Organismal Diversity Week 12 4/27/26-5/1/26

Vascular Plant Organization

Plants are built hierarchically, cells —> tissues —> organs

Cell

Fundamental unit of life (maintains homeostasis, carries genetic information)

Tissue

Collections of cells of one or more types that have a common function

Organ

Collection or multiple tissues in a single structure performing a common function

Vascular Plants have three fundamental organs

roots, leaves, and stems

roots

generally below ground with three basic functions: a) anchor plant to substrate b) acquire nutrients and water c) storage of nutrients. Composed of lateral roots extending from primary root of seedling to the side and down. Have five types of specialized roots

Root hairs

(very fine roots) maximize absorption

taproot

Large, downward root deeply anchoring plant

buttressed roots

stabilize in moist shallow soil

pneumatophore

in tidal/inundated areas to access air

strangling roots

aerial roots for plants germination above ground

prop roots

aerial roots holding tall top-heavy plants up

storage roots

expanded for nutrient storage

leaves

Photosynthetic organs (may be modified for other purposes), may be modified for many purposes: storage, reproduction, defense, climbing, etc.

blade

maximizes surface area to intercept sunlight and gas exchange

petiole

stalk of leaf (absent in many monocots)

stems

aboveground structural elements that elevate leaves and reproductive structures, expose leaves to sunlight to maximize photosynthesis. Alternating nodes and internodes, lengthening occurs at the tips or in the angle between stem and leaf, diametric growth occurs in lateral meristems

nodes

point of leaf attachment

Apical buds

Tip of the stem

axillary buds

Angle between stem and leaf

Primary growth

occurs at the tips

Secondary growth

diametric growth

Plants have three fundamental tissue systems

Dermal tissue, vascular tissue, ground tissue

dermal tissue

outer covering, epidermis= outermost layer, in leaves and stems: covered by waxy cuticle (to prevent water loss), periderm= replaces epidermis in older tissues, esp in woody plants: gives rise to cork, leading to bark. May have specialized cells: guard cells and trichomes

vascular tissue

transport nutrients via xylem and phloem in stems and roots

ground tissue

storage, support, photosynthesis

Periderm

replaces epidermis in older tissues, esp in woody plants. Gives rise to cork, leading to bark.

guard cells

allow gas exchange

trichomes

many functions (may be secretory or pointy for protection)

stele

collective of xylem and phloem, in roots vascular cylinder and in stem vascular bundles

Vascular cylinder

In roots a collection of xylem and phloem

Vascular bundles

In stem a collection of xylem and phloem

Mature xylem cells are dead and come in to types

tracheids and vessel elements

tracheids

in all vascular plants; thin tapered ends

vessel elements

in many angiosperms and others; wider, flatter ends, strengthened by lignin to prevent collapse and provide support

Mature phloem cells are alive and specialized and include

sieve tube elements

Sieve tube elements

lack many organelles so materials flow through them easily

Pith

Ground tissue within vascular tissue

Cortex

Ground tissue on the outside of vascular tissue