PLANT TISSUES AND ORGANS

PLANT TISSUES AND ORGANS

Plant Cell Types (Support and Plant Cell Types (Support and Storage)Storage)

Parenchyma cellsParenchyma cells are the most are the most numerous type of cell in young numerous type of cell in young plants.plants.

Parenchyma cells usually have Parenchyma cells usually have thin walls and large central thin walls and large central vacuoles. vacuoles.

The photosynthetic cells in The photosynthetic cells in leaves are parenchyma cells leaves are parenchyma cells filled with chloroplasts. These filled with chloroplasts. These cells are called mesophyll cells.cells are called mesophyll cells.

Some parenchyma cells store Some parenchyma cells store lipids or starch (potatoes).lipids or starch (potatoes).

Other parenchyma cells serve Other parenchyma cells serve as “packing material” and play a as “packing material” and play a vital role in supporting the stem vital role in supporting the stem especially in nonwoody stems.especially in nonwoody stems.

Collenchyma cells are supporting cells that lay down primary cell walls that are thick in the corners.

Collenchyma cells provide support to leaf petioles, nonwoody stems, and growing organs.

These cell types compose the cortex and pith tissues of the root and stems.

Sclerenchyma cells are the main supporting cells of a plant. They have a thick secondary cell wall that contains a substance called lignin, a component of wood. Therefore they are found in woody plants.

There are two types of sclerenchyma cells: elongated fibers and variously shaped sclereids.

Fibers often organize into bundles. (They are common components of xylem.)

Sclereids may pack together very densely. (Sclereids are found in fruits such as pears and this give them their gritty texture.) They are often referred to as “stone cells”.

Plant Cell Types Vascular (Transport)Plant Cell Types Vascular (Transport)

XylemXylem The xylem conducts water The xylem conducts water

from roots to above ground from roots to above ground plant parts. It contains plant parts. It contains conducting cells called conducting cells called tracheary tracheary elementselements..

Tracheids are evolutionarily Tracheids are evolutionarily more ancient tracheary more ancient tracheary elements found in elements found in gymnosperms.gymnosperms.

Both Both tracheary elements tracheary elements and and tracheidstracheids undergo undergo apoptosis(die) and do their apoptosis(die) and do their jobs as empty cells (only jobs as empty cells (only the cell walls remain).the cell walls remain).

Tracheids and vessel elements: Water conducting cells

Vessel elementsVessel elements are the are the water “pipeline” system water “pipeline” system in flowering plants, also in flowering plants, also formed from dead cells. formed from dead cells. Flowering plants have Flowering plants have both tracheids and vessel both tracheids and vessel elements.elements.

Vessel elements are Vessel elements are generally larger in generally larger in diameter than tracheids diameter than tracheids and are laid down end-to-and are laid down end-to-end to form hollow tubesend to form hollow tubes..

Sieve-tube members: Food onducting

Cells PhloemPhloem

Cells of the phloem are Cells of the phloem are alive when they do their job, alive when they do their job, unlike those of the xylem.unlike those of the xylem.

The characteristic cell of the The characteristic cell of the phloem is the phloem is the sieve tube sieve tube membermember..

Cells of the phloem are Cells of the phloem are arranged end-to-end and arranged end-to-end and form long sieve tubes, form long sieve tubes, which transport which transport carbohydrates and other carbohydrates and other materials.materials.

The plasmodesmata in sieve The plasmodesmata in sieve tube members enlarge as tube members enlarge as they mature, resulting in they mature, resulting in end walls that look like end walls that look like sieves. sieves.

At functional maturity, a At functional maturity, a sieve tube is filled with sieve tube is filled with sieve tube sap (water, sieve tube sap (water, sugars, and other solutes).sugars, and other solutes).

The sieve tube members The sieve tube members have adjacent companion have adjacent companion cells.cells.

Companion cellsCompanion cells retain all retain all their organelles and may their organelles and may regulate the performance of regulate the performance of and support the sieve tube and support the sieve tube members.members.

Plant TissuesPlant Tissues A tissue is an organization of cells that work together A tissue is an organization of cells that work together

as a functional unit.as a functional unit. Parenchyma cells make up parenchyma tissue, Parenchyma cells make up parenchyma tissue,

which is a simple tissue.which is a simple tissue. Xylem and phloem are complex tissues; they are Xylem and phloem are complex tissues; they are

composed of a number of different cell types.composed of a number of different cell types. Tissues are grouped into tissue systems that extend Tissues are grouped into tissue systems that extend

throughout the body of the plant to form the various throughout the body of the plant to form the various organs of the plant.organs of the plant.

There are three plant tissue systems: vascular, There are three plant tissue systems: vascular, dermal, and ground.dermal, and ground.

Plant TissuesPlant Tissues

THREE TISSUE SYSTEMS IN PLANT

Vascular TissueVascular Tissue The The vascular tissue system vascular tissue system

includes the xylem and includes the xylem and phloemphloem; it is the conductive ; it is the conductive or “plumbing” system of the or “plumbing” system of the plant.plant.

The The phloem transports phloem transports carbohydrates from sites of carbohydrates from sites of production (sources such as production (sources such as leaves) to sites of utilization leaves) to sites of utilization for energy or where it is for energy or where it is being stored (sinks) being stored (sinks) elsewhere in the plant.elsewhere in the plant.

Vascular TissueVascular Tissue

The The xylem distributes water xylem distributes water and mineral ions taken up and mineral ions taken up by the roots to the stem by the roots to the stem and leavesand leaves..

Dermal TissueDermal Tissue The The dermal tissue dermal tissue system is system is

the outer covering of the the outer covering of the plantplant..

All parts of the young plant All parts of the young plant body are covered by an body are covered by an epidermis, which is a single epidermis, which is a single layer or multiple layers of layer or multiple layers of cells.cells.

The epidermis contains The epidermis contains epidermal cells and other epidermal cells and other specialized cells such as specialized cells such as guard cells.guard cells.

The The shoot epidermis shoot epidermis secretes a layer of wax-secretes a layer of wax-covered cutin, the cuticle, covered cutin, the cuticle, which helps retard water which helps retard water loss from stems and leaves.loss from stems and leaves.

Ground TissueGround Tissue

The The ground tissue ground tissue system makes up the system makes up the rest of a plant and rest of a plant and consists primarily of consists primarily of parenchyma tissue.parenchyma tissue.

Ground tissue functions Ground tissue functions primarily in storage, primarily in storage, support, photosynthesis, support, photosynthesis, and the production of and the production of defensive and attractant defensive and attractant substances (oils and substances (oils and toxins).toxins).

Meristems generate cells for Meristems generate cells for new organs(Plant Stem Cells)new organs(Plant Stem Cells)

In plants the growth of roots and stems is In plants the growth of roots and stems is indeterminate and is generated from specific regions of indeterminate and is generated from specific regions of active cell division. active cell division.

The localized regions of cell division in plants, called The localized regions of cell division in plants, called meristemsmeristems, are forever embryonic. They have the , are forever embryonic. They have the ability to produce new cells indefinitely.ability to produce new cells indefinitely.

The cells of meristematic tissues are analogous to the The cells of meristematic tissues are analogous to the stems cells found in animals.stems cells found in animals.

When a meristem cell divides, one daughter cell When a meristem cell divides, one daughter cell develops into another meristem cell, and the other develops into another meristem cell, and the other differentiates into a more specialized cell. The differentiates into a more specialized cell. The meristem gives rise to all plant cell and tissue types.meristem gives rise to all plant cell and tissue types.

There are two types of meristemsThere are two types of meristems:: Apical meristems Apical meristems give rise to the primary plant body, give rise to the primary plant body,

which is the entire body of many plants.which is the entire body of many plants. Lateral meristems Lateral meristems give rise to the secondary plant give rise to the secondary plant

body. body. The stems and roots of some plants form wood and become The stems and roots of some plants form wood and become

thick; it is the lateral meristems that give rise to the tissues thick; it is the lateral meristems that give rise to the tissues responsible for this thickening.responsible for this thickening.

Apical meristems are located at the tips of roots and stems Apical meristems are located at the tips of roots and stems and in buds. and in buds.

Shoot apical meristems supply the cells that extend stems and Shoot apical meristems supply the cells that extend stems and branches.branches.

Root apical meristems supply the cells that extend roots.Root apical meristems supply the cells that extend roots. Apical meristems are responsible for primary growth, which Apical meristems are responsible for primary growth, which

leads to elongation and organ formation.leads to elongation and organ formation.

Location of Meristematic TissuesLocation of Meristematic Tissues

Primary Growth of Root

• Root Cap Thimble-like covering which protects the delicate apical meristem

• Produced from cells derived from the root apical meristem

• Secretes polysaccharide slime that lubricates the soil

• Constantly sloughed off and replaced

• Apical Meristem Region of rapid cell division of undifferentiated cells

• Most cell division is directed away from the root cap

• Quiescent Center Populations of cells in apical meristem which reproduce much more slowly than other meristematic cells

• Resistant to radiation and chemical damage

• Possibly a reserve which can be called into action if the apical meristem becomes damaged

• The Zone of Cell Division - Primary Meristems Three areas just above the apical meristem that continue to divide for some time

• Protoderm - outermost primary meristem - produces cells which will become dermal tissue

• Ground meristem - central primary meristem - produces cells which will become ground tissue

• Procambium - innermost primary meristem - produces cells which will become vascular tissue

• The Zone of Elongation Cells elongate up to ten times their original length

• This growth pushes the root further downward into the soil

• The Zone of Maturation Region of the root where completely functional cells are found

The leaf vein

stalk

lamina

midrib

The Leaf – Cross-section

• Midrib - extension of the stalk into the leaf

• Vein Branch-off from the midrib

• Lamina - the blade of the leaf

• Stalk - attaches the leaf to the stem

midrib

vein

lamina

Waxy Cuticle & Epidermis• The waxy cuticle is a thin layer

atop the epidermis.• Its function is to reduce the water

lost from the leaf.• In arid conditions this cuticle layer

can be quite thick.• Epidermis cells contain no

chloroplasts – not true of the stoma cells.

• They form layers on the upper and lower surfaces of the leaf.

• Their function is to prevent water getting out and stopping unwanted substances/organisms getting in.

cuticle

epidermis

Palisade Mesophyll Layer

• The palisade mesophyll layer is where most of the photosynthesis occurs in the leaf.

• The palisade cells contain a lot of chloroplasts to help them perform this photosynthesis.

• The palisade cells are closely packed together to maximize light absorption.

• In the leaf cross-section we can see the palisade cells are only found in the upper part of the leaf.

Spongy Mesophyll Layer

• The cells in the spongy mesophyll layer are not as closely packed as the cells in the palisade mesophyll

layer.• This creates air spaces inside

the leaf to enable gases to move in and out.

• There are not as many chloroplasts in the spongy mesophyll cells as there are in the palisade mesophyll cells – but photosynthesis still occurs in the spongy mesophyll layer.

Stomata• There are holes found in leaves

called stoma• These holes allows gases to

diffuse in and out of the leaves• The stoma are formed by two

highly specialized epidermis cells.

• These cells, called guard cells, are the only epidermis cells that contain chloroplasts.

• The stoma open and close depending upon the requirements of the plant.

• It is through these stoma that water leaves the leaf, the process that powers transpiration.

• During photosynthesis carbon dioxide diffuses in and oxygen diffuses out

• When the stomata are closed,often at night or in a humid environment, this stops gases diffusing in and out of the leaf

Open stomata

Close stomata

FLOWERS• A flower is were the reproductive

parts of the plant is held. Many parts are inside of a flower. The major parts are:

-Stamen -Stigma-Pistil -Filament-Ovary -Eggs-Pollen/Sperm -Anther

Flowers

• Flower Parts• Pistil

– Female part of plant

– Containing:• Stigma• Style• Ovary

• The pistil is the term for all the female parts of a flower. Each pistil includes an ovary (where the eggs are produced; the female reproductive cells, a style (a tube on top of the ovary), and a stigma (which the pollen sticks to during fertilization).

• Stamen– Male reproductive part– Contains

• Anther• Filament

• The male parts of the flower help fertilize the egg of

the flower. • These parts are usually in a

place that can be easily moved by insects and animals.

• Sepals– Small green

structures on the base of a flower that protect the flower bud

• Petals– Highly colored part of

the flower, may contain perfume and/or nectar glands

Parts of the Seed• Embryo

– Growing part of seed containing:• Plumule – “Shoot”• Hypocotyl – Stem• Radicle – “Root”

• Endosperm– Tissue that provides nutrition for the developing

seed

• Cotyledon– Food Storage

• Seed Coat– Protective outer covering of the seed

Parts of the Seed

• Testa -outer covering of the seed; protects the embryo

• Hilum - the scar on the seedcoat; place where the seed was attached to the ovary

• Endosperm-the food supply of the baby plant.