Theory

A cell can be thought of as a bag in which the chemistry of life is allowed to occur and partially separated from the environment outside the cell1. The thin membrane which surrounds all the cell is essential in controlling exchange between the cell and its environment. It is a very effective barrier and also allows a controlled traffic of materials across it in both directions. The membrane is therefore described as partially permeable. If it freely permeable, life could not exist because the chemicals of the cell would simply mix with surrounding chemicals by diffusion.

Animal cells and plant cell have some common features. Both cells have cytoplasm, endoplasmic reticulum, ribosome and mitochondria2. But there are some organelles which are not present in both cells. For example chloroplast only can be found in the plant cells while centriole only can be found in animal cells. Animal cells also has small vacuole will plant cell has large vacuole.

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Practical 3: Observation of animal cell:cheek cell and plant cell:leaf epidermal cell

Objective: To prepare slides of animal cell and plant cell using the correct staining technique.

Material and apparatus:

MicroscopeMicroscope slideCoverslipDropperForcepsBladeToothpickMethylene blueIodine solutionOnion

Procedure:

(a) Observation of cheek cells

1. Rinse your mouth.2. Using a toothpick, gently scrape off a thin layer of cells from the inside of your cheek.3. Mount the scrapings in a drop of methylene blue solution on a slide.4. Lower the coverslip gently over it.5. Examine the specimen under low power objective lens followed by high power objective lens.6. Draw the cheek cell and label the following parts: nucleus, chromatin material, cell membrane and cytoplasm.

If you do not like to use your own cheek cells, you can look at dead skin cells instead. Put a small piece of sellotape on your hand and then peel it off and stick it down to a slide. This will show you the the size and shape of cells but you will not be able to ses the contents.

(b) Observation of leaf epidermal cells

1. Using a forceps, peel off the epidermal layer of onion scale leaf.2. Cut off a small piece and mount the epidermal layer in a drop of iodine solution on a slide.3. Lower the coverslip gently over it.4. Examine the specimen under low power objective lens followed by high power objective lens.6. Draw the onion leaf epidermal cell and label the following parts: nucleus, chromatin material, cell membrane, cell wall, cytoplasm and vacuole.

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Results:

Drawings and labelingMagnification of drawing

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Questions:

1. Name the type of cells which lines the inner cheek.The type cells which lines the inner cheek is epithelial cell 3

2. Why is it the onion leaf epidermal cell do not contain chloroplast?This is because the onion leaf epidermal cell do not perform photosynthesis 4 .

3. State the similarities and differences between animal cells and plant cells.

Animal cells Plants cellssimilarities Both cells have nucleus, golgi apparatus, and

mitochondria2.Both cells also surrounded by a very thin of plasma membrane

differences Irregular shape Regular shapeAbsent of chloroplast Present of chloroplastPresent of centriole Absent of centriole

4. Why is the nucleus called the ‘control centre’ of the cell?Nucleus called as control centre because all the performance of the cell are instruct by nucleus 1 . Besides it also contain genetic material of cell. It control the activity of the cell by maintaining and regulating the gene inside the chromosome.

5. What is tissue? What word means collection of tissues doing one particular job?Tissue is a collection of specialised cell with a common structure and function 5 . Collection of tissues doing one particular job is known as organ 1 .

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Discussion

1. Handle the iodine solution and methylene with care because both dye will stain your cloth and skin.

2. During prepared the slide, make sure no air bubble trap inside the slide cell because this air bubble can disturb your observation.

3. At first set the objective lens at the lower power until we can see the cell. Then adjust the objective lens to higher power or high magnification so that we can see the cell clearly and can observed the cell easily.

4. The function of iodine and methylene blue are to increase the contrast so that we can see the cell clearly. But these stain are not suitable for photosynthetic cell and to living organism like protozoa because stain will kill them.

5. To avoid trapping air bubbles, set one edge of the coverslip on the slide, and then let the rest of the coverslip drop. As it drops from one side to the other, air will be pushed out, and this will reduce the number of bubbles in the wet mount.

6. When we can see both cells clearly we can see the different between the plant cell and animal cell.

ConclusionPlant cell and animal cell has similarity and differences. Centriole is not available in plant cell while chloroplast not available in animal cell. Plant cell has fixed shape will animal cell has irregular shape.

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References

Bibliographyjones, m. (2003). 1)AS LEVEL AND A LEVEL BIOLGY. cambridge: Cambridge University Press.

2) animal cell vs plant cell. (n.d.). Retrieved February 25, 2011, from diffen.com: http://www.diffen.com/difference/Animal_Cell_vs_Plant_Cell

3) wiki answer. (n.d.). Retrieved February 27, 2011, from answer.com: http://wiki.answers.com/Q/Name_the_type_of_cells_which_is_lines_the_inner_cheek

4) biology/ onion. (n.d.). Retrieved February 28, 2011, from all experts: http://en.allexperts.com/q/Biology-664/onions.htm

5) cloning- glossary. (n.d.). Retrieved February 28, 2011, from nova science in the news: http://www.science.org.au/nova/043/043glo.htm

How to prepare an onion cell slide. (n.d.). Retrieved February 28, 2011, from knowledgerush: http://www.knowledgerush.com/kr/encyclopedia/How_to_prepare_an_onion_cell_slide/

Microscope Slide Preparation of Eukaryotic Cells. (n.d.). Retrieved February 27, 2011, from suite101: http://www.suite101.com/content/microscope-slide-preparation-a165872

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