Vascular Cambium: Secondary Growth in Stems

Question 1

secondary growth

Answer 1

• increase in girth generated by cell divisions of LATERAL MERISTEMS
• observed in both stems and roots of woody plants
• ALL gymnosperms have secondary growth
• some perennial tree and shrub angiosperms: (20% dicots, 5% monocots)

Question 2

lateral meristems form in ______________

Answer 2

regions of maturation in stems and roots that have completed growing in length

Question 3

unlike primary growth where undifferentiated initial cells are arranged in meristem clusters, lateral meristems are ______________

Answer 3

they are cylindrical and allow for radial expansion

Question 4

why is secondary growth needed?

Answer 4

increases conduction and support, replace old tissue (no maintenance over hundreds of years)

Question 5

most angiosperms do not have or need secondary growth; annual plants?

Answer 5

annual plants do not develop secondary growth.
- support provided by collenchyma and sclerenchyma fibers

Question 6

secondary xylem and phloem

Answer 6

• function of cells are the same as primary xylem/phloem
• secondary xylem tends to have thicker walls due to increase in lignin content

Question 7

function of xylem/phloem, direction

Answer 7

xylem - water conducting tissue “root to shoot”
phloem - metabolite conducting tissue “shoot to root”

Question 8

2 types of lateral meristems

Answer 8

vascular cambium
-secondary xylem, wood
-secondary phloem, bark

cork cambium
-cork, bark
-phelloderm, bark

Question 9

cambial cells are derived from cells that ______

Answer 9

dedifferentiate

Question 10

dedifferentiation

Answer 10

hormones signal dedifferentiation, even in mature tissue cells (e.g. vegetative propagation)

derivative -dedifferentiate-> initial cell (totipotent)

Question 11

vascular cambium in stem forms from ___

Answer 11

dedifferentiated cortex and procambium

Question 12

vascular cambium produces ____

Answer 12

secondary xylem and secondary phloem, in between primary xylem and primary phloem

Question 13

stem vascular cambium: process, hormone name

Answer 13

in dicot and gymnosperm stems, AUXIN hormone signals formation of vascular cambium from:
- fusiform initials
-ray initials

vascular cambium = ray + fusiform initials

Question 14

fusiform initials

Answer 14

cells derived from residual procambium cells located in between primary xylem and phloem

Question 15

ray initials

Answer 15

arise from parenchyma cells or cortex between vascular bundles

Question 16

secondary growth in stem over time

Answer 16

over time, more secondary xylem produced than secondary phloem by vascular cambium

Question 17

wood = ______ _______

Answer 17

secondary xylem

Question 18

wood characteristics

Answer 18

• mostly dead cells, tracheids or vessel members
• highly lignified
• only more recent layers of secondary xylem conduct water and minerals
• primary and older secondary xylem become inactive

Question 19

hardwood vs softwood

Answer 19

dicots form hardwood: xylem (wood) made of fibres and vessels (harder, more lignin)

conifers form softwood: xylem (wood) made of primarily of tracheids (softer, less lignin)

Question 20

secondary phloem

Answer 20

• only more recent layers of living secondary phloem conduct photosynthetic products
• primary and older secondary phloem become stretched and broken as vascular cambium push them outward (bark)

Question 21

growth patterns of wood

Answer 21

• xylem growth forms annual rings
• size of cells that make up rings varies with season
• small in late summer (summerwood/late wood), large in spring (springwood/early wood)

Question 22

dendrochronology

Answer 22

• tree rings can provide info about tree age
• climate conditions and historical events (abiotic/biotic stress); stress=less growth

Question 23

heartwood

Answer 23

older, non-conducting rings of xylem in centre of trunk or root

Question 24

sapwood

Answer 24

outer xylem rings that still conduct water and minerals

Question 25

heartwood and sapwood

Answer 25

heartwood usually but not always darker than sapwood

antibacterial and antimicrobial compounds produced by parenchyma