plant tissue and plant body

PLANT TISSUE AND PLANT BODY

OBJECTIVES

Discuss the herbaceous and woody plants life cycles

Describe and discuss the different cells and tissue systems

Discuss what is meant by growth in plants

Distinguish the primary and secondary growth and its relevance to plants

HERBACEOUS PLANTS

Do not develop persistent woody parts above-ground

Annuals• Herbaceous plants that

grow, reproduce and die in 1 year or season

Examples: Corn, Geranium and Marigold

HERBACEOUS PLANTS

Biennials• Herbaceous plants that

take 2 years to complete their life cycles.

• During their first season, produce extra carbohydrates, which they store and use during their second year

Examples: Carrot, Cabbage and Queen Anne’s lace

HERBACEOUS PLANTS

Perennials• Live for more than 2 years• In temperate climates, the

aerial shoots die back each winter

• Underground parts become dormant during winter and send out new growth each spring

• In tropical climates, the aerial parts die back and underground parts become dormant during the dry season

Example: Grasses

Example: Iris, Rhubarb, Onion, Asparagus

WOODY PLANTS

Develop persistent woody parts above ground (trees and shrubs)

Perennials• Some live for hundreds or thousands of years• In temperate climates, the aerial shoots

becomes dormant during winter• Many shed their leaves before winter and

produce new stem tissue with new leaves the following spring

• Others are evergreen and shed their leaves over a long period so that some leaves are always present

• Many trees attain massive sizes because they have permanent woody stems that are the starting points for new growth the following season

PLANT ENVIRONMENT

Dark, Moist Soil• Roots branch exclusively through

the soil, forming a network that anchors the plant firmly in place and absorbs water and dissolved minerals from the soil

Illuminated, Relatively Dry Air• Leaves, the flattened organs for

photosynthesis, are attached regularly on the stem, where they absorb the sunlight and atmospheric carbon dioxide used in photosynthesis to produce carbohydrates

PLANT BODY SYSTEM

Root System• Generally underground• Obtains water and dissolved

minerals from plant • Usually anchors the plant firmly in

place

Shoot System• Aerial portion• Obtains sunlight and carbon dioxide

for plant• Consists of vertical stem bearing

leaves and in flowering plants, flowers and fruits that contain seeds

CELLS AND TISSUE OF THE PLANT BODY

Ground Tissue System• All of the tissues of the plant body

other than the vascular and dermal tissues

• The cell wall structures distinguish these tissues

• Provides structural support that surrounds each plant cell.

• A growing cell secretes a thin primary cell walls which stretches and expands as the cell increases in size

• After the cell stops growing, it sometimes secretes a thick, strong secondary cell wall, which is deposited inside the primary cell wall

GROUND TISSUE SYSTEM

Parenchyma Tissue• Simple tissue composed of

parenchyma cells• Found throughout the plant body

and it’s the most common type of cell and tissue

• Present in soft parts of plants, such as the edible part of an apple or a potato

• Performs photosynthesis, storage and secretion

• Have the ability to differentiate into other kinds of cells, particularly when a plant is injured

Contains chloroplasts

Starch grains, oil droplets, water and

salts

Resins, tannins, hormones, enzymes,

sugary nectar

Xylem is severed

A plant cell that is relatively unspecialized, is thin walled, may contain chlorophyll and

is typically loosely packed


Collenchyma Tissue• Simple tissue composed of collenchyma cells

that is usually elongated• Flexible tissue that provides much of the

support in soft, nonwoody plant organs• Support is a crucial function in plants, in part

because it allows plant to grow upward, thus enabling them to compete with other plants for available sunlight in a plant crowded area

• The primary cell walls are unevenly thickened and are especially thick in the corners

• Not uniformly found throughout the plant and often occurs as long strands near stem surfaces and along leaf veins

Examples: The “strings” in a celery

stalk (petiole)

A living plant cell with moderately but

uneven thickened primary walls


Note the unevenly thickened cell walls that are especially thick in the corners, making the cell contents appear spherical in cross section. These collenchyma cells are from a water lily (Nymphaea) petiole.


Sclerenchyma Tissue• From the Greek root word sclero,

“hard”• Simple tissue composed of

sclerenchyma cells• Specialized for structural support

whose cells have both primary and secondary cell walls

• All functional maturity, when providing support for the plant body, sclerenchyma cells are often dead

Sclereids – short cells that are variable in shape, are common in the shells of nuts and the stones of fruits, such as cherries

and peaches

Fibers – long, tapered cells that often occur in groups or clumps are particularly

abundant in wood, inner bark and leaf ribs (veins) of flowering plants


Vascular Tissue System• Embedded in the ground tissue• Main characteristic tha separates

vascular to nonvascular• Transports needed materials

throughout the plant via two complex tissues

VASCULAR TISSUE SYSTEM

Xylem• Complex vascular tissue that

conducts water and dissolved minerals from the roots to the stems and leaves and provides structural support

• In flowering plants, composed of four different cell types

Parenchyma cells – also known as xylem parenchyma that performs storage functions

Tracheids – chief water-conducting cells in gymnosperms and seedless vascular plants such as ferns, are long, tapering cells located in patchers or clumps

- water is conducted upward from roots to shoots, passing from one tracheid into another through pits, which are thin areas in the tracheid’s cell walls where a secretory cell wall did not form

Fibers – provides support

Vessel Elements – water conducting cells present in flowering plants

- hollow, have holes in their end walls known as perforations, or the end walls are entirely dissolved away

- stacked one on top of the other and water is conducted readily from one vessel element into the next

- also have pits in their side walls that permit the lateral transport of water from one vessel to another


Phloem• Conducts food materials that is

carbohydrates formed in photosynthesis throughout the plant and provides structural support

• In flowering plants, composed of four different cell types

Parenchyma cells

Companion cells – adjacent to each sieve-tube element that assists in the functioning of the sieve-tube element

- a living cell, complete with a nucleus- does not conduct nutrient itself but

plays an essential role in loading food materials into the sieve-tube element for transport to other parts of the plants

Fibers – frequently extensive in the phloem of flowering plants providing additional structural support for the plant body

Sieve-tube Elements – through these, food materials are conducted in solution that is dissolved in water

- long, thin cells that are stacked end on end to form long sieve tubes

- cell’s end walls, called sieve plates, have a series of holes through which cytoplasm extends from one sieve-tube element into the next

- alive at maturity, but many organelle disintegrate as they mature

- functions without nuclei, although they typically live for less than 1 year


Dermal Tissue System• Provides a protective covering over

plant parts• In herbaceous plants, it is a layer of

cells called epidermis• Woody plants initially produce an

epidermis, but it splits apart as the p[lant increases in girth as a result of the production od additional woody tissues underneath the epidermis


Epidermis• Outermost tissue layer,

composed primarily of relatively unspecialized living cells

• Dispersed among these cells are more specialized guard cells and outgrowths called trichomes

• In most plants, consists of single layer of cells

• Occurs in many sizes and shapes and have a variety of functions

• Plants that tolerate salty environment often have specialized trichomes on their leaves to remove excess salt that has accumulated in the plant

• Its presence on the aerial plants of desert plants may increase the reflection of light off the plants, thereby keeping the internal tissues cooler and decreasing water loss

• Others have protective function

EPIDERMIS

Epidermal Cells• Generally contain no chloroplasts,

so light can penetrate into the interior tissues of stems and leaves

• Secretes a waxy layer called cuticle over the surface of their walls; this has greatly restricted the loss of water from plant surface

• Stomata facilitate the diffusion of carbon dioxide. It has tiny pores in the epidermis between two cells called guard cells


Periderm• Semi-permeable layer of bark• Replaces when woody plant

begins to increase in girth, its epidermis sloughs off

• Profuces and is protected by rhytidome

• Forms the protective outer bark of older stems and roots

• Complex tissue composed mainly of cork cells and cork parenchyma cells

Cork cells – dead at maturity and their walls are heavily coated with a waterproof

substance called suberin

Cork parenchyma cells – also called as phelloderm that function primarily in

storage


Formed by the cork cambium, periderm is the secondary plant body replacement for epidermis and makes up the outer bark of woody stems and roots. Some herbaceous eudicots, such as geranium (Pelargonium), form a limited periderm as they age. The cells of periderm are arranged in vertical stacks. Note that the cork cambium produces many layers toward the cell’s exterior but only a few layers toward the cell’s interior.

PLANT MERISTEMS

• When plant grows, their cell divide only in specific areas called meristems

• Composed of cells whose primary function is the formation of new cells

• Meristematic cell do not differentiate

• The persistence of meristems means that plants retain the capability for growth throughout their entire life span

Primary growth – an increase in the length of a plant. All plant have primary growth, which produces the entire

body in herbaceous plants and the young, soft shoot tips and root tips of woody trees and shrubs

Secondary growth – an increase in the girth of a plant. Tissues produced compose the wood and bark, which make up most of the bulk of trees and shrubs. A few

annuals have limited secondary growth even though they lack obvious wood and bark tissues

PLANT GROWTH

A. Cell Division Essential part of growth that results in an

increase in the number of cells

B. Cell Elongation New cells elongate as the cytoplasm grows and

the vacuole fills with water, which exerts pressure on the cell wall and causes it to expland

C. Cell Differentiation Plant cells differentiate or specialize into the

various functions requires in a multicellular organisms. Although differentiation does not contribute to an increase in size, it is considered an important aspect of growth because it is essential for tissue formation

PLANT MERISTEMS

Apical Meristems• Primary growth occurs as a result of its activity, areas at the

tips of roots and shoots• A protective layer of cells called the root cap covers the root tip• Directly behind the root cap, in the area of cell division, is the

root apical meristem• Farther back from the tip of the root, just behind the area of

cell division, is an area of cell elongation where the cells have displaced from the meristem

• Farther back from the tip, in the area of cell maturation, the cells have completely differentiated and are fully mature

PLANT MERISTEMS

Apical Meristems• A shoot of apex – a terminal bud is quite

different in appearance from a root tip• Within every bud is a dome of tiny,

regularly arranged meristematic cells, the shoot apical meristem

• As cells formed by the shoot apical meristem elongate, the shoot apical meristem is pushed upward

• Subsequent cell division produce additional stem tissue and new leaf and bud primordia

• Farther back from the tip of the stem, the immature cells enlarge and differentiate into the 3 tissue systems of the mature plant body

Leaf primordia

Bud primordia

This longitudinal section through a terminal bud of coleus (Coleus) shows the stem apical meristem, leaf primordia, and bud primordia.

This diagram shows the kinds of cells in the area of cell division, the area of cell elongation, and the area

of cell maturation. The three primary meristems (protoderm, procambium, and ground meristem) in

the area of cell elongation give rise to the mature cell types in the area of cell maturation. (Procambium

cells shown in the area of cell maturation—between the primary xylem and primary phloem—may give

rise to vascular cambium later in development.)

PLANT MERISTEMS

Three Primary Meristems (Immature Tissues) – found in the are of cell elongation

- Continue to develop and differentiate into primary tissues of plant

Protoderm – young, undifferentiated tissue of a root or stem that eventually

develops into epidermis

Procambium – meristematic tissue that eventually develops into xylem

and phloem

Ground Meristem – meristematic tissue that gives rise to cortex, pith

and ground tissue

PLANT MERISTEMS

Lateral Meristems• These plants increase in

length by primary growth and increase in girth by secondary growth

Vascular Cambium – layer of meristemic cells that forms a thin, continuous cylinder within the stem and

root. It is located between the wood and bark of a woody plant. The cells divide, adding more cells to the

wood and to the inner bark

Cork Cambium – thin cylinder or irregular arrangement of meristemic cells in the outer bark

region. The cells divide, to form the cork cells toward the outside and one or more underlying layers of cork

parenchyma cells that function in storage

PLANT MERISTEMS

The vascular cambium, a thin layer of cells sandwiched between the wood and bark, produces secondary vascular tissues: the

wood, which is secondary xylem, and inner bark, which is secondary phloem. The cork cambium produces the periderm, the outer

bark tissues that replace the epidermis in the secondary plant body.

plant tissue and plant body

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