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...
1. Epidermis Outer layer Single layer of cells Thin walled/rectangular Roots hair
2. Cortex 2nd layer, under epidermis Large, thin-walled parenchyma cells Loosely-packed, irregular shape Food storage (contain starch)
3. Endodermis 3rd 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