FASAMA HILTON KOLLIEBSc. Bio, Mother Patern College of Health Sciences (MPCHS)ᴓ1

Chapter Four

E m a i l - f k o l l i e 2 5 @ g m a i l . c o m

CHAPTER OUTLINE

1. Overview of vascular plant Organs

2. Overview of plant growth and development

3. Primary plant body

(ROOTS, STEMS & LEAVES)

CHAPTER OBJECTIVES

Have an idea of the basic plant organs

Describe the structure of a root, stem and leaves

Know the general functions of roots, stems and leaves

• Plant organs are made from simple and complex tissues that adapts as a group to perform particular functions.

• Vascular plants have three types of organs: Root, Stem & leaves

• Bryophytes and some seedless vascular plants have structures that can be called stem-like, leaf-like and root-like but are not consider true root stems and leaf.

• Any part of a plant that supports leaves or reproductive structures

• Stems vary greatly in size, such as a slender stalk supporting a small flower

• Regardless of size, all stems display leaves in the best position for photosynthesis

• Stems provide pathways for the transport of leaves products to roots

Leaf is the main photosynthetic organ of modern plants

Leaves serve as the site of photosynthesis

They are an extension of the plant’s vascular tissue system

Leaves do not only conduct water but also provide most of the pressure that actually forces the water through the plant’s body

• Root has two main functions:– Anchoring the plant in the soil

– Absorption of water and minerals

• Absorption takes place near the tips of roots through trichomes called root hairs

• Many roots store food for the plant. Eg: carrot and sweet potatoes

Plants and other multicellular organisms develop from a single cell

Through cells division, elongation and specializing for different functions

Seed plants are either gymnosperms or angiosperms

Gymnosperms are plants with “naked seeds”

Angiosperms are plants with “seeds in a container”

The body of a typical plant can be described as having two connecting systems:

Root system

Shoot system

• Plant embryogenesis - is the process that produces a plant embryo from a fertilized ovule by cell division and the differentiation of undifferentiated cells into tissues and organs.

• A seed plant embryo includes the following embryonic organs that develops into a root and shoots: Cotyledon, Radicle, Plumule, Epicotyl and Hypocotyl

PLANT EMBRYOLOGY

• “seed leaves”

• It is usually the largest and most

visible parts of an embryo

• Consist of one or more seed leaves

• Main function: Stores food for the

germinating seed

Plant Embryology

“Embryonic root”

the part of a plant embryo that develops into the primary root

Plant Embryology

“Embryonic shoot”

The rudimentary shoot of an embryo plant

“Embryonic stem” The tiny shoot, which develops

into stems, leaves and flowers of the plant future

Plant Embryology

The stem of a germinating seedling, found below the cotyledons and above the radicle

Plants that have significant secondary growth are know informally as Woody plants

Plant with little or no secondary growth are know as Herbaceous plants

Plants have indeterminate growth

Plant can be categorized into three distinct groups based on how long they live:

Annual, Biennial and Perennial plants

Plants Growing Seasons

• An annual is a plant that completes its life cycle during a single growing season

• Eg: Marigolds, beans, corn etc

Annual Plants

A Plant that usually requires two growing seasons (2 years) to complete its life cycle

Eg: Carrots, beets, cabbage etc

Biennial Plants

A plant that grows for more than two years

Most are woody plants

Eg: trees, shurbs

Perennial Plants

Evergreen Tree Dragon blood tree

• The body of a typical plant can be described as having two connecting system: a root system and a shoot system

• The root system consists of all the roots, which are usually below the ground

• The shoot system consists of all the stems, leaves, and reproductive structures, which are usually aboveground

• In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil.

• Roots can also be aerial or aerating, that is growing up above the ground or especially above water.

• The first root that comes from a plant is called Radicle

• FUNCTIONS OF ROOT

– Anchoring of plant firmly in the soil

– Absorption and conduction of water and inorganic nutrients

– Storage of food and nutrients

– Vegetative reproduction

– Root produce hormones and other substances that regulated the plant’s development and structure

• On the basis of their origin there are two main patterns of root growth:

– Taproots system

– Adventitious root systems

TYPES OF ROOT SYSTEM

• The taproot is the largest, most central, and most

dominant root from which other roots sprout

laterally

• A taproot is somewhat straight and very thick

• This root function to tap deep sources of water

• It develops directly from the radicle

• Taproot produces branch roots called lateral roots

• Taproot system are typically of most dicots and gymnosperms• Eg: Dandelion, Beans, Cycads, Conifers

• Roots that develop from any other part of a plant body either than the radicle

• This is common in seedless vascular plants and grasses

• These roots can be present underground or above the ground.

• No single root stands out as the largest root in a fibrous root system

• Fibrous roots grow fairly close to the surface of the ground

• few plants with fibrous root systems: Coconut palm, Grass, Onion

• Root development occurs near the root tip, in the apical meristem

• Apical meristem has cells called Initials

• Initials are located within small spherical center of the meristem called

Quiescent center

• Initials and derivative cells can rebuild damaged or destroyed apical

meristem

• A root apical meristem produces a root cap which consist of several layers of cells

• The root caps serves as a protection for the root cells as it pushes between the soil particles

• The root cap produce slimy polysaccharide know as Mucigel

• Mucigel lubricates the passage of the root through the soil

The root apical meristem

• Cell division in a root or shoot apical meristem produces the derivative that becomes the Primary meristems: protoderm, ground meristem and procambium

• In a root, division, growth, and differentiation of cells can be traced linearly through three overlapping regions;

−

Zone of Cell Division, Elongation and Maturation

• In a cross section or transverse section, the root presents the following structures:

– Stele

– Protostele

– Epidermis

– Cortex

Stele:

• The central part of a root or stem

• The zone internal to the endodermis which contains specialized tissue responsible for the transport of water and minerals to the shoot

− Endodermis

− Pericycle

− Vascular tissues

Epidermis

Cortex

Endodermis

Pericycle

Xylem

Phloem

Stele

Root hair

• Protostele: is the most simplest type of stele and the earliest to evolve

• In the root of most seed plants, two important cell layers called the pericycle and the endodermis surround the stele

• Pericycle: a cell layer immediately encircling the stele that gives rise to lateral roots

• Endodermis: the layer of cells around the stele that regulates the flow of substances between cortex and vascular tissue

A

B

C

D

E

F

G

• Roots carry out the following functions in addition to their primary functions:

• A modified adventitious root that arise from stem tissue

• Found in plants that grow on other plants for support and nourishment (Epiphyte)

• Provides additional support for a plant such as water retention, photosynthesis, and support.

• Eg: Corn

• Flared roots that extend from tree trunks

• Provide stability to plants in thin soils

• Eg: Fig tree

• A thickened specialized root at the base of a corm, bulb, rosette or other organ

• Contractile roots are usually broad, fleshy, vertical, tapering, wrinkled looking

• It is designed to shrink vertically under conditions of seasonal drought that helps position this plant part at an appropriate level in the ground.

• Found in lilies

• Also known as air roots• They provide oxygen for plants in swampy areas where high rate of

aerobic decay reduces the oxygen supply in the water• Eg: Mangrove

• Modified parasitic roots

• They penetrates the stems and roots of other plants to obtain water, mineral and organic molecules

• Eg: Mistletoe (Viscum album)

• Roots often form mutualistic or beneficial associations with other organisms

• Mycorrhizae

• This is a form of mutualistic relationship between vascular plant roots and soil fungi

• This occur in more that 90% of plant species

• The two main types of these associations are; Endomycorrhizaeand Ectomycorrhizae

S S

• A part of a plant that supports leaves or reproductive structures

• They may vary in size, such as from a slender stalk to a big tree trunk

• They grow above the ground and together with the leaves they constitute the shoot system

• First stem of a plant develops from part of a seed embryo called Epicotyl

− Transport water and solutes between roots and leaves

− Produces & support appendages of plant (leaves, flowers, fruits)

− Stems in some plants are photosynthetic

− In some plants, stems have become adapted for specialized functions such as; Storage etc

Cauti

Herbaceous Stems

• Soft & green

• Little growth in diameter

• Tissues chiefly primary

• Chiefly annual

• Covered by epidermis

Woody Stems

• Tough & not green

• Considerable growth in diameter

• Tissues chiefly secondary

• Chiefly perennial

• Covered by corky bark

Herbaceous Stem Woody stem

All stems are recognizable from other plant organs by the presence of nodes, internodes, buds and leaves

− Node: A node is a point on the stem from which leaves or buds arise

− Internode: The portion between two successive nodes

− Buds: A bud is an undeveloped or embryonic shoot which has the potential for further plant growth.− It may develop into a leaf, flower, or both.

− Plants have three types of buds on the basis of location, namely: Terminal buds, Axillary buds and Adventitious buds

• Internal structure of a dicot stem reveals the following features: Epidermis, cortex, pericycle, vascular bundles and pith

• Two models describes how a shoot apical meristem gives rise to the primary meristems

• These are: The Zone model and the Cell-layer model

• Here the shoot apical meristem is divided into three regions: (central mother cell zone, peripheral zone, and pith zone)

A. Central mother cell zone; consist of cells that divide not frequently and give rise to peripheral and pith zone

B. Peripheral zone; form a 3D ring around the central mother cell zone

• Cells from this zone develop into the leaf primodial

• Eventually, this gives rise to the dermal and vascular cells of the stem

C. Pith zone; it is below the central and peripheral zone

• Cells of the pith zone give rise to the ground tissue in the center of the stem

• Ground tissue are in the pith.

• Also known as the Tunica Corpus model. • This consist of two layers: Outer layer (Tunica) and

the Corpus layer.• The outer layer (Tunica) is equivalent to the

peripheral zone• Here the plant divide perpendicular to the surface

known as the anticlinal division.

• The Corpus layer is equivalent to the central mother cell zone, the inner part of the peripheral zone and the pith zone

• The corpus give rise to the procambium and ground meristem while the tunica give rise to the protoderm.

• Leaves on the side of the shoot meristem comes in three basic patterns; (alternate, opposite and whorled)

• Alternate arrangement has one leaf per node, it may form a spherical or helical pattern

• Opposite arrangement consists of two leaves per node. Each pair of leaves is oriented like the previous pair

• Whorled arrangement includes three or more leaves per nodes.

• Specialized stems are: Stolon, rhizomes, tubers, bulbs, corms etc

• Horizontal stem aboveground

• Stolon often originate as axillary buds

• They help a plant reproduce asexually

• Eg: Bermuda grass, spider plant, ferns

• Underground horizontal stems with adventitious roots

• hizomes are used to store starches and proteins

• Eg: Irises, ferns, grasses, ginger

• Underground stems that store food

• Usually swollen

• The “eyes” of a potato (Irish potatoes, Solanum tuberosu) are the nodes of a starch-ladened stem

• Large buds with a small stem at the lower end surrounded by numerous fleshy leaves

• Leaves stores nutrients• Adventitious roots at the

base• Eg: Onion, tulip, daffodil and

Lily

• Composed entirely of stem tissue surrounded by a few papery scale like leaves

• Adventitious roots at the base

• Eg: Crocus and gladiolus

S

• A leaf is a thin, flattened organ, above ground and specialized for photosynthesis

• It originates from the shoot apical meristem as a bump of tissue know as the leaf primordia

• Leaf primordium develops into a leaf through cell division, growth, and differentiation

• Photosynthesis is the primary function of the leaves

• It function in water retention in desert plants. Eg: Cactus

• Function during transpiration

• Function in translocation via the leaf veins

• A leaf can be either simple leaf or compound leaf

• This concept is determined by determining the position of the bud

• A simple leaf is a single leaf that attaches to the stem

• Simple leaf contains one blade.

• A compound leaf is a leaf that is composed of two or more leaflets on a common stalk

• Blade is divided into two or more distinct leaflets.

• Leaves can be found in a variety of shapes and sizes

• Most leaves are broad, flat and typically green in color

• Leaf shape is adapted to best suit the plant's habitat and maximize photosynthesis.

• The Basic leaf features of plants include:

• Leaf blade

•Petiole

• Stipules

Tip

Midrib

Margin

VeinPetiole

Blade (Lamina)

BLADE• The broad portion of a leaf.

– Apex - leaf tip.

– Margin - leaf edge boundary area. Margins can be smooth, jagged (toothed), lobed, or parted.

– Veins - vascular tissue bundles that support the leaf and transport nutrients.

– Midrib - central main vein arising from secondary veins.

– Base - area of the leaf that connects the blade to the petiole.

• PETIOLE - thin stalk that attaches the leaf to a stem.

• STIPULES - leaf-like structures at the leaf base.

• Leaf shape, margin, and venation (vein formation) are the main features used in plant identification

• Leaf tissues are composed of layers of plant cells

• Different plant cell types form three main tissues found in leaves

• A typical leaf has three regions, namely: Upper epidermis, Mesophyll tissue layer and Lower epidermis

• Mesophyll tissue layer is sandwiched between the two layers of epidermis

• The vascular tissues of a leaf is located within the mesophyll layer as well as ground tissues

• The dermal tissues are found in the epidermal region of a leaf

1. EPIDERMIS• It is the outer layer of a leaf• It is a single layer of cells derived from the protoderm

• Epidermis protects the leafs from water loss, abrasions• It also regulates the exchange of gases and water vapor from the

plant via the leaves

• It is usually non-photosynthetic • It secretes a waxy coating called cuticle that helps the plant retain

water• It has tiny pores called Stomata• Guard cells regulates the opening and closing of the stomata

2. MESOPHYLL• The middle mesophyll leaf layer is composed of a Palisade mesophyll and

a Spongy mesophyll

• Palisade mesophyll contains columnar cells with spaces between the cells

• Most plants chloroplast are found in this region

• Spongy mesophyll is located below the palisade mesophyll

• It is composed of irregular shaped cells

• Leaf vascular tissue is found in spongy mesophyll

• Like other organs, leaves are often modified for functions other than photosynthesis. Below are a few examples:

• Insect-trapping leaves

• Leaves modified for reproduction

• Prophylls

• Cotyledons

• Tendrils

• Stipule

• Spines

• Storage leaves

• A tendril is a specialized leave or petiole with a threadlike shape

• It is used by climbing plants for support, attachment

TENDRIL STIPULE

• An outgrowths borne on either side of the base of a leafstalk

• They are used like leaves to make energy for the plants.

• Sometimes stipules protect the next leaf or bud as it grows in, then falls off after the leaf unfolds

INSECT-TRAPPING LEAVES

• Insect-trapping leaves are leaves that are specialized to trap insects.

• They may be sticky to trap the insect, may form containers or they may snap shut when the insect lands on the leaves.

SPINES

• Spines are hard, sharp leaves that are specialized to defend the plant from being eaten by animals.

• The stem makes food for the plant. Cactus and ocotillo are examples of plants with spines.