CHAPTER 9 – PLANT ORGANIZATION

9.3 – Plant Tissues

Introduction Meristem (embryonic tissue) responsible for growth  Stem and root tips (apexes) 3 types of meristem:  Protoderm (outermost primary meristem): creates epidermis  Ground Meristem: produces ground tissue  Procambium: produce vascular cambium, creating vascular tissue

3 specialized tissues:  Epidermal Tissue: forms outer protective covering  Ground Tissue: fills plant interior  Vascular Tissue: transports water/nutrients in plant and provides support

1. Epidermal Tissue Epidermis: closely packed epidermal cells, cover body of non-woody and young woody plants  Covered by cuticle – minimizes water loss and protects against invaders Root Hairs: long, slender projections found in roots on epidermal cells  Increase absorption, anchor to soil

Guard Cells: specialized cells in lower epidermis  Contain stomata instead of chloroplasts  Site of gas exchange when open

As plants age, epidermis is replaced with cork. Cork: component of bark, made of dead cells that may fall off  Made by meristem called cork cambium  Increase in volume and suberin (waterproof)  Protect plant (resistant to fungi, bacteria, and animal attacks)

2. Ground Tissue  made of parenchyma, collenchyma, and sclerenchyma cells 2 types of sclerenchyma cells:  Fibers: mostly in vascular tissue, long and slender, found in commercial used bundles (ropes/textiles)  Sclereids: shorter than fibres, irregular shape, make seed coats/nutshells tougher, gritty texture, aid in transport

3. Vascular Tissue Main function: transportation of water, food, and dissolved substances 2 types of tissues: xylem and phloem Xylem composed of vessel elements and tracheids Phloem composed of sieve tube members and companion cells

Xylem: transports water and minerals from roots to leaves  Vessel elements: form continuous pipeline for transport  Tracheids: water moves across end/side walls through pits  contains parenchyma cells for storage and fibers (sclerenchyma cells) for support Vascular Rays: flat ribbons/sheets of parenchyma cells for nutrient movement

Phloem: transports organic nutrients, usually leaves to roots Sieve Tube Elements: cytoplasm, no nuclei  Plasmodesmata pass through sieve plate Companion Cells: have both nucleus and cytoplasm  Connected to sieve tube elements by plasmodesmata, nucleus controls both cells

Vascular tissue is located...  Roots – in vascular cylinder  Stem – vascular bundles  Leaves – leaf veins

9.4 – Organization of Roots

Root Apical Meristem: area of cell division/growth  cells added to root cap and zone of elongation Zone of Elongation: cells becomes longer as they become specialized Zone of Maturation: cells are mature/fully differentiated (has root hairs)

Tissues of Dicot Root Within the zone of maturation, there are 4 specialized tissues Epidermis  Outer layer  Single layer of cells  Thin walled/rectangular  Roots hair

2. Cortex  2 nd layer, under epidermis  Large, thin-walled parenchyma cells  Loosely-packed, irregular shape  Food storage (contain starch)

3. Endodermis  3 rd layer, Single layer, rectangular cells  Fit snugly  Bordered by Casparian Strip (doesn’t allow nutrients through)  Regulates materials entering vascular cylinder

4. Vascular Tissue  Pericle: first layer of cells within cylinder  Can start development of branch/lateral roots  Contains vascular tissue  xylem is star shaped

Organization of Monocot Roots  Do not undergo secondary growth like dicots Pith: located in center of root  Vascular rings made of alternating xylem and phloem bundles

Root Diversity Functions: anchorage, water/mineral absorption, carbohydrate storage Primary Root: grows straight down, remains dominant plant root Several different types of roots depending on location and conditions...

1. Taproots  Fleshy and stores food  Thick root, few smaller/lateral branching roots Ex. carrots, beets, and turnips 2. Fibrous Root System  Large number of slender roots (instead of one main)  Grow from lower stem when primary root dies

3. Adventitious Roots  Develop from shoot system instead of root system  Rhizomes, underground stems, have adventitious roots along length Buttress Roots  Support large trunk in tropical areas

Prop Roots  Spread away from plant, help anchor it to soil  Pneumatophores: root projections above water, gather oxygen 4. Dodders and Broomrapes  Parasitic  Haustoria: root-like projections that grow into host, using their vascular tissues

5. Mycorrhizae  fungus roots (mutualistic relationship) 6. Root Nodules  Where nitrogen-fixing bacteria live  Bacteria take up/reduce atmospheric nitrogen