Post on 16-Dec-2015
Angiosperms – flowering plants
• The angiosperms are seed-bearing vascular plants
• In terms of distribution and diversity, they are the most successful plants on Earth
• The structure and function of this plant group help explain its success
Monocots and Dicots – same tissues, different features
Parallel veinsNetlike veins
3 pores1 pore
4 or 5 floral parts
3 floral parts
1 cotyledon 2 cotyledons
Vascular bundles dispersed
Vascular bundles in ring
Flowering Plant Life
Cycle Double fertilization Meiosis Meiosis
microspores
Female gametophyte
pollination
Mitosis without cytoplasmic division
Two sperms enter ovule
Diploid
Haploid
Plant Life Histories• Annuals complete life cycle in one growing season
• Biennials live for two seasons; flowers form in second
season
• Perennials grow and produce seeds year after year
Meristems – Where Tissues Originate• Regions where cell divisions produce plant growth• Apical meristems
– Responsible for primary growth (length)• Lateral meristems
– Responsible for secondary growth (width)
Apical Meristems
activity atmeristems
new cellselongateand start todifferentiateinto primarytissues
procambium primary vascular tissues
protoderm epidermis
Cells that form at apical meristems:
ground meristem ground tissues
Lengthen shoots and roots:StemAM and RootAM
Lateral Meristems
vascular cambium secondary vascular tissues
periderm cork cambium
thickening
Increases girth of older roots and stems
Cylindrical arrays of cells
Plant Tissue Systems
VASCULAR TISSUES
GROUND TISSUES
SHOOT SYSTEM
ROOT SYSTEM
EPIDERMIS
• Ground tissue system
• Vascular tissue system
• Dermal tissue system
Ground Tissue• fills space b/t dermis & vascular Parenchyma: Primary metabolic function
(photosynthesis)– Found in roots, stems & leaves– Least specialized, thin flexible walls, don’t divide unless
specializing, respire, store food & water
Schlerenchyma: support w/ thick 2o wall strengthened by lignin– Found in stems & leaves generally lack protoplasts– Very rigid cell wall, dead at maturity, cannot lengthen
scaffolding “fibers” & “Sclereids”
Collenchyma:child support– Found in stems and leaves– Grow and elongate with stems and leaves they support,
flexible in young parts of plant
Complex Tissues
Composed of a mix of cell
types
Xylem
Phloem
Epidermis
Simple Tissues
Made up of only one
type of cell
Parenchyma
Collenchyma
Sclerenchyma
Vascular Tissue
Phloem: Phood conduction, carries products of photosynthesis to non-photo cells– Found in roots, stems, leaves– Sieve cells, albuminous cells, companion cells, parenchyma– Gymnospersm: sieve, angiosperms, sieve-tube members, connected
vertically by sieve plates– Alive at maturity
Xylem: provides water & ion transport from roots to leaves– Vessel elements, tracheids, fibers, wood parenchymal– tracheids & vessel members, thick w/ secondary wall with lignin– Dead at maturity– Seedless vascular & gymnosperms have tracheids w/ tapered ends– Angiospersm have both tracheids and vessel members wh are
continuous
Xylem
• Conducts water and dissolved minerals
• Conducting cells are dead and hollow at maturity
vessel membertracheids
Phloem: A Complex Vascular Tissue
• Transports sugars
• Main conducting cells are sieve-tube members
• Companion cells assist in the loading of sugars
sieve plate
sieve-tubemember
companioncell
Epidermis: A Complex Plant Tissue
- Covers and protects plant surfaces
-Secretes a waxy, waterproof cuticle
-In plants with secondary growth,
periderm replaces epidermis
-protection, increase absorption area
in roots, reduces H2O loss in stem &
leaves,
-Regulates gas exchange in leaves
Signaling between Plants and Pathogens
water & minerals
sugar
SHOOT SYSTEM
ROOT SYSTEMRoot system
- anchors the plant
- penetrates the soil and absorbs water and minerals
- stores food
Shoot system
- produces sugars by photosynthesis
- carries out reproduction
Shoot and Root Systems:
Not independent
Shoot Development
ground meristem
primary xylempithprocambriumcortex
procambriumprotoderm
shoot apicalmeristem
primary phloem
Leaf Gross Structure-Adapted for Photosynthesis
petiole
blade
axillarybud
node
blade
sheath
node
DICOT MONOCOT
• Leaves are usually thin
– High surface area-to-volume ratio
– Promotes diffusion of carbon dioxide in, oxygen out
• Leaves are arranged to capture sunlight
– Are held perpendicular to rays of sun
– Arrange so they don’t shade one another
Leaf StructureUPPER
EPIDERMIS
PALISADEMESOPHYLL
SPONGYMESOPHYLL
LOWEREPIDERMIS
one stoma
cuticle
O2CO2
xylem
phloem
Parenchyma
Collenchyma
Mesophyll: Photosynthetic Tissue
• A type of parenchyma tissue
• Cells have chloroplasts
• Two layers in dicots
– Palisade mesophyll
– Spongy mesophyll
Leaf Veins: Vascular Bundles
• Xylem and phloem –
often strengthened with fibers
• In dicots, veins are netlike
• In monocots, they are parallel
Internal Structure of a Dicot Stem
- Outermost layer is epidermis
- Cortex lies beneath epidermis
- Ring of vascular bundles separates the cortex from the pith
- The pith lies in the center of the stem
Internal Structure
of a Monocot
Stem
• The vascular bundles
are distributed
throughout the ground
tissue
• No division of ground
tissue into cortex and
pith
Dicots
Dicots and Monocots have different stem and root anatomies
Ground tissuesystem
Vascular tissue system
Dermal tissuesystem
Monocots
Stems
Monocot stems differ from dicot stems in that they lack secondary growth
• No vascular cambium nor cork cambium
• Stems usually uniform in diameter
• Scattered vascular bundles (not in a ring like dicot stems)
The Translocation of Phloem • the process of moving
photosynthetic product through the phloem
• In angiosperms, the specialized cells that transport food in the plant are called sieve-tube members, arranged end to end to form large sieve tubes
• Phloem sap is very different from xylem sap
– sugar (sucrose) can be concentrated up to 30% by weight
• Phloem transport is bidirectional – Phloem moves from a sugar source
(a place where sugar is produce by photosynthesis or by the breakdown of sugars) to a sugar sink (an organ which consumes or stores sugar)
– What are some organs which would be sugar sinks?
Transport in Plants:
The Pressure Flow Model , 2
Root Structure• Root cap covers tip
• Apical meristem produces the cap
• Cell divisions and elongation at the apical meristem cause the root to lengthen
• Farther up, cells differentiate and mature
root apical meristem
root cap
pericycle
phloem
xylem
root hair
endodermis
epidermis
cortex
Primary Root Growth
Root Cap •Secretes polysaccharide slime that lubricates the soil •Constantly sloughed off and replaced
Apical Meristem •Region of rapid cell division of undifferentiated cells •Most cell division is directed away from the root cap
Quiescent Center •Populations of cells in apical meristem which reproduce much more slowly than other meristematic cells •Resistant to radiation and chemical damage •Possibly a reserve which can be called into action if the apical meristem becomes damaged
The Zone of Cell Division - Primary Meristems •Three areas just above the apical meristem that continue to divide for some time
•Protoderm•Ground meristem•Procambium
The Zone of Elongation •Cells elongate up to ten times their original length •This growth pushes the root further downward into the soil
The Zone of Maturation •Region of the root where completely functional cells are found
Internal Structure of a Root• Outermost layer is epidermis• Root cortex is beneath the epidermis• Endodermis, then pericycle surround the vascular cylinder• In some plants, there is a central pith
Root Anatomy - Dicot Roots Epidermis • Dermal tissue • Protection of the root Cortex • Ground tissue • Storage of photosynthetic products • Active in the uptake of water and minerals Endodermis • cylinder once cell thick that forms a boundary between the
cortex and the stele contains the casparian strip, Pericycle • found just inside of the endodermis • may become meristematic • responsible for the formation of lateral roots Vascular Tissue • Xylem and Phloem Root Anatomy - Monocot Roots Epidermis • Dermal tissue • Protection of the root Cortex • Ground tissue • Storage of photosynthetic products • Active in the uptake of water and minerals Endodermis • cylinder once cell thick that forms a boundary between the
cortex and the stele even more distinct than dicot counterpart contains the casparian strip,
Pericycle• monocot roots rarely branch, but can, and this branch will
originate from the pericycle Vascular Tissue • Xylem and Phloem • Forms a ring near center of plant Pith • Center most region of root
Root Hairs and Lateral Roots• Both increase the surface area of a root
system
• Root hairs are tiny extensions of
epidermal cells
• Lateral roots arise from the pericycle
and must push through the cortex and
epidermis to reach the soil• Root of a single rye plant (fibrous system) measure and
counted 6400 roots w/ 12.5 million root hairs = 250 km, dist
from Memphis, TN to Atlanta, GA
newlateralroot
Symplastic Movement • Movement of water and solutes through the continuous
connection of cytoplasm (though plasmodesmata) • No crossing of the plasma membrane (once it is in the
symplast) Apoplastic Movement • Movement of water and solutes through the cell walls and the
intercellular spaces • No crossing of the plasma membrane • More rapid - less resistance to the flow of water
•transpirational pull•flow from greater to lower water concentration
•relies on cohesion & adhesion of water
–cavitation breaks chain of water molecules
Ascent of xylem sap
Net flow in whole plants
Key Concepts:• Diffusion: movement
of molecules from high to low concentration.
• Osmosis: diffusion of water across a semi-permeable membrane.
• Mass or bulk flow: movement of fluid due to pressure or gravity differences.
Long-distance movement of water• Plants mostly obtain water & minerals from soil.• Water moves up the xylem by bulk flow.• Movement of water depends on transpiration pull, cohesion &
adhesion of water molecules, capillary forces, and strong cell walls.
Other mechanisms of water transport not as important:
• Diffusion (note mosses, etc.)• Capillary forces (cohesions & adhesion)• Osmotic pressure (guttation)
Fig. 39.11
Water – pushed or pulled?
• Pushing of the xylem sap occurs via root pressure – root cells expend energy to pump mineral into the xylem. Minerals accumulate in the xylem sap lowering water potential there. Thus water flows into the xylem, generating a positive pressure that pushes fluid up the xylem.
Guttation – from root pressure
The availability of soil water and minerals
Long-distance transport of water from roots to leaves
But root pressure can only push sap up a few meters and many plants generate no root pressure at all. How does water reach leaves of 100 m tall trees?Xylem sap is pulled up the plant via transpirational pull. Leaves actually generate the negative pressure necessary to bring water to them.
Translocation• The transport of food throughout a plant is
known as translocation. • Sugar from mesophyll cells in the leaves
and other sources must be loaded before it can be moved.
• Often sieve tube members accumulate very high sucrose concentrations – 2 to 3 times higher than concentrations in the mesophyll – so phloem requires active transport using proton pumps
• At the sink end of a sieve tube, the phloem unloads its sugar. Phloem unloading is a highly variable process; its mechanism depends upon the plant species and the type of organ. In any case, the concentration of sugar in the sink cells is lower than in the phloem because the sugar is either consumed or converted into insoluble polymers like starch.
• Phloem moves at up to 1 m/hour – too fast to be by diffusion. So phloem also moves via bulk flow – pressure drives it.
Secondary Growth
The Plant Body: Secondary Growth: The Vascular Cambium
• Occurs in perennials
• A ring of vascular cambium produces secondary xylem and phloem
• Wood is the accumulation of these secondary tissues, especially
xylem
Woody Stem
periderm (consists ofcork, cork cambium,and secondary cortex)
secondaryphloem
BARK
HEARTWOOD SAPWOOD
vascular cambium
Annual Rings
• Concentric rings of secondary xylem
• Alternating bands of early and late wood
• Early wood– Xylem cells with large diameter, thin walls
• Late wood– Xylem cells with smaller diameter, thicker
walls
Types of Wood
• Hardwood (oak, hickory)– Dicot wood– Xylem composed of vessels, tracheids,
and fibers
• Softwood (pine, redwood)– Gymnosperm wood– Xylem composed mostly of tracheids– Grows more quickly