chapter 9 – plant organization. 9.3 – plant tissues

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