variety of physical and chemical principles is involved in the phenomenon of osmosis
in animals and plants.
Freezing is an alternate method, based on the different freezing points of fresh and
salt water. The ice crystals are separated from the brine, washed free of salt, and
melted into fresh water. In another process, called Reverse Osmosis, pressure is
used to force fresh water through a thin membrane that does not allow the minerals
to pass.
Another important property of a solution is its ability to exert osmotic pressure. If two
solvents are separated by a semipermeable membrane (a membrane that allows the
passage of the solvent molecules but prevents passage of the solute molecules),
solvent molecules will migrate from the solution of lower concentration to the solution
of higher concentration, making the latter more dilute
Membrane (Latin membrana, “parchment"), in biology, any thin layer of connective
tissue coating individual cells and organs of the body, or lining the joints and the ducts
and tracts that open to the exterior of the body. The membrane surrounding single-
celled animals and plants and individual cells in multicellular
organisms is important in the nutritive, respiratory, and excretory processes of these
cells. Such cell membranes are semipermeable; that is, they allow the passage of
small molecules, such as those of sugars and salts, but not large molecules, such as
those of proteins. Structures inside cells, such as the nucleus, may also have
membranes.
Each organ in the animal body is surrounded by a membrane, extensions of which
often anchor the organ to the body wall. In the field of artificial membrane technology,
scientists today are interested in the development of structures that can function with
the same selectivity and efficiency as exhibited by biological membranes in nature.
Artificial membranes have been used for several years in science and industry. For
example, they are employed in desalinisation plants for removing salt from ocean
water, and in the treatment of industrial wastewater, in processes known as reverse
osmosis. More closely biomimetic membranes can be produced through such
techniques as dipping metal plates into liquids covered with monolayers of selected
lipids. Among the specialised uses of biomimetic membranes is the timed release of
pharmaceuticals into the body from ingested medicines or bandages applied to the
body.
Cells, in nature, fluctuate between being flaccid and fully turgid. However, plasmolysis is
rare(except in experiments) and will result in the cell’s death if it is prolonged, e.g. when the
cell suffers prolong drying (picture below). Such as changes may be seen down a
microscope when strips of potato epidermis are mounted in strong, medium and weak
solutions on the three different slides
Prediction
I predict that the test tubes with saturated saline solution in them will lose more water by
osmosis and will become flaccid.
Apparatus
In my experiment I used the following equipment:
6 Test Tubes
A Test Tube rack
A Measuring Cylinder
Weighing Scale
Measuring Jug
3 Beakers
6 strips of potato tubers
Saturated saline solution
Water
Plan
Firstly I cut six strips of potato and measured them all to be five centimetres long. While I
was waiting for the potato tubers to dry I labelled the test tubes I was going to use. Next I
weighed the six potato tubers and wrote down the measurements in my result table.
Afterwards I poured carefully the required amounts of water and saline into the test tubes. I
then started the timer and waited for the thirty minutes to expire. When the timer reached
thirty minutes I reweighed the potato tubers and wrote down the measurements. I made sure
that it was a fair test by doing the test tube one at each time. I also waited for all the potatoes
to dry before I weighed them. I repeated this experiment three times.
Results
Experiment 1
Experiment 2
Experiment 3
Average Results
Conclusion and Evaluation
Before writing my conclusion and evaluation I would have to consider.
? Whether the evidence is sufficient to enable firm conclusion to be drawn
The reliability of results
Reasons for anomalous results and to object such results where appropriate
The reliability of results
improvements to the methods that have been used.
Future investigation to test your conclusion.
In the water plants cells increase in size. Water enters the cell by osmosis
causing them to expand a little because the cell wall will stretch slightly ( the cells
become turgid). The cells do not burst because cell walls are tough and strong.
This increase in size is revisable - if the cells are placed into a stronger sugar
solution they decrease in size. This is because water is because water diffuses out
of the cells by osmosis. If the sugar solution is strong enough then the vacuole in
the cell shrinks pulling the cell membrane and cytoplasm away from the cell wall,
known as plasmolysis.
As I am evaluating and deducing my experiment, I have predicted that this piece of
research will dominated my experiment. and it I did, so I outlined the hypothesis in my
prediction. And anticipated my results by this theory. I stated that; Osmosis is a special
type of diffusion in which two solutions are separated by a partially permeable
membrane which allows the movement of water molecules, but not the large molecules
like sugar. Water diffuses from a dilute solution to a concentrated one. Referring this to
my results it is noticeable that the potato chip with the most water in the test tube would
swell up the most because water will keep on entering the potato chip causing it to swell
because the cell wall is being stretched. However it can be seen that the cell wall can
reduce and stop the water entering the cell. The test with the most saline solution would
shrink because the water
leaves by osmosis and becomes flaccid. However if the saline solution is to strong It will
pull the vacuole in the cell membrane and cytoplasm away from the cell
wall. This leads to the potato chip shrinking in stronger solution. Although I was able to
predict most results, I did not use the theory to achieve a perfect prediction. I should
have known that the potato chip would have a limit to the water it can hold.
Analysis
The problems I had in the experiment was pouring the correct volume in the test tubes.
Also at one point the beakers of saturated saline and distilled water were not clearly
labelled this caused allot of problems. The things I could have done to make my results
more accurate. I could have clean the potato cutter after I cut each potato chip. This
could increase mass, and this could be why I had to decrease some of the height for the
mass to be a fair test. I could have tried putting two potato chips to see if one potato
chip absorbs more or if the absorb the same amount. I could have tried putting decayed
potato chips in a strong solution and in distilled water. And see the effects on the potato.
Uche Umekwe