Plant Tissue A tissue is a group of cells that work together to perform a specialized function. These cells can be all identical or there can be several different cells within the tissue. Plants have several different kinds of tissues that occur in varying amounts depending on the needs of the plant.

Vascular Tissue The cells in the vascular tissue are organized into a transport system to move materials around the plant similar to the arteries and veins in the human circulatory system. Although both xylem & phloem carry water, one set also carries dissolved minerals while the other set carries dissolved carbohydrates. xylem and phloem are grouped together to form vascular bundles in stems or veins of leaves

Xylem: tissue to transport water, minerals, and water-soluble materials from the roots to the stems and leaves mature xylem cells are dead (form long tubes) Phloem: tissue to transport dissolved nutrients (e.g. sugar) from leaves to stems and roots phloem cells are alive

Vessel elements are found only in angiosperms Vessel elements are found only in angiosperms. Vessels allow xylem sap to flow straight upward or laterally through pits. Tracheids have angled ends and are found in all vascular plants. Cellulose and lignin are deposited on the surfaces of xylem to form rigid cell walls. When cytoplasm dies, hollow xylem is left. Sieve tube cells have sieve plates at each end and are alive. Companion cells are connected to sieve tube cells and direct their operation.

Fundamental or Ground Tissue a) Parenchyma tissue: large thin-walled, loosely packed cells in roots, stems and fruit, provide support and store sugars in leaves and young stems, contain chloroplasts for photosynthesis b) Sclerenchyma tissue: cells with thick walls to provide support in roots and stems

Meristematic Tissue tissue with cells that divide by mitosis, then later form more specialized cells found where plant is growing (e.g. in root tips, buds, vascular cambium)

Protective Tissue outer covering of roots, stems and leaves provides protection e.g. waxy cuticle on leaves reduces water loss e.g. cork protects inner tissues of woody stems

Water Transport

Root pressure: accumulation of water and dissolved minerals in roots creates pressure that pushes sap up the xylem Guttation: water droplets are exuded from leaves due to root pressure Adhesion: water clings to inner walls of xylem and creates a pulling force on the column of water Cohesion: hydrogen bonds between water molecules holds them together in a column as they move up the xylem Transpiration: evaporation of water from leaves pulls water column up xylem; as long as water molecules escape, tension pulls more molecules up xylem to replace them

Food Transport The pressure flow theory: sugars are actively pumped into phloem sieve tube cells in the leaves (source) creating a hypertonic solution, water follows by osmosis high pressure pushes sugars down phloem in roots (sink), sugar molecules are actively transported out and stored in parenchyma cells, this creates a low pressure which pulls sap down