Plant Form Flashcards
What are the three stages of plant development?
- embryogenesis
- vegetative
- reproductive
What are the meristems?
origin of all post-embryonic organs
Name the two primary and two lateral meristems.
primary:
1. root apical
2. shoot apical
(as well as the axillary meristem)
lateral (typical of woody plants):
1. vascular cambium
2. cork cambium
Define phyllotaxy and name the different types.
the arrangement of leaves (and thus branches) around the stem
a) alternate
b) spiral - golden angle between two leaves that are generated along an equiangular angle
c) opposite (eg mint)
d) whorled - more than two leaves at each node
What is the role of auxin?
it is a hormone that determines new cell/organ fate or growth rate
What is a primordium?
the simplest set of cells capable of triggering growth of the would-be organ and the initial foundation from which an organ is able to grow
Name he different zones of the meristem and state their function.
Central zone - stem cells
peripheral zone - produces organs
L1 - divides anticlinally to generate the epidermis
L2 - divide periclinally to produce the bulk of the internal tissue
L3 - same as L2 but also gives rise to vasculature
Define anticlinal and periclinal division in regard to the meristem
anticlinal - vertical divisions outwards of the meristem
periclinal - horizontal divisions across the meristem
What are the roles of the epidermis?
- protection
- light reflection/harvesting
- water/gas exchange
- surface cleaning
- structural light/colouring effect
What are the roles of the vascular tissue?
- transport of water via the xylem
- transport of photosynthetic products via the phloem
- structural support
What is the benefit of a vein-like vascular structure?
- allows efficient spacing of xylem and phloem
- allows a circulation system that is harder to disrupt
What are lenticels?
horizontal slits in wood/bark that are important for gas exchange
Where does carbon fixation take place?
in the air spaces in mesophyll cells
What is meant by an “open root apical meristem” and specify what type of plant it occurs in
not having specific tiers of initial cells in the root apical meristem, occurs in monocots
How do root hairs develop?
can be environmentally induced
as part of the epidermal cell elongates via tip growth
How are apical root meristems produced?
root apical meristem originates from the pericycle
What is the pericycle?
a primary root tissue that forms the cell layer surrounding the xylem, phloem, and procambium cells
Define heterophylly.
environmentally induced differential leaf shapes
eg two different leaf morphologies depending on growing in water/air
Define photomorphogenesis.
light-mediated development, where plant growth patterns respond to the light spectrum
What is dogma?
the fact that all living plant cells can regain totipotency
plants are highly regenerative
State the roles of both vascular and cork cambium which develop as plants grow older.
vascular cambium: produces secondary vascular tissues (eg wood) which provide more transport and structural support
cork cambium: produces cork/bark which provides new epidermis and more protection
What is apical dominance?
the process whereby the high concentrations of auxin in shoot tip inhibits the outgrowth of axillary buds further down the stem to control the number of growing shoot tips and branches
What is propagation?
a plant regenerating itself from a piece of its body
each module has a meristem and is self-sufficient to replicate itself
How do different types of stresses affect different types of trees?
deciduous (in tension) = increase of cellulose in cells and wood
conifer (in compression) = increase of lignin in cells and wood
What is meant by “closed root apical meristem” and specify what type of plant it appears in
occurs in dicots
have specific layers in the meristem to which all cell files can be traced
During formation of the apical meristems, what is cell fate determined by?
cell fate is position-dependant rather than lineage-dependant
What is the phellogen?
the dividing zone of cells in the cork cambium
How do phellogen cells divide and how does this affect the structure?
divide periclinal
results in production of phelloderm cells to the inside and phellem to the outside (cork cells)
as a result, epidermal cells divide anticlinal otherwise they would start bursting
This growth forms the Periderm
What happens to cork cells at maturity?
they die and are heavily impregnated w suberin, a waxy hydrophobic compound
provides protection for stem and roots against water loss and pathogens
How is the vascular cambium initially realised?
the cambium is first activated within the vascular bundle and spread in between dedifferentiating cells in the area
a cylinder of 1-2 cell thick cambium layer then gives rise to numerous numbers of xylem and phloem cells
Difference between xylem and phloem?
Xylem is dead tissue enforced to carry water
Phloem have companion cells (containing nuclei) and transport the products of photosynthesis
What are the 3 tissue types in the shoot apex of angiosperms?
Vasculature
Epidermis
Ground tissue (exists between the vasculature and epidermis and in the centre)
What is secondary growth?
Growing older and larger; additional cells for transport, structure, support and protection are needed
Lateral meristem (vascular and cork cambiums) growth provides these
Difference between compound leaf and branch?
Branches have auxiliary buds between leaves, no buds between the leaflets on a compound leaf
How is the anatomy of the leaf organised?
Stomata openings on the bottom
Epidermis has a cuticle on the top layer
Mesophyll with chloroplasts (also BS cells)
What is the root cap?
Provides cover for root
Arguably not part of root as it isn’t directly attached
Which tissue starts lateral root formation?
The stele at the centre of the root is surrounded by the pericycle which causes lateral root formation as it doesn’t lose the ability to divide
How are roots made to be selective
Casparian strips are impregnated with hydrophobic compound, doesn’t allow water to centre and allows selective ness in what is allowed through
What is the purpose of root hairs?
Increase surface area
Absorb water and mineral ions
Decreasing concentration of nutrients will cause the plant to make more root hairs
How does root branching take place?
Mediated by auxin
Pericycle begins to divide and root apical meristem begins to acquire shape
Apoptosis occurs around bulging structure to give way to it as to avoid bursts and ruptures
What causes lateral root formation?
Elevated nutrients causes plant to respond with root formation
Low nutrient decreases root formation
Also induced in areas with more water
If a bend in the root of formed by an obstacle, auxin causes LR formation on convex side to explore
