pokok bahasan_sito_histo tumbuhan bot 201 lab

7/23/2019 Pokok Bahasan_sito_histo Tumbuhan Bot 201 Lab

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Vegetative Features of Vascular Plants

The purpose of this lab is to acquaint you with the various

types of tissues found in Vascular Plants and to show you how

they are organized to form a "Typical Vascular Plant". Thismay seem daunting at first until you realize that basic plant

anatomy is very simple.

Cell Types & Tissues

Meristematic Tissue

Meristematic tissue produce all thecells in herbaceous plants. The cellsoriginate in the Root or shoot ApicalMeristems. Meristematic Cells areSpherical(Isodiametric) and densely

cytoplasmic. They have a relatively

large Nucleus, few Vacuolesandthin Cell Walls. Consequently, they

readily absorb biological stains andappear as dense areasin the apices

of Roots and Shoots. The Apical

Meristem in Roots is actually

subterminal because it is covered

by a Root Cap. The root capprotects the delicate meristem cells

and it also secretes

carbohydrates which

lubricate the root as it growsthrough the soil.

There are two basic types of Apical Meristems. Nonseedplants have a large Apical Cell which gives rise to the plant

body. Seed plants have Multicellular Apical Meristems whichfunction as a unit.


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Primary Tissues

There are Three Basic Tissuesthat comprise all herbaceous

(soft bodied) plants. These are Dermal, Vascular & Ground.

Plants are made like reinforcedconcrete. There is a outer mold,

steel rodsand concretewhich fills in

the rest of the volume.

The first tissue is the Epidermis

which is typically on the surface

(Dermal) and is usually one cell thick. If it is on the surfaceit is probably Epidermis. This is like the moldfor theconcrete.

The next is Vascular Tissue. It is

typically found in longitudinal

columns. There may be one largecentral column, a ringof smaller

columns or multiple ringsof smallcolumns. These columns are the steel

rods.

Finally, there is the Ground Tissuewhich occupies the rest

of the plant organ. This is like the concreteabove. I regard

the Ground Tissue asBACKGround Tissue.

Cross Section of aColeus

Stem:

Note the large Vascular Bundlesin each corner of the stem (steel

rods).

Everything else is Ground Tissue

(Concrete) except for the

Epidermis (Mold) which forms thesurface layer of cells.


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The Epidermisis readily identified by its location.

Vascular Tissues, especially Xylem, have strong

characteristic traitswhich make them relatively easy to

identify.

If it is neither Epidermis nor Vascular Tissue, it must be

Ground Tissue.

There are two Vascular Tissues, Xylem& Phloem. Theconducting cellsin the Xylemare called TrachearyElements. These have thick wallsthat stain reddue to the

presence of Lignin. Lignin makes their cell walls watertight,inflexibleand strong. Consequently,Tracheary Elementshave two main

functions, water transportandstructural support. They usually have

a hollowappearance because they are

dead at maturity. These traits makeXylemrelatively easy to spot in a

cross section.

Phloemis associated with Xylem.

Phloem cells do not generally havediagnostic traits like xylem but they

can usually be discerned by their

position. They have relatively thin cell wallsand have anarrower diameter than the largest Tracheary Elements. In

some cases, Phloemexhibits a definite pattern of smallcells andlarge cells.The large cells

are Sieve Elements(S). These arethe cells that are specialized for

Sucrose Transport. The smallercells are Companion Cells(CC).

These regulate the physiologicalactivities of the Sieve Elements.

Phloem contains Callose. Callose


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regulates the size of the openings between adjacent SieveElements. Callose is a carbohydrate that stains with Aniline

Blue and is fluorescent under Violet light. This is the bestway to verify the presence of Phloem because Callose is not

present in other cell types.

Isodiametric Parenchyma Cell

containing Chromoplasts: Each

red dot is a Chromoplast thatContains Carotenoids.

Elongate Palisade Parenchyma

with Chloroplasts

Parenchyma from Potato with

large Amyloplasts: This is acommercial slide.

Parenchyma Cells containingAmyloplasts. This was stained

with IKI which has stained

the Starch Brown.

There are two major types of Ground Tissue(Parenchyma&Sclerenchyma).

Parenchyma cellscan be Isodiametric(equal size in all

directions) to elongatein shape. They havethin cell wallswhich contain a lot of hydrophilic pectins which have a

characteristic staining reaction. They usually have well


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developed Plastidslike Chloroplastsor Amyloplasts.Amyloplasts store starch.

Sclerenchyma cellsare usually

elongatein shape and have thickwallsimpregnated with Lignin. Theystain redin most prepared slides dueto their Lignincontent. Ligninmakescell wallsextremely strongand

inflexible. This makes Sclerenchyma

a good support tissue.Sclerenchymais usually associated with Vascular

Tissuesand may completely surroundthem.

There are a wide variety of

Epidermalcell types. Thetypical

Epidermal Cellresembles

Parenchyma but it has only tiny plastids. All Epidermal Cellshave a waxy Cuticleon their outer surface. They may contain

Red/Purple Anthocyaninsin their vacuoles. This gives thecells a uniform color. Chloroplastsare present in the GuardCellswhich are part of the Stomata. The Guard Cells tend tobe smallerthan typical Epidermal Cells, and they occur indiscernable patterns. The Epidermis can produce a wide

range of hairs(Trichomes). These can be unicellular or

multicellular. They may absorb water from the soil, secrete

chemicals to the surface, inject chemicals into the skin, trap

& digest insects and perform many other functions.

Surface View of Epidermis Lily Epidermis showing the


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from a Leaf:Note theundulating Epidermal Cells plus

the Stomata (S) and Trichomes

(T).

Elongate Epidermal cells and theGuard Cells which are part of the

Stomata

Surface of Kukui Leaf with

branched Trichomes

Isolated Kukui Trichome

Cross Section of Venus Fly Trap

Leaf:Note the Epidermal Layerand the Multicellular Trichomes

which are part of the

Epidermis.

Epidermis of Silver Swordshowing the Guard Cells (GC) ofthe Stomata

Trichomes are most abundant with flowering plants! OtherDivisions generally lack hairs, except for root hairs.

Tissue Organization and

Organs

The mostsimple pattern of tissueorganization is seen in Roots.

Imagine a stack of ice cream cones.Fill the first cone with raspberry ice

cream. This is the Xylem. Coat theinside of a second cone with a layer of blueberry ice cream.


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The ice cream represents the Phloem. Place this over thefirst cone. Coat another cone with mint ice creamand place

it over the other two cones. The mint ice creamis groundtissue. We should have a stack of three cones. Theoutermost cone shellis the Epidermis.

Some Stemsand Leaveshave thesame kind oforganizational pattern!

The Root and some Stems have

concentric circles of Epidermal

Ground & Vascular Tissues

Some Leaves have only oneVascular Bundle. These are

called Microphylls.

Leaves of Monocots like

Sugarcane have many VascularBundles of similar dimensions.

Dicots like Ohi'a Lehua have a

large central Vascular Bundlecalled a Midrib, plus smaller and

smaller Lateral Bundles.

Monocot Stems have manyVascular Bundles arranged in a

complex pattern within the

Ground Tissues.

Dicot Stems have one ring of

Vascular Bundles located in the

periphery of the Ground


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Tissues.

Lab Activities

Meristematic Tissue

Examine Longitudinal sectionsfrom Rootand Shoot tips.Locatethe Apical Meristemsand note their general

features with your 40 X Objective.

Follow cell files as you scan towards the base of each ApicalMeristem & look for signs ofCell Enlargement andDifferentiation (changes in the Cell Walls).

Epidermis

Observe Commercial Slidesof Lily Epidermal. Note theGuard Cellsof the Stomata. The Guard Cells can open and

close to regulate gas exchange with the atmosphere. Alsonote the elongate Epidermal Cells

Lily EpidermisEpidermis with an extremely

thick Cuticle!

Observe a Demonstration slidewhich shows an Epidermiswith an extremely thick Cuticle.


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Take a Pigmented Coleus Leaf.

Cut a 2 x 2 cm squarepiece from the middle of

the leaf.

Placethis upside-downon a Microscope Slide.

Place this on the stageof your microscopeand move it intothe light path.

Use the 4 X Objectivebut flip upthe High Power

Condenser Lens. This should produce a small spot of light

Turn the illuminationto MAXIMUM!

Do NOT Look through the Objectiveswhen you do this.The intense beam could damage your eyes if it is not blocked

by your specimen.

Move the thin part of the leaf into the light path.

Focus up and downuntil you see details of the Epidermal

surface.

You may switch to the 10X objectiveto see more details.

You should be able to see Trichomes& Pigmented EpidermalCells& Guard Cells. The latter may be a little hard to

find.

Do NOT spend too much time on this. The goal is to giveyou an appreciation of Epidermal complexity

Dicot Root

Observe Intact Water HyacinthRoots. The hair-like projectionsare


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actually Lateral Roots. Also note the prominent Root Cap.This protects the delicate Root Apical Meristem. The latter

is the source for the Root Cap and the Root Body (everythingexcept the cap)

Observe Commercial Slides of Root Cross Sections.

Locate the Epidermis, Ground Tissueand Vascular Tissues.

The Ground Tissue is composed of Parenchymacells. Thesehave Thin Cell Wallsand a round

shape. They may have numerous,

starch-storing Amyloplasts.

Carefully examine the VascularTissuesand Identify Phloem&Xylem.

The Xylem Stains Reddue tothe presence of Lignin and has a star-like shape.

The Phloemlies between the radiating arms of the xylem. Itscells are much smaller than those in the xylem and they

have very thin walls.

The Endodermisis the innermost part of the Ground Tissueand forms a boundarylayer between the Vascular Tissues

(Stele) and the Ground Tissue. The Endodermis regulates

the movements of water and solute between the Stele and

the rest of the root. Some Endodermal Cells have Thick,Lignified Wallswhile others have relatively thin walls. The

Endodermis is one of the most important adaptations of

land plants. We will explore this topic later.

Dicot Stem

Observe a Commercial Slide of a Typical Dicot Stemand

locate the Epidermis, Vascular Bundles& Ground Tissues.


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Typical Dicot Stem: Note the

Ring of Vascular Bundles. TheFibers and Xylem stain Purple-

Red due to the presence of

Lignin Typical Dicot Vascular Bundle

The Ground Tissuein the center of the stem is called Pith.It contains Parenchyma Cells.

Examine the Vascular Bundlesat higher magnificationandlocate the Xylem, Fibersand Phloem. Phloem lies betweenthe fibers and the xylem and may not have prominent

features.

TheGround Tissuebetween the Fibers and the Epidermis is

called the Cortex.

Examine Commercial Slides of Cucumber Stemand locatethe Vascular Bundles.

Locate the Phloemwhich occurs on both sidesof the Xylem

in Cucumber. Examine the Phloem carefully and try to locatethe Sieve Elements& Companion Cells.

The Companion Cells are small andstain darklywhile theSieve Elementshave a larger diameterand have pink

contents.


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Cross Section of Cucumber

Stem

Vascular Bundle from

Cucumber: Note thepresence of Phloem on both

sides of the Xylem

Cucumber Phloem. The small dark cells are the Companion

Cells. The larger cells with Pink Contents are the Sieve

Elements.

Highly magnified image ofCucumber Phloem

Sieve Plate from a

Commercial Slide: You may

have trouble finding one likethis. We will have a Demo

for you to see.

Try to locate Sieve Plates. These occur on the endwalls ofthe Sieve Elementsand have relatively large openingscalledSieve Pores. Sieve Pores facilitate the movement of sugarsolution through the Sieve Elements.


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Monocot Stem

Examine Commercial Cross Sectionsof Corn, Sugarcane orBamboo.

The Vascular Bundlesare easy to identify because of theLarge Xylem Tracheary Elements.

Cross Section of AsparagusStem: Note the distribution

of Vascular Bundlesthroughout the surrounding

Ground Tissue

Outer region of Corn Stemwith Vascular Bundles

Vascular Bundles from Corn

Notethe Distribution of Vascular Bundles throughout theGround Tissue. There is no Pithin

most monocots.

Examine a large Vascular Bundle at

higher magnification and locate theXylem, Phloemand Fiberswhichsurroundthe vascular tissues.


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The Phloemhas a geometric organizationwhich makes iteasy to identify the Companion Cellsand Sieve Elements.

Monocot Leaves

Given the number of Vascular Bundles in monocot stems, it

should not be a surprise to see the numerous veins in theirleaves.

Examine the leaves of a typical monocot like Sugarcaneor

ti & note the many veins which run the length of the leaves.Each veincontains one Vascular Bundle. You may see that

there are large and small veins which alternate in a regularpattern.

Cross Section of a Corn (Zea mays) Leaf: Note the

Numerous Vascular Bundles.

Examine Commercial Cross Sections of Sugarcane Leafandnote the following, Upper and Lower Epidermis, Vascular

Bundlesand Ground Tissue.

The Ground Tissuein a leaf can be called Mesophyll(MiddleLeaf). Cells which contain Chloroplastsare called

ChlorenchymaorPhotosynthetic Parenchyma.

Cross Section ofSugarcane Leaf: The LargeCells in the upper Epidermis

are Bulliform Cells. Theyexpand and contract to make

the leaf unfurl or rollup. A

large Vascular Bundle is

present in the center of the


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photo. It is identical to the large Vascular Bundles in the stem.Locate the smaller vascular bundles to its left and right. Theseare specialized for Photosynthesis and contain Phloem with

little or no xylem. Photosynthetic Mesophyll Cells(Chlorenchyma) have stained darkly.

Dicot Leaves

Dicot Leaves usually have a large centralMidribwhich

contains a large Midvein (Vascular Bundle). Minor Veinsbranch from the midvein at oblique angles. Consequently, the

minor veins may be asymmetrical in cross sections.

Examine a typical Dicot leaf like Kukuiand note the Vein

Pattern(Venation). You may need to scrape of some hairsto see the lower surface. Mount the hairs in water and

examine them under the microscope.Layteral veinsgetprogressively smaller and smaller. This is called Reticulateor

Net Venation.

Monocotshave "Parallel" Venationbecause the VascularBundles appear parallel to one another and look unbranched.

However, close scrutiny shows that they produce Lateral

Veinsat angles approaching 90 degrees. Thus, they have aform of reticulate venation called Striate. The Important

Point to remember is that Monocots and Dicots have

Reticulate Venation.

They are both MEGAPHYLLS (big leaf) because they havemore than one Vascular Bundle.

Examine a Commercial Cross Section of a typical DicotLeaflike Pear(Pyrus).

Examine the Midriband locate the Xylem& Phloem.


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Cross Section of aTypical Dicot Leaf:Note the Vascular

Bundle or Midvein). Alsonote the large air

spaces in the Ground

Tissue (G) which is partof the Blade (Lamina)

Cross Section through the Blade

or Lamina of a Dicot Leaf:Notethe Variety of Cell Types which

have specialized functions.

Dicot Leaves Typically have two kinds of Mesophyll(Palisade

& Spongy). The Palisadecellsare like columnsand are tightlypacked. Spongy cellsmay be highly branched and are looselypacked. The Palisade Cellsintercept most of the light and

perform most of the Photosynthesis. The SpongyCells alsocontain chloroplasts but mainly serve as a gas reservoir.Note the Lateral Vein.

pokok bahasan_sito_histo tumbuhan bot 201 lab

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