Transcript Plant Structure, Growth, and Development

Plant Structure
Hierarchy of a Plant Body
 Extreme developmental
plasticity in plants
 Structurally change
morphology, external form,
to better suit environment
 Genetic factors play small role
too
 More variety within plant
species than animal species
 Plants have organs that are
composed of tissues that are
made of cells
 Basic organs are roots, stems,
and leaves
Cabomba caroliniana, a fanwort
Hierarchy of a Plant Body
 Plants aquires resources from 2
different environments
 CO2 and light from above ground
 Water and nutrients from soil
 Plants have organs that are
composed of tissues that are made
of cells to facilitate
 Basic organs are roots, stems, and
leaves
 Form root system and stem
system
 Systems rely on each other for
materials
Roots
 An organ that anchors, absorbs, and store
 3 types
 Taproot system has 1 main vertical root that produces small lateral,
or branched, roots
 Most eudicots and gymnosperms; i.e. carrots and beets
 Store sugars and starches for flowering; why root crops harvested before flowering
 Adventitious roots arise from stems or leaves, with each forming
separate lateral roots
 Can be modified to provide more support of anchorage; fig. 35.4
 Fibrous roots form a mat of thin roots that don’t penetrate deeply
 Seedless vascular plants and most monocots; i.e. grasses
 Root hairs found near the tips aid in absorption and increase SA
 Short lived and constantly replaced, not to be confused with lateral
roots
Stems
 Alternating nodes where leaves attach and internodes, the
segments in between
 Upper angle of each leaf contains an axillary bud which
can form a lateral shoot, but are normally dormant
 Near the shoot tips are apical buds which inhibit axillary
bud growth via apical dominance
 Concentration of resources so plant can grow taller
 If apical bud is gone then axillary buds can develop into lateral
shoots and become their own apical bud
 Reason for pruning bushes and trimming house plants
Leaves
 Main photosynthetic part of the plant
 Consist of a flattened blade and a petiole or stalk to join to
stem at node
 Veins, the vascular tissue, differ in arrangement between
eudicots and monocots
 Monocots with parallel veins
 Eudicots with branched veins
 Angiosperms classified by vein branching (floral morphology too)
 Simple have single undivided blades
 Compound blades of multiple leaflets (apical at base of blade only)
 Adaptations for support, reproduction, or storage
Leave Patterns and Deviations
Tissue Systems
 Dermal tissue system is the outer protective covering
 Nonwoody plants have an have an single layer of epidermis that
covers and protects young parts of a plant
 Secretes a waxy cuticle covering to help retain water
 Woody plants have a periderm to protect older regions of plant
 Vascular tissue system runs throughout the plant
 Xylem transports water and minerals up
 Phloem transports food down to where its needed
 Collectively know as stele
 Angiosperms have solid central vascular cylinder, leaves and stems have
vascular bundles, separate strands of vascular tissue
 Ground tissue system
 Internal to vascular is called pith, external is cortex
Plant Cell Types
 Parenchyma cells: thin and flexible primary walls, lack secondary
 ‘Typical’ plant cells because they are least specialized
 Perform most of the cell’s metabolic functions
 Can regenerate a whole plant from one cell
 Collenchyma cells: thicker primary walls, but unevenly thickened
 Grouped as strands or cylinders to support young parts of shoots
 i.e. strings of celery
 No secondary walls or lignin
 Sclerenchyma cells: thick secondary walls strengthened by lignin
 Can’t elongate and reside in parts of plants no longer growing
 Most dead at maturity, but produce the secondary cell wall before for support
 Fibers are long and slender; hemp fibers to make rope and flax fibers wove into linen
 Sclereids irregular in shape and are shorter; impart hardness to nutshells and seed coats
 Xylem
 Phloem