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Jacob Banfield

Osmosis Prac Write Up
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By Jacob Banfield
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18/03/2015

Introduction:
Figure 1 Shows the Fluid Mosaic Model (FMM) which is an updated version of the Davson-Danielli
(D-D) model
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(International, 2006-2007) The definition was later modified after researching had been
done and the discovery that the protein molecules were embedded within the lipid bilayer, rather
than coating the outside of it
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Mosaic: made up of many different parts within it like a mosaic piece of artwork
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g
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The FMM is a lipid bilayer that is made up of Phospholipids and Proteins, there are other parts that
make up the cell membrane but these two are the most important
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The phospholipids are made up of two main components, a polar
phosphate head, and a nonpolar lipid tail
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The lipid tails are
hydrophobic and do not allow water to pass through the cell membrane naturally through diffusion
like other non-polar materials
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e
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The proteins that are embedded in the cell membrane act
as transportation for polar molecules to pass through the cell membrane that otherwise would not
be able to
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Figure 2, Active transport requires the expenditure of ATP (energy) and is the process in which
molecules (substances) are passed through protein pumps which pass materials through a transmembrane protein pump
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(biologymad, 2004)
As shown in Figure 3, Passive transport (facilitated diffusion) consists of two different processes one
being a channel protein, where water and other charged ions are passed through Aquaporin’s
(protein channels) to the intracellular embodiment of the cell
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The substance will bind on the side where it is at a
high concentration and will be released by the carrier protein at a site of low concentration
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This is the way that the molecules can achieve
equilibrium
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d
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(SAS, n
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)

Glycoproteins also make up parts of the cell membrane, they are proteins attached with
carbohydrate chains that play an important role in cellular recognition and the immune response
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And help stabilise the membranes
structure
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Glycolipids act as surface receptors for neurotransmitters and hormones just like the glycoproteins
do, and act as stability for the cell membrane
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They also regulate the spacing between the lipid tails when it is hot and
cold (regulate how far away they get when it is hot, and stop them from sticking together when it is
cold)
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When a solution is hypotonic
(low concentration of solvent) there is an in-balance of solvent to solvent ratios, this in-balance
effects the osmotic potential (rate of osmosis) and the particular area that the in-balance is
occurring
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When a solution is Hypertonic, it contains a high percentage of
solvent, and in order to keep the balance between the two solutions must release water from its
high potential to the solution with a low water potential
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Once this high water
potential moves from one solution to the other, the two solutions both intracellular and
extracellular are said to be balanced and Isotonic to each other
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5, on the left hand side there is an in-balance of solvent between the two solutions,
the solution on the far left is said to be Hypotonic on the left hand side, but is said to be Hypertonic
on the right hand side
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The key idea in osmosis
is to achieve equilibrium between the two solutions
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Therefore effect weight difference
in rectangular potatoes
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The weight of the rectangular chips will depend upon the concentration of the sucrose
solution
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The rectangles of fresh potato was cut into 1cm in diameter strips by a chip slicer
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The rectangles were then cut into precisely 50mm (5cm) lengths using a knife
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The potatoes were washed repeatedly in tap water until all of the starch present was
removed
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The potatoes where then blotched with dry paper towel to remove excess water
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The potatoes were then weighed in groups of 3 initially before the experiment was
conducted and the weights were expressed to two decimal places
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The 18 potato rectangles were placed into six beakers consisting of 3 potatoes per beaker,
the beakers contained solutions of deionised water, 0
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4M, 0
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8M and 1
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Jacob Banfield

Osmosis Prac Write Up
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The beakers were covered by parafilm individually
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After 24 hours the potato rectangles were removed from the solution and were blotted dry
to remove the excess sucrose solutions
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Diagram:

Photo showing beakers containing rectangular chips before sucrose solutions
and deionised water was added
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Results:
Table 1: Showing Initial and final weights of rectangular potato chips before and after being exposed
to the different sucrose solutions over a 24 hour period
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2
0
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6

Initial (g)
Final (g)
Difference (g)
Percentage difference (%)
3
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94
0
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91
3
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71
0
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63
3
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96
-0
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9
3
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4
-0
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81

Jacob Banfield

Osmosis Prac Write Up
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8
1

3
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62

2
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54

-0
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08

-23
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83

Graph Showing Osmotic Potential of Rectangular Potato Chips
in different concentrated sucrose solutions
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change in mass (%)

20
10
0
-10

0

0
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4

0
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8

1

1
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Discussion
The graph shows that the potatoes exposed to the lower concentrations of sucrose gained weight
due to the net movement of free water (solvent) molecules moving in by osmosis
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The lower concentrations of sucrose had a higher net amount of water than the
water inside the potato chips, to achieve equilibrium and for both inside and out of the potato chips
to be isotonic to one another, the solvent in the sucrose solution moved into the potato chip in
order for equilibrium to be achieved
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This has occurred
because of the in balance of solvent between the higher concentration of sucrose and the water
suspended in the potato chips, in order for both the solution and the potato chips to achieve
equilibrium the potato chip releases some of its intracellular water to the solution to gain an isotonic
balance of solvent in both the potato chips and the solution
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These controlled variables included: Concentration, Position, Type, Amount
of each solution
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After 24 hours each individual solution still maintained the same
concentration as it did initially, resulting in a control of concentration becoming apparent from the
start of the practical
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potential in each potato chip, without interruption and recalculations of the concentrations of the
sucrose solutions
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There
was no interruptions from movement or agitation, each solution was able to react and perform its
specific function without adjustment of their positions or without needing to worry about moving
the chips from their original positions
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The type of potato used
in the practical also remained the same throughout the entire experiment, each potato was
individually cut and cleaned, and no modifications were made to them during the preparation of the
practical
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To remove this problem completely, the potato species
remained the same
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In order for each solution to have the same osmotic potential and suspended particles as
one another the solutions needed to be measured out to the nearest 0
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The SA: V ratio for the potato chips remained at a constant rate initially (before the practical) as each
potato chip was as close as human calculation allowed it to be to 15cm by 1cm
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The Volume of the potato chip itself though increased,
due to the net movement of water coming in by osmosis causing the potato chip to become heavier
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The Volume
of each chip decreased due to less amounts of water being in the potato chips
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Same going if it was cold, the
water inside the potato chips would remain inside the potato chips but the semi-permeable
membrane may not have been fully open due to the cold temperatures affecting the rate the water
molecules were able to pass through
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This would have
affected the rate osmosis could have occurred
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The Exposure that the potato chips had to the sun may have also affected the rate of osmosis, this
may have increased the rate of osmosis in the lower concentrations, resulting in them being heavier
than if the exposure to the light remained the same
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The difference in size/thicknesses of the chips during using the chip slicer and measuring the chips to
their final lengths may have affected the rate of osmosis due to an increase or decrease of SA : V
ratio between each of the individual chips
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This
may have also increased or decreased the rate of osmosis in each individual solution
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In fact it was the complete
opposite, the lower the concentration of the sucrose solutions, the greater the weight gain of the
rectangular chips will be
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Figure 2 (biologymad, 2004): Shows protein pump
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Figure 3 (biologymad, 2004): Shows channel proteins and carrier proteins
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d
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Figure 5 (Lizzi Streeter, 2015): Shows osmosis in action
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18/03/2015

Bibliography
Biology Corner
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d
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Retrieved from Biology Corner:
http://www
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com/bio1/notes_diffusion
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(2004, June 18)
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Retrieved from biologymad:
http://www
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com/cells/cellmembrane
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(2006-2007)
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In B
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2)
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H
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Osmosis
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wikispaces
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(2007, January 31)
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Retrieved from Wikipedia:
http://commons
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org/wiki/File:Cell_membrane_detailed_diagram_en
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(n
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More about Diffusion
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sas
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edu/~glauren/morediffusion

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