Plant Structure Growth and Development Chapter 35

Evolution of Plants All Plants… multicellular, eukaryotic, autotrophic, alternation of generations

Alternation of Generations Sporophyte (diploid) produces haploid spores via meiosis Gametophyte (haploid) produce haploid gametes via mitosis Fertilization joins two gametes to form a zygote

Angiosperms Monocots vs. Dicots named for the number of cotyledons (seed leaf) present on the embryo of the plant + monocots - orchids, corn, lilies, grasses + dicots - roses, beans, sunflowers, oaks

Plant Morphology Morphology (body form) shoot and root systems + inhabit two environments - shoot (aerial) + stems, leaves, flowers - root (subterranean) + taproot, lateral roots vascular tissues + transport materials between roots and shoots - xylem/phloem

Plant Anatomy Anatomy (internal structure) division of labor + cells differing in structure and function - parenchyma, collenchyma, sclerenchyma (below) - water- and food-conducting cells (next slide) Parenchyma St: “typical” plant cells Fu: perform most metabolic functions Collenchyma St: unevenly thickened primary walls Fu: provide support but allow growth in young parts of plants Sclerenchyma St: hardened secondary walls (LIGNIN) Fu: specialized for support; dead

Plant cell types Parenchyma cells Collenchyma cells Cell wall Sclerenchyma cells

Plant cell types Xylem Phloem Vessel Tracheids Tracheids and vessels WATER-CONDUCTING CELLS OF THE XYLEM Vessel Tracheids Tracheids and vessels element Pits SUGAR-CONDUCTING CELLS OF THE PHLOEM Companion cell Sieve-tube member Sieve-tube members: longitudinal view Sieve plate Nucleus Cytoplasm Companion cell

Water- and Food-conducting Cells Xylem (water) dead at functional maturity tracheids- tapered with pits vessel elements- regular tubes Phloem (food) alive at functional maturity sieve-tube members- arranged end to end with sieve plates & Companion cells

Plant Tissues Three Tissue Systems dermal tissue + epidermis (skin) - single layer of cells that covers entire body - waxy cuticle/root hairs vascular tissue + xylem and phloem - transport and support ground tissue + mostly parenchyma - occupies the space b/n dermal/vascular tissue - photosynthesis, storage, support

Plant Growth Meristems perpetually embryonic tissues located at regions of growth + divide to generate additional cells (initials and derivatives) - apical meristems (primary growth- length) + located at tips of roots and shoots - lateral meristems (secondary growth- girth)

Roots A root Is an organ that anchors the vascular plant Absorbs minerals and water Often stores organic nutrients Taproots found in dicots and gymnosperms Lateral roots (Branch roots off of the taproot) Fibrous root system in monocots (e.g. grass) Figure 35.3

Modified Roots Many plants have modified roots (a) Prop roots (b) Storage roots (c) “Strangling” aerial roots (d) Buttress roots (e) Pneumatophores (a) Prop roots (b) Storage roots

Primary Growth of Roots apical meristem + root cap + three overlapping zones - cell division - elongation - maturation

Stems A stem is an organ consisting of Nodes (point where leaf connects) Internodes (stem between nodes)

Modified Stems Stolons Storage leaves Rhizomes Stem Node Root Bulbs Tubers (c) Bulbs Stolons (a) Storage leaves Stem Root Node Rhizome

Buds An axillary bud Is a structure that has the potential to form a lateral shoot, or branch A terminal bud Is located near the shoot tip and causes elongation of a young shoot Gardening tip: Removing the terminal bud stimulates growth of axillary buds

Primary Growth in Shoots apical meristem (1, 7) + cell division occurs + produces primary meristems - protoderm (4, 8) - procambium (3, 10) - ground meristem (5, 9) axillary bud meristems + located at base of leaf primordia leaf primordium (2, 6) + gives rise to leaves

The leaf Is the main photosynthetic organ of most vascular plants Leaves generally consist of Blade Stalk Petiole

Leaf Morphology In classifying angiosperms Taxonomists may use leaf morphology as a criterion Petiole (a) Simple leaf (b) Compound leaf. (c) Doubly compound leaf. Axillary bud Leaflet

Modified Leaves Tendrils Spines Storage leaves Bracts Reproductive leaves. The leaves of some succulents produce adventitious plantlets, which fall off the leaf and take root in the soil.

Leaf Anatomy Epidermal Tissue upper/lower epidermis guard cells (stomata) Ground Tissue mesophyll +palisade/spongy parenchyma Vascular Tissue veins + xylem and phloem

Cutaway drawing of leaf tissues Leaf Anatomy Key to labels Dermal Ground Vascular Guard cells Stomatal pore Epidermal cell 50 µm Surface view of a spiderwort (Tradescantia) leaf (LM) (b) Cuticle Sclerenchyma fibers Stoma Upper epidermis Palisade mesophyll Spongy Lower Vein Xylem Phloem Bundle- sheath Cutaway drawing of leaf tissues (a) Air spaces Guard cells 100 µm Transverse section of a lilac (Syringa) leaf (LM) (c)

The Three Tissue Systems: Dermal, Vascular, and Ground

Dermal Tissue Protects plant from: Physical damage Pathogens H2O loss (Cuticle)

Vascular tissue Carries out long-distance transport of materials between roots and shoots Consists of two tissues, xylem and phloem Xylem Phloem

Ground Tissue Includes various cells specialized for functions such as storage, photosynthesis, and support Pith = ground tissue internal to the vascular tissue Cortex = ground tissue external to the vascular tissue

Secondary Growth Lateral Meristems vascular cambium + produces secondary xylem/phloem (vascular tissue) cork cambium + produces tough, thick covering (replaces epidermis) secondary growth + occurs in all gymnosperms; most dicot angiosperms

The Vascular Cambium and Secondary Vascular Tissue Is a cylinder of meristematic cells one cell thick Develops from parenchyma cells

2° Growth As a tree or woody shrub ages The older layers of secondary xylem, the heartwood, no longer transport water and minerals The outer layers, known as sapwood Still transport materials through the xylem

Cork Cambium Periderm protective coat of secondary plant body + cork cambium and dead cork cells - bark cork cambium produces cork cells