roots

Vascular Cylinder  Woody plants-cork cambium gives rise to cork cells which are dead at maturity and impervious to moisture  Growth –Determinate growth stops. Indeterminate growth occurs where growth added season after season