Plant Bio Exam 1 Flashcards
Herbaceous tissue of the primary plant body develops from the what?
apical meristem
Vascular tissues occurs in what in the stem?
distinct bundles
In woody species, what are produced in the stem & root from activity of other meristems?
secondary tissues
produces wood containing secondary xylem
vascular cambium
produces bark containing secondary phloem and cork
cork cambium
Vascular cambium and cork cambium constitute the plants what?
secondary body
Woody plants are a combination of what?
primary and secondary tissue
A herbaceous plant’s conducting capacity is set after what?
a portion of stem or root is mature
Woody plants become wider every year by what?
accumulation of wood and bark, giving them a greater conducting capacity
Disadvantages to secondary growth (being woody)
- greater need for defenses, both structural and chemical to survive for a long time
- must use energy & nutrient resources for winterizing their bodies in temperate climates
- expensive metabolically to construct wood and bark
- Woody plants may not reproduce until they are several years old due to the energy spent on other activities
All woody trees and shrubs (including gymnosperms) descended from one group of what?
ancestral woody plants that arose about 370 million years ago
- therefore ‘Wood’ is an ancient trait and has evolved infrequently
Most evidence indicates that the first flowering plants were what?
woody
What is the derived condition of the herbaceous condition?
loss of wood
True secondary growth (wood) occurs in what?
- many eudicots
- most basal angiosperms
- all gymnosperms
- but never in ferns or monocots
What initially evolved from a woody ancestor but later lost the ability to produce woody tissues?
monocots
the meristem that produces the wood of the secondary plant body
Vascular cambium
-It originates as a layer of cell that lies between the xylem
and phloem of a vascular bundle in a plant stem
- In herbaceous plants these cells do not divide (usually)
- But in woody plants this region becomes meristematic
Vascular cambium
occur between xylem and phloem within a vascular bundle
Fascicular cells
occur between vascular bundles
Interfascicular cells
To form a complete vascular cambium that completely encircles the plant stem, what two region of cells must become meristematic?
1) Fascicular cells
2) Interfascicular cells
Once developed, the vascular cambium will consist of what?
a single cell layer encircling the stem that is capable of continued division
What two types of cells does the vascular cambium contain?
1) Fusiform initials
2) Ray initials
long and narrow vascular cambium cells
fusiform initials
short, cuboid vascular cambium cells
Ray initials
- long, tapered cells
- divide to produce (to the interior) the elongate cells of xylem (wood): tracheids, vessel elements, fibers, parenchyma
- also divide to produce (to the exterior) elongate cells of phloem: sieve cells, sieve tube members, companion cells, fibers, parenchyma
Fusiform initials
Fusiform initials of the vascular cambium divide longitudinally with what to produce two elongate cells?
periclinal wall (parallel to the meristem)
- one cell remains a fusiform initial (of the meristem)
- the other differentiates into either a cell of secondary xylem or secondary phloem
What (produced to the interior) increases greatly in diameter in growth, pushing the vascular cambia cells outward?
Secondary xylem cells
- produces stress on the cambial cells that can’t keep up
Vascular cambium cells must occasionally divide longitudinally by what (perpendicular to the cambium’s surface)?
anticlinal walls
- allows the cambium to add cells and increase in diameter and keep up with the increasing girth of the woody layer underneath
- short and cube-shaped
- divide to form xylem or phloem parenchyma that functions in storage or as albuminous cells (in gymnosperms)
Ray initials
Within the vascular cambium, Fusiform initials may occur (depending on the tree species):
- in regular horizontal rows (storied cambium)
- irregularly, w/o any horizontal pattern (nonstoried cambium)
Within the vascular cambium, Ray initials are grouped together in what?
short vertical rows
- one cell wide (uniseriate)
- two cells wide (biseriate)
- many cells wide (multiseriate)
Vascular cambium never has what?
large regions of just fusiform initials or just ray initials; it is always mixed
The overall ratio of fusiform initials to ray initials for a species is what?
relatively constant
- under precise genetic/developmental control
Types of wood cells:
- secondary xylem (wood)
- an axial (vertical) system
- a radial (horizontal) system
contains all of the cell types that occur in primary xylem
Secondary xylem (wood)
derived from fusiform initials
Axial (vertical) systems
develops from the ray initials
radial (horizontal) system
The axial system contains what?
- Tracheary elements
- fibers
- parenchyma
tracheids and vessels that carry out vertical conduction of water through the wood
Tracheary elements
provide strength
fibers
serves as a temporary reservoir of water
parenchyma
Hardwoods vs softwoods
- Hardwoods contain large amounts of fibers
- Softwoods contain few or no fibers
Most gymnosperms (softwoods) contain only what?
tracheids in their axial systems
- fibers and parenchyma cells are sparse or absent
In woody angiosperms, the radial system (‘rays’) contains only what?
parenchyma
- arranged in uniserate, biseriate, or multiseriate arrays-
For woody plants in temperate regions: Where do growth rings occur?
in wood due to the differential growth of early (spring) wood versus late (summer) wood
what has high proportions of wide vessels or tracheids?
spring wood
what has fewer vessels or narrower, thick-walled tracheids?
summer wood
What makes up 1 year’s growth, or annual (growth) ring?
Early wood and late wood
wood with vessels found mostly in early wood
ring porous
Ring porous species include:
- oaks
- hickories
- ashes
wood with vessels found throughout
diffuse porous
diffuse porous species include
- red maple
- black gum
- center of a log
- darker, drier, andmore fragrant
heartwood
-outer log
- light colored
Sapwood
- denser
- contains less water
- more aromatic
- better acoustic properties
Heartwood
Heartwood forms when:
- tracheary elements of older portions of wood no longer function in water transport
- tree seals off this old vascular tissue in the wood to avoid fungal hyphae or bacteria from invading and causing rot
What forms inside the old tracheary elements?
tylosis
intruding plug from an adjacent (living) parenchyma cell
tylosis
What produces compounds that inhibit growth of bacteria and fungi?
Xylem parenchyma cells (XP)
- makes cells dark and aromatic
Eventually, the tracheary elements are completely plugged up and filled with what?
defense compounds
When the parenchyma cells die (in heartwood), they leave behind what?
dark, highly decay-resistant cells
What contributes to heartwood?
parenchyma and tracheary elements
In laterally spreading branches, what is necessary to provide support? What is the resulting wood called?
- differential wood strength
- reaction wood
In angiosperms, additional growth occurs mostly on which side of a branch?
upper side; tension wood (pulling up)
- enriched with gelatinous fibers enriched with cellulose
- grows on upper side of a branch
- thicker annual rings on top of branch provide additional strength
- thinner annual rings occur on bottom of branch
Tension wood
Conifers from reaction wood enriched with lignin on what side of the branch?
underside; compression wood (pushing down)
- thinner annual rings occur on top of branch
- thicker annual rings on bottom of branch provide additional strength
- enriched with lignin
Compression wood
Many types of wood are prized for their what?
color, density, or acoustic properties
$70/board foot
african blackwood
$100/board foot
Black wood Ebony
$12/board foot
Sandalwood
$15/board foot
Black walnut
$4-6/ board foot
Red oak
What is responsible for conduction up and down the stem (or root) by the secondary xylem and phloem?
axial system
What are formed just the same as xylem rays? They are formed by the same cuboid initials in the vascular cambium
horizontal rays into phloem
- rays consists of parenchyma storage cells
What usually conducts for less than 1 year?
Sieve tube members and sieve cells of the secondary phloem
Which layer is capable of conduction?
Only the innermost, newest layer of phloem
The functioning phloem in a woody stem is what?
a narrow layer adjacent to the vascular cambium, and is always the most recent (youngest) layer produced
As secondary tissues are added and pushed outward, tissues on the periphery either:
- grow in circumference
- are torn apart and collapse
As circumferential stretching increases and older sieve elements die, some storage parenchyma cells of the phloem what?
are activated and undergo cell division
- this activity results in a new cambium meristem arising from within the old secondary phloem (cork cambium or phellogen)
After each division, the inner cell remains _ while the outer cell differentiates into _?
cork cambium; cork (phellem) cell
Vascular cambium is what?
bifacial
- secondary xylem to the inside
- secondary phloem to the outside
Cork cambium is what?
unifacial (usually)
- cork to the outside
In a few species, the cork cambium may produce some tissue to the inside to form a parenchyma layer known as what?
phelloderm
The layers of cork cells (and the phelloderm, if present) are called what?
periderm
The cortex is a mixture of what?
original cells of the cortex, older secondary phloem, and primary phloem all scrunched to the exterior of the stem cylinder
The cork cambium is what?
irregular and not fixed in place
New cork cambium forms where?
in younger secondary phloem closer to the vascular cambium
- this continually produces new bark tissues from layers underneath the surface, as older tissues are pushed outward
All tissues of a woody stem that is exterior to the vascular cambium
bark
secondary phloem part of bark
inner bark
the dead, cork tissue produced by the cork cambium
outer bark
Cork cells become filled with what and then die?
waxy suberin and defene compounds
What makes the periderm waterproof and chemically inert?
the waxy suberin and defense compounds in cork cells
- great protection from herbivores and xylovores (wood eaters)
Building materials and textiles made of bark
- bark shingle siding
- mulch
- tanning hides
- cloth
- canoes
- ropes
- cork
- substrate for paintings and maps
Medicinals, flavorings, and drugs made of bark:
- spices: cinnamon
- hallucinogens: Ayahuasca
- Medicines:
– willow = aspirin
– birch = anti-tumor
– Pacific Yew = taxol
- process of removing the outermost layers of a woody stem in a ring
- traditional method of killing trees without felling them
Girdling
What does girdling remove?
- periderm (cork layer)
- cork cambium
- secondary phloem layers
- vascular cambium
- sometimes sap wood
Complete girdling means phloem is completely removed leading to
starvation and death of the upper tree portions
Downside of cork:
impermeability of cork blocks the absorption of oxygen, preventing respiration of internal tissues
Bark becomes permeable to oxygen when what?
special rounded cork cells are produced
- allows air spaces to develop between the outer layers of cork
- ‘lenticels’
What creates an astounding diversity of tree bark?
differences in cork cambium activity and patterns of shedding of older outer bark
What are the four main functions of roots?
- anchoring the plant firmly to a substrate
- absorbing water and minerals from soil
- producing hormones
- Storing carbohydrates in the winter
Most eudicots have what?
taproots
a single large root that develops from the radicle
taproots
what are initially produced from the taproot?
Lateral roots
Later, what may also produce more lateral roots, resulting in a highly branched root system?
Lateral roots
Most monocots have what?
a fibrous root system
- mass of many similarly sized major roots near the soil surface
- each giving rise to smaller lateral roots
- the major roots are “adventitious”, arising in development from stem tissue
fibrous root system
Major roots do not arise from what?
the radicle (as in tap-rooted plants)
Roots grow from what?
an apical meristem at the root tip
The initial apical meristem was a part of what?
the embryo in the seed
The root apical meristem is protected by what?
a root cap
Just behind the root cap and root apical meristem is the what?
zone of elongation
Cells in this region undergo expansion
zone of elongation
A region in which many of the epidermal cells extend out as narrow trichomes
- greatly increase the root’s surface area and absorbing capacity
root hair zone
New lateral roots emerge from what?
the primary tap root from behind the root hair zone
- a protective structure produced by the underlying meristem
- continually being worn away due to abrasion during growth through soil, so it continuously needs to be replaced
root cap
cells of the root cap contain large starch granules that sink to the bottom of the cell called
statoliths
What influences the flow of the hormone auxin upward in the root?
position and distribution of statoliths
For a root extending horizontally, the statoliths cause what?
an increase in auxin on the underside of the root
- this decreases cell elongation on the underside
- cell elongation increases on the upper surface
- net effect: bending of the root tip downward
Root cap cells secrete copious amounts of what?
mucigel
a complex polysaccharide rich in carbohydrates and amino acids
mucigel
- lubricates passage of the root through the soil
- chemically causes soil to release nutrients
- fosters rapid growth of beneficial soil bacteria, which further help in uptake of nutrients
Mucigel
zone around the root tip of a plant constitutes the
rhizosphere
three zones of root apical meristem
- zone that yields new root cap cells
- a quiescent center
- upper zone that yields the cells of the growing root
region of the root beyond the meristematic region
- cells are enlarging, but not fully mature yet
- epidermal, vascular tissue & cortex regions begin to differentiate
zone of elongation
zone of maturation is marked by what?
- the production of root hairs growing by the epidermal cells
- differentiation of tissues
- root cortex cells transfer water & minerals from the epidermis to the vascular region (eudicot e.g.)
cell to cell through shared cytoplasm connected by plasmodesma
symplastic
transport on the exterior of cells along the cell walls
apoplastic
transport of water through the cortex may be
symplastic or apoplastic
- is one cell layer thick ad is the inner-most layer of cortex
- marks the boundary between the cortex and vascular region
- radial cell walls are rich in waterproof lignin and suberin; these constitute the Casparian strip
Endodermis
tightly controls the flow of water and minerals that may pass through the vascular tissue
Casparian strips
How do casparian strips control flow?
by cutting off the apoplastic pathway, forcing symplastic transport of water and minerals
Materials can only pass to vascular tissues _
symplastically
The casparian strip forces what?
symplastic flow
Casparian strip options
- apoplastic flow is blocked
- apoplast to symplast
- symplastic flow
- irregular cylinder of parenchyma cells lying underneath the endodermis
- capable of becoming meristematic and giving rise to lateral roots
Pericycle
- this is the central cylinder of tissue, interior to the endodermis
- consists of pericycle, xylem, and phloem
- xylem is in the center
- phloem is outside of the xylem
- no pith in eudicots
Vascular stele
Within the xylem
- inner widest cells are metaxylem (produced last)
- outer narrow cells are protoxylem (produced first)
Within phloem regions
- protophloem occurs on outer side
- metaphloem occurs on inner side
the arrangement of tissue within the stele differs for what?
monocots
Arrangement of tissue within the stele for monocots
- large vessels and distinct bundles of phloem occur scattered throughout the region, interior to the endodermis
- plus there’s a central pith region
Mature portions of the root
- root hairs have withered away
- the endodermis deposits suberin and lignin over the radial and tangential surfaces of the casparian strip forming a completely sealed cylinder
- this blocks all symplastic and anoplastic flow into the stele
- water and minerals can therefore only enter into the cylinder from younger portions of the root
eventually lateral roots emerge:
a group of cells of the pericycle divide to form a root primordium and organize into a root apical meristem
By the time the lateral root emerges
- it has formed a root cap
- first protoxylem and protophloem of the vascular stele have begun to differentiate
- this establishes a direct connection between the lateral root to the vascular tissues of the parent root
Above the maturation zone, in the older parts of the root, big changes happen
1) Root hairs whither away
2) secondary cambia emerge to produce wood and bark of the root, just as in the stem
Vascular cambium ->
root wood
Cork cambium ->
root bark
The root vascular cambium arises within what?
the stele when parenchyma (btw xylem and phloem) and a few pericycle cells join together to form the meristem
The cambium is initially what?
irregular in shape (undulating) and positions the phloem to the exterior
As the root vascular cambium begins producing columns of cells, its outline becomes what?
more regularly circular
As in stems, the root vascular cambium produces what?
- secondary xylem to the inside (OG primary xylem remains in center)
- secondary phloem to the outside (OG primary phloem gets pushed to the exterior)
Bark on roots is produced by what?
cork cambium (phellogen) that arisesin the pericycle
Production of cork cell on the exterior of the cork cambium ultimately causes what to shed?
old endodermis, cortex, and epidermis
Most woody roots have what?
high storage capacity
storage occurs in what cells of the root?
parenchyma
storage occurs in parenchyma cells of the root found in:
- Ray parenchyma cells (horizontal)
- Axial parenchyma cells (vertical)
- both are products of the root vascular cambium
The wood of a root is different than the wood of a stem in that:
- It is mostly parenchyma
- there are few vessels and no fibers
- this wood is therefore well adapted for long-term storage
Root parenchyma stores what?
- carbohydrates
- water
- proteins
Storing materials in the roots have many advantages, including:
- roots are less visible as food for most foragers
- Root surroundings are more stable and protected from environmental fluctuations than aboveground parts
for crops like carrots and radishes, the taproot that we consume is secondary growth (wood) modified for high capacity storage
Storage taproots
- tall plate-like roots of some tropical trees
- upper side grows more rapidly than other parts of the root
- brace the trunk from being blown over by wind or in thin soils
Buttress roots
aerial roots of orchids have a specialized epidermis layer called a what?
Velamen; Velamen roots of epiphytes
What prevents water loss in dry conditions of orchids?
velamen
