Plant Structure and Function

• Plant structure lays the foundation for plant function.

Themes and Variations in Plant Form (34.1)

• Roots, shoots, and leaves are looked at more closely.
• Primary growth extends the plant body.
• Secondary growth widens shoots and roots.
• Plant tissue systems include dermal, ground, and vascular tissues and their cells.

Introduction (34.0)

• Plants have a remarkable biochemistry and use light energy, simple ions, and compounds to build complex bodies.
• Plants need tiny and low concentrated essential chemicals
• Shoots and root systems both display indeterminate growth, which continues to extend root and shoot tips and find light and compounds.

Plant Form: Themes with Many Variations (34.1)

• The vegetative plant body is made up of 2 systems

Root System

• The root system is the below-ground part of the plant
• It anchors the plant and absorbs water and nutrients (N, P, K, Mg, etc.).

Shoot System

• This is the above-ground part of the plant
• It absorbs light and CO₂ needed for photosynthesis.

Vascular Tissue

• Vascular tissue connects root and shoot systems.
• Xylem carries water and nutrients from roots to shoot.
• Phloem carries sugars from photosynthetic parts of the shoot downward to rest of plant (or from stored reserves in root upward).

Root System Functions

• Anchoring the plant in soil is another function
• It also absorbs water and ions
• Another function is to conducts water and ions to shoot
• It also obtains and stores energy (sugar) from shoot for later use as starch
• Most root systems are extensive and may exceed 80% of plant's total mass.
• Morphological diversity of root systems
• Diversity within the same habitat can minimize competition for water and nutrients.

Two Main Root Types

• Taproot system mostly exists in eudicots
• Fibrous root system mostly exists in monocots

Modified Roots

• Adventitious roots develop from the shoot system instead of from roots.
• Aerial roots are located on climbing ivy
• Prop roots can be on corn
• Pneumatophores (air roots) grow in trees in swampy habitats and acquire oxygen from the atmosphere.
• Storage roots store energy as starch and store nutrients for next growing and flowering cycles.

Shoot System

• Consists of one or more stems
• Node: where one or more leaves are attached
• Internode: segments between nodes
• Leaf: projects laterally, usually for photosynthesis

Modified Stems and Leaves

• Water storage stem: enlarged for water storage which also conducts photosynthesis
• Stolon: horizontal stem that runs above ground; function in asexual reproduction
• Rhizome: horizontal stem located below ground; can function in asexual reproduction
• Tuber: rhizome modified for carbohydrate storage
• Thorns/prickles: modified stems for protection from herbivores

Leaf Functions

• Photosynthesis
• Anatomy
  • Petiole: Stalk which attaches blade to stem which has bud at base
  • Blade = surface area for absorbing sunlight

Morphological Diversity in Leaves

• Simple vs. compound leaves
• A simple leaf blade is one piece with a bud at base
• Pinnate venation has one main vein arising from base with side veins branching off
• Compound lead blades divide into leaflets
• Compound pinnate leaflets are attached to a petiole

Leaf Arrangements

• Alternate arrangement: 1 leaf per node
• Opposite arrangement: 2 leaves per node
• Whorled arrangement: 3 or more leaves per node

Modified Leaves

• Bulb: set of thickened, nutrient-storage leaves
• Succulent leaves: leaves modified for water storage
• Tendrils: modified leaves that are found on climbing plants
• Colored bracts: modified leaves modified to attract pollinators
• Spines: modified leaves for protection
• Insect traps are leaves modified to capture insects as a source of nitrogen
• Plantlets are involved in asexual reproduction

Plant Tissues (34.2)

Epidermal Tissue

• Found on outside surface of plant
• One cell layer thick
• Shoots produce a waxy cuticle
• Roots absorb water and have root hairs to increase surface area

Ground Tissue

• Ground tissue stores starch and perform photosynthesis.
  • Parenchyma are big cells with thin walls.
  • They store starch and may contain chloroplasts.
  • sclerenchyma have thick secondary cell wall (lignin), are dead when mature
• Provides rigid support

Vascular Tissue

• Xylem conducts water upward
• Tracheids and vessels conduct fluids
• Mature xylem are dead
• Tracheids have secondary cell walls of lignin. -Phloem Conducts Food
• alive at maturity
• comprised of Seive Tube Elements

Meristematic Tissue

• This tissue divides and daughter cells become any other tissue type.

Primary Growth (37.3)

• Vertical growth
• Apical meristems at the tips of all roots and stems produce new cells. Growth is at tips.
• Cells produced by meristems become tissues in the primary structure of roots, stems, and leaves.

Primary Growth of Stems

• Stems originate in buds, which have meristematic tissue that can grow into new shoot structures
• Apical buds are at the tips of each stem
  • Growth extends the length
  • May also develop into a flower
• Axillary, lateral buds : Located right above leaf attachment

Primary Structure of Roots

• Epidermis: contains root hairs
  • Root hair = single epidermal cell with lateral extension
• Cortex: region of root between epidermis and vascular cylinder
  • parenchyma cells for starch storage
• Endodermis innermost layer of cortex
  • Casparian strip - waterproof layer covering most cells of endodermis
  • Passage cells direct movement of water into xylem

Vascular Bundle

• The location for vascular tissue (xylem and pholem)
  • Monocot contains xylem inner and P in outer with parenchyma
  • Eudicot
    • Eudicot xylem in very center

Primary Structure of Herbaceous Stems

• No wood or bark
• Epidermis (secretes waxy cuticle)
• Cortex (region between epidermis and vascular bundles)
• Parenchyma (contains chloroplasts for photosynthesis)
• Pith (center of a eudicot stem cross section Parenchyma for starch storage

Vascular Tissue

• Xylem: the inside of the bundle
• Phloem: the outside of the bundle
• sclerenchyma cap: support/protection

Leaf Structure

• Epidermis (secretes waxy cuticle)
• Mesophyll (contains parenchyma cells with chloroplasts for photosynthesis)
• Vascular bundles (xylem and phloem)

Monocot Leaf

• Vascular bundles evenly spaced apart
• Stomata on both surfaces
• Bulliform cells on upper surface causes leaf to collapse which rolls up reduces area & therefore water loss on dry days

Eudicot Leaf

• Two types of mesophyll (palisade and spongy)
• Upper palisade mesophyll is tightly packed
• Lower spongy mesophyll allows gas exchange between stomata and palisade layer; there also is no stomata on upper surface

Secondary Growth (34.4)

• Increases width of the roots and stems
• Responsible for secondary growth, is a cylinder of meristematic cells called the cambium.

Woody Stem Cross Section

• Two cambia- Cork Cambium - Located around perimeter of stem.
• Produces cork cells, replace epidermis & protect vascular tissue beneath
  • Bark - Everything from the vascular cambium to the outer core

Vaxcular Cambium

• Located between the xylem and pholem.
• Produces secondary xylem
• Toward the inside of the stem
  • this is what we call wood
• produces secondary Phleom on the outside of stem

Perennial Plants

• Live for many years -secondary growth occurs during pars of the year where conditions are favorable for growth
  • Annual rings = 1 year's growth

Wood Characteristics

• Spring Wood-Large Vessals = Lighter and less dence
• Summer wood- - Small Vessals = Darker and more dense period of dormancy (no growth)