Plant Structure and Growth

Land Plants 3 major groups: –1. non-vascular plants No conducting tissue, often grouped together as bryophytes, usually small and close to ground. (Mosses) –2. seedless vascular Well-developed vascular tissue, no seeds, (ferns, club mosses, horsetails) –3. seeded vascular Most plants are this, seeds contain an embryo, supply of nutrients and protective outer coat, extensive vascular tissue

Seeded Vascular Plants 2 divisions: –1. Gymnosperms- seeds that do not develop within an enclosed structure (evergreens) –2. Angiosperms- seeds develop within protective structure (think apple)

Plant Organs Three basic organs: Roots (root system) fibrous: mat of thin roots taproot: one large, vertical root Stems (shoot system) nodes: leaf attachment internodes: area b/t 2 nodes Leaves (shoot system) blade(flatten portion) Petiole (stalk attaching blade to stem)

Plant Organ Systems Three basic tissue types: Dermal (epidermis): prevents water loss; protection against pathogens Vascular (material transport) xylem: water and dissolved minerals roots to shoots phloem: food from leaves to roots and fruits Ground (photosynthesis, storage, support and secretion) All three derive from meristematic tissue. Initial vs. derivative

Root Tissue Epidermis- outer layer Cortex- conducts water from soil to interior vascular tissue Xylem- root to shoot Phloem- leaves to roots Endodermis- surrounds vascular tissue

Stem Tissue Plant region where leaves are attached Cambium- rapidly dividing cells that differentiate into xylem and phloem Pith- storage and support

Leaf Tissue Epidermis/cuticle (protection; desiccation) Stomata (tiny pores for gas exchange and transpiration)/guard cells Mesophyll: ground tissue between upper and lower epidermis; two types: palisade (most photosynthesis) and spongy (gas circulation) Veins/vascular bundles- xylem and phloem

Monocotyledonous vs. dicotyledonous plants

Plant Organ Modification Roots: –1. prop roots –2. storage roots –3. pneumatophores (air roots) –4. buttress roots

Plant Organ Modification Stems –Bulbs –Tubers –Rhizomes –Stolons

Plant Organ Modification Leaves –Tendrils –Reproductive leaves –Bracts or floral leaves –spines

Plant Growth Life Cycles annuals: 1 year (wildflowers; food crops) biennials: 2 years (beets; carrots) perennials: many years (trees; shrubs) Indeterminate growth Meristems apical: tips of roots and buds; primary growth, non-woody stems and roots lateral: growth is thickness; secondary growth (wood)

Secondary Growth Two lateral meristems vascular cambium ~ produces secondary xylem (wood) and secondary phloem (diameter increase; annual growth rings) cork cambium ~ produces thick covering that replaces the epidermis; produces cork cells

Tropism Tropism: movement toward or away from a stimulus –Phototropism (auxin) –Gravitropism –Thigmotropism

Auxin Hormone that cause positive phototropism of plant shoots and seedlings IAA (indoleacetic acid) the specific plant auxin that causes this action Location: seed embryo; meristems of apical buds and young leaves Function: stem elongation; root growth, differentiation, branching; fruit development; apical dominance; tropisms Often get unequal distribution of auxin.WHY?