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Title: Effect of concentration on osmosis (biology practical)
Description: aimed at year 11 or 12 students undergoing biology science studies. A practical undertaken during a focus on cells and macromolecules and transport processes in and out of the cell. Aim of the investigation: The Aim of the investigation was to observe the biological process of osmosis through testing the change of mass of potato discs different concentrations and test a viable hypothesis which could then be justified using the information and knowledge gained from learning about passive transport and functions of the cell membrane in class.

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Mckenzie Andrews

Biology Stage 2 Practical Report: The Effect of Solute Concentration on

Osmosis
Abstract: brief summary of the practical including hypothesis, method, results and conclusion
...
It is critical for the maintenance of a constant internal
environment within cells
...
A semi-permeable membrane has tiny opening which only allow for the water
molecules to pass through
...
They are often used to observe the effects of osmosis because vegetables are
storage organs of the plant
...
Vegetable tissue provides an excellent model to assist the
understanding of the function of membranes
...
As cells
swell and gain mass from osmosis they are referred to as turgid as the strength of the cell wall
prevents them from bursting
...
Like diffusion, the
process of osmosis is dependent on a concentration gradient
...

Hypothesis: Increasing the concentration of sodium chloride solute will increase the percentage of
change in mass of the potato cubes
...

The independent variable (x axis) in this investigation is the concentration of the sodium chloride
solute
...
Variables that needed to be controlled in this practical order to correctly test the hypothesis
include: amount of distilled water and amount of solute contained in the beakers, the size of the
beakers, and the surrounding environmental conditions such as temperature, pressure and
humidity
...
The beakers had to be the same size to maintain the same distance travelled
by the water molecules through osmosis for each tested solute concentration
...
The
surface area and volume of the potato discs needs to be consistent throughout each pair and for the
other groups whose results are required to determine the averages for the processed data
...
If they are all the same size then the distance required for osmosis to occur along
the concentration gradient is consistent
...
The type of potato
needs to same for each group collaborated results as different kinds of potatoes absorb water
molecules at different rates
...
The same electronic scales will be used
to measure each pair of discs as measurements may differ slightly between balances
...
This allows
students to gain a clearer insight into the current course work including the function of cells,
macromolecules and focusing on passive (doesn’t require energy) cell transport by using visual and
hands on (practical) learning
...
Peel the potato and use the ruler and use a cork borer to obtain ten potato cylinders
measuring 1cm in diameter x 1cm in length
...

2
...

3
...
Place four other pairs of cubes in the beakers with the solutions of 1%, 5%, 10% and
20% of NaCl solute respectively
...
Leave the cubes sitting in the beakers for 20 minutes
...
Do not squeeze them!
6
...

7
...

Record this data in your table
...
When you have finished with your potato cubes, wrap them up in the paper towel
and dispose of them in the bin
...
Write up this experiment according to the Mark Scheme on the criteria sheet
...
Collect data from all the solute concentration used format least two other groups in
the class
...

This can be done by: % change in mass =
Or

100
(𝐴)

πΉπ‘–π‘›π‘Žπ‘™ π‘šπ‘Žπ‘ π‘  (𝐡)βˆ’πΌπ‘›π‘–π‘‘π‘–π‘Žπ‘™ π‘šπ‘Žπ‘ π‘  (𝐴)
πΌπ‘›π‘–π‘‘π‘–π‘Žπ‘™ π‘šπ‘Žπ‘ π‘  (𝐴)

(100) = (%)

(𝐡 βˆ’ 𝐴) = (%)

Results: The most obvious pattern identified in the recording of the data in the averaged table and
graph shows that the smallest cube of the sample size (10mm) has the largest surface to volume
ratio and the largest percentage of clear cube where the phenolphthalein indicator has diffused out
to the extracellular environment (sulphuric acid) of a lower concentration
...


Processed data table:
Averages of all three groups results:
Concentration of
NaCl solute (%)

Replicate
(dimensions of
potato disc in cm)
1x 1
1x 1
1x 1
1x 1
1x 1

0 (distilled water)
1
5
10
20

Initial mass (pair
total) (mg)

Final mass (pair
total) (mg)

Change in mass
(B- A) %

2
...
13
2
...
15
2
...
21
2
...
76
1
...
78

7%
1%
-14%
-22%
-18%

Graph of averages:

Effect ofsolute concentraion on change in
mass through osmosis
10
change in mass (%) (g)

5
0
-5

0

1

5

10

Average

-10
-15
-20
-25

20

concentraion of sodium chloride solute (%)

Mckenzie Andrews

Biology Stage 2 Practical Report: The Effect of Solute Concentration on

Osmosis

Safety Assessment: It was the responsibility of the group to critically analyse an experiment before
commencing and to identify hazards associated with the practical and suggest a safe procedures of
operation
...
We carried out the experiment near sinks in the biology lab so that the acid
was able to be safely poured down the drain and if any acid spills or splashes were to occur, the acid
could be quickly cleaned up using the water and paper towel
...
It was also advised not to eat
the agar cubes or drink the sulphuric acid due to toxicity of both
...
The beaker containing the sulfuric acid is fragile glassware so care was taken to
prevent the hazard of broken glass during the practical
...
The closer the water molecules approach an equal
concentration inside and outside the cell, the closer the smaller the change of mass
...


The average of the integrated group data (the line of best fit) shows that as the cube size is
increased (therefor surface area: volume ratio is decreased), the rate of diffusion is slower however
the decrease in the amount of exchange is more drastic as can be seen from the graph from the
results recorded from the cube of 20mm to the cube of 30mm dimensions
...
This observation clarifies the need for cells to be microscopic as having the
smallest surface area to volume ratio as possible will enable cells to exchange substances at a fast
enough rate to aid their survival
...

Evaluation:
Although no obvious sources of error were identified to have taken place during the
investigation, random errors that may have occurred during the investigation include:
possible inconsistency in the measurements of the amount of coloured cube which would

Mckenzie Andrews

Biology Stage 2 Practical Report: The Effect of Solute Concentration on

Osmosis
then effect the calculations of the percentage of clear cube and the slight time difference
(seconds) as the cubes were placed in and out of the beaker which may have had a small
impact on the measurements of the amount of diffusion taken
...
In this practical a relatively small sample
size of three was used
...
In this investigation the minimum sample size of
three was used as this is the least number of tested examples of the independent variable
needed to be able to have an average of results
...
If the practical was to be repeated a
larger variation of the sample size would ideally produce more precise values and reduce
scatter and a more reliable exponential curve of the line of best fit
...
The results are precise within the biological
context of the increase of surface area to volume ratio increasing the rate/amount of
diffusion
...

Systematic errors:
Not every group whose results were used to determine the averages used the same
electronic scales meaning the initial and final masses recorded could vary slightly from the
values if measured using another scale
...

To minimise the effects systematic error through the recording of incorrect initial mass of
the potato discs each pair was weighed and recorded individually as each pair of discs had a
slightly different mass
...
By merging our group results with two other groups, any consistent errors in the
measurements that may have occurred within our groups results were able to be detected
and therefore accuracy was increased as it is assumed if results of all three groups are close
to the true values and closely spaced that results are reliable and increase the accuracy of
the average and exponential curve line of best fit
...
It is necessary to repeat an
experiment to increase the precision of the results and ensure consistency of data by

Mckenzie Andrews

Biology Stage 2 Practical Report: The Effect of Solute Concentration on

Osmosis
minimising random error
...
If as a group we were
to repeat the practical more times or collect more group’s data we would further be able to
verify our results and ensure the validity of the experimental design in accurately testing the
rate of diffusion
...

The values of the sample size could be considered a weakness in this practical as only the
minimum of three was used
...
As each group only used a sample size of three a strength of the
investigation was integrating the results with two other groups in order to be able to identify
any random or systematic errors that would be evident in the difference between each
groups results and allowed us to be able to average results which was used to base the line
of best fit
...


Conclusion: The hypothesis of the practical was supported as it was found and is visually evident in
the graph and table in the results section that as the surface area to volume ratio of the cube was
increased so to was the amount/ rate of diffusion
...

Review:
As a group, Henry and I worked effectively and cooperatively and divided tasks evenly between us
...
I used the cork borer to cut the potatoes into
cylinders and Annalise used the ruler to measure and cut the potatoes into discs with 1 x1 cm discs
...
We then systematically placed
each pair into its respective labelled beakers
...
I then took the potato out of
the beakers in the same order as put them in and placed them next to where I had marked their
concentration
...
Through the completion
of this osmosis and the previous osmosis practical I have found me and Annalise work effectively and
as a group and have improved our ability to efficiently communicate our actions throughout the
practical
...
31
2)2
...
91

1)2
...
74
3)1
...
71%)-11%
(-25
...
18%)-15%

20

(2)1x1

All Group data Graph:

1)2
...
33
3)1
...
33
2)2
...
76
1)2
...
15
3)1
...
25
2)2
...
86

1) 2
...
21
3)1
...
34
2)2
...
96
1)1
...
92
3)1
...
99
2)1
...
52

(4
...
3%) 5%
(12
...
1%) 3%
(0
...
5%
(0%) 0%
(-14
...
95%)-5%
(-20
...
85%)14%
(-21
...
66%)26%

Biology Stage 2 Practical Report: The Effect of Solute Concentration on

Mckenzie Andrews

Osmosis

Effect of solute concetration on change in
mass through osmosis
15
10
change in mass (%)

5
0
-5

0

1

5

10

20

Group 1
Group 2

-10

Group 3

-15

Average

-20
-25
-30

Concentration of sodium chloride solute (%)

Abpischools
...
uk, (2015)
...

[online] Available at:
http://www
...
org
...
cfm?coSiteNavigatio
n_allTopic=1 [Accessed 11 Mar
...



Title: Effect of concentration on osmosis (biology practical)
Description: aimed at year 11 or 12 students undergoing biology science studies. A practical undertaken during a focus on cells and macromolecules and transport processes in and out of the cell. Aim of the investigation: The Aim of the investigation was to observe the biological process of osmosis through testing the change of mass of potato discs different concentrations and test a viable hypothesis which could then be justified using the information and knowledge gained from learning about passive transport and functions of the cell membrane in class.