Plant Structure, Growth, and Differentiation Chapter 31 Plant Structure, Growth, and Differentiation
Plants Herbaceous Woody In temperate climates, aerial parts die back Annuals, biennials, perennials Woody In temperate climates, aerial parts persist Perennials
Annuals Grow, reproduce, and die in one year or less Corn Geranium Marigold
Duckweeds, with Wolffia on frog’s back
Biennials Take two years to complete their life cycles before dying Carrot Queen Anne’s lace
Perennials Have the potential to live for more than two years Asparagus Oak trees
Eucalyptus regnans
Life history strategies Long-lived trees compete successfully against smaller plants in favorable environments (e.g., tropical rain forests) Small, short-lived plants thrive in unfavorable environments (e.g., deserts after a rainy spell)
Vascular plant body Root system Generally underground Obtains water and dissolved nutrient minerals Anchor plant in place
The plant body: Arabidopsis thaliana
Vascular plant body, cont. Shoot system consists of A vertical stem bearing leaves (organs of photosynthesis) Reproductive structures (flowers and fruits in flowering plants) Buds (undeveloped embryonic shoots that develop on stems)
Vascular plant body, shoot system, cont. Generally aerial Obtains sunlight and exchanges gases, such as CO2, oxygen, and water vapor
Vascular plant body, cont. Plant body is composed of Ground tissue system Vascular tissue system Dermal tissue system Although separate organs exist, tissue systems are integrated throughout plant body
The three tissue systems in the plant body
Ground tissue system Parenchyma tissue Collenchyma tissue Sclerenchyma tissue
Parenchyma cells
Collenchyma cell Schlerenchyma cells
Parenchyma tissue Composed of living parenchyma cells with thin primary cell walls Functions Photosynthesis Storage Secretion
Collenchyma tissue Consists of collenchyma cells with unevenly thickened primary cell walls Function is to provide flexible structural support
Sclerenchyma tissue Composed of sclerenchyma cells (sclereids or fibers) with Primary cell walls Secondary cell walls Function is to provide structural support, although Sclerenchyma cells are often dead at maturity
Parenchyma cell type Sclerenchyma cell type Collenchyma cell type
Vascular tissue system Conducts materials throughout plant body Provides strength and support Consists of Xylem Phloem
Tracheid (xylem cell Sieve tube element Vessel element (xylem cell) Phloem tissue
Vascular tissue system, cont. Xylem Complex tissue conducting water and dissolved nutrient minerals Conducting cells are tracheids and vessel elements
Vascular tissue system, cont. Phloem Complex tissue conducting sugar in solution Conducting cells are sieve tube elements; they are assisted by companion cells
Tracheid Vessel element
Sieve tube element Companion cell
Dermal tissue system Outer protective covering of the plant body Consists of Epidermis Periderm
Dermal tissue system, cont. Epidermis Complex tissue covering herbaceous plant body Epidermis of aerial parts secretes a waxy cuticle to reduce water loss Stomata permit gas exchange Trichomes (outgrowths or hairs)
Dermal tissue system, cont. Periderm Complex tissue covering woody parts of plant body in woody plants
Epidermal cell Guard cell
Trichome Cork cell
Growth in plants versus animals Localized in meristems Involves Cell division Cell elongation Cell differentiation
Primary growth Secondary growth Increase in stem or root length Occurs in all plants Secondary growth Increase in stem or root girth Localized Typically occurs in long cylinders of meristematic cells throughout length of older stems and roots
Apical meristems Localized Activity herein results in primary growth At tips of roots At tips of shoots Within buds of stems Activity herein results in primary growth
A root tip
Lateral meristems Vascular cambium Cork cambium Responsible for secondary growth
Longitudinal section through shoot apex
Secondary growth