Plant growth Flashcards
Generally describe how plants grow
Irreversible quantitative change in cell size + no.
Not all cells contribute to growth
Where is growth localised to in plants?
Embryonic regions = meristems
How is growth in plants different to growth in animals?
Plants:
> growth is restricted to certain regions
> growth is accompanied by increase in no. of parts
> constantly need to replace organs
Animals:
> body plan + organs are laid down in embryogenesis
Which organs only have determinate growth?
When do they cease to grow?
Flowers
Fruit
Leaves
Maturity
What is phyllotaxy and what causes it?
Where do floral primordial form?
Arrangement on leaves on a stem
- opposite or spiral arrangement
Caused by regular changes in distribution of auxin in meristem
Regions of high auxin conc
What do meristems give rise to?
Initials (=stem cells) which remain in meristem
Derivatives which become specialised in mature tissue
Where are apical meristems located?
Tips of roots and shoots + in axillary buds of shoots
What is primary growth?
Apical meristems elongating shoots + roots
What are the types of primary meristem that apical meristems may differentiate into?
Protoderm
Procambium
Ground meristem
Where is protoderm located and what does it develop into?
Around outside of stem
Develops into epidermis
Where is procambium located and what does it develop into?
What does it produce?
Inside of the protoderm
Develops into primary xylem + phloem
Produces vascular cambium (secondary meristem)
Where the ground meristem located and what does it develop into?
What does it produce?
Inside the protoderm and surrounds the procambium
Develops into cortex + pith
Produces cork cambium (secondary meristem)
What is secondary growth?
When lateral meristems add thickness to woody plants
What are the 2 secondary lateral meristems?
Vascular cambium
Cork cambium
What does the vascular cambium do?
Adds layers of vascular tissue = secondary xylem (wood) + secondary phloem
What does the cork cambium do?
Replaces the epidermis with periderm
= thicker + tougher
What are the 3 categories of plants based on their life-cycle length?
Annuals = life completed in 1yr or less
Biennials = 2 growing seasons
Perennials = long lived
What is the root tip covered by and what is its purpose?
Root cap
= protects apical meristem as root pushes through soil + secretes a polysaccharide slime that lubricates soil
What are the 3 overlapping zones fo growth behind the root tip?
Zone of:
> cell division
> elongation
> differentiation/maturation
Where do lateral roots arise from?
The pericycle
What is the pericycle?
Cylinder of parenchyma or sclerenchyma cells that lies inside the endodermis
What is a SAM?
Shoot apical meristem
= dome-shaped mass of dividing cells at shoot tip
Where do axillary buds develop from?
Meristematic cells left at the bases of leaf primordia
Where do leaves develop from?
Leaf primordia along the sides of the apical meristem
How does auxin affect axillary buds?
Represses development of axillary buds into shoots
= acts as an inhibitor
What is apical dominance?
Where the central stem is dominant over smaller side stems
What does apical dominance help to do?
Maintain dormancy of most non-apical buds
- dormancy depends on proximity to active apical bud
What does pruning plants do?
Removes the dominance of the active apical bud
- auxin is produced at apex which inhibits growth of lateral buds further down stem
What are intercalary meristems?
Only in monocotyledons
At base of internodes + leaf blades
-> growth occurs at base of stems + leaves
= allows for rapid growth after defoliation by herbivores
Which types of plants have secondary growth?
(Woody plants)
Gymnosperms
Eudicots
NOT monocots
How many times has secondary growth evolved?
3 in 420my of vascular plant existence
Which group has lost secondary growth?
Monocots
type of angiosperm
What is the purpose of secondary growth via the vascular cambium?
Adds structural support + increases vascular flow
What does the cork cambium produce?
What is the purpose of this?
A tough, thick covering of wax-impregnated cells
Protects stem from: water loss fire insect attack bacteria fungi
Which 2 tissues does the cork cambium give rise to?
Phelloderm
= thin layer of parenchyma cells that forms on the interior of the cork cambium
Cork cells (phellem)
= accumulates to the exterior of the cork cambium
= deposit waxy suberin in their walls + then die
What does periderm consist of?
Cork cambium
Phelloderm
Cork cells
How do spring, summer + winter wood differ?
Spring/Early in season = Xylem vessels w/ large diameters + thin cell walls
- maximises transports of water to new leaves
Summer/Late season = thick cell walls to provide support
Winter = no growth
- vascular cambium inactive
What does bark consist of?
Al tissues external to vascular cambium
- including secondary phloem + periderm
Wha happens as secondary growth continues?
Layers of secondary xylem form consisting of tracheids (gymnosperms), vessel elements + fibres
Walls os secondary xylem cells become heavily lignified
What are tracheids?
type of water-conducting cell in xylem which lacks perforations in the cell wall but have pits
What is the difference between softwoods + hardwoods?
Soft:
> gymnosperms
> no vessels
> few fibres
Hard:
> angiosperms
> many vessels
> fibres
How do living cells in the stem respire if surrounded by dead cells?
Lenticel = porous tissue consisting of cells w/ large intercellular spaces
What are the evolutionary advantages of secondary growth?
Grow taller
-> shade neighbours
Support
Water conduction
Fire resistance
