study a slide of a single cell using a light microscope with both low and high power objective

8/7/2019 Study a Slide of a Single Cell Using a Light Microscope With Both Low and High Power Objective

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Aim.

The aim of my investigation is to study a slide of a single cell using a light microscope with both

low and high power objective.

Apparatus.

y Light microscope.

y Slide.

Method.

1) Firstly, I placed the slide onto the stage of the microscope.

2) I then adjusted the light source, so that I could see a bright light when looking through the

eyepiece lens.

3) I was careful not to push the objective lens so far down because it might break the slide.

As good microscope technique:

y I set the objective lens on low power.

y I looked at the side of the microscope and carefully lowered the objective lens

until it was nearly but not quite touching the slide.

y Then I looked through the eyepiece and gradually raised the objective lens until

the slide came into focus.

4) I then carefully moved the slide around the stage until I found the area I wished to

observe.

5) To change to high power, I did not refocus, but instead changed the objective lens from

low to high power. The slide was almost in focus, so only a fine adjustment to the focus

was necessary.

6) I then repeated steps 1 through 5, focusing the slide on both low and high power, until I

was familiar with the technique.



Observation.

Figure 1 shows a photograph of a cross section through the stem of a flowering plant magnified

10 times.



Figure 2 shows a photograph of a cross section through the stem of a flowering plant magnified

40 times.



Comparison of the light and electron microscope.

Light Microscope. Electron Microscope.

y Small, light in weight, and easily

portable.

y Large, and can only be used in a fixed

location, usually a specially designated

room.

y R elatively cheap to buy (found in

schools)

y Extremely expensive (found in research

labs)

y Low operating cost. y Expensive operating cost ± images are

formed on fluorescent paper or electron

micrographs are prepared.

y Living and dead material can beviewed.

y S pecimen must be dead, anddehydrated.

y S pecimen is not compromised during

preparation.

y S pecimen may be distorted during

preparation.

y Slide can be prepared and viewed

quickly.

y Preparation and viewing is time

consuming.

y Only the surface of specimen can be

viewed, often only vague shapes.

y Details of structures within specimen

cannot be viewed.

y Provide 3D images of surface.

y Allow details of internal structures to

be viewed.

y Glass lens allows image to be viewed

by naked eye.

y Electrons prevent images from being

viewed by the naked eye.

y They have a maximum magnification

of x2000. (variable)

y They have a much greater maximum

magnification of x20000. (variable)

y S pecimens maybe stained. y S pecimen must be treated by heavy

metals (e.g. Lead), therefore natural

color cannot be seen

y S pecimen must be one cell

thick/transparent. O paque objects

cannot be viewed.

y S pecimen is scanned and an image is

printed ± allowing both transparent and

opaque objects to be examined.



y Only an electricity supply is needed. y R equire an electron beam, which is

expensive to produce.

y Unaffected by magnetic fields. y Affected by magnetic fields.

Discussion.

1) Plant cells are a uniform and regular shape. This feature is due to each cell being bounded

by a plant cell wall.

2) The cell wall is comprised mainly of insoluble cellulose which is a polymer made up of

many beta-glucose molecules linked together by beta1:4 glycosidic bonds.

3) The cell wall acts a semi permeable membrane which allows water to move in/out by

osmosis and other solutes by simple diffusion. This keeps the plant cell turgid hence the

cell walls importance in supporting the structure of the plant cell.

4) Plant cells have plasmodesmata which act as cytoplasmic bridges allowing

communication between adjacent cells.

5) Plant cells have a large central vacuole surrounded by a membrane called the tonoplast. It

is filled with cell sap, a solution of various substances in water.6) Plants contain chloroplasts which are the site of photosynthesis. They contain

chlorophyll, the green pigment, which is largely responsible for trapping energy from

light, making it available for plants to use.

7) Plants have amyloplasts which store amylopectin, a form of starch. This can be

hydrolysed into glucose, providing energy when the cell requires.

8) Under x10 magnification, the cortex, epidermis, and vascular bundle are seen.

9) The epidermis is the external layer of cells which is covered in a waxy cuticle to prevent

water loss. It may contain stomata and trichomes.

10) The cortex is a layer between the epidermis and vascular bundle which acts as a storage

organ in many plants. Carbohydrates and protein are deposited in the cells of the cortex

during the fall, providing food reserves for the plant to grow more efficiently during the

spring..



11) The vascular bundle which contains the phloem, xylem, and strengthening cells

(sclerenchyma).

12) Under x40 magnification strengthening cells (sclerenchyma), companion cells, sieve

tube, phloem and xylem are seen.

13) Strengthening cells (sclerenchyma) have thick secondary walls with lignin deposits.

Lignin is a highly resistant organic substance that makes the walls very tough and hard.

Most of sclerenchyma cells are fibres and sclereids.

14) The role of the companion cell is to support the activity of the sieve tube. They are

metabolically active as they carry out all functions necessary for living cells.

15) The sieve tubes are elongated cells with porous connections between the ends of cells

known as sieve plates. Sieve tubes play a vital role in transporting the dissolved products

of photosynthesis.

16) Phloem cells are comprised of sieve tubes and companion cells. Their primary function is

to distribute the dissolved products of photosynthesis (sucrose) from the leaves to where

it is needed for growth or storage as starch. The flow through the phloem can go both up

and down the plant.

17) Xylem tissues carry water and dissolved minerals from the roots to the photosynthetic

parts of the plant. Xylem is made up of several different types of cells, most of which are

dead. The flow through the xylem is always upwards.

18) During my investigation I used x10 magnification for the low power, and x40

magnification as the higher power.

19) The magnified image is viewed through the eye piece.

20) The eyepiece is held by the body tube.

21) The body tube is connected to the base via the arm. This is the part which is held by the

user when moving the microscope.

22) The whole structure of the microscope rests on the base, which is the lowest portion of

the microscope.

23) Under low magnification, the coarse adjustment helps to focus the image of the

specimen.

24) The fine adjustment can be used to focus the image of the specimen under either high or

low magnification.



25) Larger specimens are normally viewed using the low power lens; however the high

power lens gives a more detailed view.

26) Smaller specimens are normally viewed under the high power lens.

27) The stage supports the specimen and keeps it in a fixed position for comfortable viewing.

28) The amount of light and the contrast is regulated by the diaphragm.

Conclusion.

The aim of my investigation was to study a slide of a single cell using a light microscope with

both low and high power objective. I was able to achieve my aim, and see the difference in detail

of the image I saw using both the low and high power objective. The light microscope served its

purpose for my investigation and provided me with an accurate view of a plant cell.

Additional Notes.

Light Microscope.



A light microscope (LM) is an instrument that uses visible light and magnifying lenses to

examine small objects not visible to the naked eye, or in finer detail than the naked eye allows.

Magnification, however, is not the most important issue in microscopy. Mere magnification

without added detail is scientifically useless, just as endlessly enlarging a small photograph may

not reveal any more detail, but only larger blurs. The usefulness of any microscope is that it

produces better resolution than the eye. R esolution is the ability to distinguish two objects as

separate entities, rather than seeing them blurred together as a single smudge. The history of

microscopy has revolved largely around technological advances that have produced better

resolution.

History of the Light Microscope.

Light microscopes date at least to 1595, when Zacharias Jansen (1580±1638) of Holland

invented a compound light microscope, one that used two lenses, with the second lens further

magnifying the image produced by the first. His microscopes were collapsing tubes used like a

telescope in reverse, and produced magnifications up to nine times (9x).

Antony van Leeuwenhoek (1632±1723) invented a simple (one-lens) microscope around 1670

that magnified up to 200x and achieved twice the resolution of the best compound microscopes

of his day, mainly because he crafted better lenses. While others were making lenses by suchmethods as squashing molten glass between pieces of wood, Leeuwenhoek made them by

carefully grinding and polishing solid glass. He thus became the first to see individual cells,

including bacteria, protozoans, muscle cells, and sperm.

Englishman R obert Hooke (1635±1703) further refined the compound microscope, adding such

features as a stage to hold the specimen, an illuminator, and coarse and fine focus controls. Until

1800, compound microscopes designed by Hooke and others were limited to magnifications of

30x to 50x, and their images exhibited blurry edges (spherical aberration) and rainbowlike

distortions (chromatic aberration). The most significant improvement in microscope optics was

achieved in the nineteenth century, when business partners Carl Zeiss (1816±1888) and Ernst

Abbe (1840±1905) added the substage condenser and developed superior lenses that greatly



reduced chromatic and spherical aberration, while permitting vastly improved resolution and

higher magnification.

Tissue Preparation.

The advancement of light microscopy also required methods for preserving plant and animal

tissues and making their cellular details more visible, methods collectively called histotechnique

(from histo, meaning "tissue"). In brief, classical histotechnique involves preserving a specimen

in a fixative, such as formalin, to prevent decay; embedding it in a block of paraffin and slicing it

very thinly with an instrument called a microtome; removing the paraffin with a solvent; and

then staining the tissue, usually with two or more dyes. The slices of tissue, called histological

sections, are typically thinner than a single cell. The colors of a prepared tissue are not natural

colors, but they make the tissue's structural details more visible. A widely used stain combination

called hematoxylin and eosin, for example, typically colors cell nuclei violet and

the cytoplasm pink.



Electron Microscope.

Electron Microscopes are scientific instruments that use a beam of highly energetic electrons to

examine objects on a very fine scale. This examination can yield the following information:

y Topography - The surface features of an object or "how it looks", its texture; direct

relation between these features and materials properties (hardness, reflectivity...etc.)

y Morphology - The shape and size of the particles making up the object; direct relation

between these structures and materials properties (ductility, strength, reactivity...etc.)

y Composition - The elements and compounds that the object is composed of and the

relative amounts of them; direct relationship between composition and materials

properties (melting point, reactivity, hardness...etc.)



y Crystallographic Information - How the atoms are arranged in the object; direct relation

between these arrangements and materials properties (conductivity, electrical properties,

strength...etc.)

History of the Electron Microscope.

Electron Microscopes were developed due to the limitations of Light Microscopes which are

limited by the physics of light to 500x or 1000x magnification and a resolution of 0.2

micrometers. In the early 1930's this theoretical limit had been reached and there was a scientific

desire to see the fine details of the interior structures of organic cells (nucleus,

mitochondria...etc.). This required 10,000x plus magnification which was just not possible using

Light Microscopes. The Transmission Electron Microscope (TEM) was the first type of Electron

Microscope to be developed and is patterned exactly on the Light Transmission Microscope

except that a focused beam of electrons is used instead of light to "see through" the specimen. It

was developed by Max Knoll and Ernst R uska in Germany in 1931. The first Scanning Electron

Microscope (SEM) debuted in 1942 with the first commercial instruments around 1965. Its late

development was due to the electronics involved in "scanning" the beam of electrons across the

sample. An excellent article was just published in Scanning detailing the history of SEMs and I

would encourage those interested to read it.

How do Electron Microscopes Work?

Electron Microscopes(EMs) function exactly as their optical counterparts except that they use a

focused beam of electrons instead of light to "image" the specimen and gain information as to its

structure and composition.

The basic steps involved in all EMs:

1. A stream of electrons is formed (by the Electron Source) and accelerated toward the

specimen using a positive electrical potential

2. This stream is confined and focused using metal apertures and magnetic lenses into a

thin, focused, monochromatic beam.

3. This beam is focused onto the sample using a magnetic lens

4. Interactions occur inside the irradiated sample, affecting the electron beam



These interactions and effects are detected and transformed into an image

The above steps are carried out in all EMs regardless of type.



R ef erences.

y http://www.biologyreference.com/La-Ma/Light-Microscopy.html

y http://www.astbury.leeds.ac.uk/facil/ElectronMicro/emsuite.htm

y http://www.unl.edu/CMRAcfem/em.htm

y http://en.wikipedia.org/wiki/Plant_stem#Stem_structure

y Edexcel AS Biology ± Ann Fullick.

study a slide of a single cell using a light microscope with both low and high power objective

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