Plant Structure & Organization

Structure vs. Function

Cabomba

Review of Life Hierarchy Cells Tissues Organs Systems

Two Basic Systems Root System—Functions in

obtaining water & minerals from the soil; found underground (usually)

Shoot System—Obtaining CO2 from the air & obtaining light; carrying out photosynthesis; found above ground (usually)

Systems are interdependent

Three Main Organs of Plants

Roots—absorb water and minerals; anchor the plants

Stems—responsible for growth of the plant; holds leaves; transports materials between leaves and roots

Leaves—site of photosynthesis; reproduction--flowers are modified leaves

Types of Root Systems Fibrous Root Systems

– Mat of thin roots

– Increases plant’s exposure to water

– Anchors plant in the ground

– Holds topsoil in place; prevents erosion

– Associated with monocots

Types of Root Systems Taproot System

– One large, vertical root

– Often store food (carrot, turnips, beets)

– Really long in desert plants

– Associated with dicots

Root Facts Root hairs increase surface area for

water absorption; extensions of root epidermis

Adventitious Roots (extra roots)—roots that grow above ground; corn for example—above ground roots are used to “prop” up the plant

Types of Shoot Systems Vegetative—leaf bearing Reproductive—flower bearing

Stem Anatomy Node—point at

which leaves are attached

Internodes—Stem segments between nodes

Stem Anatomy Axillary bud—Can

form vegetative branch; angle between stem & leaf; most are dormant

Terminal bud—located at tip of stem; site of stem growth

Stem Growth The presence of the terminal bud

inhibits growth of axillary buds therefore there is apical dominance.

This increases a plant’s exposure to light.

Removing terminal bud will stimulate growth of axillary budy.

Modified Stems

Stolons; Rhizomes; Tubers; Bulbs

Leaf Anatomy Blade—Flattened part Petiole—stalk of leaf; joins to node

Modified Leaves

Three types of tissues in plant organs

Dermal—single layer of cells to cover and protect

Vascular—continuous throughout plant; transport materials between roots and shoots

Ground tissue—All other tissue; functions in photosynthesis, storage & support.

Vascular Tissue Xylem—conducts water & minerals

from roots to the shoot; against gravity Phloem—transports sugars

manufactured in shoot to non-photosynthetic areas (roots; fruits, etc.)

Xylem Composed of

tracheids & vessel elements; elongated cells

Dead at maturity Remaining cell

walls provide a conduit through which water can flow

Phloem Composed of sieve-tube

members and companion cells

Sieve tubes are alive at maturity; lack nucleus, ribosomes, and vacuole

Companion cells connect to sieve tubes by plasmodesmata; their nuclei & ribosomes serve sieve tubes.

Types of Plant Cells Parenchyma

– Thin & flexible primary cell walls; lack secondary walls

– “Typical” plant cells– Perform most metabolic function of plants– Developing plant cells are parenchyma

cells

Types of Plant Cells Collenchyma

– Have thicker primary walls; no secondary walls

– Supports young parts of plant shoot without restraining growth

– “Strings” of celery are collenchyma

Types of Plant Cells Sclerenchyma

– Thick secondary walls– Cannot elongate– Occur in regions where growth has stopped– For support; many dead at maturity– Vessel elements & tracheids are sclerenchyma

cells– Hemp & flax (rope & linen) are sclerenchyma