Plant Structure

1. Plant Structure

2. Hierarchy of a Plant Body • Extreme developmental plasticity in plants • Structurally change morphology, external form, to better suit environment • Genetic factors play small role too • More variety within plant species than animal species • Plants have organs that are composed of tissues that are made of cells • Basic organs are roots, stems, and leaves • Cabomba caroliniana, a fanwort

3. Hierarchy of a Plant Body • Plants aquires resources from 2 different environments • CO2 and light from above ground • Water and nutrients from soil • Plants have organs that are composed of tissues that are made of cells to facilitate • Basic organs are roots, stems, and leaves • Form root system and stem system • Systems rely on each other for materials

4. Roots • An organ that anchors, absorbs, and store • 3 types • Taproot system has 1 main vertical root that produces small lateral, or branched, roots • Most eudicots and gymnosperms; i.e. carrots and beets • Store sugars and starches for flowering; why root crops harvested before flowering • Adventitious roots arise from stems or leaves, with each forming separate lateral roots • Can be modified to provide more support of anchorage; fig. 35.4 • Fibrous roots form a mat of thin roots that don’t penetrate deeply • Seedless vascular plants and most monocots; i.e. grasses • Root hairs found near the tips aid in absorption and increase SA • Short lived and constantly replaced, not to be confused with lateral roots

6. Stems • Alternating nodes where leaves attach and internodes, the segments in between • Upper angle of each leaf contains an axillary bud which can form a lateral shoot, but are normally dormant • Near the shoot tips are apical buds which inhibit axillary bud growth via apical dominance • Concentration of resources so plant can grow taller • If apical bud is gone then axillary buds can develop into lateral shoots and become their own apical bud • Reason for pruning bushes and trimming house plants

7. Leaves • Main photosynthetic part of the plant • Consist of a flattened blade and a petiole or stalk to join to stem at node • Veins, the vascular tissue, differ in arrangement between eudicots and monocots • Monocots with parallel veins • Eudicots with branched veins • Angiosperms classified by vein branching (floral morphology too) • Simple have single undivided blades • Compound blades of multiple leaflets (apical at base of blade only) • Adaptations for support, reproduction, or storage

8. Leave Patterns and Deviations

9. Tissue Systems • Dermal tissue system is the outer protective covering • Nonwoody plants have an have an single layer of epidermis that covers and protects young parts of a plant • Secretes a waxy cuticle covering to help retain water • Woody plants have a periderm to protect older regions of plant • Vascular tissue system runs throughout the plant • Xylem transports water and minerals up • Phloem transports food down to where its needed • Collectively know as stele • Angiosperms have solid central vascular cylinder, leaves and stems have vascular bundles, separate strands of vascular tissue • Ground tissue system • Internal to vascular is called pith, external is cortex

10. Plant Cell Types • Parenchyma cells: thin and flexible primary walls, lack secondary • ‘Typical’ plant cells because they are least specialized • Perform most of the cell’s metabolic functions • Can regenerate a whole plant from one cell • Collenchyma cells:thicker primary walls, but unevenly thickened • Grouped as strands or cylinders to support young parts of shoots • i.e. strings of celery • No secondary walls or lignin • Sclerenchyma cells: thick secondary walls strengthened by lignin • Can’t elongate and reside in parts of plants no longer growing • Most dead at maturity, but produce the secondary cell wall before for support • Fibers are long and slender; hemp fibers to make rope and flax fibers wove into linen • Sclereids irregular in shape and are shorter; impart hardness to nutshells and seed coats • Xylem • Phloem