Cell Structure 11/30/09 10:55 PM

CELL STRUCTURE

Objectives:

To learn to use a compound microscope properly

To review the main parts of a cell, using your textbook as a reference

Before you leave at the end of the laboratory period you should know the parts of a microscope and how to

determine total magnification. You should be able to recognize the organelles in a plant and an animal cell, and

recall the functions of each. You should also know the stains that you used and what they stained.

Introduction:

As you will find in this course, there is no such thing as a "typical" cell. During this period you will look at four

"representative" eukaryotic cells: two plant cells (one with chloroplasts that are easy to focus on, and one without

chloroplasts that will be more challenging), one animal cell, and one example of a single-celled organism. In each

case you will try to locate as many organelles as you can. You will also examine a prepared slide of some

prokaryotic bacterial cells. Your textbook is an excellent reference, so you may want to refer to it during this

exercise.

I. MICROSCOPES

A. Parts of a Compound Microscope

Your goal in this section is to learn the names of all of the parts of the microscope.

B. Magnification

The magnifying power of the ocular and objective lenses used

on the microscope is usually engraved on the lens.

Let's look at some typical lenses.

The magnification of the ocular lens is 10 X or

ten times magnification.

There are three objective lenses shown on this microscope.

You can magnify the image and move around to see the

magnification engraved on each lens.

The lowest power lens on this microscope is 4 X

magnification. It is often referred to as the

scanning lens and should be used first when

viewing a new specimen. On this microscope the

scanning lens has a red band around it to make it

easy to identify.

The next highest magnification is the 10 X lens

also called the low power lens. It has a yellow band.

The highest power dry lens is the 40 X lens. It has a blue band.

Some microscopes will have additional higher power objective lenses (for example 100 X). These lenses require

that a drop of immersion oil be placed between the lens and the specimen.

Now that we know the magnifying power of the ocular and objective lenses, we can calculate the total

magnification using each of the lens combinations.

To calculate the total magnification, multiply the power of the ocular lens times the power of the

objective lens you are using.

C. Field of View

Sometimes it is necessary to determine the size of an object that you are viewing under the microscope. There is an

easy way for you to estimate size. If you know the diameter of the field you are seeing in the microscope, you can

estimate the size of the object you are viewing.

For example:

Here you see the same object with increasing magnification. At the lowest magnification the object occupies only a

small portion of the field.

At the highest magnification the object nearly fills the field.

If you could fit a clear ruler under the microscope you could determine exactly how wide the field

diameter is at the different magnifications and determine the approximate size of the object you are

viewing. In fact, you can buy a ruler mounted on a microscope slide that is especially designed for

this.

You will do this more simply by placing a piece of graph paper on a microscope slide and viewing it under the

microscope. Each box on the paper is a 1 mm square, but for microscopy, millimeters are too large of a unit of

measure. Microscopic objects are measured in micrometers.

1 mm = 1000 micrometers

Let's try this at our lowest magnification using the scanning lens (40 X total magnification).

Now estimate the field diameter in micrometers.

Now do the same using the 10 X ocular and the 10 X low power objective lens at a total magnification of 100 X

(shown on the right).

As you can see, each time the magnification is increased, the block on the graph paper gets larger.

If we try to estimate field size using graph paper with the 40 X objective, the block will be so large that we will not

be able see the lines clearly and it will be difficult, if not impossible, to estimate the field size.

So, how do we estimate a field size for the 40 X objective lens?

We know that the higher the magnification is, the smaller the field diameter is. Therefore, the field diameter is

inversely proportional to the magnification. We can use a mathematical formula to estimate the field size at 40

X.

Let's do this using the numbers we just calculated for the 10 X objective. Remember, the field diameter with the 10

X objective lens was 1700 micrometers. Now fill in the numbers in the equation.

Now solve the equation for the field diameter of the high magnification lens, you get the .

D. Image Formation

When a microscope magnifies an image it shifts the orientation of the object you are viewing.

For example, if you cut out the letter "e" from a newspaper and put it under the microscope what happens to the

orientation of the letter?

The "e" is now inverted and shifted from right to left. What happens if we move the specimen stage to the right?

To simulate this, place your cursor on the letter "e". Hold down the left mouse button and slide the cursor to the

right.

Now move the cursor to the left.

What happened?

Now try this.

Place your cursor on the letter "e". Hold down the left mouse button and slide the cursor upward.

Now move the cursor downward.

What happened?

II. Cells

A. Plant Cells

1. Elodea: leaf cells

Elodea is a decorative aquatic plant often found in fish tanks. A small leaf has been removed from the plant and

placed with the lower surface down in a drop of water on a microscope slide. If you examine the leaf using the

scanning lens you will find the midrib running down the center of the leaf. The midrib contains the main vein for

conducting materials to and from the leaf.

Now turn to higher magnification and examine a portion of the leaf away from the midrib. Can you identify the

chloroplasts in the upper photo and the cell walls in the lower photo?

Click here to confirm your answers..

Remember that a cell, such as this leaf cell, is a three-dimensional structure. The cell wall surrounds the cell on all

six sides. The chloroplasts and other organelles are held against the sides of the cell by the large central vacuole.

You can confirm the 3 dimensional nature of the cell by focusing up and down on while observing one cell.

Try this.

The cytoplasm of the cell is not static but "streams" around the perimeter of the cell. The chloroplasts are carried

by the streaming cytoplasm.

In the biology laboratory you also will treat your specimens with different stains to enhance the contrast and make

them easier to see under your microscope. This portion of the lab is not done in the virtual laboratory.

2. Onion: Epidermis

A small piece of epidermis from the scale of an onion bulb has been removed and a a wet mount has been prepared

for microscopic examination. If you are not experienced with the microscope, you may be able to see little besides

the cell walls which appear as little boxes. If you reduce the amount of light by using the condenser diaphragm, you

may be able to see the nucleus, cytoplasm, and vacuole.

Look at the onion preparation with the condenser diaphragm wide open. Now place the cursor over the image of

the onion and close the diaphragm. What happens to the contrast?

With the diaphragm closed you can easily see the onion epidermal cells. Now determine the size of a single cell

using the estimate of the field diameter.

In this example, the diameter of the field is about 560 micrometers. What is the approximate length of the

cell?

Now try another cell from the same field.

B. An Animal Cell

You will use a cheek cell (simple squamous epithelium) as an example of an animal cell. A small amount of material

has been gently scraped from the inside of a mouth and mixed with a drop of water on a glass slide. A cover slip

was then added. What do you see under the microscope?

The image has low contrast. You can increase the contrast by closing down the diaphragm. When the diaphragm is

in the closed position, you will have maximum contrast. When it is in the fully open position, you have maximum

resolution but the image has very low contrast. Most of the time, we compromise and close the diaphragm about

half way to maximize resolution and contrast as much as possible.

Now look at a higher magnification view of an epithelial cell.

What cell structures can you identify?

C. Euglena

a single-celled eukaryote

Euglena is a single-celled eukaryotic organism that is often called a "plant-like" organism since it is photosynthetic.

Look at the swimming Euglena cells.

Now look at a single Euglena cell. What organelles can you see in the cell?

Flagellum –

Nucleus –

Eyespot –

Chloroplast –

D. Bacteria

single-celled prokaryotes

Bacteria are extremely small and often are not visible with the 10 X objective lens. The prepared slide of bacteria

has three types of bacteria on it.

The round bacteria are often clustered in groups of two, four or more cells.

Now find the rod-shaped bacteria. Notice that not all of the rods are of the same length.

Now find the spiral-shaped bacteria.

To estimate the sizes of these bacteria switch to a higher magnification image.

At this magnification the field diameter is about 45 micrometers.

1. Estimate the size of the rod-shaped bacteria.

2. Estimate the size of the spiral-shaped bacteria.

3. Estimate the size of the round bacteria.

Cell Reproduction 11/30/09 10:55 PM

How do cells reproduce?

Introduction to the Lab:

The emphasis of this laboratory period will be on mitosis.

Mitosis is the sequence of events by which the nuclear material of one cell is distributed, by a process involving

chromosomes, into two equal parts.

At the right is a longitudinal section through an onion (Allium) root tip. The root tip is responsible for the downward

growth of the root and therefore, is one of the regions in the plant where cells are actively dividing and elongating.

Because of this, the root tip is an excellent system in which to study the process of cell division (cytokinesis)and

nuclear division (mitosis) Furthermore, the chromosomes are fairly large and distinct, and this species has a

relatively small number of chromosomes.

Part 1.

a. Click on the root tip to magnify the image.

Can you find dividing cells in the onion root tip?

b.What differences can you see when you compare the nucleus of a

dividing cell with that of a non-dividing cell?

Part 2.

a. Review the diagrammatic summary of cell division in your textbook before you begin.

b. View a video of mitosis in an animal cell

Part 3.

Microscopy Lab Now that you have seen how nuclei divide, you can begin the microscope exercises.

Identify the stage:

Interphase - At interphase the nuclear envelope is still intact, the nucleolus is present and

chromosomes are not distinct.

Prophase - During prophase the nuclear envelope disappears, the nucleolus is gone and chromosomes

are distinct and wound throughout the nucleus.

Metaphase – During metaphase the chromosomes are distinct and line up near the center of the cell.

Anaphase - During anaphase the chromatids are separated and the two groups of chromosomes

migrate towards opposite sides of the cell.

Telophase/Cytokinesis - By telophase the two groups of chromosomes have completely separated and are

positioned at opposite sides of the cell. The nuclear envelope begins to reform.

When you have identified at least one cell in each stage, proceed to the next section.

Part 4.

Mitosis in an Animal Cell.

Click to begin

Slides of whitefish blastulae will be used to show mitosis and cell division in animal cells.

Although the result of these processes and many of the events are the same or very similar to that of the plant

cells, there are some differences. See what differences you can detect.

Click on any of the slides at the right to magnify.

Use the scroll bars to move around the slide.

Place the cursor over a dividing cell and click once. Identify the stage of division.

Identify at least one cell in each stage.

Identify the stage:

Interphase - At interphase the nuclear envelope is still intact, the nucleolus is present and

chromosomes are not distinct.

Prophase - During prophase the nuclear envelope disappears, the nucleolus is gone and chromosomes

are distinct and wound throughout the nucleus.

Metaphase – During metaphase the chromosomes are distinct and line up near the center of the cell.

Anaphase - During anaphase the chromatids are separated and the two groups of chromosomes

migrate towards opposite sides of the cell.

Telophase/Cytokinesis - By telophase the two groups of chromosomes have completely separated and are

positioned at opposite sides of the cell. The nuclear envelope begins to reform.

Reproduction: Protists and Fungi 11/30/09 10:55 PM

Reproduction: Protists and Fungi

Objectives:

To examine some of the structural variation found in the simpler organisms on earth,

noting the transition from single-celled or multi-cellular organisms. (The animal-like

protists will be examined next semester.)

To understand how the relative position of meiosis and fertilization varies in different life

cycles.

To appreciate the tremendous reproductive capacity of organisms reproducing asexually.

This capacity may also be observed in some sexual cycles, as in the mushrooms.

Before you leave at the end of the laboratory period you should be able to tell a plant-like protist (alga) from a

fungus, and specify the kingdom of each. You should know how to recognize the haploid and diploid (and dikaryotic)

phases of each organism studied, and what cells were formed by mitosis and by meiosis.

Introduction:

Most plant and animal cells are diploid (2n), meaning that they contain two complete sets of their genetic materials,

located on two complete sets of chromosomes. Alternately, some plant and animal cells are haploid (1n), containing

only one complete set. [You may want to review the discussion of these terms in Lab 2.]

Dependent upon the organism, both diploid and haploid cells can divide by mitosis. In both cases, each "daughter

cell" has the same amount of genetic material (chromosome number) as the "mother cell".

During a second type of cell division called meiosis, a diploid cell undergoes a "reduction division" to form four

haploid cells. (The reason that four cells are formed will be covered later in the semester.)

The diploid number is restored when two haploid cells fuse during fertilization.

The actual location of meiosis and fertilization in a sexual cycle depends upon the organism. For example, the only

haploid cells produced by humans (and other animals as well) are the sex cells (gametes). The gametes, egg and

sperm, are formed by meiosis; they immediately combine to restore the diploid condition by fertilization, forming

the zygote. The mature adult is then formed by a large number of mitotic divisions. Therefore, the relative number

of haploid cells is small, as indicated in the sexual cycle to the right.

On the other hand, many protists have a sexual cycle where the only diploid cell is the zygote. This zygote

immediately undergoes meiosis upon "germination"; all of the other cells are formed by mitosis - including the cells

that are capable of fusion again.

Compare these sexual cycles.

These two cycles can be abbreviated by simply showing meiosis and fertilization as gray arrows. On the right, the

only diploid cell is the zygote; on the left, the only haploid cells are the gametes. To help you keep track of which

cycle goes with each organism you will study in this lab, a simplified cycle will be found at the upper right corner of

each illustrated cycle.

In some instances the "many haploid cells" remain separate (e.g., Chlamydomonas), in other cases the cells are

attached to form a filament (e.g., Oedogoniium and Spyrogyra), and in still other cases the cells actually form a

multicellular organism (not seen in lab, but described in your textbook).

Plants (and some larger plant-like protists) have a third sexual cycle in which both diploid and haploid phases are

multicellular, resulting in an "alternation of generations". We will study this cycle in the next two laboratories.

Finally, the alternation of meiosis and fertilization, and the resultant recombination of genes, is associated with the

sexual cycle. Many organisms also have an asexual cycle where the offspring are simply produced by mitosis and

therefore are genetically identical to the parent (in other words, they are "clones"). This can be an asexual

reproduction of diploid organisms, as in the propagation of some commercial plants. It can be an asexual

reproduction of the haploid organisms, as the production of spores by many fungi. And some organisms, such as

yeast, can produce both diploid and haploid cells asexually.

Most biologists today subdivide all of life on earth into six kingdoms. The prokaryotic organisms, such as the

bacteria you observed in Laboratory 1, are in Kingdom Eubacteria and Kingdom Archaebacteria. Many if not all of

the simpler plant-like organisms ("algae") are placed with simpler animal-like organisms into a Kingdom Protista;

they are therefore called protists. The fungi that you will observe today are given their own kingdom.

I. Some Plant-Like Protists

Although the term "algae" is no longer used in classification, it is still a useful term to describe aquatic

photosynthetic organisms with little tissue differentiation. Chlamydomonas is a single-celled protist; Spirogyra and

Oedogonium are filamentous. Fucus is a macroscopic organism, placed in the plant kingdom in some textbooks.

A. Single-celled protists

1. Euglena

What characteristics do these cells have that are like plants?

Are like animals?

hints

Note that these cells divide by mitosis, and therefore asexually. Does Euglena have a sexual cycle?

Yes     No

2. Paramecium

Although you will spend more time looking at animal-like protists ("protozoa") in Bio 102, one example is added

here.

Observe Paramecium under low and then high power.

What characteristics do these cells have that are like animals? Are like plants?

3. Chlamydomonas

This small organism requires that you use a high-power objective for viewing.

If you look carefully, you may observe in each tiny cell: a cup-shaped chloroplast with a round starch-like product in

the middle, two flagella, an eyespot (similar to Euglena), and you may even discern the centrally-located nucleus.

Do you see any of these specialized structures in the cell below?

3. Chlamydomonas fusion

This small organism has at least two "mating types". Since you cannot tell one from the other microscopically, they

are called "plus" and "minus".

Click the thumbnail below to view a video of the first stage of mating, where plus and minus types "clump"

together.

Next, click the thumbnail below to view a video clip of "pairing", where two Chlamydomonas cells come together to

mate. Watch the two cells at the top of the window.

After pairing, fusion begins. On the right, each mating stage is shown in its correct temporal sequence.

Chlamydomonas cells have a sexual cycle, but may also reproduce clonally, by undergoing mitotic division, as

shown below.

Are the cells above haploid or diploid?

haploid       diploid

How can you distinguish the haploid from the diploid phases in Chlamydomonas? In any organism?

You have observed "fertilization" in this organism. What compensating process must occur in the diploid (2n) cells?

Mitosis      Meiosis

Chlamydomonas life cycle

In the figure below, identify which cells are haploid and which are diploid.

Click on the image at the right to begin.

B. Some filamentous algae

1. Oedogonium

Note the top image on the right, from a prepared slide of this alga. It shows the chain of cells that makes up one

filamentous Oedogonium organism.

In the middle image, note the clear, round structures within some of the cells; these are the eggs.

The lower image shows a fertilized egg, or zygote.

As in Chlamydomonas, the zygote is the only diploid structure in the alga's life cycle. The Chlamydomonas zygote

goes through meiosis to form four mobile "zoospores" that swim about, eventually becoming attached to the lake

bottom and differentiating into a new filament. This organism also reproduces asexually by simple fragmentation or

by the formation and liberation of single zoospores from vegetative cells.

Oedogonium is a filamentous organism. In this image, notice that

cells are connected end-to-end to form a long chain of cells. Also

note the small brown nucleus centrally located in each cell.

The bulb-like cells in the

filament are egg cells.

Also notice the smaller,

sperm forming cells below

the egg on the top

filament.

Zygotes are similar in size and shape to

unfertilized eggs. They are distinguished by

their thickened cell walls, increased starch

content, and darker color when stained.

2. Spirogyra

This is another filamentous alga, commonly found in ponds and puddles around New Jersey. From wet mounts, and

the figure below, you can see that it is also a long filament of cells.

Note the shape of the chloroplast(s) in the figure below. The protoplast of the cell is mostly transparent; therefore,

you can see both the front and back of the single spiral-shaped chloroplast that gives this genus its name.

Fusion in this genus begins as two filaments attach. In the image below, notice the small conjugation tube that joins

adjacent cells.

Conjugation is complete after the cytoplasm from the adjacent cells fuse to form zygotes.

The heavily stained ovoid structures in the figure below are zygotes. Notice that the filament on the left is empty of

cytoplasm, and though cell walls remain visible, you can no longer see the spring-like chloroplasts inside.

Spirogyra life cycle

C. Specialization in a large alga

The marine alga Fucus has adapted to life in the intertidal region: part of the day it is submerged, while other times

it is exposed to air.

a. Look at the images of Fucus below. Note the various specialized structures such as holdfast, air bladder, and

receptacles containing conceptacles.

Describe how these specializations are adaptations to an intertidal existence.

Fucus

b. Inside the receptacles are small pit-like areas that contain the male and female reproductive

structures. Examine images of these conceptacles below. How are male and female structures similar? How do

they differ?

Why is one called "male" and the other "female"?

What is the adaptive significance of this differentiation?

The male conceptacle (above) can be identified by the many small, darkly-stained, antheridia. The

antheridia contain sperm or sperm progenitors. The lighter-stained thread-like hairs are non-sexual; they help retain

moisture when the receptacle is exposed to dry conditions.

The female conceptacle is characterized by its large, bulb-shaped oogonia with egg or egg progenitor cells

inside. As in the male conceptacle, sterile hairs protect against dessication.

b. Male and female reproductive structures are located inside the conceptacles. Examine images of the antheridia

and oogonia below. How are these male and female structures similar? How do they differ?

Why is one called "male" and the other "female"?

What is the adaptive significance of this differentiation?

In these higher magnification images and diagrams, compare the small, slim antheridia (above) with the bigger,

rounder oogonium (below). Reproductive structures are stained red in the micrographs, sterile hairs appear blue.

Study the life cycle of Fucus below. Decide whether each structure is part of the haploid or diploid phase of the life

cycle.

II. Some Fungi

The sexual cycles of the fungi are basically the same as you have seen before, with the zygote being the only

diploid cell in the entire cycle. However, in fungi the fusion of the cytoplasm, or plasmogamy, is not immediately

followed by the fusion of the nuclei, or karyogamy. The stage between plasmogamy and karyogamy is called

dikaryotic, or (n + n), since each cell has two haploid nuclei: one from the plus strain and one from the

minus strain. Each mitotic division therefore results in two pair of nuclei that are dikaryotic, each having

one nucleus from the plus strain and one from the minus strain.

Fungal Life Cycle:

In the diagram above, each arrowhead represents an event in the life cycle of many fungal cells.

A.   A Filamentous Fungus: Rhizopus (Black bread mold)

On an amenable medium, Rhizopus can be seen with the naked eye, appearing as a fuzzy white mat

growing all over the surface. (And down into the medium. And even over the top of the petri dish

sometimes.) This is the mycelium, or "body" of a fungus. Each strand is called a hypha

(plural, hyphae).

Through a microscope, one may note small, black balls growing at the ends of certain hyphae. These

are the sporangia. Sporangia can be seen in the image of Rhizopus at the right (top). Note that each

sporangium is composed of hundreds of smaller spores - the asexual reproductive cells of

the fungus.

After the organisms in a culture initiate the sexual cycle, one may find zygotes (actually, zygospores

composed of numerous nuclei) in regions where the plus and minus join.

Rhizopus:

Rhizopus sporangium

as seen through 16x objective.

Rhizopus

zygosporangium as seen through 16x objective.

Rhizopus life cycle

In the figure below, identify which cells are haploid and which are diploid.

B.   Mushrooms

Examine the diagrams and images of the mushroom Coprinus below.

Basidiospores are formed by meiosis. Remember that the product of a meiotic division is four daughter cells.

Therefore, in Coprinus four basisiospores arise from each basidium. Can you find all four basidiospores attached to

a basidium in Figure 4 on the right? (Why not?)

Figure 1 above: Diagram of cross section through mushroom cap. Notice the gills radiating from the central stalk.

Figures 2 and 3: Higher magnification (as seen through 10x objective) through the basidiocarp. Notice the

basidiospores (stained red in Figure 2, above, and Figure 4, below) attached to gills at basidia.

Figure 4 above: Basidiocarp gills as seen through 40x objective. Notice the different stages of development of

basidiospores.

What is the ploidy of basidiospores?

Haploid    or    Diploid

Coprinus

In the life cycle below determine if each tissue is haploid, diploid, or dikaryotic (n + n). Remember that plasmogamy

refers to the fusion of the cytoplasm; karyogamy, of the nuclei.

Make a diagram like the one below, showing how one dikaryotic cell can divide by mitosis to form two dikaryotic

cells. (Click here to review mitosis).

C.  A Cup Fungus

Examine the diagrams and images of Peziza (an ascomycete) that show longitudinal sections through the fruiting

structure, or "cup". In the lower image, look for the sac-like structures, or asci, holding the spores (each ascus

contains 8 ascospores, numbered in one ascus in the lower image). The eight ascospores are formed by meiosis

(to produce 4 cells) followed by a mitotic division (to double the number to 8).

Peziza

The life cycle is similar to that for basidiomycetes (like Coprinus) except the dikaryotic stage is much shorter.

Are the spores part of the sexual or asexual cycle of a basidiomycete's life history?

Sexual    or    Asexual

Plant Evolution 11/30/09 10:55 PM

Plant Evolution

Objectives:

The objectives of this lab are as follows:

1. To look at cellular specialization in plants, with emphasis on lignified cells that function

in water transport and/or support.

2. To study the evolution of these vegetative structures in representative plants: a moss, a

fern, a gymnosperm, and both a woody and a nonwoody angiosperm.

3. To examine the evolution of sexual cycles in a moss, a typical fern, and a gymnosperm.

By the end of this exercise, you should be able to identify the various lignified cell types in cross sections of stem.

You should know how to tell a moss from a fern; a gametophyte from a sporophyte. You should understand which

cells are haploid and which diploid, and whether they are formed by mitosis, meiosis, or fertilization. You should be

able to apply this information to the reproductive cycle in gymnosperms such as pine.

Section 1:

The evolution of multicellular plants involved the modification of different cells to perform distinct functions. Part of

the success of land plants was based upon the evolution of a very strong molecule called lignin. In this laboratory

you will learn how to identify three lignified cells.

1.Tracheids: first to evolve, combined the functions of support and water transport.

2.Vessel elements: subsequently evolved from tracheids, specialized for water transport.

3.Fibers:also evolved from tracheids, cells specialized for support only.

All three can be found in xylem, while fibers can be found in xylem, phloem, and other parts of the plant.

I. Evolution of Vegetative Structures

A. Moss

1. Observe the living green "leafy" gametophyte stage on the right. Remember that these organisms have leaf-like,

stem-like, and root-like structures. You can see more of the details by magnifying the image.

2. Now examine the cross section of a moss (Mnium) "stem". You can see the general structure of the "stem."

Magnify the image and identify the following structures.

Find:

a. the outer epidermal cells - Epidermal cells are located on the outer wall of the moss stem.

b. the "leaves" attached to the epidermis - "Leaves" are an extension of the epidermis.

c. the multicellular cortex region - The cortex is composed of all the tissue from the epidermal

cells to the transport tissue.

d. the transport tissue - The transport tissue is located in the middle of the stem.

(Although some of the cell walls in the cortex are stained red, moss is a nonlignified plant.

The central portion of the "stem" is composed of much thinner cells. While the central cells are specialized to

transport water, they are not lignified so they are not called "vascular tissue." [And therefore, moss plants do not

have leaves, stems, and roots.]

B. Ferns

1. Examine the pictures of live ferns. How tall are these sporophytes? What structures are specialized for

photosynthesis?

2. Study the cross section of a fern rhizome (an underground stem) of the Cinnamon fern, Osmunda cinnamomea.

In the fern, the leaves extend in clusters from an upright position of the stem. Thus, you will find a central vascular

region surrounded by a ring of vascular bundles; each smaller bundle extends to a different leaf, or frond. Magnify

the image to identify the different structures.

Find:

a. the central vascular region

b. the vascular bundles

Click here to enlarge the image yet again.

Within a vascular bundle find:

a. xylem tracheid cells

As is the case with most ferns, the xylem in this fern is composed of tracheids only. (Remember, lignified cell walls

are stained red -- along with tannins and other materials with a net negative charge.)

C. Pine (a gymnosperm)

1. Examine the picture of a live pine tree. How tall is the sporophyte stage? Are there specialized photosynthetic

structures, and other portions of the plant to support them? Do these organisms have specific structures that

penetrate deep into the soil to obtain water?

2. Examine the cross sections of a young twig on the right of a 3-year-old pine (Pinus) stem.

Under low magnification find:

a. the central pith

b. three layers (annual rings) of xylem

c. the bark

1. cork

2. cortex

3. phloem

Now click here to magnify the image even more. You should see more of the cellular detail.

You should notice that all of the cells with red cell walls look alike -- other than slight differences in diameter in the

early "spring" wood and the late "summer" wood found in each annual ring. Remember that in pine wood, the only

lignified cells are tracheids, cells that function both for water transport and support.

The cylindrical structures surrounded by green-staining cells are the resin canals. Under low magnification you

can see them in both the woody part of the twig as well as in the bark. This resin makes the cut ends of twigs

sticky, and are a defense mechanism in these plants.

Under high magnification find:

a. the tracheids

b. the resin canals

c. the thin-walled phloem cells that transport "food" throughout the tree

d. the protective cell that surrounds the outside of the stem (What are they called?)

Since it is difficult to determine the cell types using cross sections, an alternative method can be used called

"maceration." The wood is treated with chemicals to make the cells come apart. Examine the macerated pine

wood on the right to see what the tracheids look like from the side. Note the bordered pits in the cell walls. Click on

the image to magnify it.

D. Angiosperms

I. A Woody Plant: Basswood (Tilia)

1. Examine the cross section through a basswood twig.

Find:

a. the central pith

b. three layers (annual rings) of xylem

c. the bark

1. phloem

2. cortex

3. cork

Notice that although the water conducting cells in pine wood were fairly uniform (Pinus stem), those in angiosperm

wood are composed of at least two cell types. Click here.

The lignified cells with the largest diameters are the vessel elements. The lignified cells with smaller diameters

are either tracheids or fibers; the difference can only be determined from a side view (see diagram of lignin cells

in this lab's introductory page).

In the outer portion of the twig, the outermost layer is cork and the inner bark is phloem. But note that there are

lignified cells in the phloem region also! Click here.

Under higher magnification you will be able to see that the red-stained cell walls are very thick, and that the hollow

cavity is very narrow. Therefore, if you identify anything with red-stained cell walls as xylem, you may be wrong!

Lignified fiber cells can be found in the phloem as well.

It is easy to tell vessel elements in cross sections because of their size, but more difficult to distinguish a tracheid

from a fiber. Therefore, examine the prepared slide of macerated basswood . You can click on the image to

magnify it.

Identify:

a. a tracheid

b. a fiber

c. a vessel element

II. A nonwoody plant: Buttercup (Ranunculus)

Examine the Cross-Section of a Buttercup Ranunculus Stem.

Under low magnification find:

1. the vascular bundles

2. the pith

3. the cortex

Using higher magnification find in the vascular bundle:

1. vessel elements

2. fibers

There are lignified cells in the portion of each vascular bundle closest to the outside (cortex) and other lignified cells

in each bundle closest to the pith. The large diameters of the lignified cells on the inside are indicative of vessel

elements, and are therefore in the xylem. However, the cells on the outside have red-stained cell walls that are

very thick, and the hollow cavity is very narrow. Once again, you are seeing fibers. And, once again, since this is

the phloem on the outside of each bundle, these are phloem fibers.

Section 2

The evolution of plants also involved alterations in the sexual cycle. All plants have the sexual cycle that alternates

a diploid sporophyte generation and a haploid gametophyte generation. The sporophyte forms spores by

meiosis; the gametophyte forms gametes by mitosis.

In moss, the gametophyte is "dominant" (or predominant; you are more likely to encounter this phase of the sexual

cycle). In ferns and all other vascular plants, the sporophyte is predominant. In ferns (and other "seedless vascular

plants") the gametophyte is a free-living, autotrophic organism. While the fern sporophyte is well adapted to land,

the fern gametophyte is not. Therefore, in the subsequent evolution of land plants, this haploid portion of the

sexual cycle was modified in several ways that allow these plants to survive increasingly dry climates. These

changes will be observed in the coniferous gymnosperm, pine.

Changes in Sexual Cycles

Remember that in the last lab you learned two types of sexual cycles.

In one, fertilization is immediately followed by meiosis, the only diploid cell being the zygote (top).

The rest of the cells in this cycle are haploid.

In the other, meiosis is immediately followed by fertilization, the only haploid cells being the

gametes (bottom). In this instance, the diploid phase is usually multicellular.

A third cycle (center) occurs in all plants and some multicellular protists. In this cycle, haploid spores

are formed by meiosis. These spores divide by mitosis to produce a multicellular haploid phase that

produces gametes by mitosis. The zygote formed by the fusion of two gametes divides by mitosis to

produce a multicellular diploid phase.

In the alternation of haploid and diploid generations the diploid phase produces spores and is therefore called the

sporophyte (“spore-plant”). The haploid phase produces gametes and is therefore called the gametophyte

(“gamete-plant”). See the top diagram to the right.

NOTE: Both the gametophyte and the sporophyte stage may be duplicated by asexual reproduction - the resulting

offspring being clones.

This basic alternation of generations has two variations. In the bryophytes such as moss, the gametophyte

generation is predominant ("dominant") and the sporophyte grows out of the gametophyte (right bottom). In all

vascular plants the sporophyte is predominant (left bottom); the gametophyte may be free-living, as in ferns, or

may be dependent upon the sporophyte, as in seed plants.

ALWAYS REMEMBER:

Mitosis: one diploid cell dividing to form two diploid cells - or - one haploid cell dividing to form two haploid cells

Meiosis: one diploid cell dividing to form four haploid cells

Fertilization: two haploid cells fusing to form one diploid cell (the zygote)

A. Moss

1. Study the image of a moss antheridium. What type of cells are formed in these structures? Click on the image or

the word "magnify" to get a better look at the cells.

2. Now study the image of a moss archegonium. If it is a good section, you will see a large cell (egg) within a vase-

like structure. The sperm must swim through liquid water to the opening at the top of the vase, then swim down the

channel before the egg is fertilized, forming the zygote. Click on the image or the word "magnify" to enlarge the

image.

Is this method of gamete transfer well adapted to a terrestrial habitat?

3. Examine the whole moss plant in the sporophyte stage. Do you think this brown structure can carry on

photosynthesis, or is it dependent upon "food" from the gametophyte?

Label each stage as either:

a. sporophyte or..

b. gametophyte

Label:

a. antheridium

b. sperm

c. archegonium

d. egg

e. zygote

f. spore

g. protonema

NOTE:If you should discover living sporophytes outdoors, you can pass your hand across the top. The results will be

a cloud of fine particles. These are the spores formed by meiosis that will germinate to develop into the new

gametophyte generation.

B. Ferns

1. Examine the live fern leaf ("frond") that has brown or black specks ("sori") on the underside. The small brown or

black cells are spores that, under the correct conditions, will germinate to form the gametophyte generation. Some

ferns, such as the cinnamon fern (previous section), have all of the sporangia on a separate "fertile fond." The

sporophyte cells are diploid; the spores (and gametophyte cells) are haploid. Were the spores formed by mitosis or

meiosis?

2. Examine the images of the fern antheridium and archegonium. Click on the images to get a closer look at the

cells.

Answer the following questions:

A. Are the gametophyte plants haploid or diploid?

B. Are the egg and sperm haploid or diploid?

C. Are the gametes formed by mitosis or meiosis?

D. Do the gametophyte cells contain chloroplasts? How do you know?

Examine the drawing of the fern life cycle to the right.

Label each stage as either...

a) sporophyte or..

b)gametophyte

Click here to reload the image. Now...

Label:

a. antheridium

b. sperm

c. archegonium

d. egg

e. zygote

f. spore

C. Pine

In both of the plants you have observed so far, the spores formed by meiosis all look the same; the plants were

homosporous. A variation on this theme is where some spores are larger than others; these plants are

heterosporous. All gymnosperms and angiosperms are heterosporous.

Each scale in the smaller male "staminate" cones contains numerous diploid microsporocytes or "microspore"

mother cells that go through meiosis, each forming four haploid microspores. Each microspore undergoes several

mitotic divisions to form a microgametophyte, or pollen grain. Some of the nuclei, the sperm nuclei, are capable

of fusion with an egg nucleus.

The scale in the larger female ("ovulate") cone has two ovules, each containing a single megasporocyte

(megaspore) mother cell which goes through meiosis to form four haploid megaspores. In this case, three

megaspores degenerate while the fourth continues to divide mitotically, forming a multicellular

megagametophyte. This megagametophyte has two archegonia, each containing one egg.

1. Observe the image of the smaller male pine cone.

What kinds of cells are found in these cones? Are the cells released from these cones haploid or diploid?

(Remember, pollen is a MICROGAMETOPHYTE.)

You can see pollen being released from the male pine cones in the third image on the right.

The forth image on the right is a magnified picture of actual pollen grains.

2. Now observe the image of the larger female (ovulate) pine cone, the type you usually see in pine

cone wreaths.

What kinds of cells were formed WITHIN each of these leaf-like scales? The sixth image on the right depicts a pine

seed found within the scales of the female pine cone.

How do the gametes produced by the male cone get to the egg in the female cone? And THEN what happens?

3. Examine a seed which is cut open, the seventh image on the right.

Look for the embryo with its numerous cotyledons. Look for the white storage tissues around the embryo.

Remember, this storage tissue is the MEGAGAMETOPHYTE.

Where was this seed formed?

What specialized structures help disperse these seeds away from the parent plant? (And why is this important?)

Which of these cells are haploid and which diploid?

1. embryo with cotyledons

2. surrounding nutrient tissues (MEGAGAMETOPHYTE)

3. outside seed coat (including a larger "wing"):

Examine the drawing of a pine life cycle.

Label each stage as either..

a) sporophyte or..

b) gametophyte

Now click here to reload the image.

Label:

a. megaspores

b. megagametophyte

c. archegonium

d. microspore

e. microgametophyte (= pollen)

f. pollen tube

g. embryo

h. seed coat

i. seedling

Pine is only one example of a gymnosperm. What other gymnosperms still live on earth? How are they grouped by

taxonomists? Do any gymnosperms have a wider distribution than conifers?

III Review:

Putting It All Together

This is a complicated lab, with lots of parts, so it is essential that you get an overview before try to sort out the

details.

1. Think about all of the figures that illustrate tracheids. What are the functions for tracheids? How

can you identify a tracheid in a cross section? What plants did you observe today that had tracheids?

What do they have in common?

2. Think about all of the figures that illustrate vessel elements. What is the main function of a vessel

element? How can you identify a vessel element in a cross section? What plants did you observe today

that had vessel elements? What do they have in common?

3. Think about all of the figures that illustrate fibers. What is the main function of a fiber? How can

you identify a fiber in a cross section? In what tissues did you find fibers? What plants did you observe

today that had fibers? What do they have in common?

4. Compare the sexual cycles for moss and ferns. What do they have in common? How do they differ?

5. Compare the sexual cycles for ferns and pine. What do they have in common? How do they differ?

6. The "basic life cycle" illustrated in this lab is for a homosporous plant, such as most ferns. Change

this life cycle to represent the situation for a heterosporous plant, such as pine.

Angiosperm Reproduction 11/30/09 10:55 PM

Angiosperm Reproduction

Objectives:

To study the development of the different parts of the flower, and how these regions

further develop to form the fruit with its seeds.

To practice forming three-dimensional images from two-dimensional observations.

To observe some of the variation in different parts of sample fruits, and relate these

modifications to changes in function.

After completing the laboratory exercise you should know the parts of a flower and the functions of each. You

should be able to recall which part of the flower develops into each portion of a fruit. Again, you should be able to

recognize which cells are haploid and which diploid, and whether they are formed by mitosis or meiosis. Finally, you

should appreciate how plants have evolved different structures for pollen transfer and for fruit dispersal.

Introduction:

This lab is a continuation of the previous lab in which you studied some of the basic aspects of plant evolution. Click

here to briefly review the evolution of land plants. Next, review the generalized life cycle at the beginning of Part II

of lab 7.

Finally, review the evolution of the gametophyte generation, starting as a free-living, multicellular, photosynthetic

organism in ferns. In gymnosperms like pine, the microgametophyte was reduced to a small, wind-blown structure

called "pollen". The megagametophyte was maintained within the sporophyte cone, and surrounded by the

sporophyte layer called the integument (later to become the seed coat). The megagametophyte was still large

enough to provide the nutrients for the young embryo in the mature seed. This trend of reducing the gametophyte

generation is continued in angiosperms. These and other trends in plant evolution are diagrammed on the next

page.

In this laboratory, you will observe several of the structures associated with the reproductive portion of the plant

life cycle. You will start by observing the development of the megagametophyte ("embryo sac") as well as that of

the microgametophyte ("pollen"). You will then study the subsequent development of the seed and fruit.

You will also examine examples of the different types of fruits to see how they have evolved different structures for

protection and dispersion.

I. The Flower

You have now come to a major evolutionary advancement of the plant kingdom. Review the main parts of the

flower below.

In the diagram, parts of the male reproductive structures, or stamen, are labeled in green. There are six stamen in

this flower.

The female reproductive structures are labeled in blue. The stigma, style and ovary make up the single pistil in this

flower. Note that the ovary is not visible in the diagram, but is located in the center of the flower, at the base of the

style.

The diagram below illustrates the components associated with sexual reproduction.

On the left, label the parts of the stamen, the male reproductive structures.

On the right, label the external parts of the pistil (sometimes also called the "carpel"), the female reproductive

structure.

Sexual Structures of a Flower

1.Anther

2. Filament

3. Stigma

4. Style

5. OvaryAlthough you did not label the sepals (outer

whorl(s) of modified leaves) and petals (inner

whorl(s) of modified leaves) in the previous

illustration, you should know the function of

each:

Sepal: To protect the developing

flower bud.

Petal: To attract pollinators with colors and/or odors; to provide a landing area for insect pollinators.

We can speculate that one of the functions of sepals is to hide developing flowers from pollinators. This prevents

colored petals from attracting insect visitors before pollen is ready for dispersal, and may be one of the selective

advantages for having inconspicuously colored sepals--they are often green! They may also protect fragile flower

parts from damage, and so they are sometimes thicker, or fleshier, than petals. Are there other ways to distinguish

sepals from petals?

The figure below depicts the internal features of the pistil after pollination. Label the parts and identify each as

belonging to either the sporophyte (diploid) or gametophyte (haploid) generation.

Flower Pistil After Pollination

1. Pollen grains

2. Stigma

3. Style

4. Pollen tube

5. Ovary

6. Ovule

7. Gladeolus Flower Dissection

If the petals and sepals are removed from a gladeolus flower, the remaining

parts are the stamens and the pistil (sometimes called the carpel.)

When a longitudinal cut is made down the ovary, the line of ovules inside

becomes visible.

The following diagram shows the gladeolus flower dissected in this way.

A.   The

Anther

Study the

diagram below, which illustrates a cross

section through flower sexual

structures. Note the style in the center of

the circle of anthers. Each anther consists of

two pollen sacs, one on each side of a

vascular bundle.

1. Stigma

2. Style

3. Ovary

4. Ovules

5. Anther

6. Filament

Cross Section through Flower Pistil and Anther

1. Anther (pollen sacs are within the anthers, two pairs per anther.)

2. Style

Compare the diagram above with the prepared slide of the Lilium anther, to the right. This is a large structure-- this

image was captured with the 6x scanning lens! Scroll to find the style, anthers (and their pollen sacs),

filament, and vascular bundles.

A.   The Anther, continued.

An anther with mature pollen is drawn in the diagram below.

Two features of the pollen are worth noting: First, each pollen grain has two nuclei. (You will have to look to find a

pollen grain where the histological section was made in such a manner that both nuclei were in the same slice.)

Second, the cell wall has a definite structure. (Look for grains where the section was right across the upper or lower

surface of the pollen.)

Remember that pollen is a MICROGAMETOPHYTE formed from a MICROSPORE.

Examine a prepared anther using higher power by clicking on the image below to magnify.

Cross section through Lilium anther

In the high magnification image to the right (http://bio.rutgers.edu/~gb101/lab8_angio_repro/lilyanther2.jpg), find

pollen, pollen sacs, and vascular bundles. Then estimate the size of the pollen grains.

If the field of view in the thumbnail image below is 1.2mm, how large is one pollen grain? Find a cluster of grains

that line up across the diameter of the field. Count the number of grains and divide this into the known field of view.

1.

2.

3.

You may review the procedures for estimating cell size using a known field of view in Laboratory 1.

Do you estimate that the lily pollen is 0.003 mm,     0.05 mm,     or     0.1 mm?

Microgametophyte Development

The development of the microgametophyte (male gametophyte) in flowering plants involves three stages:

A diploid microsporocyte, or microspore mother cell, divides to give rise to four haploid

microspores.

Each microspore divides by mitosis to form two haploid nuclei (the tube nucleus and the generative

nucleus); this is mature pollen in Lilium.

After landing on the stigma, the pollen germinates forming a pollen tube; the generative nucleus

then divides by mitosis to form two haploid sperm nuclei.

B.   The Ovary

The image below is an illustration of a cross section through Lilium ovary, as might be seen using a scanning lens.

In the Lilium ovary, the ovules are attached in pairs to a central stalk. In prepared slides, you may not always see

all three pairs of ovules in one section.

In the image to the right, note the small vascular strands in the central region, the ovules, and the protective ovary

tissues around the outside.

How many ovules are in this ovary cross section?

2,    3,    or 6?

The development of the megagametophyte ("embryo sac") in most angiosperms involves three stages.

A diploid megasporocyte (megaspore mother cell) undergoes meiosis, giving rise to four haploid megaspore nuclei

(3 of which disintegrate).

The remaining megaspore nucleus undergoes three mitotic divisions to form eight haploid nuclei.

Nuclear migration and cytokinesis occur to form the mature megagametophyte

While the above is "typical", the number of antipodals can vary from none to many, depending upon the species.

The smallest megagametophyte only has an egg cell plus one polar nucleus.

III.  Seed and Fruit Development

A.   Development of a Seed

Capsella: a dicot

Examine several slides of the cosmopolitan weed Capsella bursa-pastoris (Shepherd's purse). This plant has

numerous heart-shaped fruits ("purses") on a long stem. Each of these fruits contains dozens of minute seeds. (See

the illustration below.) The white flowers and developing fruits are at the very top of the plant, and fruit at more

mature stages are at the bottom.

Capsella seed development

Review some of the basic parts of the developing seed using the illustrations below.

Note that in this plant the endosperm is absorbed by the developing cotyledons, so that the stored food in the

mature seed is in the cotyledons. (The same pattern is also true for the legumes, including the pea and bean seeds

that you will study in the next section.)

The sections from the previous illustrations, and in the illustration below, are exactly parallel to the embryonic axis.

As you examine the prepared slides, however, you will note that many of the seeds have been cut at other angles.

Use the following illustration to help understand these sections.

The diagram above shows four of the infinite planes where the seed could be sectioned. The angle of the cut is

shown in blue. Identify what the resulting section would look like if the section were made at the blue line.

III.  Seed and Fruit Development

B.   Fruit Development

Fruit development is a complex process, varying considerably among different plant groups. Three examples of the

flower and then the fruit are found in the figures to the right.

For example, in peas the flower is "irregular" (that is, it has bilateral rather than radial symmetry), with sepals and

petals modified into several different shapes. The ovules are attached down a single row in the ovary so that the

seeds develop in the same way. When you split open a pea pod, you can get a good impression of how the flower

develops into the fruit.

Complete your collection of life histories by adding two angiosperm sexual cycles.

The figure on the right is the sexual cycle of a dicot, the bush bean.

Corn, Zea mays

The images below show a monocot, corn.

While completing the corn life cycle, note that while the materials in the endosperm have been transported to the

cotyledons during bean seed development (as in Capsella), the endosperm still exists in the mature corn kernel.

C.   Fruit Diversity

Dispersal: Angiosperms have evolved a number of different methods for protection and dispersal of

the next generation. These dispersal mechanisms range from structural modifications such as barbs

that stick in fur, or buoyant structures that carry fruits and/or seeds through water; to sweet fruits that

are eaten by animals that disperse seeds (such as the peach, on the right).

Domestication: A variety of plants have been cultivated, often because of the fruits. The original

evolution of the fruit was for dispersal. For example, note the three layers of a peach on the image

below.

The Peach:

an example of fruit dispersal mechanisms

The outer layer ("skin") protects the next layer from drying out. The main central layer attracts animals, who

consume the whole fruit. The inner layer ("pit") protects the seed during the process.

The pit is later deposited, along with some "fertilizer", after in has passed through the animal's gut.

To continue, click on the area of the image that was the ovule when this fruit was still a flower.

3. Significance of grains

Examine a corn "cob". (http://bio.rutgers.edu/~gb101/lab8_angio_repro/cornkernelhigh.jpg)

The kernel is technically a fruit, not a seed, since the seed coat and fruit wall are fused.

Examine the prepared slide of a corn kernel above. (The scientific name for corn is Zea mays).

Biology Lab Practical Lab 9

Transport Systems in Plants

Objectives:

1. To study water transport in plants.

2. To investigate the structures associated with transport of water and of organic nutrients.

Introduction:

The transport systems in plants are quite different than the circulatory system found in vertebrates. Vascular plants

have two transport systems, one to move water (and the minerals dissolved in it) from the roots to the leaves and

the other to move organic compounds (mainly sucrose) from the "source" to the "sink". The cells responsible for

long-range water transport have already been studied in Lab 7: the tracheids and vessel elements found in xylem.

The cells responsible for long-range transport of organic compounds are found in the phloem.

The hierarchial nomenclature used in plant anatomy is often confusing, and is therefore outlined to the right. Click

here to get table. Note that both xylem and phloem tissues may also contain cell types that do not function in

transport, such as the phloem fibers observed in Lab 7.

In this laboratory you will:

1. confirm the path of water movement between the uptake by root hairs and the loss

through stomata

2. perform an experiment that suggests a mechanism for this movement

3. examine prepared slides to study the cellular structures in more detail

II. Water Transport Pathway

The purpose of this experiment is to examine the movement and pathway of water up an Impatiens stem. In

the first part of the experiment, congo red dye will be added to the water to trace the pathway of water up the

stem. Cross-sections of the stem demonstrate where in the stem the water is moving and oblique-sections allow

identification of the actual cells involved in water transport. The second part of the experiment identifies which

parts of the stem, and more specifically, which cells, are lignified. Are the cells involved in water transport

lignified? Lets start the experiment and see!!!

Part I :

Step 1: Impatients have translucent stems (due to the presence of large, thin-walled cells). Therefore, the vascular

strands running longitudinally in the stem can be observed directly. Notice the strands in the picture to the right.

Click on the picture to label the strands with arrows.

Step 2: Cut the root system from the plant and immediately place the cut surface of the stem in water. Cut off

another centimeter of stem under water to ensure there are no air bubbles in the transport tissue that could disrupt

water transfer. Click here to see how that was done.

Step 3: Quickly transfer the cut stem to a test tube containing a solution of Congo red and prepare your controls

while you wait for water transport to occur up through the stem. Click here to observe the congo red set-up.

Step 4: Two controls are needed for this experiment. Since the purpose of the experiment is to trace the

movement of congo red dye to follow the pathway of water transport, it is first necessary to see if any of the cell

walls of the plant are already stained red. To do this mount a thinly cut section of stem from the piece cut off in

step 2 on a microscope slide and view it under a dissecting microscope. This is control

1. The second control is prepared in the same way, however, this control is to check which parts of the stem

Congo red will stain (Congo red stains cellulose). Add a drop of Congo red to a second slide for

control

2. Click on the following to observe each each part of step 4.

a.Preparation of sections

b.View Control 1 and 2 on the slide

c.View Control 1 under the dissecting scope

d.View Control 2 under the dissecting scope

Step 5: After the dye has moved to the stem apex, cut cross-sections of the stem at various points along the

stem. Examine the location of the congo red. Also make longitudinal sections at the same points to identify the

cell type.  Click on the following to observe each part of step 5.

a. Sections at various points along the stem

b. View slides of cross and oblique sections from each point

Part II:

The purpose of the second part of the experiment is to determine whether or not the cells involved in water

transport are lignified. Click on each step to observe the procedure.

Step1: Cut additional cross and longitudinal sections to stain lignified cell walls using

phloroglucinol.

Step2: Soak sections in 2-3 drops of phloroglucinol for about 3 minutes.

Step3: Drain the stain off using a paper towel.

Step4: Add 2-3 drops of concentrated HCl. (Lignin stains red)

Step5: Place a cover slip over the sections and examine it under the dissecting microscope.

II. Water Transport Mechanism

According to the transpiration-adhesion-cohesion-tension mechanism of water transport in xylem, water

evaporating through the stomata produces a tension, or negative pressure, that pulls the water column up

the plant. This column is maintained by the hydrogen bonding between water molecules (cohesion) and the

hydrogen bonding between water molecules and the molecules that make up the cell walls (adhesion).

If the above mechanism is correct, then a twig that has been removed from the rest of the plant and attached to an

artificial water column (as in a pipette) could pull water up the pipette. The rate of movement can be determined by

adding a dye to the water at the bottom of the pipette.

Begin Experiment:

1. Place a transport apparatus (1 mL pipette with a piece of clear tubing on the larger end) under water using the

large dish pan. Manipulate the apparatus until it is completely filled with water - NO air bubbles.

To do this, click on the yellow tubing to place it on the pipette. Next, click on the pipette to place it in

the dish pan. It will fill with water.

2. Place the cut end of the juniper twig under water and cut off another centimeter to insure that there are no

bubbles in the transport tissue that would disrupt water transport. Insert the freshly cut end into the above tubing

while under water, making certain that NO air bubbles are trapped within the assembly. If the twig does not fit

tightly in the clear tubing, wrap several strips of Parafilm around the stem before inserting it into the tubing. Attach

the twig firmly with wire using the pliers.

Click on the juniper twig to place it into the dish pan. Click on the knife to cut off an additional cm

under water. Next click on the twig again to insert it into the tubing. For our purposes, assume it fits

snugly.

3. Add about 20 mL of red colored dye (Congo red) to the bottom of a small beaker. With your finger over the tip of

the pipette, transfer the assembly so that the tip is now into the dye. Remember: NO air bubbles!

Click on the test tube to add the Congo red. Next click on the pipette/twig assembly to place it into the

test tube.

4. Transfer the whole thing to the ring stand. Clamp it into place and turn on the light at the top of the assembly.

Click on your set up to complete assembly.

5. This same set-up is repeated with a juniper stem without leaves to use as a control.

Click here to see the control's set-up.

6. At periodic intervals, look for a movement of dye up the pipette. Click here to start the experiment.

NOTE: The movement of the dye observed takes approximately half an hour in real time.

Click here to see the set-up and results of this experiment from a laboratory class. Click on either beaker in the

experiment to get a close-up of the final results.

A. The Root

1. Whole Roots

Before examining the root ultrastructure, lets take a look at the parts of the whole root. We're going to examine the

root system of a Cyperus(top right)

and a Begonia (bottom right)

. Click on the cyperus to examine its rooting structures under water.

Next click on the roots to examine a single root shoot. Note that the Cyperus has a large primary root (thick

black arrow). Thinner secondary roots (thin black arrow) emerge from the older primary root.

Note how the secondary roots originate at a definite position behind the root apex and become progressively longer

(older) as you go up the primary root. This form of continuous development is characteristic of higher plant

structures.

Now click on the Begonia roots. This plant had been clipped and the stem was placed in water. The stem grew

new root shoots. Notice the numerous root hairs. The root hairs increase the surface area of the root.

Below to your left, view the cross section of the root as if you were using a microscope. Increase magnification by

using the + sign and decrease magnification using the - sign. You can also move the stage of the microscope by

clicking on the button on the far right and moving the hand. Once you have examined the section, label the parts of

the root by clicking on the image to your right.  Identify the epidermis and the xylem at low magnification and

identify the phloem cells, cortex, and endodermis at high magnification.

Indentify:

Epidermis at low magnification – The epidermis is a one-cell thick outer covering of the root.

Xylem - The xylem is in the center of the circular root.

Identify:

phloem cells – The phloem cells are the cluster of green-stained cells in the arms of the X-shaped

xylem

Vessel Elements - The vessel elements are the large conducting cells in the xylem in the middle of

the vascular region.

cortex - The cortex is the intermediate portion of the bark, between the epidermis and the vascular

tissue.

endodermis at high magnification - The endodermis is a single layer of cells that encircles the

vascular cylinder.

Just as in the root exercise, the image to your left can be manipulated as if viewed through a microscope. Click on

the image to your right to identify the epidermis, cortex, and vascular bundles. You may then click on "high

magnification" to label the parts of the vascular region. Identify the phloem fibers, sieve tube members,

vessel elements and tracheids.

Identify:

Epidermis - The epidermis is a one-cell thick outer covering of the stem. It has a thick waxy cuticle and stomata.

cortex - The cortex is external from the vascular bundles and internal from the epidermis.

vascular bundles –

Identify:

phloem fibers - The phloem fibers are clustered toward the outside of the vascular bundle, forming a cap that

strengthens the stem.

sieve tube members - The seive tube members are located in the phloem. They are on the inner side of the

phloem fiber cap.

vessel elements - The vessel elements are the larger, more efficient conducting cells in the xylem.

tracheids. – The tracheids are the smaller conducting cells located in the xylem.

C. The Leaf

1. Whole Leafs

Before we examine the ultrastructure of the leaf, lets take a look at a whole living leaf. Notice the two leafs on your

right. The top leaf is from the plant zebrine

and the bottom leaf is from the plant coleus.

Notice the major and minor veins (vascular bundles) running throughout the leafs. The major vein(s) are

labeled with a large arrow(s) and the minor vein(s) are labeled with small arrow(s).

It is also possible to visualize the stomata on the leaf's surface. To do so, each leaf was painted with clear nail

polish on both sides. The film of nail polish was peeled off and mounted on a slide to examine under the

microscope. If all goes well, an impression of the leaf cells on the surface will be left. Click on the zebrina leaf to

examine the leaf's surface. Notice which surface the stomata are located and their distribution. Next click on the

coleus leaf.

Again, the image to your left can be manipulated as if viewed through a microscope. Click on the image to your

right to identify the upper epidermis, lower epidermis, cuticle, guard cells, stoma, palisade mesophyll

(with chloroplasts), and spongy mesophyll.

Identify:

upper epidermis - The upper epidermis is a one-cell thick outer covering of the top of the leaf.

lower epidermis - The lower epidermis is a one-cell thick outer covering of the bottom of the leaf.

Cuticle - The cuticle is the waxy layer secreted by the upper epidermal cells to reduce water loss. In this image

only a small area is visible.

guard cells - Guard cells are specialized lower epidermal cells that are responsible for opening and closing the

stoma.

Stoma - The stoma is a minute air space opening at the base of the leaf.

palisade mesophyll (with chloroplasts) - The palisade mesophyll is the layer of closely packed columnar cells

near the upper epidermis.

spongy mesophyll - The spongy mesophyll is the layer of loosely and irregularly arranged cells near the lower

epidermis.

Chromosome Structure and Meiosis 11/30/09 10:55 PM

Objectives:

The objectives of this lab are as follows:

1. To review the structure of a chromosome.

2. To study the events associated with meiosis.

3. To apply this knowledge to human genetics by analyzing a karyotype.

Introduction:

Meiosis is the second important kind of nuclear division. It resembles mitosis in many ways but the

consequences of meiotic divisions are very different from those of mitotic divisions. While mitotic

division may occur in almost any living cell of an organism, meiosis occurs only in special cells. In

animals, meiosis is restricted to cells that form gametes (eggs and sperm). Each species has a

characteristic number of chromosomes per somatic cell. Fruit flies have 8; normal humans have 46.

They exist as homologous pairs (partners) that are similar in size and shape and carry the same kinds

of genes. Thus humans have 23 homologous pairs. The full complement of 46 chromosomes is referred

to as the diploid number

(referring to the fact that each

kind of chromosome is

represented twice). In higher

organisms when an egg is

fertilized the egg and sperm fuse

to form a single cell called a

zygote which develops into a

new organism. If the egg and

sperm were both diploid (46

chromosomes each in the case of

humans) then the resulting

zygote would be tetraploid. This

would be an intolerable situation, so a mechanism has evolved to insure that each gamete (egg or

sperm) contains only one representative of each homologous pair (or half the diploid number). This is

referred to as the haploid number.

Haploid Egg + Haploid Sperm = Diploid Zygote

The mechanism that makes this possible is meiosis. Meiosis consists of two divisions, Meiosis I and

Meiosis II, and can potentially result in the production of four cells. However the DNA is only

synthesized once (prior to Meiosis I). The subdivisions of meiosis are named like the subdivisions of

mitosis (prophase, metaphase, anaphase, telophase) but as we shall see the events are somewhat

different.

Part I:

Lets review the stages of Meiosis.

1. Study the diagrammatic summary of cell division in Meiosis I and Meiosis II in your textbook before

you begin.

Part II:

You are now ready to find the actual stages of meiosis, using the lily anther. The lily flower has six

anthers surrounding one carpel. Each anther has two pair of microsporangia ("pollen sacs"). It is in

these microsporangia that you will observe the stages of meiosis.

REMEMBER: These slides are thin two-dimensional sections through three-dimensional reality.

Therefore, you will have to look at several different cells in each microsporangium to see exactly what

is going on. Luckily, in the early stages of meiosis, all the cells in the sac are in the same

stage.

Meiosis in the anther starts with the diploid microsporocyte. Each nucleus has a diploid number of

duplicated chromosomes. These cells are still attached in the microsporangium.

We will now begin to identify the different stages of meiosis. The cross-section of the lily anther to the

left is in the early stages of meiosis.

Are the cells in:

1. Early prophase I - In early prophase, the chromosomes are long and slender, and the bright red

nucleoli are still present. The nuclear region will be clear and the nuclear envelope is still present.

2. Late prophase I - In late prophase I, the chromosomes are short, thick, and condensed. The

nucleolus is absent and the nuclear envelope has broken down.

3. Metaphase I - During metaphase I the pairs of chromosomes are distinct and line up near the

center of the cell.

4. Anaphase I - During anaphase I the chromosome pairs are separated and the two groups of

chromosomes migrate towards opposite sides of the cell.

5. Telophase I - By telophase the two groups of chromosomes have completely separated and are

positioned at opposite sides of the cell.

6. Interkinesis - The nuclear envelope begins to reform. The cell plate becomes visible between the

duaghter cells after interkinesis.

In Meiosis II, all the cells in a microsporangium are not in the same stage of division. Therefore,

images of single cells have been taken for identification of these stages.

Look for:

1. Prophase II - In prophase II, the chromosomes are condensed and two new nuclear envelopes are

present.

2. Metaphase II - During metaphase II the chromosomes are distinct and line up near the center of

the cell.

3. Anaphase II - During anaphase II the chromatid are separated and the migrate towards opposite

sides of the cell.

4. Telophase II - By telophase the two groups of chromosomes have completely separated and are

positioned at opposite sides of the cell.

5. Cytokinesis II - In cytokinesis, the nuclear envelope begins to reform. The cell plate becomes

visible between the dividing cells. Four cells are now visible.

Part III:

You finally graduated top of your class and have taken a position as a cytogeneticist. Your job is to

construct the karyotypes of your patients in order to look for possible chromosomal abnormalities.

Each karyotype has been started for you. The first 12 chromosomes have been matched. Your job is to

match the remaining 11 chromosomes, determine whether or not your patient has a chromosomal

abnormality and if so, which one, and to diagnose the patient with the expected symptoms of their

karyotype. You better get started, your patient list is growing.....

Case 1: This is a female with Patau Syndrome.

Autosomal trisomy that produces physical malformations, and mental and developmental retardation,

so severe that most afflicted infants die within a few weeks after birth.

Case 2: This is a normal male karyotype. Healthy male.

Case 3: This is a normal female karyotype. Healthy female.

Case 4: This is a male with the XYY karyotype. Trisomy of the sex chromosomes producing males with

less severe abnormalities, though they often have poorly developed genetalia and subnormal

intelligence. This genotype is significantly higher in individuals found in penal institutions compared to

the general public and has been suggested to predispose these men to aggressive behaviour

Case 5: This is a male with Trisomy 22. Autosomal trisomy in which the fetus does not survive.

Case 6: This is a male with Downs Syndrome. Autosomal trisomy associated with physical features

including broad head, rounded face, perceptible epicanthic folds of the eyes, a flattened bridge of the

nose, protruding tongue, small irregular teeth, and short stature. Mental retardations is also

characteristic. It is also called mongolian idiocy.

Case 7: This is a male with Edwards Syndrome. Autosomal trisomy that produces physical

malformations, and mental and developmental retardation, so severe that most afflicted infants die

within a few weeks after birth.

Case 8: This is a female with Patau Syndrome. Autosomal trisomy that produces physical

malformations, and mental and developmental retardation, so severe that most afflicted infants die

within a few weeks after birth.

Now that you have correctly determined each of the above karyotypes, it is essential to understand

how they occur. The abnormalities viewed above are mostly cases of trisomies. Trisomy occurs during

meiosis when nondisjunction occurs. Nondisjunction is a failure of chromosome or chromatid to

separate to opposite poles during nuclear division. When nondisjunction occurs, two chromosomes or

chromatid go to one pole and none go to the other.

Two homologous pairs of chromosomes are present within the cell depicted below. The

large chromosomes are homologous and the small chromosomes are homologous. The red

chromosomes represent maternal genes and blue chromosomes represent paternal genes.

Depending on which gamete meets which gamete, three scenarios are possible. The gamete with the

extra chromosome could meet a normal chromosome. In this case the patient would have a

trisomy in their karyotype, as seen in the previous case studies (i.e. Down's syndrome). The gamete

missing a chromosome could meet a normal gamete. The result of this match would be a patient

with a monosomy (i.e. Turners syndrome). A normal gamete may also meet a normal gamete in

which the patient would be a normal male or female. The following illustrate these scenarios.

You have now completed the meiosis laboratory.

11/30/09 10:55 PM