BTNY LS1203 - Plant Biology
To Be A Plant
Challenges Facing Plants
water acquisition The Basic Plant Body Plan: Roots, Stems, Leaves
Roots: Functions Stems:
Functions Leaves: Functions
stems + leaves = shoot system Plant Growth meristem = a collection of dividing cells found in specific places in a plant
apical meristem, primary meristems, lateral (secondary) meristems
Primary Growth (herbaceous growth) Ground Tissue Roots Stems Leaves VIDEO!!
The Private Life of
Plants: Putting Down Roots. Take notes!! Review Stems: functions Secondary growth Return to Botany 1203 Home Page. Return to Botany 1203 Syllabus Return to Harley Home. 27 January 2011
water conservation
CO2 collection
light collection
solar radiation
heat
cold
herbivory
anchorage: deep roots or spreading roots
absorption of water and minerals
storage (food or water)
conduction
support and display leaves (for photosynthesis) and flowers (for
pollination)
conduction between the leaves and roots via xylem and phloem
photosynthesis
storage (food, water)
Primary function => PHOTOSYNTHESIS;
challenge =>transpiration
performed by all plants at some point in their lives
occurs at tips of roots and stems
results in increase in plant length
divisions of cells in the apical meristem produce three moderately
differentiated primary meristems that make the three primary tissues:
apical meristem —> primary meristems: —> primary
tissues:
ground meristem
ground tissue
protoderm
epidermis
procambium 1°
xylem and 1° phloem (vascular tissues)
Secondary Growth (woody growth)
not performed by all plants
lateral meristems produce increase in plant girth
provide new vascular and protective tissues
new cells are laid down in rings
vascular cambium —> 2° xylem and 2° phloem
cork cambium —> cork and phelloderm
food or water storage, photosynthesis, respiration, support,
mechanical protection
might be divided into regions of cortex and pith by the vascular
tissue; called mesophyll in leaves
Parenchyma Cells
alive at maturity
found in all tissues, esp. ground tissue
thin primary cell wall, polyhedral shape
large vacuole
photosynthesis, food storage, water storage, respiration
least specialized cell, therefore shows totipotency best:
wound healing, vegetative propagation
Collenchyma Cells
alive at maturity
generally found just inside the epidermis, in strands or cylinders
unevenly thickened 1° cell walls: provide flexible support
for young plant parts
Sclerenchyma Cells
usually dead at maturity
thick 2° walls, often lignified
two types: fibers (long, thin) and sclereids (boxy,
branching)
provide mechanical protection, support, sometime storage
Dermal Tissues
outermost cell layers
mechanical protection, chemical protection, gas exchange, water
conservation
Epidermis
epidermal cells
guard cells (monocot vs. dicot), stoma
trichomes: one cell, multicellular, glandular
bulliform cells
cuticle: cutin, wax
Periderm
cork cambium: produces cork to the outside and phelloderm to the
inside
cork: cork cells, dead at maturity, suberized, no air
spaces, gas exchange via lenticels
phelloderm: parenchyma cells, alive at maturity,
photosynthesis
Vascular Tissues
Xylem
transport of water and dissolved minerals obtained from soil
parenchyma cells
fibers
tracheids (found in all vascular plants)
vessel elements/vessel members (found mostly in just the
angiosperms)
Phloem
transport of sucrose and other soluble organic molecules
parenchyma cells
fibers
sieve tube elements/sieve tube members with sieve plate; no
nucleus at maturity
companion cells
(sieve cells and albuminous cells in non-flowering plants)
Radicle: the embryonic root
Dicots (Eudicots): taproot system
the radicle grows into a single primary root; additional roots
branch off of the primary root
can grow very deep into soils
can enlarge radially for storage
Monocots: fibrous root system
after the radicle begins to grow, additional roots grow from the
stem (adventitious roots) that are uniform in diameter with the radicle; still
have extensive branch roots
tend to be shallower than taproots
very good at anchorage and preventing soil erosion
Adventitious Roots
grow on organs other than roots: stems, leaves
on cuttings, growth is enhance by auxins (a class of plant
hormones)
can perform all root functions
vegetative propagation
Root Tip
region of cell maturation: where cells become specialized;
has root hairs
region of cell elongation: where cells enlarge
region of cell division: where the apical and primary
meristems are located
root cap:
protects the meristems as expendable cells
face the ripping action of the soil
senses gravity
secretes mucigel
prevents
dessication
better contact
with soil for water and mineral absorption
lubricates the
soil for easier root passage
provides a
specific microhabitat (rhizosphere) for beneficial soil
microorganisms
Epidermis
covers the entire root surface except the root cap
usually lacks stomata
no or very thin cuticle: thin cuticle lets water and
minerals in, provides protection from harmful bacteria and fungi; thicker
cuticle on older roots near the soil surface where drying is a problem
root hairs: extensions of epidermal cells; greatly increase
the root surface area for absorption
Cortex
ground tissue between the epidermis and the vascular cylinder
innermost cell layer = endodermis
tightly packed
cells
Casperian strip of
suberin and lignin to force filtering of dissolved minerals
Vascular Cylinder (stele)
everything inside the endodermis
pericycle
a meristematic tissue
source of lateral (branch) roots (arise
internally from mature root)
contributes to lateral meristems in woody
root systems
primary xylem and phloem
Modified Roots
Storage: beet, turnip, radish, carrot, sweet potato,
dandelion
Propagation: adventitious buds of aspen, apple
Parasitism: haustoria of mistletoe
Beneficial Root/Microbe Interactions
Mycorrhizae (fungi) and Rhizobial Bacteria: to be covered
later with Mineral Nutrition
Uses of Roots
veggies: carrots, turnips
staple food crops: sweet potato, cassava
flavors: licorice, sarsparilla
drugs: ipecac, ginseng
erosion control
dyes: madder
External features of stems
nodes vs. internodes
axillary (lateral) buds
spare apical meristems
branches, with next set of leaves
phyllotaxy: alternate, opposite, whorled
lenticels
leaf scar
vascular bundle scar
bud scale scar
Internal Stem Anatomy
Epidermis
epidermal cells
stomata with guard cells
trichomes
cuticle
Ground Tissue
parenchyma
fibers
collenchyma
pith, cortex
Vascular Tissue
vascular bundles, xylem towards in the inside and phloem towards
the outside
procambium persists in dicots
In most dicots, the vascular bundles are arranged in a ring and
divide the ground tissue into pith and cortex regions.
In most monocots, the vascular bundles are found throughout the
ground tissue.
Secondary Growth in Stems
new cells are produced internally, in rings
external most cells are continually destroyed and must be
replaced; internal most cells accumulate as wood
vascular cambium
2° xylem and 2° phloem
cork cambium
cork: dead at maturity, suberized, gas
exchange via lenticels
phelloderm: parenchyma cells, alive at maturity,
photosynthesis
cork + phelloderm + cork
cambium = periderm
wood = 2° xylem
hardwood (dicots) vs. softwood (conifers)
sapwood vs. heartwood
growth rings: spring (early) wood + summer (late) wood
knots
bark = all tissues to the outside of the vascular cambium; includes the periderm
and the phloem
splits and gets crushed as secondary growth continues; does not
accumulate like xylem does
Modified Stems
tendrils: to anchor climbing plants (some tendrils are
modified leaves)
succulence: for water storage, e.g. cacti
runner: horizontal, above ground stem (strawberry)
rhizome: horizontal, under ground stem (iris, begonia)
bulb: rosette stem with fleshy leaves (onion)
tubers: underground, swollen stem tips for storage (potato)
thorns: protection
Uses of stems
sugar cane
flax (for linen fibers)
potato tubers
from secondary growth:
lumber
paper
fuel
spices: cinnamon (from bark)
medicines: quinine (from bark)
as intact trees: ceremonial,
commemorative, shade, etc.
Leaf = blade + petiole
can be sessile; sheath
simple leaf = undivided blade (blade margin can be smooth or with
various indentations)
compound leaf = blade divided into leaflets (leaflets on
same plane, no buds)
pinnately compound ==> rachis
palmately compound
veins: netted venation (dicots = “broad leafed plants”),
parallel venation (monocots = “narrow leafed plants”)
Epidermis
usually transparent
no chloroplasts (exceptions: guard cells)
lots of stomata
horizontal leaves ==> preferential
distribution to lower epidermis, especially in leaves of woody dicots
vertical leaves ==> even
distribution to lower and upper epidermis
in rows between parallel veins of
monocots; scattered in dicots
transpiration/photosynthesis compromise
bulliform cells
trichomes
cuticle
Vascular Tissue
xylem and phloem in bundles (veins); xylem toward upper
epidermis
Ground Tissue = Mesophyll
sclerenchyma
parenchyma with lots of chloroplasts (chlorenchyma)
dicot: palisade mesophyll, spongy mesophyll
monocot: uniform mesophyll
Moisture affects leaf development and features: xerophytes, hydrophytes, mesophytes
Mesophytes: grow best in moist, but not wet, environments
find structures for moderate conservation of water: adequate
cuticle, stomata on lower epidermis
Xerophytes: grow in seasonal or persistent arid conditions
water conservation vs. water storage (succulence)
small, thick leaves
multiple palisade and spongy mesophyll layers
multiple epidermis
very thick cuticle
often lots of stomata (for maximum CO2 collection = photosynthesis =
when water is available)
sunken stomata, with trichome overlays
lots of sclerenchyma cells for support when water (turgor
pressure) is low
special type of photosynthesis found in most succulents
deciduous in dry season
Hydrophytes: grow partially or completely submerged in water
problems getting enough light and CO2 for
photosynthesis
Elodea: submerged ==> no cuticle or stomata, only a
few cells thick, no extensive vascular tissue
large, thin leaves
poorly developed mesophyll
lots of aerenchyma for gas exchange and buoyancy
thin (if any) cuticle
stomata on air-exposed surfaces, e.g. the upper epidermis of
floating leaves (water lily)
low in xylem, support cells
thin cell walls
reduced root systems
leaf dimorphism in emerged vs. submerged leaves of the same plant
Leaf Abscission
deciduous vs. evergreen
Abscission zone
fewer sclerenchyma cells
separation layer forms in the zone
cells get suberin that seals off the vascular tissue and other
cells —> leaf scar
Signs: loss of chlorophyll; leaves change color to yellow, red, etc.
also losing proteins, nucleic acids, etc.
Where do the leaf materials go?
Modified leaves
tendrils (pea): compound leaves of peas: the end
leaflets are tendrils
stipules: at the base of petioles; photosynthesis, tendrils
spines (cactus): for protection
bud scales: overlapping, tough, waterproof. Protect
buds from frost, drying, pathogens
storage (succulence, for water storage; food storage of onion)
insect trapping by carnivorous plants: pitchers, sticky
surfaces, fast movements
asexual reproduction (e.g. Kalenchoë), propagation (Begonia,
Sedum)
cotyledons: storage, absorption
flower parts
Uses of leaves
veggies: lettuce, cabbage, spinach
herbs: parsley, bay, thyme
drinks: tea, herbal teas
dyes: henna
fibers: sisal (Agave)
drugs: digitalis (foxglove), belladonna (atropine), tobacco,
marijuana
Cells and tissues
primary tissues: epidermis, ground tissue, vascular tissue
functions of the tissues; know the cell types found in each
tissue; know the tissue specific functions of the cells
primary meristems: protoderm, ground meristem, procambium;
development (apical meristem —> 1° meristems —>
1° tissues)
be able to identify, describe, and give the function(s) of various
plant cell types: parenchyma, collenchyma, sclerenchyma (fiber, sclereid),
vessel element, sieve tube element, trichome, guard cells
Roots: functions; types of root systems
modifications and their functions
root regions
functions of tissues
cell types found in tissues
root hairs
modifications and their functions
compare tissue arrangements in monocots and dicots
functions of tissues
cell types found in tissues
How does the origin of branch stems differ from the origin of
branch roots?
secondary tissues (2° xylem, 2° phloem, cork, and phelloderm),
their functions, and their cell types
wood: early wood vs. late wood; sapwood vs.
heartwood; hardwood vs. softwood
How do knots form?
bark vs. wood; bark vs. periderm
external features of stems
Where are the youngest tissues located? The oldest?
Leaves: functions
modifications and their functions
development (apical meristem —> 1° meristems —>
1° tissues)
compare tissue arrangements in monocots and dicots
functions of tissues
cell types found in tissues
abscission
venation patterns: parallel, netted
petiole, blade, stipules, sessile, compound leaves (palmate and
pinnate), simple leaves, sheath
mesophytes vs. xerophytes vs. hydrophytes: be familiar with the anatomical
differences between the leaves of these three groups of plants. How do the
anatomical features provide a survival advantage to a xerophyte or hydrophyte in
its particular environment?
Be able to trace the lineage of tissues from the apical meristem to 1°
tissues, both forwards and backwards.
What products do we obtain from various plant organs? What features of the
anatomy of the plants make them good for these uses?