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EXPERIMENT 1: PREPARATION OF BIOLOGICAL MATERIALS FOR MICROSCOPIC EXAMINATION
Introduction:
Cell is the smallest structural and functional unit of an organism, and is often called the building blocks of life. All organisms are composed of one or more cells, they are classified into 2 groups which are unicellular organisms and multicellular organisms. Plants and animals are made up of cells too. There are two basic classes of cells, prokaryotic and eukaryotic cells. The structurally simpler, prokaryotic cells are found among bacteria. All other types of organisms such as protists, fungi, plants and animals consist of structurally more complex eukaryotic cells. In this experiment, we took an animal cell (cheek cell) and a plant cell (onion cell) as well as starch (potato cell) as representatives of the eukaryotes to be examined under a light microscope with the magnification of 100x and 400x.
Objective:
To understand the structure of plant cells and animal cells.
To study the structure of cells under different magnifications.
To differentiate between the structure of plant cells and animal cells.
To learn the steps and techniques to use a microscope.
Materials:
Potato, onion, cheek cell, distilled water, iodine solution, filter paper, toothpick and methylene blue solution.
Apparatus:
Knife, light microscope, glass slide, cover slip, forceps, mounting needle, dropper and white tile.Methods:
I) Observation of starch grains
The potato was cut to obtain smaller piece of it.
The small piece of potato was placed on the center of the glass slide and enough pressure was applied with fingers to squeeze it until small amount of juice was forced out. The piece of potato was discarded leaving the juice behind on the glass microscope slide.
A drop of water was added to the potato juice and the glass slide was then covered with a clean cover slip.
The slide was examined under low power (10X), then high power (40X). A drawing of 4-6 starch grains had been drawn to illustrate the shape and other observable details for each, low power (10X) and high power (40X).
The grains were stained using irrigation technique.
The iodine-stained mount was examined under low power (10X) and high power (40X). A drawing of 4-6 starch grains was drawn to illustrate their shape and structure. These drawings were included in the microscope data sheet as our results.
II) Observation of onion cells
An onion was cut into half and one of its fleshy scale petals was removed.
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 1 cm square piece of lining was placed onto a microscope glass slide.
A drop of water was placed on the onion epidermal lining and the lining is covered with a cover slip. The onion epidermal lining was examined under a microscope at low power (10X) and then high power (40X). A drawing of the observation was made by including the only details we can observed in our preparation. Each of the structure was labelled accordingly.
The onion lining was stained with iodine by irrigation technique.
The stained onion epidermal lining was examined again under low power (10X) and high power (40X). A drawing of 4-6 of the onion cells was drawn in the microscope data sheet. The parts of the onion cell were labelled completely.
III) Observation of cheek cells
A clean glass microscope slide was obtained and a drop of water was placed in the center of the slide.
A toothpick was held flat against the inner cheek and the cheek was scraped gently with the flat edge of toothpick. The cheek cells were spread in the drop of water on a microscope slide.
The specimen was covered with a cover slip and air bubbles were avoided.
The specimen was observed under high power (40X), and a drawing of 4-6 cells was made.
The only details that can be observed in the preparation was included and labelled accordingly.
The cheek cell slide was stained with methylene blue by irrigation technique.
The cell was drawn.
Discussion
I)Observation of Starch Grains
From the result we obtained ,without staining the grains with iodine, under low power (10X), colourless starch grains are seen. Under high power (40X), the starch grains appeared are clearer and black stripes are seen inside the starch grain. By staining the grains with iodine, under 10X power, blue-black starch grains are seen. Under 40X power, the blue-black starch grains appeared is bigger. The iodine stains the starch grains blue-black. Therefore, potato contains starch grains.II)Observation of Onion Cells
Without staining the onion cell with iodine, under 10X power, cytoplasm and cell wall of the onion cell is seen. Under 40X power, cytoplasm, cell wall, cell membrane and nucleus which is black in colour are seen. After staining the onion cell with iodine, under 10X power, cytoplasm, cell wall and cell membrane of the onion cell are seen. By staining the onion cell with iodine, under 10X power,. Under 40X power, cytoplasm, cell wall, cell membrane, vacuole and nucleus which is brown in colour are seen. The iodine solution stains the nucleus brown. Therefore, onion cell has cytoplasm, vacuole, nucleus, cell membrane and cell wall.
III)Observation of Cheek Cells
Without staining the cheek cell with methylene blue solution, cytoplasm and cell membrane of the cheek cell are observed under 40X power. On the other hand, by staining the cheek cell with methylene blue solution, cell membrane, cytoplasm and nucleus which is blue in colour are observed under 40X power. The methylene blue solution stains the cytoplasm and nucleus blue. Therefore, cheek cell has cytoplasm, nucleus and cell membrane.
Conclusion
From this experiment, we have learnt that different cell have different structure to carry out different function. A typical plant cell (onion cell) has a fixed shape, a cell wall, a plasma membrane, a nucleus, cytoplasm and a large vacuole. Onion cell does not have chloroplast, only plant cells that carry out photosynthesis have chloroplasts. A typical animal cell (cheek cell) does not have a fixed shape. A typical animal cell has a plasma membrane, cytoplasm and a nucleus. Potato cell contains starch grains which are visible under a light microscope. We also learnt the proper way to use a microscope. At magnification of 400X of a microscope we can see the cell clearer compared to magnification of 100X.