Cells Biological

Experiment title: Preparation of Biological Materials for Microscopic Examination
Objectives:
1. To learn how to use a microscope. 2. To study the cell structure of starch grains, onion cells and cheek cells. 3. To differentiate the difference between starch grains, onion cells and cheek cells.
Introduction:
Microscope is an optical instrument use to magnify micro objects that hardly or impossible to be observed by naked eyes, so that the objects can be studied. Compound light microscope is one of the microscopes that is often used. It has a lens or a combination of lenses which magnifies objects, and a variety of knobs to adjust the stage. One of the lens system enlarge the image of the object and the second magnifies the image formed by the first. It uses light reflected from or passed through the sample being observed to form a magnified image of the object, refracting the light with an arrangement of lenses and mirrors similar to those found in telescopes (Houghton Mifflin Company 2003). On the other hand, the adjustment of knobs enables exact focus by moving object slightly while the coarse adjustment knob enables the adjustment of stage for the object to be in the right distance for it to be viewed. Biological materials may refer to any biologically-derived material containing biological agents. It can be tissues, microorganisms, cell lines, microbial toxins, recombinant DNA and more. In this microscopic examination, starch grains, onion cells and cheek cells are observed .Difference between starch grains, onion cells and cheek cells could be differentiate.
Materials:
* * Small piece of potato, * distilled water, * iodine solution * a petal of onion * methylene blue solution * cheek cells.

Apparatus: * * Cork barrier * glass slides * cover slips * light microscope * Forceps * Knife * filter paper * Dropper * Toothpicks * white tile

Methods:
I) Observation of starch grains
1. A potato was cut by using a cork barrier to obtain a piece of it.
2. The small piece of potato was placed on the centre of the glass slide and enough pressure was applied with fingers to squeeze it until small amount of juice was force out. The piece of potato was discarded leaving the juice behind on the glass microscope slide.
3. A drop of water was added to the potato juice and the glass slide was then covered with a clean cover slip.
4. The slide was examined: under low power (10X), then high power (40X). A drawing of 4-6 starch grains was made to illustrate the shape and other observable details for each, low power (10X) and high power (40X).
5. The experiment was preceded by staining the grains using the irrigation technique.
(Irrigation technique: A drop of iodine was placed at one edge of the cover slip. A filter paper was brought into contact with the water at the opposite edge of the cover slip. As water was absorbed by the filter paper, iodine on the other side of the cover slip was drawn underneath it and the sample was stained.)
6. The iodine-stained mount was examined under low power (10X) and high power (40X). 4-6 starch grains were drawn to illustrate their shape and structure. These drawings were included in the microscope data sheet as results.

II) Observation of onion cells
1. An onion was cut into half and one of its fleshy scale petals was removed.
2. The onion petal was snapped backwards and a forceps was used to tear away a piece of thin epidermal lining from inside the onion. A 1cm square piece of lining was placed onto the microscopic glass slide.
3. A drop of water was placed on the onion epidermal lining and the lining was covered with a cover slip. It was examined under a microscope at low power (10X) and then high power (40X). A drawing of the observations was made. The details that were observed in the preparation were included. . The parts of the onion cells were labelled accordingly.
4. The experiment was preceded by staining the onion lining with iodine by irrigation technique as described earlier.
5. It was examined again under low power (10X) and high power (40X). 4-6 onion cells were drawn in the microscope data sheet as observation. The parts of the onion cells were labelled completely.

III) Observation of cheek cells
1. A clean glass microscope slide was obtained and a drop of water was placed in the centre of the slide.
2. A flat toothpick was hold against the inner cheek and the inner cheek was gently scraped with the flat edge of a toothpick. The cheek cells were spread in the drop of water on a microscope slide.
3. The specimen was covered with a cover slip and air bubbles were avoided.
4. It was observed under high power (40X) and a drawing of 4-6 cells was made.
5. The details that can be observed in the preparation were included and were labelled accordingly.
6. The experiment was preceded by staining the cheek cell slide with methylene blue by irrigation technique.
7. The cell with structures observed was drawn in the microscope data sheet as part of the results. Nucleus, nuclear membrane and cell membrane were labelled.

Discussion:
Under microscopic examination, organelles of the cell are enlarged to be observed. In onion cells (plant cell), cell wall, cell membrane, cytoplasm and nucleus are observed. In cheek cells (animal cells), cell membrane, cytoplasm and nucleus are observed. The difference between plant cells and animal cells are presence of organelles and their cell shape. From the observation of onion cells and cheek cells, it there is presence of cell wall in onion cell (plant cell) but it is absent in animal cell .The presence of cell wall contributes to the fixed, rigid shape of plant cell whereas animal cell is irregular in shape.
Different types of stain colour for particular parts of a cell respectively so that the translucent parts of the cells can be viewed more clearly and can be studied easily. Iodine is often used as an indicator for starch. Hence, starch grains and onion cells are more clear and visible when iodine stains starch present in the cells. During observation of starch grains, starch is mixed with iodine solution where dark blue solution is observed, representing a starch/iodine complex. Staining a plant cell with iodine allows us to see the onion cell wall. Methylene blue binds well with negative charge molecules (DNA) which allows us to see the nucleus of the cell. It stains nuclei acid found in the nucleus, making nucleus more observable.
For precaution, glass slide is make sure is clean and perfectly transparent by holding the slide by its edge. Glass slide is make sure not to be dry so that the cell can be observed under the microscope. During wet mount, air bubbles that will interfere the viewing the organisms’ movement is to be avoided by putting the covers lip gently on the slide. When observing the specimen, adjust the iris diaphragm or light level to achieve optimum contrast. Low power is always to be used first as to know the location of a good area for observation.
Conclusion:
Starch grains

Onion cells
Cell wall, cell membrane, cytoplasm and nucleus are observed in plant cells.
Cheek cells
Cell membrane, cytoplasm and nucleus are observed in animal cells.

References: 1. Houghton Mifflin Company, 2005. Microscope [Online]. Available from: <http://www.thefreedictionary.com/microscope> [Accessed on 11 January 2013].

2. After F. A. Jenkins and H. E. White, McGraw-Hill, 1976. Fundamental of Optics, 4th ed. [Online]. Available from: <http://www.answers.com/topic/microscope#ixzz2HqZvBf2R> [Accessed on 11 January 2013]

Microscope Data Sheet

Object : Onion cell

Magnification : 10X

Description : Several rectangular cells can be observed

Object : Onion cell
Magnification : 40X
Description : Cell wall, cytoplasm and nucleus can be observed

Object : Onion cell
Magnification : 10X
Description : nucleus can be seen after adding drops of iodine to the cell. Cell wall can be seen more clearly compare to the cell without iodine.

Object : Onion cells Magnification : 40X Description : After iodine is added to the cell , under 40X magnification of microscope, cell wall, cytoplasm and nucleus can be seen clearly.

Object : Cheek cell Magnification : 40X Description : In a single cheek cell, cytoplasm , nucleus ,nuclear membrane and cell membrane can be observed .

Object : Cheek cell Magnification : 40X Description : With methylene blue, structure of cheek cell can be observed more clearly. Nucleus stains with methylene blue becomes dark blue. Cytoplasm stains colour becomes light blue.

References: 1. Houghton Mifflin Company, 2005. Microscope [Online]. Available from: &lt;http://www.thefreedictionary.com/microscope&gt; [Accessed on 11 January 2013]. 2. After F. A. Jenkins and H. E. White, McGraw-Hill, 1976. Fundamental of Optics, 4th ed. [Online]. Available from: &lt;http://www.answers.com/topic/microscope#ixzz2HqZvBf2R&gt; [Accessed on 11 January 2013] Microscope Data Sheet