Stems and secondary growth Flashcards
What are 8 functions of stems?
- Support photosynthetic and reproductive parts
- Transport water and nutrients
- Mechanical support
- Coordinates chemical responses of the plant
- Storage
- Support the roots and transport photosynthates down to them
- Growth response
- Position seeds for dispersal
What are the 3 ways the vascular tissue can be orientated in the stem?
Continuous cylinder, discrete bundles, scattered
In a continuous cylinder vascular bundle:
a) Which way is the phloem
b) which way is the xylem
c) which group of plants
d) secondary growth?
a) Outside
b) inside
c) eudicots
d) yes
In discrete vascular bundles:
a) Which way is the phloem
b) which way is the xylem
c) which group of plants
d) secondary growth?
a) outside
b) inside
c) eudicots
d) yes
In a scattered vascular bundle:
a) Which way is the phloem
b) which way is the xylem
c) which group of plants
d) secondary growth?
a) outside or in
b) outside or in
Note: one half of the bundle will be xylem, one half phloem, but orientations will be different
c) Monocots
d) no
Why is there no secondary growth with monocots?
Secondary growth only happens around individual bundles, which would create pressure points due to the scattered arrangement
If they don’t have secondary growth, how can palm trees grow so tall? What does that have to do with their distribution?
Their canopy and stem width is exactly the same size as they were as seedlings. Because they don’t grow wider, they can’t support more leaves. The strategy only lets them grow in tropical environments, since their vasculature will freeze in the winter and will become damaged. Without secondary growth, they can’t replace their vasculature and will die if they freeze
What are 6 types of specialized stems?
- Corms
- Tendrils
- Succulents
- Tubers
- Rhizomes
- Stolons
What are corms for?
Fleshy underground storage stem
What are stolons for?
Found in strawberry plants. Are stems modified for transport to bring the babies away from the mother plant
How is the stem modified in succulents?
The leaves are reduced and the stem does the life cycle functions and photosynthesis instead
What is primary growth?
Growth that makes a plant taller, through internode elongation and cell division
Where does cell division happen in the shoots?
The shoot apical meristem
How differentiated are the cells in the apical meristem?
Undifferentiated. The leaf primordium (future leaf tissue) and apical meristem (future stem tissue) arise from the SAM
How differentiated are cells slightly below the shoot apical meristem? What can they become?
Only slightly differentiated to become one type of cells. Are the protoderm, procambium, and ground meristem
What is indeterminate growth?
The plant keeps growing throughout its life, and keeps producing flowers and fruits until the frost sets in
What is determinate growth?
The plant grows until it reaches a certain size, then starts producing flowers and fruits in one go
Why do pines and larches grow in clusters?
They’re determinate shoots
What type of shoot did flowers evolve from?
Determinate shoot. Plants can cause the end of every shoot to become a flower
What are the 2 secondary meristems?
Vascular cambium and cork cambium
How is wood produced by trees?
Secondary growth of the vascular cambium
What is the vascular cambium?
A layer of cells that separates the xylem and the phloem
Where is the secondary xylem located?
In the wood, more towards the outside of the tree
Is there a difference between the primary and secondary xylem?
Primary xylem is the innermost layer and is smaller, and the secondary xylem is outside of the primary xylem and is larger
Where is the secondary phloem located?
Innermost layer of the bark
Is there a difference between the primary and secondary phloem?
Not really
Why don’t you find primary phloem in trees that have undergone secondary growth?
It gets squashed by the expanding cells and isn’t functional
Why is there a size difference in tree rings?
Trees can undergo more secondary growth in the summer because conditions are better, so rings are larger. In later parts of the season, conditions aren’t as good so the rings are smaller because of less secondary growth
What is dendrochronology?
Study of tree growth rings to determine what the conditions were in each year (ie drought, flood, etc)
Is the wood of gymnosperms considered “hardwood” or “softwood”? How is it structured?
Softwood. Gymnosperms have no vessel elements, so only the tracheids are there and are very small. There’s a few larger holes scattered here and there to transport resin
Is the wood of angiosperms considered “hardwood” or “softwood”? How is it structured?
Hardwood. Angiosperms have vessel elements, and some trees produce really large vessels each spring
What does the cork cambium do?
Produces periderms and bark to protect the tree
Why does girdling kill a tree?
Cuts the phloem, so the tree can’t transport nutrients
