Plant and Animal Cells

I. Introduction

All organisms in life are composed of at least one or more

cells. Cells are the basic units of life. There are three main

features of a cell. First, all organisms consist of one or more

cells. Second, cells are the smallest units of life and third,

cells arise only from preexisting cells. These three facts are

referred to as the cell theory.

All cells can be categorized into two basic cell types.

They are prokaryotic and eukaryotic. To distinguish where cells

are placed in the two categories, what is inside the cell must

first be looked at. Every cell, either prokaryotic or eukaryotic

all contain basic cell parts. They are: a plasma membrane,

cytoplasm, DNA (the genetic material), and ribosomes.

Prokaryotic cells have a simple structure and they are usually

smaller than eukaryotic cells. Also, most prokaryotic cells

contain a cell wall. In addition to having the basic cell parts,

eukaryotic cells also contain a membrane-bounded nucleus and cell

organelles. The membrane surrounding the nucleus in eukaryotic

cells, separate the nucleus from the cytoplasm.

Most of the cells we used in the experiments held, were

multicellular or consisting of more than one cell. A variety of

cells were used in completing the experiments. We used union

cells, cheek cells, potato cells, and Elodeo cells. We also used

Planaria which is a unicellular organism. Many stains and dyes

were used in the experiments. They were water, methylene blue,

salts, and iodine.

In our studies of cells, we conducted three experiments to

test the different features of cells. The first two experiments

were on how membranes were selectively permeable, diffusion, and

osmosis. To test this, we set up two experiments. The first

experiment we set up had three cups. In each cup a potato slice

and a different liquid was put in. In the first cup was filled

with distilled water. The second cup was filled with salt water

and the third was left empty. We left these cups sit for twenty-

four hours and then we observed them.

The second experiment we set up involved dialysis tubing

which was acting like a membrane. In the dialysis tubing we put

a liquid that was made of starches and sugars. We then put the

dialysis tubing into a beaker of water which had a few drops of

iodine. We left this over time and observed it.

Our third experiment dealt with the different parts of a

cell. To complete this we had to make wet-mount slides and

observe them under a light microscope. To prepare a wet-mount

slide you must first obtain your specimen you are going to look

at. You then put the specimen on a clean glass slide in the

middle. Next, you take a medicine dropper and place one drop of

water on the specimen. After that, you hold a clean coverslip

and place the bottom edge of the coverslip in the drop of water.

Next, slowly lower the rest of the coverslip so that there are no

air bubbles, onto the remaining part of the specimen. By putting

specimens into wet-mount slides it saves a lot of time and energy

instead of putting them into set slides. Also, a wet-mount slide

can be cleaned and re-used.

We put onion cells, cheek cells, and Elodeo cells into wet-

mount slides. After we made slides for each one we observe them

under the microscope. For some of the cells, we had to apply a

dye to have make the cell more visible under the microscope.

Methylene blue was applied to the cheek cells and iodine to the

onion cells. To see the cheek cells, we had to reduce the amount

of light coming into the microscope. We had to do this because

when we reduced the amount of light, we could see the cells more

clear. Elodeo cells were observed as a wet-mount slide and also

with salt water. To apply a die to a previously made wet-mount

slide, an edge of the coverslip must be lifted just enough to get

the dropper under the apply the dye. At first, some of the

epidermal cells of the onion were folded.