Plant Structure, Growth & Development

Packet #35Chapters #35 & #38

The Plant Body

Introduction Genes and the environment affect plant

structure. Plants exhibit structural responses to their

specific environment. Plasticity

Explains why no two plants are identical. Mangroves and cacti

Introduction II Plants are multi-cellular, have organs that are

composed of different tissue (previously covered), and tissue which are composed of different cell types (previously covered).

Roots, Stems & Leaves

Introduction The basic morphology

of plants reflects adaptations that have developed so that an organism can inhabit and obtain resources from soil and air.

Two systems Subterranean root

system Aerial root system

Stems and leaves Neither system is

independent of the other

Introduction II Most absorption occurs near the root tips

Vast number of root hairs found Increase the surface area of the root Extensions of epidermal cells

Previously covered

Adventitious tissue is any tissue that grows in an atypical location

Roots that develop out of above ground stems or leaves are called adventitious roots Provide additional support for taller plants.

Root System Roots are generally

underground, obtains water and dissolved nutrient minerals for the plant and stores food.

Anchors the plant firmly in place.

Fibrous root systems Observed in seedless

vascular plants and most monocots.

Mats of thin roots that spread out through the soil Grasses and mangroves

Root System Taproot System

Make up many eudicots and gymnosperms Consist of one large vertical root that produces

many smaller lateral or branch roots Firmly anchors the plant in the soil Some store food (starch) that can be consumed by

the plant when the plant is fruiting or flowering Most tree species

Modified Roots

Modified Roots I Prop Roots

Develop from branches, or a vertical stem and grow downward into the soil to help support certain plants in an upright position Fichus tree South Florida?

Buttress Roots Swollen bases or braces

that support certain tropical rainforest trees that have shallow root systems

Modified Roots II Pneumatophores

Aerial “breathing” roots that may assist in getting oxygen to submerged roots

Contractile Roots Roots that grow into

the soil and then contract

Pulling plant deeper into the soil Corms bulbs

Mutualistic Relationship Between Roots & Other Organisms

Relationships Mycorrhizae

Mutually beneficial associations between roots and soil fungi

Root nodules Swellings that develop on roots of legumes and

house millions of rhizobia (nitrogen fixing bacteria) Root Graft

Natural connection between the roots of trees belonging to the same or different species.

Shoot System

Introduction I Shoots consist of stems and leaves

Vegetative Leaf bearing

Reproductive Flower bearing

Stems Stem

Alternating system of nodes Locations where the

leaves are attached Internodes

Stem segments between nodes

Auxiliary Bud Angle, or axil, formed

by each leaf of the stem

Has the potential to form a branch Most though are

dormant

Stems II Growth of a young shoot is usually

concentrated at its apex (tip), where there is a terminal bud with developing leaves and a compact series if nodes and internodes

The presence of terminal bud prohibits the growth of the axillary bud Apical dominance

“evolutionary response that directs growth toward light

Modified Stems Stolons/Runners

Grow on the surface of the ground

Increase surface area Can colonize asexually if plant is

fragmented Strawberry

Rhizomes Horizontal stems that grow

underground Ginger

Tubers Swollen ends of rhizomes

specialized for storing food Potato

Bulbs Vertical, underground shoots

consisting mostly of swollen bases of leaves that store food onions

Leaves The main photosynthetic organ Consist of a flattened blade and a petiole

Stalk Joins the leaf to the node on the stem

Leaves are in various sizes, shapes and arrangement of leaves.

Differences Between Plant & Animal Growth

Differences Between Plant & Animal Growth Growth in plants, unlike animals, is localized in

specific regions called meristems, and involves three processes Cell division Cell elongation Cell differentiation

Plant growth is not limited to an embryonic period

Most plants have indeterminate growth

Life Cycles

Life Cycles Annuals

Complete their life cycle from germination to flowering and seed production and death in one year or less Wildflowers

Biennials Live for two years There is a dormant period between vegetative

growth and flowering Carrots Beets

Perennials Long lived plants and include trees, shrubs and

some grasses.

Indeterminate Growth Unrestricted growth in

stems and growth This pattern of growth

depends in the location of the meristems Meristems are regions of

undifferentiated, embryonic cells. Initially, the cells are totipotent and can differentiate/mature into any other type of cell.

Apical meristems Responsible for primary

growth Located at the tips of

roots, shoots and within the buds of stems

Indeterminate Growth Lateral meristems

Cylinders of dividing cells that extend along the length of the roots and shoots provide for an increase in girth

Responsible for secondary growth Vascular cambium Cork cambium

Primary vs. Secondary Growth

Primary Growth Increase in stem or root length Occurs in all plants Restricted to the youngest part of the plant.

Primary Growth

Fig 34.12Primary Growth of Root

Fig 35.15Primary Growth of Shoot

Secondary Growth Increase in stem or root girth Typically occurring in long cylinders of

meristematic cells throughout the length of older stems and roots

Occurs in all gymnosperms, most eudicots and rarely in monocots.

Secondary Growth IILateral Meristems Vascular cambium

Produces secondary xylem (wood) and secondary phloem Secondary xylem

Interior Secondary phloem

Exterior

Cork Cambium Produces thick, tough covering (cork cells) for stems and

roots that replace the epidermis Recall what wood is composed of?

Tracheids Vessel elements Fibers

An overview of primary and secondary growth

Figure. 35.10

In woody plants, there are lateral meristems that add secondary

growth, increasing the girth of

roots and stems.

Apical meristemsadd primary growth,or growth in length.

Vascularcambium

Corkcambium

Lateralmeristems

Root apicalmeristems

Primary growth in stems

Epidermis

Cortex

Primary phloem

Primary xylem

Pith

Secondary growth in stems

PeridermCorkcambium

CortexPrimary phloem

Secondaryphloem

Vascular cambium

Secondaryxylem

Primaryxylem

Pith

Shoot apicalmeristems(in buds)

The corkcambium addssecondarydermal tissue.

The vascularcambium addssecondaryxylem andphloem.