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BIOLOGY SAMPLE LAB
Comment [-1]: This is the main topic
that the lab is based on. It is usually one or
two words.
TITLE: Osmosis
AIM: To determine the effect of three solutions on potato tissue.
APPARATUS: 10ml each of solutions A ,B and C, 3 petri dishes, 1 knife, 3 rods of potato,1 ruler, 1
stopwatch.
METHOD:
Comment [-2]: Also include the
quantity for each apparatus. For solutions,
include the concentration if it is known.
Comment [-3]: This is written in past
tense and in the sequence in which it was
done. Do not write something like….”3
petri dishes were half filled with solution
after each of them were labelled” It should
be written….”3 petri dishes were labelled
and then each of them half filled with
solution”.
Three petri dishes were labelled A, B or C.
Solution A was poured into petri dish A until it was approximately half full.
This was repeated using Solutions B and C and petri dishes B and C respectively.
Using a ruler, 3 potato rods, each of 3cm in length, were measured and cut.
One rod was then placed in each of the petri dishes and left for 20 minutes. This was timed using a
stopwatch.
Comment [-4]: Ensure that volumes
and measurements are as precise as
possible.
At the end of the 20 minutes, then length of the rod in each petri dish was measured and recorded.
The texture and appearance of each rod was also recorded.
RESULTS:
TABLE SHOWING THE LENGTH OF THE POTATO RODS IN EACH OF THE SOLUTIONS A,B AND C.
Solution
Final Length (cm)
A
Initial Length
(cm)
3.0
3.2
Change in
length (cm)
+0.2
B
3.0
3.0
0.0
C
3.0
2.8
-0.2
Observation
The rod became very firm
and swollen
The rod remained the
same
The rod became softer and
slightly wrinkled
Change in length= Final length-Initial length
DISCUSSION:
Osmosis is the movement of water molecules from a dilute solution to a concentrated solution
through a semi permeable membrane. When cells gain water through osmosis they become swollen and
turgid causing the tissue to feel firm. If cells lose water, they can shrink and become flaccid causing the
tissue to get wrinkled and soft. If a cell is placed in a solution of a different concentration than its
cytoplasm, it can either gain or lose water through osmosis.
Comment [-5]: The title is placed at the
TOP, in CAPITALS and UNDERLINED.
The title should describe what data the
table is showing. A title such as….”TABLE
SHOWING RESULTS” is very vague.
Comment [-6]: The unit for each
column must be included in the heading for
each column. This unit will apply to every
numerical value in that particular column,
therefore there is no need to write the unit
after every value in the column. The table
must be a completely boxed around.
Comment [-7]: Keep all values in the
table to the same decimal place. One or
two decimal places are usually sufficient.
Comment [-8]: A negative sign
indicates a decrease and a positive sign an
increase. These values were calculated and
very often one example to show the
calculation should be written below the
table.
Comment [-9]: This is made up of four
parts: Introduction, Description,
Explanation, Sources of
error/Limitations/Improvements.
Comment [-10]: Introduction. A brief
explanation surrounding the theory behind
the experiment. The last few lines should
relate directly to the particular experiment
and link what is being measured (the
change in length of potato rod) to the
theory (osmosis)
From the results it was observed that the potato strip in Solution A became firm and increased
in length by 0.2cm; solution C became soft and decreased in length by 0.2cm and solution B remained
unchanged.
Solution A was more dilute than the potato cells and therefore water moved from Solution A
into the potato cells by osmosis causing the cells to become swollen and the rod firm. Solution C was
more concentrated than the potato cells. Water therefore moved out of the cells into Solution C by
osmosis causing the cells to shrink and the rod to become soft. Since the rod did not change in Solution
B, this solution therefore had the same concentration as the potato cells and there was no movement of
water either in or out of these cells.
The potato skin which is impermeable was removed so that it would not hinder the movement
of water through osmosis. This method could have been improved by finding the mass of the rods
instead of the length since the overall size of the rods may have increased, not just the length.
CONCLUSION: A solution that was more concentrated caused the potato rods to decrease in length and
become soft whereas a solution that was more dilute caused the potato rods to increase in length and
become firm.
Comment [-11]: Description. The
results are described and values should be
quoted. Do not write over all that is written
in the table. Results can be summarised.
Only the increase or decrease is mentioned
here, not the initial length, final length and
then change in length.
Comment [-12]: Explanation. The
results that were previously described are
now explained using theoretical principles.
Comment [-13]: Improvements/Source
of Error/Limitations. At least two of these
should be mentioned. Do not just state
them but say why.
A limitation is a short coming in the design
of the experiment or procedure.
A source of error is an inaccuracy that can
be caused due to the experimental design
or by the person conducting the
experiment.
Comment [-14]: Conclusion. This
answers the aim which can be thought of
as a question…..”What is the effect of 3
solutions on potato tissue?” The conclusion
is the answer to this question. It is usually
not more than 1-3 sentences.