PRACTICAL 3: Observation of animal and plant cells

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Practical 3

OBSERVATION OF ANIMAL AND PLANT CELLS

BY ELISA OCAMPO AND VIOLETA PALOMO

2. Materials and equipment

1. Objectives

• To study the ability of the optical microscope to show cell structures.
• To observe animal and plant cells under the light microscope and compare them

• Methalyne blue
• Chopped onion bulb
• 2 slides and 2 coverslips, one extra of each for the buccal epithelium
• Microscope
• Petri dish with a diameter smaller than the lenght of the slide
• Forceps and lancet
• Scrper or flat stick
• Piece of filter paper
• Spatula

3. Basis

• Many epithelia, both animal and plant, provide excellent material for observing cells under the light microscope. Epithelial cells are held together in continuous layers, which facilitates the extraction of monolayered cell films, easily spread out on and can be stained directly with methylene blue.
• The inner epidermis of the bracts of the onion bulb is an easily extractable tissue which allows good observation of plant cells, while the buccal flat epithelium is good for the observation of animal cells.

• By making slides of the two tissues, it is possible to compare the two cell types and experiment with the ability of the light microscope to show cell structures such as the nucleus, nucleolus and cell wall.

4. Methodology

Onion slice over Petri dish

a) Onion epidermis: 1. With the forceps and lancet, you separate a very thing layer of the onion, and place it on a slide. 2. Place the slide over the perti dish, so that, when now you drop a frew drops of methalyne blue, it won't stain anything. 3. While the onion is absorbing the solution, you take the coverlip, and prepare to place it over the onion. If there is more solution than necessary, you can use the filter paper to take it out carefully. 4. Place the slide with the coverlip on in the microscope, and move it around until you see the cells stained blue. b) Spring onion epidermis: Repeat the same process, but changing the sample.

Methalyne blue solution being dropped into the onion

Retiring the solution excess from the sample

Sample under the microscope

4. Methodology

c) Buccal epithelium:1. With a clean spatula, take some of the inner lining of the cheek, carefully, and put it on the slide. 2. Repeat the process, of putting the slide over the Petri dish and dropping some methalyne blue over it. This time you have to be very careful, as the sample is very delicate. 3. Retire the excess solution with the filter paper, and put the slide under the microscope.

Preparing to drop methalyne blue

Buccal epithelium

5. Results

Onion epidermis

Spring onion epidermis

Buccal epithelium

• We observe different types of cells, with different shapes and sizes. The one belonging to plants are more compact and organised, meanwhile the buccal cells are more isolated.
• The onion cells are bigger, and more rounded, while the spring onion cells are super compact, enlongated, and absorbe color better. The buccal epothelium cells have an irregular shape and a light color. The nucleous in every one of them is very little and hard to be, but in the buccal epithelium it is perceptible. In the onion epidermis you can distinguish vacoules, and in the spring onion some organelles, in which vacuoles are also included.
• Membranes (and cell walls) are visible, especially in the onion epidermis and buccal epithelium. In the spring onion some are visible, but the rest are blurry.

6. Observations

We can observe that plant cells, specially in defined layers, cells are more clear and abundant, meanwhile in the buccal sample it was difficult to find the cell. Plant cells are really transparent, and really easy to see the vacuoles, as they occupy most of the space inside the cell. They are also very joint together, so when you catch sight of the sample in the microscope you don't have to look around anymore.

7. References

What we have observed in the lab; practical script.