Plant Structure An overview

Plant Cells

Cell Walls  Primary  Secondary  Middle lamella  Plasmodesmata

Plant Body  Root System  Underground  Shoot system  Leaves  Stems  Flowers

Plant tissues  Simple tissues vs. complex tissues  Vascular plants have 3 tissue systems:  Ground  Vascular  Dermal

Ground tissue  Makes up most of plant body  Variety of functions:  Photosynthesis  Storage of materials  Support  Composed of 3 simple tissues  Based on composition of cell wall

Ground tissue, cont.  Parenchyma tissue  Most common type of cell and tissue  Thin primary cell walls  Edible parts of plants  Functions: photosynthesis, secretion, storage  Metabolically active  Have ability to differentiate

Ground tissue, cont.  Collenchyma cells  Provides support in herbaceous plants  Primary cell wall is unevenly thick  Thickest at corners  Alive at maturity  Schlerenchyma cells  Thick secondary cell walls  Strength and support  Often dead at maturity

Vascular Tissue  Embedded in ground tissue  Transports material  Made of 2 complex tissues  Xylem  Phloem

Xylem  Conducts water  Provides support  Made of 4 cell types:  Fibers  Xylem parenchyma  Tracheids  Vessel elements

Conducting Cells in Xylem  Tracheids  Dead at maturity  Hollow  Long, tapering  Pits  Vessel elements  Dead at maturity  Larger diameter  End walls perforated or absent  Pits in side wall

Phloem  Conducts carbohydrates throughout the plant  Provides support  Composed of 4 cell types:  Phloem parenchyma  Fibers  Sieve tube elements  Companion cells

Conducting Cells in Phloem  Sieve tube elements  Alive at maturity  Lack many organelles  Sieve plate at end  Carry dissolved sugars  Companion cells  Connected to sieve tube elements by plasmodesmata  Assist in functioning of sieve tube elements

Dermal tissue  Covers and protects the plant  Composed of 2 complex tissues  Epidermis  Periderm

Epidermis  Primarily unspecialized epidermal cells  Transparent  Secrete cuticle  Specialized guard cells  Open and close stomata  Trichomes  Outgrowths, hair

Periderm  Replaces epidermis in woody plants  Composed of:  Cork parenchyma  Cork cell  Dead at maturity  Walls coated with waxy suberin  Periderm forms outer bark

Plant Growth

Plant growth involves:  Cell division  Mitosis  Cytokinesis – cell plate divides new cells  Cell elongation  Cytoplasm grows  Vacuole increases in size  Cell differentiation - specialization

Growth  Indeterminate  Continues throughout plant’s life  Determinate  Plant part reaches a certain size then stops  Primary vs. Secondary  Primary – length  Secondary - girth

Meristems  Only locations where plant cells divide  Undifferentiated cells  Primary function is mitosis

Primary Growth  Occurs at apical meristems  Tips of roots and shoots  In roots, meristem is directly behind root cap  Shoot apical meristem forms  Leaf primordia  Bud primordia  Further away cells move from apical meristems, begin to differentiate

Secondary Growth  Occurs in trees and shrubs  Due to lateral meristems  2 lateral meristems  Vascular cambium – located between wood and bark - forms secondary xylem and secondary phloem  Cork cambium – in outer bark – forms cork cells and cork parenchyma

Bark  Outermost covering of woody stems and roots  All plant tissues located outside the vascular cambium  2 regions:  Living inner bark  secondary phloem  Dead outer bark  periderm