Plant Structure, Growth, and Development
(Ch. 35)
What are Angiosperms?
Angiosperm Body2 Taxonomic classes• monocots• eudicotsMonocots• One cotyledon • Parallel veins • Floral parts in 3’s • Fibrous RootsEudicots • Two cotyledons -• Netlike veins• -Floral parts in 4’s and 5’s• Tap root
Angiosperm BodyNeed to be able to inhabit soil and air at the same time• roots and shoots
Plant morphology• study of the external structure• arrangement of flower parts, etc.
Plant anatomy• study of the internal structure• arrangement of cells, tissues in a leaf, etc.• Tissue – groups of cells, consisting of one or more types,
that perform a specialized function• Organ – consists of several types of tissues that together
carry out specific functions
Angiosperm Body
Two basic systems• root system• aerial shoot system
(stems, leaves, flowers)
Vascular Tissues• transport materials• xylem transports
water and dissolved minerals
• phloem transports food
Root System• Anchoring, absorbing water
and minerals, storing carbohydrates
Taproot system• one large, vertical root• mostly eudicots• firm anchorage; one large
vertical root• stores lots of reserve food• gives rise to lateral roots
Root SystemFibrous root system• mat of threadlike
roots• mostly monocots• extensive exposure to
soil, water, minerals• concentrated in
topsoil; prevents erosion
Root SystemAdventitious roots
• plant organ that grows in an unusual location
• arising above ground or from stems/leaves
Root hairs
• thin, tubular extension of a root epidermal cells
• increase SA near root tip
Root SystemMycorrhizae
• mutualistic relationship between fungi and roots
Root nodules
• contain symbiotic bacteria to convert atmospheric nitrogen to compounds usable by the plant
Modified Roots
(a) Prop roots (b) Storage roots (c) “Strangling” aerialroots
(d) Buttress roots (e) Pneumatophores
Shoot SystemVegetative shoots• Stems and leavesFloral shoots• FlowersStem• Alternating system of
nodes and internodes• Raises or separates
leaves• Raise reproductive
structures
Shoot System - StemsNodes• where leaves attach to stemsInternodes• segment of stem between nodesAxillary bud• embryonic side shoot• has potential to form a branch shoot• usually dormant in young plants• pruning
Shoot System - Stems
Terminal (apical) bud
• bud on shoot tip; composed of developing leaves and a compact series of nodes and internodes
• where most of the growth of a young plant occurs
• May inhibit growth of axillary buds– apical dominance
Modified StemsStolons• Runners allow plant to colonize a large
area & reproduce asexuallyRhizomes• Horizontal stem that grows below groundTubers• Swollen ends of rhizomes; store foodBulbs• Vertical, underground shoots
Modified Stems
Rhizomes. The edible base of this ginger plant is an example of a rhizome, a horizontal stem that grows just below the surface or emerges and grows along thesurface.
(d)
Tubers. Tubers, such as these red potatoes, are enlarged ends of rhizomes specializedfor storing food. The “eyes” arranged in a spiral pattern around a potato are clusters of axillary buds that markthe nodes.
(c)Bulbs. Bulbs are vertical,underground shoots consistingmostly of the enlarged bases of leaves that store food. You can see the many layers of modified leaves attached to the short stem by slicing an onion bulb lengthwise.
(b)
Stolons. Shown here on a strawberry plant, stolons are horizontal stems that grow along the surface. These “runners”enable a plant to reproduce asexually, as plantlets form at nodes along each runner.
(a)
Storage leaves
Stem
Root Node
Rhizome
Root
Shoot System - Leaves
Main photosynthetic organ
• Blade
• Joined to node by a petiole
Venation (vascular tissue)
• parallel
• netted
Classification
• shape
• spatial arrangement
• venation
Petiole
(a) Simple leaf. A simple leafis a single, undivided blade.Some simple leaves are deeply lobed, as in anoak leaf.
(b) Compound leaf. In acompound leaf, theblade consists of multiple leaflets.Notice that a leaflethas no axillary budat its base.
(c) Doubly compound leaf. In a doubly compound leaf, each leaflet is divided into smaller leaflets.
Axillary bud
Leaflet
Petiole
Axillary bud
Axillary bud
Leaflet
Petiole
Modified Leaves• Tendrils on vines
• Spines of cacti
• Storage
• Reproductive
• Bracts
Dermal, Vascular, and Ground TissuesTissue system• A functional unit
connecting all of the plant’s organs
Dermal tissue system• Outer protective
covering• Epidermis in
nonwoody plants• Cuticle
• Periderm in woody plants
Dermal, Vascular, and Ground TissuesVascular tissue system• Long distance
transport b/w roots and stems
• Xylem and phloem• Collectively called the
steleGround tissue system• If internal to the
vascular tissue pith• If external to the
vascular tissue cortex
Plant CellsProtoplast• contents of a plant cell not
including the cell wallLignin• Structural component of cell
wallsAll start out similar to
parenchyma cells; become more specialized
• Can generate an entire plant from one parenchyma cell
Plant CellsParenchyma cells• “typical” plant cell• chloroplasts for photosynthesis• large central vacuole• store starch• comprise fleshy tissue of fruits
Collenchyma cells• unevenly thick primary walls• support for young plants
without restraining growth• living and flexible throughout
life
Plant CellsSclerenchyma cells• rigid, thick secondary walls
with lignin• function only in support• may be dead at maturity but
produce secondary walls before protoplast dies
• Sclereids– Very thick cell lignified cell
walls; nutshells & seed coats
• Fibers – Long, slender and tapered
Plant CellsWater-conducting cells of xylem
• dead at functional maturity
• allow water to flow from cell to cell
• tracheids
– In nearly all vascular plants
– Water moves through pits
• vessel elements
– Angiosperms and some gymnosperms
– Water moves through perforation plates
Plant CellsFood-conducting cells of phloem
• alive at functional maturity
• sieve-tube cells make the sieve tube elements/members that transport sucrose and other organic nutrients
• sieve plate
– Pores that allow flow from cell to cell
• companion cells
– Ribosomes and nucleus serve the sieve tube cell too
Figure 35.12 Locations of major meristems: an overview of plant growth
Meristems generate cells for primary and secondary growth
Begins with germination and occurs throughout life of plant
• Indeterminate growth
Meristems• perpetually undifferentiated tissues
Apical meristems• Responsible for primary growth
(growth in length)
Lateral meristems• Responsible for secondary growth
(growth in thickness)
Meristems generate cells for primary and secondary growth
Two types of lateral meristems
Vascular cambium• Add layers of vascular
tissue called secondary xylem (wood) and secondary phloem
Cork cambium• Replaces the epidermis with
thicker, tougher periderm
Plant GrowthFinite life span
• genetically & environmentally determined
• annuals, biennials, and perennialsAnnuals• Complete their life cycle in a year• Cereal grains, legumes, wildflowersPerennials• Live many years• Trees, shrubs, some grassesBiennials• Life span –generally 2 years• Live through an intervening cold period between vegetative
growth and flowering• Beets, carrots
Figure 35.14 Primary growth of a root
Primary Growth Lengthens Roots and ShootsPrimary growth of roots• pushes roots through soil;
root cap covers apical meristem
• Zone of cell division – apical and primary
meristems• Zone of cell elongation
– elongate in size• Zone of maturation
– specialize in function
Primary Growth Lengthens Roots and ShootsEpidermisGround tissueVascular tissueSteleEndodermisPericycle
Primary Growth Lengthens Roots and Shoots
Primary growth of shoots• Apical meristems give rise
to primary meristems• Leaf primordia give rise
to leaves• Shoot elongation is due to
lengthening of internode cells below the shoot tip
• Branching occurs due to activation of axillary buds
Tissue Organization of Stems
Epidermis• Covers stemsVascular tissue in bundlesAxillary buds meristems
develop lateral shootsParenchyma, collenchyma,
and scelerenchyma cells are present
Tissue Organization of Leaves Epidermis• tightly locked cells• protect from damage &
pathogens• waxy cuticleStomata • pores on underside of leaf• site of gas exchangeGuard cells• control stomata opening for
gas exchange• Flaccid stomata are closed
due to lack of water
Tissue Organization of LeavesMesophyll• Ground tissue of leaf
between epidermal layers
• palisade parenchyma – upper half of leaf
• spongy parenchyma
– air spaces to allow O2 and CO2 to circulate
– lower half of leaf
Tissue Organization of Leaves
Vascular Cambium and Secondary Vascular Tissue
Secondary growth of stems• Stems and roots of woody plants• vascular cambium
– transport and storage of starch– Adds secondary xylem (wood) and secondary phloem
• cork cambium – protective layers
• Bark (refers to all tissues external to vascular cambium)
• phloem, phelloderm, cork cambium, corkSecondary growth of roots
An overview of primary and secondary growth
Cork Cambium and Production of Periderm
Phelloderm• Thin layer of parenchyma cells that forms to
the interior of the cork cambiumAccumulation of cork cells• Deposit suberin in walls then die
– Protects from water loss, physical damage, pathogens
Lenticels• Small, raised areas in the periderm• Help cells to exchange gases
Growth, Morphogenesis, and Cell Differentiation Produce the Plant Body
Development• Specific series of changes by which cells form tissues, organs, and
organismsGrowth• Irreversible change in size• Cell division and expansionMorphogenesis• Process that gives a tissue, organ, or organism its shape and
determines the positions of cell types• Pattern formationDifferentiation• Process by which cells with the same genes become different from
one another• Control of gene expression