structure of primary root and origin of secondary growth

Question 1

apical meristem

Answer 1

• region of active cell division… in center of the growing root, behind root cap.
• cells are. parenchyma (soft, not elongated)
• protoderm: on surface of cell
• ground meristem: just under the protoderm, gives rise to tissue in cortex of root
• procambium: under ground meristem, cylinder in middle of root, gives rise to vascular tissue (xylem and phloem)
• pith: tissue not present in dicot root, can be present in monocot, produced by ground meristem, would be located in middle

Question 2

root. cap

Answer 2

• thimble shaped
• covers the apical meristem
• slough off
• lubricate the growing root… encourages bacterial growth (N fixing),
• gravitropism: if peeled off, root will grow in disordered direction

Question 3

zone of elongation

Answer 3

• cells elongate or widen
• grow due to hydrostatic pressure of vacuole
• cells behind zone no longer elongate

Question 4

zone of maturation

Answer 4

1. root hair
   -grow root hair…all part of one cell, sometimes the nucleus will be in this root.
   - extension of single cell
   - important for absorbing minerals and water
2. cortex
   - underneath are the cortex cells: parenchyma, store food, many layers
3. endodermis
   - located inside the cortex, one layer of cell…
4. casparian strips
   - junction between one cell and the cell next to it,
   - made of suberin
   - forms a water tight seal to prevent water from passing into vascular cylinder
5. vascular cylinder (stele)
   - at center of root,
   - primary xylem: very center of stele, (inside)
   - primary phloem: located between the arms of the primary xylem (outside)
   - pericycle: single row of cells lining endodermis, forms the side roots, starts the secondary growth
   - older phloem gets sloughed off in dicots
6. cork cambium
   - begins to produce bark

Question 5

shoot apical meristem at growing tip

Answer 5

protoderm: forms the epidermic
ground meristem: not very important in secondary growth
procambium: forms vascular tissue

Question 6

procambium

Answer 6

has stele patterns:
1. protostele: xylem in center and phloem around it
2. siphonostele: pith in the middle, vascular tissue around it
3. eustele: common in flowering plants

Question 7

leaf and bud gaps

Answer 7

bud scars: leave leaf gaps
small space where it is missing a vascular bundle

Question 8

origin of secondary growth

Answer 8

vascular cambium

Question 9

vascular cambium

Answer 9

• between primary xylem and phloem
• divide horizontally
• form secondary xylem and phloem
• xylem to inside (cells pushed to inside), phloem to outside