Topic 14.1 The Structure & Growth of Flowering Plants Biology 1001 November 4, 2005

I. The structure of Flowering Plants The Plant Body Plants are multicellular organisms with organs and organ systems, tissues, and cells (see Fig. 1.3) The three basic plant organs are roots, stems, and leaves They are organized into a root system and a shoot system The two systems are interdependent and each accesses a different part of the plant’s environment Figure 35.2(!!)

Plant Organs - Roots A root is an organ that anchors a vascular plant, absorbs water and minerals, and may store organic nutrients Root hairs increase the surface area of the root for absorption Variations of a theme: taproots, lateral roots, fibrous roots, storage roots, aerial roots, adventitious roots…

Plant Organs - Stems A stem is a shoot organ consisting of alternating nodes and internodes that supports leaves and flowers Axillary buds are located at the apexes of leaves and have the potential to form lateral shoots (branches) The terminal bud contains developing leaves and a compact series of nodes and internodes, and is the site at which most shoot elongation occurs Stem variations include stolons, bulbs, tubers, rhizomes

Plant Organs - Leaves The leaf is the main photosynthetic organ of most plants, and consists of a blade and petiole (stalk) Flowers, the reproductive organs of flowering plants, are shoots composed of highly modified leaves and stems Leaves also contain veins of vascular tissue Leaf morphology and venation pattern are used to classify plants Modified leaves include tendrils, spines, storage leaves, bracts, and reproductive leaves

Plant Tissues Systems Each plant organ has dermal, vascular and ground tissue systems These tissue systems are continuous throughout the plant and connect the organs The dermal tissue system is the outer protective covering of the plant – usually a single layer of tightly packed cells called the epidermis The vascular tissue system contains xylem & phloem which are used for long-distance transport in the plant The ground tissue functions in storage, photosynthesis, and support Figure 35.8(!) The three plant tissue systems

Plant Cells Fig a generic plant cell Like other multicellular organisms, plant cells are differentiated into specialized types with particular functions Differentiation can be at the level of the protoplast (living part of the cell) or at the level of the cell wall Plant cells can have primary and secondary cell walls Plants cells can be living or dead at functional maturity

Figure 35.9(!) - Exploring Examples of Differentiated Plant Cells Parenchyma cells are living cells with flexible primary cell walls, large vacuoles, and no secondary cell walls  They are the least differentiated of plant cells and perform most of the metabolic synthesis and storage functions of the plant  They retain the ability to divide and differentiate into other cell types  Examples include photosynthetic cells, the fleshy part of a fruit, and cells that store starch in plastids

Figure 35.9(!) - Exploring Examples of Differentiated Plant Cells Collenchyma cells are living cells with unevenly thickened primary walls that remain flexible  Grouped in strands or cylinders, they provide support for a young growing plant

Figure 35.9(!) - Exploring Examples of Differentiated Plant Cells Sclerenchyma cells are dead at functional maturity, and they have thick secondary cell walls strengthened with lignin  They support the non-growing parts of the plant  Sclereids and fibers are two types of sclerenchyma cells

Figure 35.9(!) - Exploring Examples of Differentiated Plant Cells Phloem contains two types of sugar- conducting cells called sieve-tube members and companion cells  Both types are alive at functional maturity  Sieve-tube members lack organelles, and are connected end-to-end to form sieve tubes with porous sieve plates at the ends of each cell. These are the cells that conduct organic nutrients  Companion cells are adjacent to sieve- tube members and perform the metabolic functions for both cell types; they also function to load sugars into the sieve tubes

Figure 35.9(!) - Exploring Examples of Differentiated Plant Cells  Xylem contains two types of water- conducting cells called tracheids and vessel elements Tubular, elongated cells with thickened secondary walls that are dead at functional maturity and act as conduits for the flow of water Tracheids are thin tapered cells whose secondary walls are thickened by lignin; water moves laterally between tracheids via pits Vessel elements are connected end-to- end to form vessels. Water moves into vessel elements laterally via pits, and then flows vertically through porous end plates