Реферат: Plant And Animal Cells Essay Research Paper

Plant And Animal Cells Essay, Research Paper

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. This indicates that

the cells were thick and there was more than one layer of cells.

II. Discussion

In the experiment involving the three cups and the potato

slices, we observed the different amounts of turgor pressure. In

the cup with the distilled water, the turgor pressure increased.

Turgor pressure is the internal pressure that results from being

filled with water. The potato slice in the first cup was very

rigid from having water move into the potato cells from the

concentration gradient. The water moved into the cells by the

process of diffusion. In the second cup, with the salt water,

the turgor pressure decreased. The salt water environment was

hypotonic and sucked up the water from the potato cells. This

made the slice very bendable and squishy. In the third cup, with

the potato slice only in air, the turgor pressure stayed the

same. The potato did loose some water due to evaporation though.

Sitting out in the air made the potato slice start to rot and it

was turning brown.

In the second experiment involving the dialysis tubing, we

observed the cell membrane and diffusion. Before even starting

the experiment, we had to run a two diagnostic tests. The first,

dealt with how to detect if starch was in a solution. To do

this, we poured some of our liquid containing starch and sugar,

into a test tube. After doing this, we added iodine. When the

iodine was poured into the test tube, the liquid turned blue

because the iodine reacted with the starch. From this, we

concluded that if starch was in a liquid and iodine was poured

into it, the liquid would turn blue.

In the second test, we used tes-tape to detect if any

glucose was in the liquid. Like the first test, we poured some

of the liquid into a test tube and put a piece of tes-tape into

the liquid. As we pulled the tes-tape out of the liquid, it was

colored green, indicating that there was glucose in the liquid.

We concluded that if the tes-tape turned out to be green, then

there must be glucose in the liquid.

After completing the diagnostic tests, we observed the

dialysis bag after it had been sitting in the water for seven

hours. When observing it, we noticed that the dialysis bag had

filled up more. We massed the bag and found that it’s mass was

17.6 grams. It’s original mass was 13 grams. We made a

hypothesis that water was diffusing into the dialysis bag by

osmosis. To detect if glucose or starch had diffused out of the

dialysis bag we added a few drops of iodine and put in the tes-

tape to the liquid in the beaker. We found out that the iodine

diffused into the dialysis bag and turned blue and the tes-tape

turned green in the beaker. We concluded that the glucose and

water had reached equilibrium and the starch and iodine didn’t.

In the last experiment, after we made wet-mount slides for

each specimen, we observed them under the light microscope. In

the onion and Elodeo cells, we observed that there was a nucleus

and chloroplast that were in constant motion and towards the

outer part of the cell. They were moving around the central

vacuole in the cell that pushes everything towards the outside

part of the cell. In the Elodeo cells that were in salt water,

we observed that the cells were a slight bit smaller than the

Elodeo cells just in water. This occurred because the salt water

was a hypotonic solution and sucked up some of the water in the


When we observed the cheek cells we found they were very

different from the plant cells. The nucleus was in the middle of

the cheek cells and there were a few cell organelles. The

Planaria cell was all red and had lines running down it. In this

cell though, the nucleus was not present.

The plant cells and animal cells were very different. In

the plant cells there was motion of cell parts but in the animal

cells there was no motion. Also, the nucleus and chloroplast of

the plant cell were towards the outside of the cell because the

chloroplast can receive sunlight better on the outside of the

cell than on the inside. In the animal cells though, the nucleus

and cell organelles, were towards the middle of the cell.

III. Conclusions

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

cells. Cells are the basic units to life. Without cells life

cannot exist. In our experiments we went to look how cells

function and what are their features. In finding this

information, I know have a better understanding of how cells

function and their specific features.


еще рефераты
Еще работы по на английском языке