Human And Plant Cells Essay, Research Paper
subject = Honors Biology
title = PLant and Animal Cells
papers = 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. 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 amount
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
cells.
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.