Plant Structure

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

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

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

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

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

Leave Patterns and Deviations

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

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