Plant Tissue

1. 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.

2. 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

3. 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

5. 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

7. 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)

8. 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

9. Water Transport

10. 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

11. 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